Braking issue - out of ideas!!!

[yaryar]

Hi all,
Long time lurker, first time poster as I've always been able to keep my 95 Chevy going and fixed, until now. Here's the story. Last year I had both rear wheel cylinders replaced as they were leaking, and had the rear pads replaced as well. Braking system working good as new, until....
2 weeks ago, I was driving in the rain and had to brake really fast and hard. The anti-lock kicked in, pumping the wheels quickly, but the pedal traveled to the floor as the antilock was doing its thing, until the truck finally stopped. I proceeded driving until I came to a stop sign, when I braked normally. The pedal traveled almost all the way to the floor, but finally stopped before it reached bottom. I suspected master cylinder so I replaced it, and bench bled it before installing. A week later and no change. Basically when you first apply the brakes, the pedal is firm immediately and brakes work well, but as the truck rolls to a stop, the pedal slowly travels to the floor, but gets firm again right before bottoming out completely. Fluid level in the reservoir is ok after a week of city driving, so the system isn't leaking. Any ideas, as I'm stumped?????

[j cAT]

Originally Posted by yaryar

Hi all,
Long time lurker, first time poster as I've always been able to keep my 95 Chevy going and fixed, until now. Here's the story. Last year I had both rear wheel cylinders replaced as they were leaking, and had the rear pads replaced as well. Braking system working good as new, until....
2 weeks ago, I was driving in the rain and had to brake really fast and hard. The anti-lock kicked in, pumping the wheels quickly, but the pedal traveled to the floor as the antilock was doing its thing, until the truck finally stopped. I proceeded driving until I came to a stop sign, when I braked normally. The pedal traveled almost all the way to the floor, but finally stopped before it reached bottom. I suspected master cylinder so I replaced it, and bench bled it before installing. A week later and no change. Basically when you first apply the brakes, the pedal is firm immediately and brakes work well, but as the truck rolls to a stop, the pedal slowly travels to the floor, but gets firm again right before bottoming out completely. Fluid level in the reservoir is ok after a week of city driving, so the system isn't leaking. Any ideas, as I'm stumped?????

pedal to the floor is most often the brake system has a fluid leak..
some however have found the ABS unit to be internally causing this problem ...going to the scrap yard is what they did ..vehicle is too old for a new unit ..

[twinly01]

I have read post online about the brake booster causing similar problems. Check all of your hoses for leaks. In the engine as well as all of the lines going to the brakes for a hissing noise, or fluid leakage.

[yaryar]

Did some Googling and found that the problem could likely be the EH(electro-hydraulic) valve involved with the ABS module. A faulty one would cause the exact symptoms I'm having. Would the entire module need to be replaced, as when I looked around trying to buy an 'EH valve', I couldn't find any????

[twinly01]

I am not sure what that part is, if I need to find a hard to find item I go to ebay, they have almost any part that one could need, so far the parts that I have purchased are proving to be high in quality and fairly priced, just make sure you get them from a person with high ratings and alot of stars. If you can't find it there try a few of your local junk yards. I always start with the cheapest stuff first when I am trying to figure out a problem.

[j cAT]

Originally Posted by yaryar

Did some Googling and found that the problem could likely be the EH(electro-hydraulic) valve involved with the ABS module. A faulty one would cause the exact symptoms I'm having. Would the entire module need to be replaced, as when I looked around trying to buy an 'EH valve', I couldn't find any????

this maybe possible to repair , but I doubt it..this is why like I said the other forum members got a scrap yard replacement...

If you are sure no leaks then this ABS valve assembly is highly suspect...new it too expensive ..as a test you could bypass the ABS ...

[j cAT]

Originally Posted by twinly01

I have read post online about the brake booster causing similar problems. Check all of your hoses for leaks. In the engine as well as all of the lines going to the brakes for a hissing noise, or fluid leakage.

with a leaking brake booster you get a hard brake pedal...not pedal to the floor...

[yaryar]

OK, so one of my friends at work called his buddy who is an ASE mechanic and he said that there is a valve within the Kelsey-Hayes ABS module that is known for sticking when the ABS is activated. So assuming the problem was within the ABS module, I thought it wouldn't hurt to reactivate the ABS again. So on the way home yesterday, the streets were slick from a light rain. When I was going around 45 and it was safe, I locked up the brakes. The ABS kicked in as it should have. Amazingly, the brakes now work perfect again!!! I guess whatever valve was sticking unstuck itself. So if you guys ever hear of this problem again, you've got a possible solution!! Thanks to all who took the time to contribute to this thread.

[j cAT]

Originally Posted by yaryar

OK, so one of my friends at work called his buddy who is an ASE mechanic and he said that there is a valve within the Kelsey-Hayes ABS module that is known for sticking when the ABS is activated. So assuming the problem was within the ABS module, I thought it wouldn't hurt to reactivate the ABS again. So on the way home yesterday, the streets were slick from a light rain. When I was going around 45 and it was safe, I locked up the brakes. The ABS kicked in as it should have. Amazingly, the brakes now work perfect again!!! I guess whatever valve was sticking unstuck itself. So if you guys ever hear of this problem again, you've got a possible solution!! Thanks to all who took the time to contribute to this thread.

since this is an old vehicle the brake fluid should be replaced..moisture over time gets into the fluid and then these type of problems occur..some vehicles have sensors that will throw a indicator light pointing out that the brake fluid needs servicing, when the moisture absorbtion gets too high..