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Old 08-08-2000   #1
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89 GTA: Help!! Rear disk brakes are too weak!

My name is Phillip Luong, in California. My car is a 1989 GTA TransAm, with four wheel disk brakes. I am the original owner of the car. It currently has 220K miles on it with the original engine and original of everything else.

The problem is my rear brakes are extremely weak. I am not sure when the problem started. I just discovered the weak brakes when my car was tested for a smog check. New California smog-check rules required that the drive wheels must run on the dynamo rollers during the test. The technician could not use the brake to stop the running rear wheels.

When I had my car on the lift, with the gear in Drive, engine on idle, even when I stood on the brake pedal, the rear wheels still rotated. I took the car out to an empty lot and tested the brakes. No matter how I tried, the rear brakes never locked up. I remember when the car was new, the rear wheels locked up easily. The mechanic said he would not worry too much because: a- The rear wheels rotated because the engine is too strong for the rear brakes b- When the car is on four wheels, the front brakes do most of the braking and the rear brakes are weak so it would not lock-up. However, I am very worried about this problem it is the safety issue and I want to fix it.

The rear pads are very new and still are thick enough. My mechanic disassembled the rear brakes but could not find any adjustable level, nut for them (the usual self-adjust level that is activated by the parking brakes). He said if I really want to fix it, I might start by replacing the rear brake calibers, and then the brake master cylinder. . . However, he is not sure if those would fix the problem.

Please help me. Where could the problem be? Can we adjust some where to divert more brake force to the rear (he said the proportional valve in my car is not adjustable)? If I have to replace brake parts, which one should I start on?

Thank you very much. My email address is pluong@rainbow.com . Phillip Luong.
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Old 08-08-2000   #2
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Re: 89 GTA: Help!! Rear disk brakes are too weak!

Philip,
You're not alone. I have the same problem with my 90 GTA (4 wheel discs). I also discovered this at emissions testing. I haven't pursued this problem yet as the front brakes seem to do a fine job for the moment. Maybe someone else knows if this is a common problem.

TAG
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Old 08-08-2000   #3
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Re: 89 GTA: Help!! Rear disk brakes are too weak!

I find that the front brakes alone do not bring the car to stop fast enough, specially in Southern California traffic. Many times, while moving inline along with many other cars on the crowded freeway, we all had to come to some sudden stops. While other cars came to stop, I guessed, with ease, I had to stand on my brake pedal, the front wheels got locked-up, I came within inches of the car in front of me. The safety is my main concern, not counting my embarrassment (the screeching of the tire, the smoke from the brake, the smell from brunt rubber and the looks from other drivers...) Any help will be appreciated. Thanks.
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Old 08-11-2000   #4
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Re: 89 GTA: Help!! Rear disk brakes are too weak!

Phillip,

Though I am not a mechanic.. one thing I might try on my own is the Bleed the entire system, Front and Back. also I would be sure to bleed them well enough to clear out all the old fluid and have new fresh fluid running though the system... This can only be good for the whole system.. and probably pretty cheap to do the process at home on your how..

I know for a fact there are hand held bleeders on the market that are quite cheap, My neighbor has one and he helps me to bleed my brakes. you can do this whole process by yourself... just the bleeder tool. and plenty of fresh break fluid. *smile..

Like I said I am not a mechanic.. but if it were me. . this is what I would try first...

Karl Van Lith
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Old 08-22-2000   #5
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Rear Break

I'm not a mechanic, too and my English might be worse but I've an Idea:
In the earlier years of my driving license I've got many VW Rabbits and they have rear drum breakes. Some of them have got the same problem and some of them have the problem that the rear wheels locked-up while breaking. The problem was an automatic rear brake adjusting at the rear axle. It works with the vehicle weight. If the vehicle has more loaded than normal the switch opens the line for brake fluid. Perhabs it could be the same at our cars? That this adjustment don't work right.
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Old 08-25-2000   #6
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Re: Rear Break

Hi guys!I come from Quebec and I have the same problem with my 89 GTA. I discovered that on the dyno of my mechanic. He told me that camaro Iroc-Z have the same problem with their rear disc brake. My pads are new and my caliper are in good condition but when I put the brake pedal in the floor only the front wheels lock. It looks that this is a common problem on GTA...
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Old 08-25-2000   #7
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Look for ways to improve rear brakes

After getting information from this board and other boards, I found out that weak rear disk brake is a common problem. However, not many owners of these cars aware of this problem, unless their cars are on the dyno-rollers or on a lift. You all should test your rear brakes. If many of us are having this same problems, maybe someone will figure a way to correct it and will post the answer here. Any technical bulletin from Pontiac on rear brakes?

I am NOT looking for an expensive, total replacement fix. We could always go for an aftermarket race-oriented company and get a total brake package: calibers, disk rotors, pads, master cylinder, brake lines ... But that will cost an arm and a leg! I would save this option for last. If any of you can help, I would appreciate it.

First, the car originally does not have a "distribution valve" to adjust more brake force to the rear. I think there are aftermarket products for this. Let me know more detail on this valve if you have one. Thanks.

Second, just FYI, according to the Chilton Repair Manual, our rear disks' minimum thickness is 0.986 (I think in inch unit). If your disks are thinner than this, you might want to change the disks first. I did this.

Next, I bled the rear brakes real well, but that was no help, neither.

I am thinking of replacing the rear calibers but they expensive AND I am not sure if that would fix the problem (I wouldn't mind if they actually fix the problem). My caliber seem to be OK, no leaks. How do I know if they need to be replaced? Thanks.
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Old 08-27-2000   #8
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Re: Look for ways to improve rear brakes

I have the exact same problem as well. My chiltons manual says there is no adjustment for disc brakes on our cars (?). Infact my emergency brake does not even seem like it works. It clicks and it seems pretty tight, however it does not seem like it works. I checked my oil and it really seems to smell like burnt tranny fluid. I think I will have a shop bleed and completely put new fluid in system. By the way, the brakes and rotors look almost brand new.
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Old 08-28-2000   #9
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Re: Look for ways to improve rear brakes

I remember reading a magazine article when I bought my 1989 GTA new critical of the braking system. You may find it in one of the articles Frankie has on this page. I replaced all my pads in August 1992 at 56,340 km with metallic pads which increased breaking performance. At 113,454 km in 1997 all pads were replaced as were the front rotors indicating they are taking most of the wear. You may want to try some heaver metallic pads but they will wear out your rotors faster.

Ray
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Old 09-03-2000   #10
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Re: Look for ways to improve rear brakes

I'd like to add one thing.These rear brakes are not ment to stop the car,the fronts do 70% or more of the work.

Yeah the rears suck and it has alot to do with the type of pad you use too.I've learned that on TTA's different brakepads will either allow me or stop me from being ablt to build boost with the brakes.Sometimes just changing a set of the same brakes yeilded the same.

All I'm saying is don't worry about it,our brakes were not ment to have good static power they were ment to stop you from speed.

If you really want static power so bad even though you don't need it,switch over to the 87 and earlier brakes which basicly use front calipers all around(somewhat smaller but same design)

Steve
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Old 12-23-2000   #11
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Re: Look for ways to improve rear brakes

hi. I have an 88 gta and i also had a problem with the rear disk brakes. If my car was up on a lift and you put it in drive and stepped on the brakes it didnt stop the wheels. The problem was that the rear calipers were frozen. I heard if you dont use your ebrake every once in a while the calipers can freeze. Anyway I put new calipers on. like $50 I think. I'm not sure though. It still failed inspection for the rear brakes. The only thing that solved it was to put OEM brake pads on. That may sound dumb but it worked. I had brand new raybestos pads on there and they sucked. I had also changed the proportioning valve but that was for a different problem. The car was pulling to the right when I hit the brake. And the proportioning valve didnt fix that. And neither did new front caliper and hoses.. Now I need help. Becuase My car still pulls to the right when I hit the brake..
Crystal
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Old 12-23-2000   #12
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Brake Lines

Just wanted to say that on my 88 GTA the front right brake line (original) got clogged by its own material on the inside. The car would never stop straight, it always drifted. I had both sides on the fron replaced, and they work like new. Also I replaced the calipers and rotors on each side. Note: try getting your rotors truned (resurfaced). This will improve their performanc. With 200K miles, they will most likely need to be replaced b\c the rotors wear down to a point where they can not be resurfaced. Id reccomend getting new rotors and calipers all around. Check those brake lines too.


Jesse
88 GTA
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Old 12-25-2000   #13
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Re: Brake Lines

I too have bad rear brakes, but I didn't find out when I was up on a lift. I was driving my car into our garage in the middle of a bad snowstorm. I pulled in, and I was standing on the brake pedal, trying to figure out how to line myself up correctly. All of a sudden, the car starts shuddering, and the rear end starts kicking out under me (this while I was totally stopped). My front brakes held, but my rear tires were spinning because they were still in the snow. It was pretty funny in retrospect, but at the time it made parking very difficult.
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Old 12-26-2000   #14
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Re: 89 GTA: Help!! Rear disk brakes are too weak!

Just a note on this subject .......USE YOUR E-BREAK AT ALL TIMES WHEN PARKED......this will help keep problems to a minimum on your rear disc breaks :-) see my GTA at www.geocities.com/haunted...0/GTA.html
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Old 12-27-2000   #15
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Rear Brake Fix

As I scrolled through this topic it seems everyone has experienced the same problem. I was able to fix mine by replacing the proportioning valve (yes there is one) on my '87 and of course bleeding them again. Problem solved.
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Old 12-28-2000   #16
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Brake proportional valve?

I am the one who original posted this problem. Sadly, the problem still exists. I do use the hand brake every time I park (from day 1 of the car). Someone (brent87LT1)just mentioned replacing the proportional valve. Could you please explain that some more? My mechanic and Chilton book both say there is no variable valve to adjust. Can you just replace the proportional valve separately and not the whole master cylinder? Where is the valve in the car? Where do you buy the valve? Part number? etc. . . Any detail information would help many, many GTA owners here. Thanks.
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Old 01-02-2001   #17
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Valve

I'll do my best to explain. When I changed the rear brake pads, I attempted to bleed the brakes. This was when I noticed there was no pressure going to the rear of the car. I gave up, reassembled the brakes, mounted the wheels back up and took the car to a trusted mechanic the next morning. He called me at noon and the car was finished. He said the proportioning valve stopped functioning or perhaps siezed up. This is not an adjustable part (like the aftermarket versions you hear about)it is more like a distribution block. This was performed about two years ago and I'm sure he will not remember it if I call him for more details. The bill for this service was no more than $75 so the part is cheap and does not take long to replace.
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