96CERon

On my 96 2500 with 150K miles, the brake pedal suddenly started going on down under constant pressure as when you have a master cylinder going bad--still stops OK but it is a worry. Replaced the master cylinder with two new units all exhibit the same problem. Also replaced the ABS modulator valve which was suggested as another possible solution. That is not it. All this work was carefully done with vauum bleeding and bench bleeding of components and wheel cyclinders. This is the truck with the vacuum booster, rear ABS and does not have the rear load sensing valve. I have searched this forum and it appears that there have been other occurances of this issue but I could not find anyone that posted a solution. Suggestions???

gmctd

Inspect rear shoes for wore out - if serviceable, adjust the adjusters for proper lining to drum clearance to restore pedal

John Faughn

You did not say anything about , brake / ABS lite , if theres no lites and they come on when you start the truck and then go off , you should not have a hydrolic problem , chances are . I would check out the vacume pump on the back of the power steering pump .

JKM

Honestly , I am wanting to say "live with it" , that's what i finally did after replacing everything but one hard line , and the rear shoes...

post:

https://www.dieseltruckresource.com/...d.php?t=124075

After re-reading that post , i am sitting here windering if it is the new flex lines that are giving us grief , the new lines would be softer , and likely flex easier under pressure , giving a spongy feeling.

96CERon

No brake or ABS lights are on.

TURBOWINE

mine had same problem i replace rear brake line from master cyl to the back of the truck and replace the wheel cylinders with the chevy 1 ton ones WOW the truck stops like a car now and no more soft pedal

John Faughn

With no lites , I would look at machanical issues , also put a vacume gage on the booster hose to see if the vac. goes down quick or not , if not the diaphram is ok in the booster , if it drops fast look for leak .

realtreehunter

i would check the wheel cylinders and shoes and also any leaks around hoses or hard lines

TIMMY22

sounds like symptoms of a small leak to me.

get a really brite flashlight, look for a leak between the fuel tank and the frame. this is where they go.

DL1221

I have the same problem with my 96. Truck stops fine, but the stupid pedal keeps creeping to the floor.

With the exception of the combination valve and the ABS modulator valve, I've replaced every other hydraulic component at least twice, and still the pedal goes to the floor. Unless there is some small seepage somewhere I can't see, I don't have any leaks, and I don't think I have any air in the system.

I've decided to replace one more thing, the combination valve, and that's it. If that doesn't fix the problem then I give up.

I wish I could help more. . .

JKM

Please let me know if the combination valve helps anything, i would sure like to fix my truck for good too!

I have been driving mine for a month and a half or so now since i decided to live with it as is, and my fluid level has not dropped at all ( i marked the outside of the res with a marker way back when) so i have completely ruled out any leaks...

My rear abs does work too , i have discovered that since swapping in the chevy rear cyls, my front brakes don't work worth a fart though.

DL1221

OK, I'll let you know. But it might not be for a while--right now I'm sick and tired of screwing around with the brakes.

I can tell you that swapping in the Chevy wheel cylinders had nothing to do with it, the pedal creped to the floor before and after I swapped in the cylinders. But they did make a big difference in terms of stopping distance, that's at least one good thing.

Dave D(SK)

I have the same truck and have experienced the same problem. Took it to the dealer (twice) and they said everything is OK but I have only been having about a 20% success rate with them fixing any problem I bring in but that's another story. I'll be following this post closely to see if anyone has a solution.

Dave D

Racer9

First, are you bleeding in the proper sequence? With the '94-'98 trucks the brakes must be bled in this order, LF-RR-RABS-LR-RF. The system is diagonal.

Next try removing the abs fuse. I was losing brakes during hard braking, even though I still had good pedal, until I removed the fuse, now no problem.

JKM

I am not sure about your truck , but mine sure as heck is not diagonal! It is Front/rear split with RWAL only. a Truck with 4 wheel abs MIGHT be diagonal split , but i have never worked on one of them , so i don't know for sure.

And yes , my brakes are bled properly, everything from the flex lines , and up , is good on my system , if i pinch the lines , i have a very firm pedal , unclip the front ones , and the pedal hits the floor on command...