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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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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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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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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.
 

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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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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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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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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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... 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 - ???

.. 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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Discussion Starter #10
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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Discussion Starter #11
Dealership says they used their equipment to bleed the ABS system and couldn't get it to bleed. Is this any indication that the ABS PUMP is dead?

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I keep hoping some one with a 1996 FSM will chime in on this.

The 94-95 is different from the 96 but they are a Bosch 2u system and should be similar.

If your engine/exhaust system is not too loud you can check the pump by ear.

Find a quiet downhill spot. Turn the car ignition to off. Then start the car and let it roll down the hill. At 4 MPH you should hear a short buzz of the ABS pump doing it's "Auto Test" (automatic test). If you are sure that you can turn and stop the car with the engine off. (no power steering and no power brakes) you might hear it better (key in run ). It sounds a bit like the fuel pump noise you get when you just turn the ignition switch to run. Buzz stop.

The ABS system does this every time you start the car and get it over 4 MPH (fwd or rev). If the pump or valves failed electronically The ABS light would be turned on and they would have a fail code to read.

The 1994 system with the correct dealer/aftermarket scan tool can go Mode 4 (misc. tests). Some one who knows what they are doing will be able to do the "Auto Test" with the car standing still. The valves can also be checked.

Dealership says they used their equipment to bleed the ABS system and couldn't get it to bleed. Is this any indication that the ABS PUMP is dead?
No, the pump and valves are one unit and will be replaced as one piece. It would take pages to discuss how they decided "couldn't get it to bleed" The short question is why there is no ABS trouble codes if they were really unable to move the valves. To be fair there are failures like yours that do not trip a code.

Now for a short rant. I would not let these guys oil the chain on a pedal car. They do not seem to understand ABS systems. The ford system on my crown victoria does all the same things all the same way. I have had to read the Chevy FSM to make sure I am not confusing the two. My personal opinion is they do not know how to use the correct scan tool or do not have it. When you fix it get a report from the shop. Get a couple of 6 ft friends and have a talk with the dealership's general manager about getting some of your money back.

I would talk to some other repair shops and find one that show you the "Auto Test" triggered by the scan tool. I still think pressure gauge will lead you to replace the ABS module.

I almost never recommend "just tossing parts at a problem" In this case it might be cheaper for you to install a junk yard ABS module then have a shop that can do a ABS bleed finish the problem. You would know you were on the right track because the brake pedal would not go to the floor.
 

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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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well if I had it I could fix it . pedal to floor is the master cylinder most all the time . This can be tested on the vehicle .you block off the 2 lines and if pedal stays high it is good.. 17K miles I doubt it is the ABS since these are in a protected area unlike my GM truck which I had to take apart and fix due to the fasteners rusting out on that aluminum body.

the ABS is possible the problem, I doubt it but if a valve is hung up it can do it. try to get the abs to cycle. drive the vehicle on a soft shoulder and hit the brakes so the abs cycles ..
 

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I'd suggest taking it to a local hot rod shop and having them remove
the ABS module completely and neatly flare the lines together.
Replacing the module with one from the junk yard as someone suggested is another idea, but
if you plan on keeping the car, it will fail again as these cars get closer to 30 years old.
Like the Vehicle Anti Theft System VATS that is giving everyone fits these days,
these abs systems were not designed to last that long.

Nab
 

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Dealership replaced the master cylinder twice. Didn't fix the problem.

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as I stated the master does not require removal to test it . plug the 2 lines and see if it holds the pedal high if so , no master problem. dealership did not test it, crooks !

drive vehicle on shoulder to activate the ABS .. with the right wheels slipping the left NOT the ABS will cycle the valves. 17K miles the ABS should not be damaged but a valve could be sticking or not sealing properly from lack of use.

also IMO YOU NEVER BRING A GM VEHICLE TO THE DEALERSHIP THIS OLD !!! Those repair techs probably were not even born , or were in the sand box school when this was produced .

cycle the ABS then bleed the system .. bring to a repair shop not a dealership , if your not up to it.

you may have a small leak it can happen . you sure the calipers and the bleed screws are not wet ?

this ever had a brake job done ,probably not @17K miles ...

was this stored outside or in a garage ? If it was outside could be steel lines leaking around the rear axle. driver side <<<,
 

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Huh - never connected the dots with this one being the same. Wasn't this the one where the dealer "replaced" the ABS module "twice" without fixing? If so, then still not as impressive as the warranty "replaced head gaskets" on my wife's Explorer that the dealer managed without even breaking the paint or seals anywhere.
 

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A poster deleted his post so I deleted the answer. I looked over the thread and want to clarify post#3.


If the master cylinder can make pressure but it is not getting to the wheels then it (can be) is leaking past the ABS reservoir valves. The fluid leaks into the ABS reservoirs (4 possible) (3 on a b-body) instead of going to the wheel cylinders. No external leaks. The ABS pump will return the fluid after the (a panic stop runs the valves and ABS pump) 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.

For the record the dealer replaced the master cylinder twice but would not explain where the fluid was going. The dealer did the same repair twice which did not resolve the problem. Unless a master cylinder leaks back into the booster, or drips around the fluid reservoir it is not the cause of missing fluid.
 

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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.

The combination valves can be rebuilt nowadays. I have a rebuild kit and instructions available for anyone who wants to take on the job. It does require a specialty tool to extract the internal piston, but I have instructions available to deal with that, too. Send me a PM if interested.
 
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