On my 95 2500 4wd, I have always had soft brakes since I bought the trcuk 3 yrs ago. I now have been told that I need to have a scanner that has the brake bleed sequence to bleed the brakes correctlym because of the ABS unit.

I also have the ABS kick in slightly almost every morning after a damp night.

I have put 80K on the truck - 2 sets of front brake pads - went to do the rear for the first time a few weeks ago and found frozen adjusters, one leaking cylinder and brake shoes with over half life left. No good pressure when bleeding these. This is what started this research.

Thanks

 

Any input from anybody? Did I post this in the wrong forum?

 

I must have missed your post. I try to respond to every post that I have knowledge on.

My truck was the same when I got it. Seized rear brake cylinders. After redoing all my steel lines and front brake hoses, the pedal was very nearly the same as before, with only slight improvement. What I found to work, is having properly working rear brakes. Your proportioning/metering valve kicks in the rear brakes before the front disc brakes, which is why it feels like your pedal is soft.

I'd say rebuild both rear drum brake systems with fresh drums, new cylinders, a brake spring hardware kit and scuff up the rear pads a bit. Apply a small coating of Permatex Anti-seize to each brake shoe contact pads on the backing plate, install all the springs and new (or cleaned, freely moving) adjusters and adjust the brakes so that the shoes only barely drag on the drum. You should be able to spin your axle about one full revolution (360 degrees) and have the axles come to a stop from the brake drag.

You'll find your brakes come to life. Warning: Possible face to windshield contact may occur if you aren't ready :P

Pump up the brake pedal before moving the truck! Also be sure to use a brake cleaner and a paper towel on your new drums! Also use some brake clean on the pads themselves when you're all done. Make sure there is no grease/dust/contamination on the shoes.

Good luck!

 

Thanks for the reply. I am used a discussion forum having lots of discussion, seems like your the main person keeping this forum going.

In reply to some of your reply - I have replaced the shoes, cylinders, and adjuster components(a kit with everything adjuster related). When bleeding the brakes after that job, I discovers a weak pressure at the rear bleeders. No offense, but I don't see how going back into the brakes and cleaning and scuffing will do any good when I don't have pressure.
As for the proportioning valve, where is it? I thought that on modern vehicles, the master cylinder did the proportioning, thus the line going to the rear from the smaller resevior and end of the pistion, and the line going to the front brakes from the larger. I thought the only thing in between on these trucks is the ABS unit.

Update: local mechanic friends say the ABS has a bleed sequence using a computer. Went to one of them and used their Snap -On computer to try and do this. The computer has the option to select ABS bleeding after we entered the VIN info, but when we used the adapter specified by the computer and hit go, it says it can't comunicate. They spent 2 hrs trying to make this work, and they believe they have done this successfully on other 95's before.

 

I guess I didn't know about weak hydraulic pressure to the rear brakes. I was under the impression that your rear brakes simply weren't working like they should be. My mistake.

As far as proportioning goes, that isn't done by the master cylinder. It is done by either the ABS unit, or the combination valve. On your truck, I suspect the metering is done by the ABS unit. If you have weak hydraulic pressure to the rears, I suspect a master cylinder issue, kinked brake line, collapsed hose (the one that goes from the steel line to the splitter block on the rear axle) or a blockage inside the ABS unit.

The Snap-on scan tools are great, but for GM vehicles, I'd say use a GM Tech-II/Tech-I. Mitchels ondemand says to use a Tech-I (Tech one) and the RWAL/4WAL cartridge to do the ABS bleed.

I suspect a hydraulic issue though, if you say there is low pressure to the rear. Have you checked the rubber hose that runs from the rear steel line to the axle housing? You could disconnect the steel like from the output of the ABS unit and open up the bleaders and use compressed air to blow the lines clean. Maybe there's debris clogging the line.

Sorry if this is a recap of anything you've done, I'm just running through the thoughts in my head.

EDIT: I'm more leaning toward the master cylinder being bad. That's where the pressure starts. If you have low pressure, then bleeding out air isn't going to fix it. Air in the lines will only make the pedal feel springy/spongy - that is because you can compress air and not liquid.

 

Thanks for your reply again.
I don't get online regularly, so it has been a while.
I understand what your are saying about the pressure starting with the master cylinder. I have made arrangements to use a test kit from a mechanic friend, just have not got around to it - partly becuase I need to know what I am testing for. How many psi should it do?
I get tired of throwing time and money into lost causes so I will hold off on the ABS bleed until I test the MC.
I will let you know the results.

 

Sorry I have no clue about the pressure tester.

What does the brake fluid reservoir when you push the brake pedal slowly? Does the level rise in one and lower in the other? That example would indicate that the seals are bad in the master cylinder.