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Old 07-05-2001   #1
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Rear Brake fix $5.00 ALL GTA's

$300.00 and a lot of cursing, rear brakes still were not working up to par. WHY?
I spent 2 solid weekends on this !@#$%*problem and I finally solved it. The problem is the distribution block, potentiometer or proportioning valve, it has several names.
However purchasing a new one will not solve the problem. On most GTA's the front brakes do 95% of the stopping, my research on this topic indicates that the engineering of the front brakes is more than adequate to stop a vehicle except not within the limits we are use to now a days.
THE FIX!!! Buy 1qt brake fluid, a couple of good cotton rags, and a 7/8" wrench. Wrap the rags below the front of the (PV=prop valve) wrap it tight, so you don't get any on the paint. Take a small shot glass and take all of the fluid out of the front reservoir, with a rag soak up the rest. Now on the front of the PV there is a brick red flat nut/cap which looks like a big bleeder. Take it out, CAREFUL there is a strong spring inside, so keep pressure on it with your other hand. Now take it out, remove spring and of course fluid will come out, no biggy. You will now see this little tube on the inside, get a pair of needle nose pliers and remove this tube/piston.
Take the spring and tube, place it on the bench and spit on it and curse it. Reassemble:A little tricky, you need to seal the hole in the middle of this nut. I tapped it with a #8/32 tap put a phillips head screw with a tiny gasket under it and it was sealed. Don't try epoxy or silicone, brake fluid is semi acidic. Or go to your local auto store and try to find a manifold plug that will work. Put the nut or plug back in, DO NOT touch the brake pedal, have someone sit in the car while you get your wrench on the nut/plug. Tell them to SLOWLY press the pedal down while you loosen the nut until air/fluid comes out. Do this 3 times SLOWLY and it will be bled properly. Take it for a ride, YOU OWE ME A STIFF DRINK!
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Old 07-05-2001   #2
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Good work

Good job D. way to be a pioneer.

Do you happen to have any idea what the distribution percentage works out to be after this? Autocrossers "high speed tourers" will still need the majority of stopping power up front.
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Old 07-06-2001   #3
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proportioning valve

hey, where is the proportioning valve anyways?
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Old 07-09-2001   #4
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Percentage distribution

That i am working on, i have a few calls into GM and am trying tor reach the dep.t which handles the brakes and figure out what type of retrofit spring or piston will give us the proper pressure to the rear wheels. However i have tried to lock the rear's up on a wet slippery surface and beileve it or not they don't it almost feels like the distribution is perfect. I don't beileve it however, i will update as soon as i can.
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Old 07-09-2001   #5
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Location of PV

it is approx 4-5 inches below master cylinder, it is aluminum and has 2 lines running into it and 3 running out of it with a 1 wire plug yellow at top.
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Old 07-11-2001   #6
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e brake

hey if you crank on the e brake while driveing, does your rear weels lock up, or even slow you down? as it stands right now, my rear brakes are virtualy useless. the e-brake does nothing at all in my car, it doesnt even slow me down in the slightest bit.
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Old 07-11-2001   #7
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e-brake

Your e-brake cable is too slack get under the car and there is a connection near the rear end which has a running thread in it which then connects to the cables running to each wheel wd-40 it up wait and hour and start to tighten it up, careful do not make it too tight there has to be some slack in it.
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Old 07-12-2001   #8
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rear brakes

so basicaly what your saying is that my e-brake "should" work even though my rear brakes dont actualy work when i hit the brake peddle? last winter when i was driveing around on the icy roads, my rear wheels could not be stopped, when i would slow to a red light, if the ground was covered in ice, my rear wheels would keep turning even with the rear brakes fully pressed down. i looked at the brakes and everything seems in order, but for some reason they just dont work properly.....
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Old 08-06-2001   #9
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rear brake fix

hey, has anyone else here tryed what denis suggested? i really would like to fix my rear brakes or actualy make them work. not many people seem to bring up this topic and actualy "solve" it. i was gona try it, but i dont wana mess up the only 2 brakes that i got just in case i screw up the opperation. he never got back to us.....
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Old 08-06-2001   #10
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rear brake fix

hey, i got impatient and tryed it out, and my brakes work GREAT!!!! i can almost stop on a dime going 60 and my brakes dont lock up and go into a skid. you should all try this out. denis i owe you a stiff drink
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Old 08-07-2001   #11
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brakes

I've got the old style rear disks on my 85 IROC and they don't do a thing! There's rust on the rotors for christ's sake! My pedal is also very inconsistant. Sometimes (most of the time) I've got to push it pretty far before anything works. Sometimes I've got to push farther. Once in a while the pedal is good and near the top. It's not like air in the lines though. It's totally random. First pump is good, next pump is crap. Next time they're all crap, other times they're all good. Uphill, downhill, fast, slow, it doesn't seem to matter, although it does seem that I get a good pedal more often at low speeds than high speeds. It's been this way since I bought the car. I checked the rear calipers, put on new rear pads and rotors, new front pads, and 3 master cyllinders.

Any ideas? Could this proportioning valve mod be my answer?
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Old 08-07-2001   #12
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Finally (some interest)

For a second i thought i was the only person interested in stopping the dam car. FYI the validity of my claim is plain and simple, i have 2 kids who love to ride in the (shiny car) as they call it. I would never ever endanger them. My instructions are accurate and if more people try it out more people will realize i am right. Don't get me wrong this fix is for a completely functioning system. If your calipers are frozen or your losing brake fluid somewhere DIFFERENT STORY. However i hope everybody spreads the word around about this fix. I am suprised that Frankie hasn't said anything about this. STOP WELL, BE WELL

P.S. I am a mechanic of 13 years
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Old 08-07-2001   #13
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Re: Finally (some interest)

Hey Denis, i think my brakes are due for a bleed sometime soon. since we're in NYC, you mind giving me a few pointers on a free day? Still learning to be a DIY person. And I'll actually buy you a stiff drink too!!!
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Old 08-08-2001   #14
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No Problem

Fred, just let the weather cool down a bit and i will help you out no problem.
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Old 08-15-2001   #15
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Rear brakes

Denis, what an interesting post. I have read thousands of lines of text on this and other sites dealing with how to "fix" the rear brakes. None that I can remember mentioned anything like what you wrote. You may have found a cure for the common cold!!! How did you arrive at your solution? Have you had any feedback from GM? Any ideal on the distribution percentages? Have you measured before and after braking distances? Please excuse my questions, no mechanic here. By no means is this an attack on your efforts, I am just looking for some additional data. Thanks for your efforts to date.
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Old 08-16-2001   #16
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Answers

JC i am not taking your questions in a negative manner you have valid questions and here are some answers.
As far as GM is concerned my letters and phone calls have fell on deaf ears. It seems that GM is too big and really couldn't care less for our dilemma. By the way this is not the first time that I encountered that attitude from GM.
The solution: Simple logic, for a caliper to compress it needs hydraulic pressure, no matter what. At full depressed pedal pressure it was 20psi. Not enough it needs approx. 80-120psi (depending on vehicle). I shortened the spring within the (DV) several times in increments, however it had no positive effect. So after that i removed the piston/ damper within the DV and checked the pressure at the rear caliper it was 75psi. That was acceptable, i then proceeded to raise the rear end start the engine put into drive and then measured "free braking" meaning to see at what point of pedal depression would the rear calipers start compressing, @ 1" down the rears started to compress slightly. VERY GOOD.General Note: The rear brakes must always start braking before the fronts start, otherwise the car will tend to fish tail or swing. I have gotten a formula from Car Craft magazine which will help me determine the percentage distribution. This formula is almost a half a page long, so it will take some time. The formula is a standard braking formula that engineers use. Factors ( Vehicle weight, rotor size, pad surface area, wheel base length, etc...) I will update this post with an answer.
Stopping distance, unfortunately i did not measure it before but the difference is extremely noticeable. Wet surface, they have not locked on me yet.
Hope this helps DR
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Old 09-08-2001   #17
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brake mod

Well I got bad news for you guys, I tried this mod out the other day and I find my tires lockup no problem on dry pavement. One thing I have to say is when i try not to locking them up the car stops pritty good but this is something I can't trust for everyday use especially if it rains.
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Old 09-10-2001   #18
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Lock up

Explain why your does, and several other people i have spoken to who did the modification have no trouble.
#1 These vehicles were not equipped with anti lock
#2 Any vehicle with a good solid rear brake set up w/o anti lock will lock rears at full depression, everyones.
#3 If you read my post you would have noticed i mentioned altering the spring length, did you try this as well.
#4 If you have a better solution please let me know, i am open to all suggestions.
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Old 09-16-2001   #19
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lock up

Well it could be that my car is a 89 so I got the PRB calipers, that might be the problem or that my car has only 26,000 miles I don't know, all I know is that I had to be very carfull in how I aplied my brakes (no sudden depression) or i'll be leaving two black lines behind me. Also in the rain I was locking up even under light peddle depression, and thats with brand new tires. So in fear of killing someone or smashing up my car in case I had to stop in a emergency I had to put it all back to how it was.

I still might try the spring idea and see if that works but I was hoping that your fix would have work for me.
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Old 09-17-2001   #20
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An idea

Tony, i have an idea for you, maybe it will help. Jack the rear end and replace the spring/piston. Mark the distance that you depress the pedal to when the rears start to slow down and then stop. It just maybe that for some reason your brakes are working fine. If you depress the pedal 1/2 way and rears stop you really don't have a problem, however if you completely depress the pedal and the wheels are still turning slightly then try altering the spring length. Your case might be different why? i don't know but just maybe. I altered the spring in increments of 1 coil at a time Approx 1/16 of inch.
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