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95 GMC K2500 brake issue driving us crazy!

JBK
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JBK Enthusiast

JBK

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Not able to keep this topic short as I want to try to explain all I've done with no success. I have a 95 GMC K2500 (6 lug axles) 5.7 engine, JB6 brake code in glove box. About 2 years ago I replaced all the brake lines with stainless lines and also installed stainless braided front  brake hoses, rear brakes are drum, no problems what so ever. About four months ago we used the truck to go on a short vacation, on way home my brake booster went up, brakes were soft and every time I applied them you heard the vacuum in the cab from the leaking diaphragm. For this year truck could not find a new power brake booster so had to buy a rebuilt one, got a GM rebuilt. My mechanic installed it and the brakes worked great for 3 months. I think my problem started when I went about 150 miles from home to pick up a small front end loader for my mower, pulled my small utility trailer to haul it, total weight of loader and trailer maybe 1,000 lbs. On way home a stop light changed quickly and I had to apply the brakes hard to stop but did not lock up any wheels, when I took off from the light the truck seemed lack power but think my brakes were partly locked up then released. Forgot to mention the truck only has 80,000 miles on it. Ever since then "at times" when stopping my brakes lock up. I have tried to make them lock up at times trying to figure out what's going on but cannot, never know when it's going to happen. We had already changed the power booster as I said and it had been working great. Since this has started I've tried everything I know experimenting to try to find the problem. I have put on a rebuilt master cylinder as NAPA did not have a new one at the time, Pulled the ABS fuse, and Brake light fuses, still same problem. No dash warning lights have ever come on except when I had the ABS fuse out. Another strange thing is when the brakes lock up the brake pedal sticks down but the brake lights on the back of the truck are not lit, any other time all I have to do is just barely touch the pedal and the brake lights on the back work fine. I have found that when the pedal is stuck down if I take my foot and press a little harder down the brake lights on the back will light up. Even though a new one came with the rebuilt Power Booster I have also bought and installed a new GM vacuum check valve. When I unplug the vacuum line and put my finger over it you can feel it is pulling plenty of vacuum. I have bled the brake system 3 times now with all new fluid. Another thing I tried is one time when they were stuck on I loosen the bolts holding the master cylinder to the power booster to free up the master cylinder from the power booster push rod to see if they would release but they did not.

Now here's another thing we cannot figure out, when the brakes stick on sometimes I can still move the truck by giving it more fuel, lately if they stick on and I wait a bout five minutes (leaving the truck running) it seems like they stick even harder and the truck will not move at all. Since the weather here has changed I've also noticed when it cold and damp they stick on even more often. Truck had all new brake pads installed couple of years ago and they are in good shape.

Here's another thing we can't figure out. When the brakes stick the pedal stay's down, I have found that if I turn the truck off within about 5 to 10 seconds the pedal releases and comes back up to it's normal position, you can also hear the brakes release and feel them free up (feel's like all the brakes are locking up not just front or rear) another thing I found is one time while they were locked up I left the engine running and pulled the vacuum line off the power booster and the brakes released.

Have thought about jacking the truck up and making sure all wheel's are locking but never know when it's going to happen and if it does I would have to leave the truck running the whole time to check all the wheel's cause soon as you cut the engine off they release. Still when they release sounds like all wheels are releasing.

I have searched the internet for hours trying to find a solution or if someone else has had this problem with no results. I hope someone on this site can point us in the right direction cause we're going crazy trying to find the problem and I'm almost afraid to use my truck till I find how to fix it.

Thank's in advance for any replies!!

 

 

bronyaur Enthusiast

bronyaur

Posted
Posted

The biggest clue here is the brake pedal sticking down, which leads me to suspect something mechanical related to the pedal.  Either the brake booster itself is binding it up or there's something in the connector rod or pedal fulcrum that's catching.  Check the rod connected at the top of the pedal.  The clip that holds it on there is a pain in the ass.  It typically gets removed/installed by feel as it's almost impossible to get your hands up there and see what you're doing at the same time.  Perhaps the clip is not on straight or the top may be pointed in an unfavorable direction and it's catching on something.  I don't recall how that rod attaches to the brake booster but that's another thing to check.  The final thing is the pedal fulcrum.  Make sure it's not binding in some manner.

JBK Enthusiast

JBK

Posted
  • Author
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Thanks so much for your reply Matt,  I have checked the pedal and can not find anything that is binding so do not think that is my problem. Also a few other issues with my problem that to me wouldn't point to a binding issue.

1. Why do the pedal and brakes release when I turn off the ignition?

2. Why do the pedal and brakes release when I pull off the vacuum line?

3. Why is it that my rear brake lights work perfect whenever I barely touch the brake pedal but when the brakes lock up and the pedal is down the rear brake lights are not on?

4. When the brakes and pedal do stick after I turn off the ignition it only takes about 5 to 10 seconds for the pedal to come back up and the brakes to release, if it were binding just turning off the ignition shouldn't release everything.

I will recheck under the dash to make sure nothing is binding but with the issues I have I can't explain why the above items occur.

Again thanks for replying!!

OZRY83 Enthusiast

OZRY83

Posted
Posted

Im thinking something with ABS module, it controls brake pressure to different wheels. Have you had ABS scanned? Think you have to have a special code reader for that a regular obd2 doesn't check that.

HD! New Member

HD!

Posted
Posted

If all else fails change the brake lite switch, it maybe the plastic in this switch has cracked, deteriorated, or whatever!  It would explain a lot of what you are experiencing and GM buys their parts from the lowest bidder!  I came on this site looking for help on another problem - I have a set of 1999 GM Manuals and they are worse than garbage - a lot of words and pics but of no help!

  • 2 weeks later...
JBK Enthusiast

JBK

Posted
  • Author
Posted

Thanks to all who replied to my problem. Think I may have fixed it. A couple of times when the brakes stuck on I did not cut the truck off or pull the vacuum line to release the brakes, when the brakes were stuck on I did jack up a front wheel and a back wheel to check that both front and back were locking, both were locked up. What I found was that if I did not cut the truck off for ten of fifteen minutes I would get a squeal which could be heard inside and in the engine compartment, I traced the squeal to the Power Brake Booster, that told me there was a vacuum leak in the booster. The booster was a reman ACDelco since you can not purchase a new one for a 1995. I took a chance and got another booster also ACDeloco and replaced the booster, while I was at it since they don't cost much I also replaced the stop light switch which fits on the booster rod. I have driven  the truck for a week now and everything is working fine. Hope it stay's that way. Thinking it was just my bad luck to end up with a bad booster with the first one. 

  • 1 year later...
  • 1 year later...
Davy57 New Member

Davy57

Posted
Posted

Thanks very much fellas I have a 95 k2500 and I’m having the same problem,, I replaced all brake parts under the hood,, I’m going to replace my brake booster and pray that fixes my problem,, thanks again 

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