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Chevy/GM Suburban, Tahoe & Pickup - By JimL & Edited by KathyV - Consumers Union Box 2015 Yonkers, NY 10703 Subject: Brake problems in the nation's SUV fleet Dear Board Members: I am sure you know that the government is investigating the brakes in a number of SUV's (Suburbans, Explorers, Windstars). I own a 1985 Suburban, and beginning in 1986 helped to instigate a similar government brake investigation. I also watched several years pass, and saw the manufacturer escape without having to fix the problem vehicles. I am concerned that the same thing will happen again, with these current investigations. I believe that Consumers Union should become involved, and could make a big difference. There are several good reasons for CU to become involved. 1. Many CU members drive new SUV's, have these chronic brake problems, but are reluctant to take the SUV out of service because they have spent such a large amount of money for the vehicle and will take a big "hit" to return it to the dealer. CU members will continue to drive the vehicles, and have costly, preventable, accidents. 2. Based upon NHTSA's track record, that Federal agency's investigation is not likely to find that the brakes don't meet the relaxed stopping standards and distances specified in Federal Motor Vehicle Safety Standards. Unfortunately, the FMVSS don't anticipate many common situations found in daily driving. But CU is not bound by those standards. CU can use engineering common sense, and can act when NHTSA can't. 3. These brake problems occur mostly at lower speeds so haven't resulted in many reported fatalities. Thus, even if it finds that the brakes do not meet FMVSS, NHTSA can only ask for the fix, and has no recourse but suing if the manufacturer refuses to do it. This takes years. However, CU can persuade through the power of the press - which will get some results during the useful life of the vehicle. What credentials do I have to make the above claims? I have been through all this before. Recently I was having a problem figuring out how to repair the very slow power windows on my 1985 3/4 ton Suburban, so I began visiting several on-line news groups that deal with pickups and Suburbans (see newsgroups rec.autos.tech, rec.autos.4x4, rec.autos.misc, and the web bulletin board: http:4x44u.vmag.com/forum/chevysub [now forums.vmag.com/suvsuburban0900]). While I was looking for someone who knew about power windows, I noticed that there were a lot of posts about brake problems in newer Suburbans and SUV's. One post mentioned that there was a government investigation. I was reminded of the braking problems I went through more than 10 years ago, when my Suburban was new. I bought my truck in August of 1985. When my truck was brand new I had braking problems - in some panic stops there was little or no power assist for the first second or two, and my leg simply wasn't strong enough to get the brakes engaged quickly without the assistance of the power unit. After 5 visits to the dealer (who tried but couldn't duplicate the problem and couldn't fix it), hitting two cars, and a number of close calls, I began my own investigation. Nobody that I knew personally knew what was wrong, so I put a "help wanted" ad in a RV magazine. I got a lot of calls from people with the same problem. One fellow from a distant town mentioned that his problem was cured when his dealer replaced his vacuum-powered brake booster with the hydraulically powered "Hydro-Boost" system that was standard in Chevy 1 ton pick-ups. He said it was expensive, though - over $1000.00. A neighbor of mine had Hydro-Boost on his huge, nose heavy, 1-1/2 ton crew cab Dually, so I asked him to demonstrate the panic stopping ability for me. We had set-up an electro-mechanical system to measure stopping distance, but after the testing I didn't need to look at the numbers to know that his brakes engaged much quicker than mine could; after just three test panic stops in my neighbor's truck my neck was sore, whereas my neck had never been bothered by numerous test stops in my own truck. On 6-20-86 I wrote to NHTSA (copy enclosed) to tell them about my brake problem and the response to my ad. I continued to get more responses to my ad, and I asked the respondents to file complaints with NHTSA. Most did. On 7-14-86 I petitioned NHTSA to open a Defects Investigation. On 11-19-86, they declined, stating that there had already been two investigations (files PE85-012 and PE86-005) of 84-85 Suburban brakes, and since in those investigations no defect had been found, there was no justification for additional investigation. I continued advertising the brake problem and asking the respondents to file complaints with NHTSA. In the Fall of 1987 I again petitioned NHTSA, and on 1-28-88 NHTSA granted the petition (file EA88-018). At that time my vehicle was 2-1/2 years old. In the meantime, since I had already tried a number of less expensive fixes to little avail, in the Fall of 1986 I installed Hydro-Boost on my truck. The panic stop problem ceased. I then wrote a paper about how to install Hydro-Boost, and why it was needed, and distributed over 250 copies of it. I'm glad I didn't choose to wait until the conclusion of NHTSA's investigation to fix my Suburban. It was not until early 1989 (at which time my truck was 3-1/2 years old) that NHTSA's testing contractor started the testing. They borrowed a Suburban from an owner who had complained of the panic stopping problem (See APPENDIX for copy of a letter sent to me by that owner.), tested it and found it to meet FMVSS. Thereafter, NHTSA closed the matter. The government was also unsuccessful in the highly publicized suit it had earlier brought against GM about K or X car brakes. [Correction: GM brought a successful suit against NHTSA to force it to close its investigation into the brakes of the X cars - front-wheel drive sedans of the early 80's. K cars were not involved.] But there was no great public upset when the government wasn't able to get the K/X cars and the 84-86 Suburbans recalled and repaired - the vehicles were much less valuable second-hand cars by the time the suits/investigations were terminated. I think that the manufacturers count on the fact that as time passes and the vehicles go to politically less-active second and third owners, the hue and cry will die down. GM did eventually fix the Suburban brakes, but only for new owners beginning in the early 90's when they began installing Hydro-Boost as standard equipment on all new 3/4 ton Suburbans. But GM has not fixed the earlier vehicles that are still on the street - perhaps there is one behind you right now. [And, even as of year 2000, they have not fitted their 1/2 ton Suburbans with Hydro-Boost.] Earlier this week I received the microfiche of NHTSA's public files for their current investigations into SUV brakes (EA94-038, EA95-026, EA95-017, EA96-026), and have spent some time reading them. The consumer complaint forms, which are reproduced in the microfiche, indicate that people are again having terrible problems, and accidents, because of their brakes - so terrible that many of the vehicles shouldn't be driven at all. Yet, these investigations have been going on since 1994, and involve vehicles as old as 1992. The pattern is repeating itself. Will we continue to allow manufacturers to use delay in order to escape fixing these crucial systems? Sincerely, James L... Enclosures: James L... to NHTSA, 6-20-86 Omer U... to James L..., 3-22-89 (The enclosures are in the APPENDIX to this paper. I urge you to read them.) Making GM Do A Fleet-wide Fix - Actions For You To Take My letter didn't spur CU into action. So I would like to suggest that you too bring your brake problems to the attention of CU. The address, again, is Consumers Union, Box 2015, Yonkers, NY 10703. Your letter need not be long to be effective. And, if you haven't filed a complaint with NHTSA (the people who do the government investigations), you should try to do that too. The quickest way to file your complaint with NHTSA is to call them and give the details to their operator. The toll free number is (888) 327-4236, and the operators are there only between 8 a.m. and 10 p.m. Eastern time Monday through Friday. However, if you have a little more time, and want them to have a more detailed description of your brake problem, you should ask them to mail you their form for you to fill out. To get the form, you can call the toll free number at any hour, and leave your address on their tape. Fixing Your Brakes Now I may not know exactly what's happening with your brakes, but I can give you a little mechanical background and some leads to follow. If your vehicle came with the power-steering-pump-powered "Hydro-Boost" brake booster (as opposed to the engine-vacuum-powered booster), the information that follows won't help you much, because it mostly deals with intermittent/occasional insufficient assist from the vacuum booster. This insufficient assist is apparent during your first stop in the morning (brake technicians call it "Morning Sickness "), and during some panic stops. It is more apparent at high altitude. It is less apparent to drivers with very strong legs. The Design If you're certain that you know how a vacuum booster works, skip this section and go to "The Contribution, ..." below. The following is adapted and condensed from HP Books Brake Handbook, by Fred Puhn, pages 78-80. "The extra force on the master cylinder piston is provided by a large piston inside the power booster called a diaphragm. Vacuum boosters have a large diameter because vacuum exerts a very low "pressure." "All early boosters operated, when under no pedal load, with air on both sides of the diaphragm at one atmosphere pressure. When the brakes were applied, a valve between the booster and intake manifold was opened. Air was pumped from one side of the diaphragm causing it to move and supply assist." "The more modern type of vacuum booster is called 'vacuum suspended.' It has a vacuum on both sides of the diaphragm when there is no pedal force on it. When the brakes are applied the movement of the pedal opens a large diameter valve - about 1" - and atmospheric air is let into the power chamber on the rear side of the diaphragm. It is easier to let air into a vacuum than it is to pump air out - particularly when it must be done quickly. The diaphragm is pushed forward by the air pressure on its rear side." The Contribution Of Design Evolution Morning Sickness and intermittent poor panic stopping are not the result of assembly line errors. They are a by-product of design changes that have been made to meet environmental regulations. No amount of installation of new stock parts or adjustments to the original equipment will eliminate the Morning Sickness and poor panic stopping. And they are not a product of wear-and-tear - vehicles that experience Morning Sickness and/or poor panic stopping have had it from "mile one." The designed-in contributors to these braking problems are the low temperature characteristics of our "semi-metallic" brake pads and the side-effects of emission-control modifications. The semi-metallic pads have, since the 80's, replaced the long time standard-of-the-industry "organic" pads. The organics had to go because they contain asbestos. They also fade when very hot. The semi-metallic pads react to temperature just the opposite from the old organics. The semi-mets grip best when hot and are more slippery than organics when cold. When semi-mets are cool you'll need a lot of assistance from the brake booster to get enough caliper pressure to make them grip the rotor. Unfortunately, in order to provide a lot of assist, a vacuum brake booster needs a strong vacuum to power it, but gets less from our low-compression, smogged engines than was available from earlier, high-compression, engines. (A little technical background: 1. Engines put out their highest vacuum when they're idling, less when they're on fast idle, and very little when the throttle is wide open. 2. One long-time technique used to reduce the emission of oxides of nitrogen is lowering the compression ratio of engines - but lower-compression engines make lower vacuum than do high-compression engines.) Another emission-control device contributes to stopping problems in a variety of ways, thus warrants its own section: TRC's (Throttle Return Controls) (My carburetted Suburban has one. Do any of the current fuel-injected Suburbans and pickups have a TRC or some other emission-control device whose side-effects are similar to those of a TRC? I don't know!) More than 35 years ago, engineers went to work to reduce tailpipe emissions of unburned hydrocarbons (HC, or, common name: unburned gasoline). They noticed that a cloud of HC would be emitted whenever drivers would suddenly remove their foot from the throttle. They also saw that very high manifold vacuum coincided with these gross emissions. They reasoned that if they could make devices to keep the vacuum inside the engines from zooming upward after these throttle releases, there would be less HC. GM equipped many vehicles with such devices. One such device used by GM was called a Throttle Return Control, or TRC. The TRC's reduced peak vacuum by keeping a just-released throttle from returning all the way to the idle stop immediately. Engine RPM had to drop below 1800 before the TRC would allow the butterflies to close fully. (On my carbureted '85, engine RPM is sensed by a small circuit mounted in a horn-relay style can on the driver's side valve cover. Whenever RPM is above 1800, that circuit sends 12 volts to a magnetically operated valve mounted on one of the thermostat housing studs. That valve in turn controls a little vacuum actuator mounted on the carburetor. When the vacuum actuator is "on," its rod extends and becomes a temporary throttle stop that holds the throttles open somewhat more than the regular idle stop screw.) Propping the throttle open a little extra while the engine RPM coasts down does achieve the goal of reducing HC emissions. But there are two side effects, both of which affect braking. 1. Since it is the braking effect of vacuum that makes engine RPM's drop, any limiting of the strength of that vacuum also means that the engine takes longer to rev down. With a TRC, when you yank your foot off the gas pedal in order to make a panic stop the engine will continue to push you along for an extra moment or two instead of dropping to idle speed quickly. 2. Many power brake boosters are powered by manifold vacuum. Limiting the peak strength of manifold vacuum available to "vacuum out" the booster lengthens the recovery time between closely-spaced stops and also reduces the peak strength of assist available from the booster. I wasn't aware of TRC's, or that my vehicle had one, until well after the conclusion of the brake testing I did (some results from that testing are noted below, in the section entitled "Install Hydro-Boost, Or?"). But I was able to determine that my TRC had been inoperative during all of the testing - I found that someone, probably a mechanic at the dealership, responding to my complaints about poor braking during low speed panic stops, had stuffed a small screw into one of the TRC vacuum lines. Whoever did that to make the TRC inoperative wouldn't have been able to admit to me that he did it, as there is a big fine for disabling emission controls. Morning Sickness Cold pad temperatures and low engine "vacuum output" (due to high "cold idle" speed) coincide at morning start up. That's why the unprepared driver can roll through the stop sign down at the corner of the block. The extra propulsion from the fast-idling engine adds to the problem. Vehicles with Hydro-Boost generally don't experience this problem because the booster is so much more powerful that it can make even cold pads grip, and isn't dependent upon engine vacuum to drive it. The "Stop And GO" Problem - Intermittent Poor Panic Stopping Later in the day, poor panic stopping can occur after you have made a series of low speed gentle stops in quick succession (such as while creeping forward in the line at a traffic light), followed immediately by a hard acceleration. The series of stops will have depleted the vacuum stored inside the booster. During the hard acceleration that follows, the engine will produce very little vacuum (because the throttle is wide open), so will be unable to replace the depleted vacuum in the booster. So, if you're suddenly forced to interrupt that acceleration and hit the brakes, there will be insufficient assist to get the pads to grab well during the first critical second or two of the stop. You'll feel a hard pedal. And, it will be even harder to stop if the pads are semi-mets and are cool. (And, if you have a TRC on your vehicle, it will limit the peak manifold vacuum available for the first few moments, and it will also allow the engine to take longer "revving-down" and to continue to propel the vehicle forward.) For example, if you were going just 30 mph (which is 44 feet per second), the typical panic stop will cover 40 to 60 feet and will be all over in just a few seconds; and during the entire course of that panic stop, it will be almost impossible for you to provide the right amount of push on the brake pedal. At first, you may not be physically capable of pushing the pedal hard enough. But then, just when your brain is telling your leg to push as hard as it can, and your knee has locked, the brake booster will begin to give you some assist, because the engine, slowing against a closed throttle (partially closed, if you have a TRC), will have begun to vacuum the booster out. And the pads, if they originally were cold, will have warmed up and become less slippery. If you aren't athletic and practiced enough to quickly make a dramatic reduction in how hard you are pushing on the pedal, and you don't have front wheel ABS, your front wheels will lock up and slide until you stop or hit something. Chevrolet has acknowledged this (above-described) problem, in bulletin 88-311-5 of July 1988, where they entitled it "Improved brake pedal feel - cold engine/quick brake reapply." (I call this the " Stop and GO" problem.) The bulletin suggested installing a "High Flow Vacuum Brake Kit," which replaced the vacuum hose running from the engine over to the booster with one having a larger bore. Presumably, vehicles made after July 1988 should already have the larger bore hose. Why didn't the investigation that NHTSA did on Suburban brakes in the late 1980's detect the "Stop and GO" problem? Probably because NHTSA's track testing of 30 mph panic stopping distance is done as follows: The test driver accelerates up to approximately 35 mph, shifts into neutral, coasts down to 30 mph, and then hits the brakes. NHTSA's shift into neutral has a couple effects. It disconnects the engine from the rear wheels, so that the engine cannot continue to push the vehicle along during the braking. This is an important difference from "Real World" conditions, where the transmission will be in gear and the engine may be on high "cold engine" idle, or may even have been revving at 3000 RPM's a fraction of a second before the driver hit the brakes. The extra push coming from an engine that had been revving will be even more pronounced if the engine is TRC equipped. And NHTSA's coasting time has one major effect. It provides a lot of extra time for the engine to vacuum out the booster. Driving at high altitude also reduces the assist available from your vacuum booster, though the effect is continuous, not intermittent as are Morning Sickness and "Stop and GO." Install Hydro-Boost, Or? By now, you surely will have received lots of suggestions, from friends, mechanics, magazines, and parts suppliers, as to the things, some of them less expensive, you could do to fix your brakes. Here are some of the suggestions I have seen being passed around and my opinion of them, plus my own suggestions. 1. My suggestion: "Add Hydro-Boost," as I did. My 30 mph (I did not do 60 mph tests) panic stop distances decreased from 51 and 54 feet with a vacuum booster (depending whether the vacuum inside the booster was high, or low as it would be in the "stop and GO" situation), down to 44 feet with the H-B. This works out to decreases of 14% and 19%. The cost to do the same conversion today would be around $1000 including labor, or $53 to $71 per percent of improvement. If you do your own labor, the parts alone are about $600 (see " Installing Hydro-Boost" below for more details about shopping for parts), so the cost would be $32 to $43 per percent of improvement. The H-B also eliminated the Morning Sickness. (Please note that my throttle return control - see TRC section above for more info about them - was inoperative during all of the testing I did. The stopping distances noted above, particularly for the stops done with a vacuum booster, would have been longer had the TRC been in operation.) 2. Many people suggested: "Adjust the rear brakes." Because Suburbans are so nose-heavy, Suburban rear brakes wear much more slowly than do the fronts. Also, the rear brakes are supposed to be self-adjusting. Nonetheless, if your brake pedal, or emergency brake, has a lot of travel, or if you seem to be going through front pads too quickly, or if your fluid is old, have the system bled, and the rear brakes checked and adjusted if necessary (often the self-adjusters get rusty or full of dust, and stop working). 3. If your truck is pre-89, Chevrolet suggests that you install a larger-bore vacuum line. (See third paragraph of " Stop And Go" section, above.) 4. Some people suggested: "Use hi-tech (Kevlar/carbon matrix, such as "Praise Dyno Brake" brand, (972) 636-2722) pads and shoes." None of these hi-tech pads were available at the time I was testing my brakes, so I haven't tested them. But I am skeptical when I see so many lavish performance claims for them. Also, they are many times more expensive than stock pads - and it will be a "recurring expense." Before I invested in them I would want to know: (A) Why, if they are such a big improvement, hasn't GM issued them to dealers as a quick and relatively inexpensive (to them) way to stop the complaints they are getting on the vacuum boosted 1/2 ton Suburbans? (B) Why doesn't GM install Kevlar pads at the factory so that they could get away with using a vacuum booster instead of the expensive Hydro-Boost units that they've been using for the last few years in the 3/4 ton Subs? And (C), what is the stopping distance improvement in a professionally conducted test, from 30 mph, with both hot and cold brakes, a vacuum booster, and a small (100-120 lb.) driver? Truckin' magazine (June 1999 issue), installed some hi-tech pads and shoes on a 3/4 ton Hydro-Boosted Suburban, and got a 3% improvement in the 60 mph stopping distance. It cost them $330 (not including labor, which they did themselves), which equals $110 per percent of improvement. If that same percentage improvement can be replicated in a 30 mph stop and the potential 1.5 foot improvement in stopping distance will make you more comfortable, you may want to investigate hi-tech pads and shoes. But you will want to make sure that the distance decrease comes without a trade-off of higher pedal pressure or the worsening of Morning Sickness, important considerations if you have a vacuum booster. I have suggested to Truckin' that they do some 30 mph tests of the pads. It has also been claimed that the hi-tech pads are more resistant to the high temperature fade that can occur when braking down a long downgrade with a heavy load on a hot day - so if you have fade problems, that would help to justify the cost of installing and maintaining hi-tech pads. 5. Someone said: "A lot of the "soft" (pedal) comes from the expansion of the rubber brake hoses as you apply the brakes." He continued: "Russell makes DOT approved Stainless Steel braided Teflon hoses that DO NOT expand, so that pressure goes toward braking force." Another claim for the stainless lines is that they give better "feel." I am skeptical about both claims. I have always had stock brake hoses and my personal experience was that the soft pedal and lack of "feel" went away when I got rid of the vacuum booster. If your primary goal is achieving shorter stopping distances, stainless lines may be a poor application of your money because there's been no claim that they reduce stopping distance. If these lines were an easy fix, GM would have their dealers install them to satisfy brake problems during warranty, or would be installing them at the factory. 6. Someone said: "Use hi-tech brake fluid." A waste of money. The garden-variety fluid sold in the supermarket is fine so long as it is fresh and clean when installed and you don't leave it in there forever. Note to sections below: Information given in sections 7 and 8 below about prices, range of kits available and performance info for those kits, is as of Fall 1999. 7. A magazine wrote: "Install bigger front rotors and calipers." The August 1999 issue of Truckin' (page 228) has an article about installing Baer Claw brand (phone (602) 233-1411) front rotors and calipers on a vacuum-boosted 4WD Tahoe with rear drum brakes. (At that time, Baer did not have a kit for 3/4 ton trucks.) The article shows the results of before and after tests that were made by Baer. In the 60 mph stops, the Baer brakes reduced the stopping distance by 25% (comparing the worst stop of the stock brakes to the worst stop of the Baer brakes). Per the article, the cost was $1995 plus 3 - 4 hours labor. However, when I called Baer, they said that while it's an easy job, most mechanics would charge 5 - 6 hours of labor. Also, for a 2WD vehicle, the kit would be more money, $2145. I also inquired about replacement pads. They are $183 a set, but are claimed to last around 2x longer (unless you start driving harder because you have better brakes!). So, with labor, the total cost would be $2300 to $2450, or $92 to $98 per percent of improvement. Baer did not do before and after stopping distances from 30 mph. 8. Many people suggest: "Install rear disk brakes." Rear disk kits are available from a number of manufacturers. Truckin's test (June 1999 issue, graph on page 166) showed a 60 mph stop distance improvement of 15 feet (9%) for rear disks by Dynatrac mounted on a Hydro-Boosted '95 3/4 ton 4WD Suburban. I was so impressed with that claimed improvement that I called Dynatrac, as well as another disk brake manufacturer that was mentioned in Truckin'. Dynatrac's setup has an emergency brake mechanism that squeezes the pads in the caliper, and costs $1395 for parts. The other manufacturer said that their current setup saves 6 feet at 60 mph, and that they are expecting twice that improvement in their new setup due in 2-3 months. The upcoming new setup will also have a greatly improved emergency brake (drum-style shoes inside the rotor hat), and will cost about $1000 for parts. For both brands of brakes I estimate about $400 labor to install - making totals of $1795 and $1400. Assuming that the amount of improvement is the higher figure Truckin' got from the Dynatrac setup, and that you could get that same improvement from the less expensive setup made by the other manufacturer, that equals $156 per percent of improvement. If the improvement is more realistically the 12 feet (7%) projected by the 'other manufacturer,' that works out to $196 per percent of improvement. Therefore... Check the adjustment of your rear brakes. If your truck is pre-89 and you're not going to immediately install Hydro-Boost, do at least install the very inexpensive "High Flow Vacuum Brake Kit" described in #3 above. Bigger front disks, #7 above, while they have the biggest price tag by far, claim the greatest % decrease in stopping distance. However, no one has tested to see if the bigger disks provide the same % decrease in stopping distances from 30 mph as they do from 60 mph, or when they're cold (Morning Sickness); And they have a high cost per percent of improvement. H-B is less expensive per increment of improvement (and can be much less if you do your own labor), does not have the recurring expense of very expensive brake pads, and definitely cures Morning Sickness. I would have the rear brakes checked and adjusted and then install H-B. If I continued to have a high temperature fade problem, I would then consider installing the hi-tech pads. Then, if I still felt the brakes needed improvement, I would look into the bigger front disks. Installing Hydro-Boost The Suburban I converted is a 3/4 ton, 4x2, and older too, so did not use exactly the same conversion parts as your truck will. Thus the following doesn't contain the part numbers I used. My 3/4 ton gas-powered Sub had the same size rotors, calipers, drums and rear wheel cylinders as the 3/4 ton Diesel Sub of the same year, which came with H-B - so all I had to do was copy the setup from the Diesel. The hardest part for you will be to figure out which H-B unit to use. If, for example, you have a 1/2 ton, and the parts books list a Diesel-powered 1/2 ton of the same year and model, and it has the same size brakes (rotor and drum dia.) as yours, you probably can use the H-B unit (and master cylinder, if different bore dia.) that was used on that vehicle. Otherwise, you will have to do a little creative research. One method would be to call Bendix div. of Allied Signal, the company that makes H-B's for everyone, and ask one of their techs to recommend a unit. The H-B unit can be bought new, rebuilt, or used from a wrecking yard. I was quoted a price of $174, including core charge, on a rebuilt, from a local parts store. I was quoted $290 on new genuine GM, from Jeff at Brasleton Chevrolet, (800) 535-4608. New units are no longer available direct from Bendix distributors. These prices are based upon the H-B unit from a 1997 2WD 1/2 ton Diesel with 11" x 2.75" rear brakes. The part numbers were 15003099 (new) or R2771790 (rebuilt). I recommend using the new unit. You will want to triple check the part number application before ordering. I had to change a number of parts that one might not expect to have to. One was the pedal arm (the vertically mounted swinging lever that has the pedal at its bottom end) and another was the master cylinder (the hydro boost setup called for a MC with a slightly different bore diameter). These two pieces had to be changed in order to make them compatible with the distance that a H-B unit will travel, which I believe is shorter than what a vacuum booster will travel. But I don't remember for sure - and in any case the situation on your truck may be different. I just know that you don't want your H-B unit to come to the end of its travel before the MC has displaced enough fluid to lock up the brakes (including situations where the rear brakes have a little extra play due to lack of adjustment). I'll give a worked example here. If it turns out that the H-B unit has maximum piston travel that is 20% less than your vacuum booster, you'll want to want to change to a MC whose piston has 20% more area, and to a pedal arm that provides 20% more force magnification (a shorter distance between the top pivot and the hole where the horizontal piston rod connects). I did not have to change anything else in the brake system downstream from the MC - the pads, rotors, proportioning valves, calipers, shoes, and rear wheel cylinders are stock. You will also want to check to see if your power steering pump is the same, in three respects, as the pump used on a Sub with H-B - it will save you money if you can avoid automatically buying a new one. First, you will need to make sure that your pump puts out the 1200 psi required by all H-B's, rather than the 800 psi that is found on some vehicles with power steering only. You can confirm this if the part numbers for the front (pumping portion, including the pressure relief valve that determines output pressure) of your present pump (not including the reservoir can on the back), are the same in either the Chevy catalog, or in a re-built pump catalog, as the part numbers for the pump and relief valve used on a vehicle that came stock with H-B. If necessary, you could change the pressure relief valve (the big nut fitting on the rear face of the can) to a 1200 psi one. Or, you could buy a rebuilt pump meant for a H-B'ed vehicle (one that puts out 1200 psi) for about $54. The second way in which the pump will have to be the same is that it will need to have an extra return nipple. Some stock pumps already have that extra nipple, blocked off but ready to be used. Or, you could braze an extra nipple on your can - but see caution about adequate reservoir volume, next. Third, while the can on the back of the H-B compatible pump will have an obvious difference - the extra nipple for the low pressure return line from the H-B unit, it could also have a less obvious, but still important, difference. Since the H-B system has more fluid in it, the can may be larger, to leave room for the expansion of the extra fluid due to heat. You don't want fluid expanding out of the can and onto the headers - that could cause a fire! A complete new genuine GM pump, made to work with H-B so it has 1200 psi, and including the can with extra nipple, is $220 at Brasleton. Part number 26065182. (In my case, I was able to re-use the front of my pump, but had to buy a different, larger, pump can from Chevy.) Also, if you live somewhere where it gets hot, or you're gonna drive it hard, I'd recommend adding a cooler for the fluid. Since it has to go on the low pressure return line, you don't want any significant back pressure due to the cooler (back pressure on a H-B can cause the brakes to remain applied), so use a cooler that is fairly large. Or buy the one Chevy puts on their extra heavy duty trucks with H-B. High pressure hoses: You do not have to buy these from a Chevy dealer. These are available from a variety of reputable manufacturers, and are about $30 each. These stock hoses have a reputation for seeping after a number of years of use. When my high pressure hose from the pump to the H-B unit began seeping a little, I figured: "Replace it with AeroQuip steel braided hose - that'll never leak." I did, and indeed, it hasn't leaked, but it is noisy. Evidently, the fabric reinforced stock hoses (as well as those sold by Moog and others in the aftermarket) have been designed to expand enough to dampen the pulses coming from the pump, whereas the steel braid won't give as much, so is noisy - even when insulated with the foam cover as used on the stock lines. Change the PS fluid in the system at least an hour of driving before doing the conversion - so that the pristine H-B won't get full of old dirt. And change the fluid again shortly after the conversion. Final Notes 1. About Magazines And Grains Of Salt The Truckin' articles mentioned above should be available at your local library, or from back issues dept. at Truckin' at (714) 939-2400, $7 each issue inclusive of postage. These articles are not your typical glossy car mag articles, either. Most car mags try to tread a middle ground, not publishing anything critical about their advertisers' products, and also avoiding obvious editorial promotion of those products. Not so the guys at Truckin'. They seem to have an "open" relationship with their advertisers. The August 1999 brake article contains examples of both heavy criticism (of GM, which has a full-page ad on the back cover) and fawning (towards Baer, which has a 1/12 page ad). Criticism (page 228): "Poll owners of all '92-'99 1/2 ton Chevy and GMC Suburbans, Tahoes, and Yukons and question them about their brake systems and odds are that these lifesaving devices will fall well short of expected objectives. Simply put, the factory brakes are horrible." Criticism (photo caption, page 228): "Tahoe, Suburban, and Yukon owners should unite and begin a serious letter writing campaign to have these vehicles equipped with decent braking systems." Fawning, pages 229 and 234: "The kit is pleasantly affordable at $1995, and believe us, it is well worth every penny. To date, the Baer Racing kits are the most complete and easily installed braking systems on the market." "In many situations, you cannot afford to be without a set of Baer Claws brakes." 2. Don't Forget To Write Even if you don't get around to fixing your brakes right away, I hope you will not delay writing to Consumers Union, and filling out one of the NHTSA forms. (Address and phone numbers are in paragraph headed "Making GM Do A Fleet-Wide Fix - Actions For You To Take," above.) 3. This Is Not A Professional Paper If the advice seems wrong, check it out before taking it. Let me know about any error, omission or ambiguity, so that I can correct it. I plan to add more part numbers to later editions, so I will appreciate knowing what part numbers you have used. 4. Reproduction Of This Paper If you provide a copy of this paper to someone else, or post it somewhere, please supply, or post, the complete paper, including this note. Leaving out the (admittedly long) section encouraging owners to contact Consumers Union and NHTSA will play into GM's hands by reducing the amount of pressure that is put on them to fix their brakes. JimL papeXXXles@earthlink.net (remove anti-Spam X's) APPENDIX I. Enclosure #1 To June 10, 1998 Letter To Consumers Union: June 20, 1986 Mr. Richard Boyd NHTSA Office of Defects Investigation 400 Seventh Street SW Washington, DC 20590 Dear Mr. Boyd: Thank you for calling me on Wednesday. Here is a list of people who responded to my ad and have the "hard pedal on panic stops" brake problem on their Suburban. I have told them that they will be contacted by your office. I have left three of the people who called me with "hard pedal..." off this list. One had a 1972 vintage truck. The second owns an '85 with far too many problems - In addition to having a hard pedal on panic stops it pulls hard to the left on moderately hard brake applications, and shimmies at 45 mph. Despite seven dealer visits! The third owner asked to be deleted because he has made possibly illicit improvements to the engine on his '84. The vehicles listed are notable for several reasons. With few exceptions (those noted) all have had, since they were new, exactly the same brake problem, hard pedal on panic stops, and no others (if you don't count Morning Sickness on the first stop coming out of the driveway with cold pads in the a.m.). Most are used to pull heavy trailers, and all those owners volunteered that the brakes were better when trailering than not, probably due to the instant assist from the trailer brakes. (I personally pull a light trailer having no brakes and I have a harder time stopping quickly when I'm towing it.) Finally, the trucks are surprisingly stock. Most have the factory wheels, tires, and unmodified engines and ride height. You may wonder why you haven't had more complaints about these brakes. One possibility is, of course, that most Suburbans have excellent brakes and ours are the exceptions, due to the small percentage of manufacturing goof-ups. I think that the more likely possibility is that many, if not all, Suburbans have this brake problem, and those owners who have figured out that the brakes aren't normal simply are reluctant to contact the "authorities" about it. Our group is an example of that reluctance - out of the ten people on the attached list, only two (T... and myself) have done anything beyond bitching at the dealer. None of the remaining eight has used any of the no-cost remedies available to them, such as talking to the Chevy zone representative, going to the BBB arbitration program, or calling your Hot Line. Another factor may be that the group's accidents resulting from the brake problem, excluding "T...'s" and mine, have been for the most part at low speed and have caused little personal injury. You'll find, when you've talked to the people on this list, that many are devising "fixes" for their brakes. On my Suburban I've installed an electric vacuum pump from a Cadillac, to keep the booster vacuum up all the time. One or two guys are changing to earlier booster units because they've heard the internal valving is better. At least two are running around with organic pads instead of the stock semi-metallics. Nobody has done any rigorous testing of these modifications, so there is the possibility that some of them could be as dangerous as the unmodified brakes. I hope that with your help we can get GM to supply a proper "fix," one that has been thoroughly tested for safety and durability. If you need more information from me, please do not hesitate to call. I appreciate your interest in this problem. Sincerely, James L... Enclosure To June 20, 1986 Letter To NHTSA: [List of affected owners that was attached to June 20, 1986 letter (For public distribution, last names, addresses, and phone numbers have been redacted):] James L..., Owns '85 Suburban C20, 454. VIN 1G8GC26W2FF185xxx. Bought 8-31-85. 8100 Miles to date Paul B..., California: In the light truck business and knows of many affected Suburbans. Can contact their owners. Chris T..., California: Owns '85 Suburban C20, 454. Is in tire business and has contact with many other affected Suburbans. Henry W..., New York: '84 Suburban C20, 454, belonging to a customer. Henry is a professional mechanic. John S..., Maryland: Owns '78 Suburban C20, 454. John is a professional mechanic. Julian D..., California: Owns '85 Suburban C20, 454. Close friend has identical truck with same brake problem. Dave S..., California: Owns '85 Suburban C20, 454. Steve W..., California: Owns '84 Suburban K20, 454. In addition to hard pedal on panic stops he had sub-par rear brakes possibly due to raised rear springs affecting the height-sensing valve. Jesse R..., California: Owns '85 Suburban C20, 454. Jesse, who weighs 275 pounds, is only person to report being able to lock up front brakes in a panic stop in spite of hard pedal. At same time, rear brakes will not lock up. Michael C..., California: Owns '84 Suburban C20, 454. Has noticed problem only since worn out original pads were replaced at 30,000 miles, so may or may not have same source of hard pedal as do other owners. End of list. II. Enclosure #2 To June 10, 1998 Letter To Consumers Union: Omer U... Illinois March 22, 1989 Dear Mr. L...: I wanted to let you know of my recent experience in regard to my 1986 Suburban Silverado 20 with a 454 engine and the brake problem. I had contacted the NHTSA on 10-30-87 and got no response. I called the 800 telephone number at the U.S. Dep't. of Transportation in Washington, D.C. again in January, 1989. They sent me a complaint form to fill out which I did and sent it to them. In a few weeks I received a call from the U.S. Testing Research Center near Columbus, Ohio. They were interested in testing my vehicle in regard to the brakes. I decided to let them test my vehicle which had 22,000 miles on it. They said they had not yet tested one. After thorough brake testing, they concluded that all brake tests were within government guidelines and found no deficiency in that regard. These test results should be available in 6 months to a year. I'm sure that you and I agree that we have had occasions when braking with a hard pedal was a frightening experience; however, they never had it happen to them. After testing, they put on new rotors and brake pads, new rear brake shoes and drums, two brake kits (now sold by GM to improve the braking problem), and a new set of tires. They certainly treated me right but really did not experience the braking problem as I had and consequently will probably not pressure GM to recall and correct the problem. Thought you would like to know. Sincerely, Omer U... END OF APPENDIX |
