Brake Issue 96 SS - Chevy Impala SS Forum
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post #1 of 21 (permalink) Old 05-27-2017, 06:02 PM Thread Starter
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Brake Issue 96 SS

Pedal slowly goes to the floor. If you pump it you have brake but as soon as you stop it goes to the floor. There are NO fluid leaks anywhere. No brake locking. No ABS light. Nothing. My brother and I bled the lines manually and this didn't help. So now the car is at a Chevy Dealership in Illinois and they have replaced the MS... twice. Now they are telling me the problem could be ABS related and that the parts are obsolete. There was a proportioning valve add done to the car by my Dad after he bought the car. They can't find this part either. This car has 17k on it. My Dad passed away in 2015 and left it to his family. I want to drive it. Show it. And enjoy it in his memory. I can't believe it can't be fixed and I'm at my wit's end.

Does anyone have any ideas? Can anyone point me to where I can get the proper proportioning valve for the car? Can the valve currently on the car be bled?

If anyone has experience with this issue please do offer me any direction you can.

Thank you very much.



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post #2 of 21 (permalink) Old 05-27-2017, 09:33 PM
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If it is the proportioning valve, you can not bleed it, and you can not rebuild it. There are none available new. You only option is to get a used one. I PMed you.
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post #3 of 21 (permalink) Old 05-28-2017, 12:16 AM
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Quote:
There are NO fluid leaks anywhere
Find a shop that can put a pressure gauge on each bleeder. If the master cylinder can make pressure but it is not getting to the wheels then it is leaking past the ABS reservoir valves. The fluid leaks into the ABS reservoirs (4 possible) instead of going to the wheel cylinders. No external leaks. The ABS pump will return the fluid after the stop.

Some of the symptoms are like a master cylinder fail.The difference is that you will see the fluid level in the master cylinder go up and down. When the master cylinder fails the fluid does not drop.

Check around there are several suppliers for rebuilt ABS.

Think about a proportion valve failure. The fluid may equalize (front to back) but the pedal would not go down differently because the system volume is the same.

You need to ask around and find a better shop. It can be very hard to find mechanics that can think through a problem. They should have done a pressure test on the master cylinder before the second one was installed.

When this happened on my dodge truck it drove me crazy. The pedal would drop once, the reserve would be low. I would add fluid then later find the reserve overfull. No leaks! There is no pump so the fluid would stay in the "anti-skid" system until a panic stop would return it. I found some information on the dodge forums. They would bypass the "anti-skid" valve and all would work.

I like the Bosch ABS so I promote fixing it. If you do your own work a used JY ABS may be a cheap fix.

I can not think of a way the ABS computer could do this to you but you could pull the fuse to take it out of the problem.

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post #4 of 21 (permalink) Old 05-28-2017, 06:16 AM
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Another thing you can check is whether the brake fluid transfers to the rear brake (front) portion of the reservoir from the front brake (rear) partition when applying the brakes. I believe mine did that when the proportioning valve failed.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
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post #5 of 21 (permalink) Old 05-28-2017, 07:53 AM
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Brakes

Many of us took the guts out of the proportioning valve back in the day in order to get more rear brake pressure and had no issues. If the shop replaced the MC twice it sounds like they never found the problem and just threw parts at it. The GM Tech II scanner tool can run diagnostics on the ABS system. It should help to determine if the ABS module is the problem. Just bleeding the brakes does not flush any fluid through the ABS module. If you bleed the brakes and run the resviour dry you can get air in the lines that may end up in the ABS module. The only way to fix that is to get a gm mechanic to use the Tech II and cycle the ABS and push new fluid through it while bleeding the brakes. I would try that before I took things apart.

Assuming it is the ABS module, I have a spare you could use for a core. if you don't want the car down while waiting for a rebuilt unit.

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post #6 of 21 (permalink) Old 05-28-2017, 08:30 AM
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Quote:
Originally Posted by ImpalaGal14LTZ View Post
Pedal slowly goes to the floor. If you pump it you have brake but as soon as you stop it goes to the floor. There are NO fluid leaks anywhere. No brake locking. No ABS light. Nothing. My brother and I bled the lines manually and this didn't help. So now the car is at a Chevy Dealership in Illinois and they have replaced the MS... twice. Now they are telling me the problem could be ABS related and that the parts are obsolete. There was a proportioning valve add done to the car by my Dad after he bought the car. They can't find this part either. This car has 17k on it. My Dad passed away in 2015 and left it to his family. I want to drive it. Show it. And enjoy it in his memory. I can't believe it can't be fixed and I'm at my wit's end.

Does anyone have any ideas? Can anyone point me to where I can get the proper proportioning valve for the car? Can the valve currently on the car be bled?

If anyone has experience with this issue please do offer me any direction you can.

Thank you very much.
If they're simply replacing parts "hoping" it'll work, I trust you will hold them to account for this. That isn't professional and they shouldn't be compensated for their laziness. You can bypass the ABS either permanently or temporarily. If that's what they suspect, why are they throwing parts at it? Hope you get it sorted out
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post #7 of 21 (permalink) Old 05-29-2017, 09:49 AM
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Quote:
Originally Posted by Z09B4U View Post

If the master cylinder can make pressure but it is not getting to the wheels then it is leaking past the ABS reservoir valves. The fluid leaks into the ABS reservoirs (4 possible) instead of going to the wheel cylinders. No external leaks. The ABS pump will return the fluid after the stop.

Some of the symptoms are like a master cylinder fail.The difference is that you will see the fluid level in the master cylinder go up and down. When the master cylinder fails the fluid does not drop.

Think about a proportion valve failure. The fluid may equalize (front to back) but the pedal would not go down differently because the system volume is the same.

When this happened on my dodge truck it drove me crazy. The pedal would drop once, the reserve would be low. I would add fluid then later find the reserve overfull. No leaks! There is no pump so the fluid would stay in the "anti-skid" system until a panic stop would return it. I found some information on the dodge forums. They would bypass the "anti-skid" valve and all would work.

I like the Bosch ABS so I promote fixing it. If you do your own work a used JY ABS may be a cheap fix.
Seconding this great post - seen the same thing before and drove me insane.

My $.04: Double check that there are no speed bleeders on any caliper, had one of those fail in a weird way not unlike what you describe. Double check each inch of brake line, esp sections that travel through an area that could hide fluid.

I would suggest performance shops that know our cars - dealers no long attract the best talent for a long list of reasons.

You will get this done and will be rolling with pops for years to come. I am very sorry for your loss, and I'm glad you're honoring his memory by keeping this car road-safe and well maintained.
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post #8 of 21 (permalink) Old 05-29-2017, 12:06 PM
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Quote:
Originally Posted by Fred Kiehl View Post
Another thing you can check is whether the brake fluid transfers to the rear brake (front) portion of the reservoir from the front brake (rear) partition when applying the brakes. I believe mine did that when the proportioning valve failed.
If we are talking about the stock piece we are actually talking about the Combination Valve Assembly.
The FSM says it has the Metering valve, Proportioning valve, and the Pressure Differential switch.

In Fred's case it could cause fluid to move between the front and back systems. It is modified by some people to increase rear brake disk force.(metering) When a brake bleed goes wrong it is the switch that you reset to turn out the brake warning light.(hammer the brake pedal to the floor and hope for a reset)

On a 94 it is just under the master cylinder with two input lines and two output lines to the ABS. One wire to the brake warning light.

When finding a shop for this fix you would do better if they had the Tech 1 (dealer) or some one whose equipment can do the same. If they know how to use it. The Tech 1 can do "Mode 4" which allows some one to play with the ABS valves.

Personally I think it could be diagnosed by someone with pressure gauges and some head scratching.

The FSM says that normal brake bleeding will not disturb the ABS system.

Hope this helps.

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post #9 of 21 (permalink) Old 05-30-2017, 05:53 PM
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Quote:
Originally Posted by ImpalaGal14LTZ View Post
... There was a proportioning valve add done to the car by my Dad after he bought the car. They can't find this part either...
I've been hoping to glean just exactly what this 'proportioning valve add' is or was, but sure haven't caught any better description or more detail from posts to now. Z09B4U made me post just to check if it could possibly be that POP did one or both the bolt mods. If I presume "they can't find this part either" is referring to the dealer, then it shows they don't know what these popular owner hacks are in the first place. There's really nothing else to "add" to the stock valve - ???

Quote:
Originally Posted by ImpalaGal14LTZ View Post
.. I can't believe it can't be fixed and I'm at my wit's end.

Does anyone have any ideas?

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You see it's not you. The consensus is pretty much none of us can believe what we're hearing about the dealer either.

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post #10 of 21 (permalink) Old 05-30-2017, 06:31 PM Thread Starter
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Quote:
Originally Posted by 96 Black View Post
I've been hoping to glean just exactly what this 'proportioning valve add' is or was, but sure haven't caught any better description or more detail from posts to now. Z09B4U made me post just to check if it could possibly be that POP did one or both the bolt mods. If I presume "they can't find this part either" is referring to the dealer, then it shows they don't know what these popular owner hacks are in the first place. There's really nothing else to "add" to the stock valve - ???



You see it's not you. The consensus is pretty much none of us can believe what we're hearing about the dealer either.
96 Black:

It's the stealth bolt mod. In the proportioning valve. Had to get that info from my bro. I'm no car dummy but I don't mod my car.

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