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Old 09-17-2001   #21
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lock up

Well I just tried what you said with the spring/piston in and I guess my brakes work fine, I just have to touch the peddle really to stop the rears. So I'll just leave it at that for now, but choping a few coils would probably work good for me in my situation.
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Old 09-24-2001   #22
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I've tried it, and it works good.

I've tried it, and it works good. Friday I will test it at a Brake Testing Machine to get some values. I will report.
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Old 10-10-2001   #23
Denis R
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89 Germany

Have you performed your brake test and if so what are the results i am extremely curious?
THNX
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Old 10-15-2001   #24
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Cool Values

Hello,

They have tested it and they give me the following informations:

Stock:
Front: 250
Rear: 100
E-brake: 100

After remove this bloody thing:

Front: 250
Rear: 150
E-brake: 100

I think thats enough, but it's just not possible -even on wet surface- to stop the rear wheels when I push the brake pedal on the floor. Might be another problem.
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Old 04-11-2002   #25
BretD 88GTA
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Tony,
It is my understanding that only the pre-89 cars have the rear braking problem. Your PBR calipers shouldn't require this mod, to my knowledge.

The rear brakes on my 88 seem to work pretty well. But I also CONSISTANTLY use the parking brake whenever I park the car. This is ESSENTIAL to keep the rear brakes functioning correctly. Otherwise they freeze up and become non-functional.
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Old 04-12-2002   #26
zimmstoy
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This has been tested on Impala SS'. I did this mod on my Impala and the improvement was great. It was tested and revealed a 70 front to 30 rear difference on some cars.

People on the impalassforum sell the bolts sealed that will replace the one that gets removed with the little hole.

I never thought to try this mod out, but it may be successful on these cars if the braking system is not much different.
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Old 06-07-2002   #27
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modding the end cap

I will do the mod on Saturday, pulling the spring and plunger out, and gladly spitting and cursing it. Someone else suggested adding washers to give the spring more preload. Several have told me that is backwards. It does seems to me that less spring pressure would give more output pressure.

On the cars this mod has been applied to, is the brake line closest to the front of the prop-valve the rear brake line? That would confirm (for me) less spring pressure = more rear brakes, and boy is that what I want!

I have a question going back to the very first post - the how to:

Before the helper pumps the pedal three times, I assume fluid is supposed to be added to the resoiver?

Also, is there a reason why three pumps is all that is needed? Would it be wise to bleed at each wheel to be safe?

If in fact, the mod does not work, is there any ill-effects in tapping the hole in the end cap? Is there any reason why the cap would be no good in returning the setup to stock with the vent hole enlarged? If I need to get a spare to do this to, I'll do that.

Thanks,
Brent
'88 GTA with no rear brakes and all new hardware in the back
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Old 06-12-2002   #28
yachtmd
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Smile adjustable proportioning valve

Hi people, I have a 87GTA/350TPI, I was reading about the Brake mod, I was looking around for adjustable proportioning valves, at jegs I saw a decent lookin one, part # 950-260-2220 $39.99,I think I will try the adjustable valve before I spend Big bucks on real brakes, I have been shopping around for drilled/slotted rotors and maybe some better calipers, u can find some really killer brakes at Baer,or check out the tirerack for some crossdrilled, slotted, or crossdrilled and slotted rotors, and better pads, just throw all the stock parts in the garage so u can go back to stock if u want so just add the wwwdotcom to jegs tirerack or Baer,always Drive safe and if u drive fast u need to be able to stop fast also : )
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Old 11-21-2002   #29
Randy Osborne
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Talking

Denis R: Just completed the proportioning valve mod ~ works great!!! I owe you one. Wish I had ran accross this before I spent $ on calipers, pads, master cylinder & grief!
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Old 11-21-2002   #30
Denis R
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Glad to be of service

To all you gentlemen out there that have tried this modification and have found it to be helpful I am glad to hear. Please be advised humans are not perfect and humans run GM therefore GM can make mistakes. Should anyone require any further info on this topic do not hesitate to write. I will be checking the site more often.
Good Luck
Denis R.
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Old 11-21-2002   #31
The Anvil
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1989's?

Denis, this sounds like a great mod, but is this for pre-89 GTA's without the PBR calipers?

My '89 GTA has the PBR's and I'm wondering if I will see benefits from doing this mod as others without PBR's have?

Thanks for any info.

Dave
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Old 11-22-2002   #32
Denis R
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Pre-89

My vehicle is late 89 with PBR calipers. Please make note of this for some reason there are PV's out there that are set up differently. If you read all of the threads u will notice one gentlemen who's brakes worked properly and i advised him on how to check it. Read that post and try my test. This will tell you if your system is working properly and no modification is needed.

Good luck
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Old 11-22-2002   #33
The Anvil
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Thanks Denis, I must have missed the gist of that post. Will re-read and test.

Thanks.
Dave
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Old 11-25-2002   #34
MrNova
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Little question. I was just checkin my car to see if the rear wheels stop when the car is raised and the brake is applied. I jacked up the rear end and tried to get the tires moving by hand but they wont go. My ebrake is off, i tried in neutral and drive. If I try really hard the wheels will budge a bit but they wont spin freely. Am I that stupid? Also, what do you guys use for jack points? Can I use the pumkin rear diff. for the back, and my new spohn SFC's for the front? I wana make sure im not breaking anything

Last edited by MrNova; 11-25-2002 at 11:16 AM.
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Old 11-25-2002   #35
Denis R
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No you are not stupid. The problem is that the diff is a posi diff.
This is nearly impossible to turn by hand. Jack the rear by the bottom of the diff (a little flat piece of wood is good) not to bend anything. Chock the front wheels and put (2) jack stands under the diff or rear shocks (Safety first) Now start the car put it in gear and get out (both wheels should be spinnin). Now apply the brakes and see what happens. (BE CAREFUL DO NOT PUT THE CAR BACK IN PARK UNLESS BOTH WHEELS ARE COMPLETELY STOPPED) It is easy to forget when car is not movin. Lifting the front is best under the chasis crossmember in the center. The problem with these cars are that they are so low to begin use 2 - 2x6's on both sides and drive the car up on them and then use the jack. Hope i was help
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Old 11-25-2002   #36
MrNova
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Thanks Dennis. Yup, rear wheels dont stop when I fully depress breaks. They slow down, stop for a millisecond it seems, and keep going at a slow speed. Guess its time to try your fix. Also, theres a bar going below my rear axle, the sway bar or something. I can get my jack under the pumpkin, but the bar runs even with the axle so I can't get my jack stands under the axle. Sway bar looks too flimsy for a stand point. Its too bad I bought a cheap jack cause the handle is only a foot or so long, making it VERY hard to jack the car by the diff. There is a piece of skinny black pipe, looks like my SFCs, that goes along the edge of the car under the door, from front to rear tires. Is this the frame rail or whatever, and can I put jack stands there?
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Old 11-25-2002   #37
Denis R
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I do not recommed since i don't know what type you have installed. Mine are very heavy duty and welded into the chasis. I can use them even though i rarely do. I have a heavy duty jack 3-ton lincoln. When i jack the car the wheels are a good 24" off the ground and i can work comfortably. Or i go to my friends shop and put it on a lift.
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Old 11-25-2002   #38
MrNova
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About your brake mod dennis, when you reassemble, do you just leave the tube/spring out? It wasn't clear in your first post, and then later you talk about cutting the spring?
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Old 11-25-2002   #39
Denis R
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Yes it is to remain out. What i wrote was before i removed it all together i modified the spring several times before i came to my final decision.
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Old 11-28-2002   #40
Chick Walter
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Re: rear brakes

Quote:
Originally posted by Psyte
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.....
A hard-core firebird guy/pontiac service manager explained to me that I have to use the emergency/parking brake when I park in order to keep the rear brakes adjusted. Rear brake adjusters work when backin up and when emergency/parking brake is applied.
Chick W. 89 GTA ASC Convert. 5.7L
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