1995 C1500 Brake Issues

[95C1500]

Okay I've ranted about this many times, I just want to put it all in one thread.

My truck is a 1995 C1500 that originally came with the 10 bolt rear axle. At some point, I started having awful brake noises. Like a grinding sound the last half a second before coming to a complete stop. So I rebuilt the brakes and all was good for 4,000 miles until it happened again. I replaced them under warranty, about 6000 miles later, it was happening again. Brakes worked as good as you can expect a 400's brakes to work, it just pissed me the hell off. So for my birthday, my family decided that my present would be having a shop work on the truck and fix it once and for all. At this point, I was perfectly content with that. They kept the truck for 4 days, claimed they drove it multiple times an never heard a sound out of it (I call complete bs). They said the rear brakes looked brand new (which they basically were) so they just cleaned them and replaced the fronts (which were not the problem). I got to pull out of the parking lot and there's that God awful grinding noise again. I had somewhere to be so I left. Brought it back a couple more times, realized they were incompetent (or they thought I was) and never went back. I should also mention that I had the system flush and filled with new fluid.

I came across a 14 bolt on craigslist. I snatched that up. Did the 6 lug swap, rebuilt the rear drums down to the backing plates. All was good until one of the shoe hold down pins ripped through the cup and one of my shoes was loose inside the drums as well as the spring and cup. That did a number on my drum and the noises were starting again. I replaced that rear drum under warranty, and it was great for about 100 miles and the noises were as bad as they were with the 10 bolt.

As if that wasn't bad enough, I realized my bakes lock up under heavy braking. And i don't mean panic stops, I mean coming to a stop at a traffic light and applying a lot of brake. I know I will not hit that car in front of me but my rear brakes lock up and then I get flipped off. And then I noticed my truck liked to lurch when coming to a gradual stop in traffic. So great, the damn things are grabbing.

So I ordered an adjustable proportioning valve from jegs.
http://www.jegs.com/i/JEGS-Performance-Products/555/63020/10002/-1
It may be the wrong one, if it is, no big deal, I'll return it and get the right one. That's not the point though. My question is, is it possible to keep the abs and use the adjustable prop valve? Is it worth it? Should I delete the abs all together? I don't want to delete the abs, install the adj prop valve and still have the dam things lock up in the rain. JR, I know you did yours recently, can you brake pretty hard without locking anything up? In dry/wet conditions? I want to know what I'm getting into before I attack this. So pictures would be great.

I've beat this crap to death but help a guy out. I'm stupid when it comes to brakes, and I just want them to work properly.

 

[ShadowRejects]

Not sure about your truck, but The factory proportioning valve is part of the RWAL brakes (or rear ABS, same stuff) I wouldnt run two proportioning valves. I would run just that aftermarket one.

Now that I actually read it, it sounds like your rears have a higher pressure than the fronts, since the rears are locking up and making noise. Now it could be completely possible that your factory propositioning valve is screwed up and sending too-much pressure to the rear brakes, causing them to have a much higher brake line pressure than the front. I'm not a brake master-tech though so do not take my word. But that is what it sounds like.

If I were you, I would delete the RWAL/ABS, ditch the proportioning valve and splice in that one from Jegs, and try to turn the rear pressure down some, bleed the brakes and give it a shot. If all else fails, you are not out a whole lot of money, so its worth the shot.

 

[michael hurd]

Did you also change the master cylinder to match the new rear brake size, and bleed the system properly?

 

[95C1500]

Not sure about your truck, but The factory proportioning valve is part of the RWAL brakes (or rear ABS, same stuff) I wouldnt run two proportioning valves. I would run just that aftermarket one.

Now that I actually read it, it sounds like your rears have a higher pressure than the fronts, since the rears are locking up and making noise. Now it could be completely possible that your factory propositioning valve is screwed up and sending too-much pressure to the rear brakes, causing them to have a much higher brake line pressure than the front. I'm not a brake master-tech though so do not take my word. But that is what it sounds like.

If I were you, I would delete the RWAL/ABS, ditch the proportioning valve and splice in that one from Jegs, and try to turn the rear pressure down some, bleed the brakes and give it a shot. If all else fails, you are not out a whole lot of money, so its worth the shot.

Yeah I was just curious if I could use the new prop valve in place of the prop valve on the abs unit

Did you also change the master cylinder to match the new rear brake size, and bleed the system properly?

I didn't change the master because I read over and over again that it was not needed. I bled the brakes but someone mentioned I might have air in the abs system. So I should find a thread on how to properly bleed the system before messing with anything else

 

[michael hurd]

Yeah I was just curious if I could use the new prop valve in place of the prop valve on the abs unit

I didn't change the master because I read over and over again that it was not needed. I bled the brakes but someone mentioned I might have air in the abs system. So I should find a thread on how to properly bleed the system before messing with anything else

The master cylinder bore is a different diameter.

Look in the listings on Rock Auto for a K1500 of the same year. Different master cylinder for 10 inch brakes vs the 11 5/32 inch.

Who told you the master cylinder was the same?

Common sense should prevail here, your braking system is now unbalanced.

Yes, the abs system is a pain to bleed properly. GM uses a scan tool to perform a bleed procedure, it activates the abs module.

There are backyard methods to get the abs to activate without a scan tool.

 

[95C1500]

I researched over an over for weeks before actually doing it. I know I read a couple people say they didn't swap masters and their brakes worked fine. But good to know

 

[michael hurd]

I researched over an over for weeks before actually doing it. I know I read a couple people say they didn't swap masters and their brakes worked fine. But good to know

Some people couldn't tell you if their axle was on fire behind them, they are oblivious. Fine is 'subjective' not objective. Again, some people drive on totally bald tires, and they are 'fine'.

I am willing to bet if you install the correct master cylinder, and have the brakes bled properly, you will have a new appreciation for the factory brakes, when balanced correctly.

 

[95C1500]

Thye could have had the same issues and called it fine for all I know. I'm definitely willing to give that a shot before deleting abs. I actually like abs unlike most it seems. I've learned to live with the "crappy" brakes on this truck. So that seems to be my best option. New master and bleeding the system. Thanks!

 

[95C1500]

So correct me if I'm wrong, but
JB5 = 10"
JB6 = 11"
JB7 = 13"

The master cylinders I am finding at autozone, rockauto, even ac delco say the same master is for jb5 (10" - what my brakes used to be) and jb6 (11" - what they are now).

Edit: I went back and looked and did find the two different masters for 10"/11" brakes from that one company.

 

[michael hurd]

Strange, newgmparts.com is showing the same master cylinder for all models, even the pressure metering valve buried in the abs module.

I know I have seen different part numbers in the past for 10/11" brakes for the master cylinder.

Hold off on replacing the master cylinder. Bleed the brakes with a tech 2 scan tool to cycle the ABS, or try one of the backyard methods.

Jack up the vehicle and support it well so it cannot fall off stands or blocks, keeping the rear wheels off of the ground. Start the engine, apply brakes and put the vehicle in gear. Accelerate up to about 50 mph with the rear wheels spinning, then apply the brakes hard. Wait for the driveshaft and the rear axle to stop rotating, then put it in park. The ABS controller will look at 'road speed' and front wheel speed, sensing a lock condition ( front wheels not rotating ) and pulse the brake module.

Repeat the bleeding procedure, all 4 corners, then repeat the in gear, wheels rotating, brake, as many times as you need to get a good pedal.

Keep in mind when bleeding you need to have the rear brakes adjusted up before bleeding.

You may go through a few quarts of fluid to get good clean fluid throughout the system with no bubbles.

Lower the vehicle and take it for a road test.

How good are the front brakes, have you taken the calipers off recently to check the pad and rotor condition, especially the rear side you can't see with the dust shield in the way?

Hope that helps you out.