Brake Question - 1995 c1500

[long_bed]

I just finished repairing the rear brakes on my 1995 c1500 ext. cab with the 10" drums. I was experiencing major vibration that did not affect steering and didn't begin until I pushed the pedal about halfway down. Found out the wheel cylinders had seized up and warped the drums.

I had the drums turned and put on new pads, wheel cylinders, self adjusters and put it all back together and bled the system out. The truck will stop on a dime now but still has a very small pulsation coming from the brake pedal the slower I get. The front brakes are also fairly new and since there's no shimmy in the steering I'm ruling them out.

Is it possible my drums are still warped after being turned, or could this be some other issue?

 

[RichLo]

it may take a little while to break in the fresh drums, just dont stop too hard especially when breaking them in otherwise you'll warp them right away since they're thinner and have a super aggressive finish.

 

[long_bed]

it may take a little while to break in the fresh drums, just dont stop too hard especially when breaking them in otherwise you'll warp them right away since they're thinner and have a super aggressive finish.

Good point, I've only driven about 30 miles on them so far with no hard stops.

 

[Ironhead]

I have had some experience with warped rotors on the front of a Caprice I used to own. The symptom was a pulsating brake pedal, but it did not give any symptoms at the steering wheel. It just might be worthwhile to use a dial indicator to check the front disks for runout, just so you know what's what.

And BTW, I've got a 98 C-1500 with the long bed and those pathetically small rear drums. Can't understand why the General did not specify 12" for these trucks. I just drive accordingly.

 

[df2x4]

I have had some experience with warped rotors on the front of a Caprice I used to own. The symptom was a pulsating brake pedal, but it did not give any symptoms at the steering wheel.

For what it's worth, I have absolutely experienced front rotors that were warped badly enough to create steering wheel feedback. It is possible, and it is scary.

EDIT - To clarify as that kind of seems like gibberish when I just threw it in the middle of things here...

I'd be checking your rotors and drums both. Definitely sounds like a warping issue.

 

[michael hurd]

Did you have a shop perform the brake bleeding with a scan tool? These trucks are a pain to bleed all of the air out of the brake system when it has been opened.

It is possible the rear brakes aren't contributing enough to stopping and your front rotors are doing most of the work. An uneven deposit of pad material on the face of the rotor can cause pulsation as well.

 

[Ironhead]

Did you have a shop perform the brake bleeding with a scan tool? These trucks are a pain to bleed all of the air out of the brake system when it has been opened.

It is possible the rear brakes aren't contributing enough to stopping and your front rotors are doing most of the work. An uneven deposit of pad material on the face of the rotor can cause pulsation as well.

If you cannot get the ABS cycled with a scan tool, you can also make the ABS operate by braking hard on a slippery surface. Then bleed the brakes. I do this with a Mityvac vacuum bleeder, but you do not need to do the bleeding this way. There's a god YouTube on using a vacuum pump to bleed the brakes, and I'd sure check it out if I was going to do this.

I agree that surface deposits on the rotors can give you a pulsing, similar to the pulsing you get with a warped rotor.

 

[michael hurd]

There are some other things that can affect the feel of the brake system. If you have access to a dial indicator, you can measure the rotor run out yourself fairly easily.

If both rotors are good, ensure the mounting surfaces are clean, the back of the rims are clean, the studs are lubricated lightly and the nuts are torqued to specifications.

Assuming the run out measurement is good, my suggestion would be to take it out and burnish in the pads properly and drive to let the brakes cool down, and then try your low speed stop again to see if that took care of the pulsation.

 

[long_bed]

I have had some experience with warped rotors on the front of a Caprice I used to own. The symptom was a pulsating brake pedal, but it did not give any symptoms at the steering wheel. It just might be worthwhile to use a dial indicator to check the front disks for runout, just so you know what's what.

And BTW, I've got a 98 C-1500 with the long bed and those pathetically small rear drums. Can't understand why the General did not specify 12" for these trucks. I just drive accordingly.

There are some other things that can affect the feel of the brake system. If you have access to a dial indicator, you can measure the rotor run out yourself fairly easily.

If both rotors are good, ensure the mounting surfaces are clean, the back of the rims are clean, the studs are lubricated lightly and the nuts are torqued to specifications.

Assuming the run out measurement is good, my suggestion would be to take it out and burnish in the pads properly and drive to let the brakes cool down, and then try your low speed stop again to see if that took care of the pulsation.

For what it's worth, I have absolutely experienced front rotors that were warped badly enough to create steering wheel feedback. It is possible, and it is scary.

EDIT - To clarify as that kind of seems like gibberish when I just threw it in the middle of things here...

I'd be checking your rotors and drums both. Definitely sounds like a warping issue.

I will find a dial indicator and do my due diligence. It got progressively worse on the way home tonight so I'm starting to wonder if these drums are just done. 180,000 on the original set, there may not be enough material left to stay strong even after being turned Also, my tires are in pretty bad shape so it already has a small vibration when driving.

Did you have a shop perform the brake bleeding with a scan tool? These trucks are a pain to bleed all of the air out of the brake system when it has been opened.

It is possible the rear brakes aren't contributing enough to stopping and your front rotors are doing most of the work. An uneven deposit of pad material on the face of the rotor can cause pulsation as well.

If you cannot get the ABS cycled with a scan tool, you can also make the ABS operate by braking hard on a slippery surface. Then bleed the brakes. I do this with a Mityvac vacuum bleeder, but you do not need to do the bleeding this way. There's a god YouTube on using a vacuum pump to bleed the brakes, and I'd sure check it out if I was going to do this.

I agree that surface deposits on the rotors can give you a pulsing, similar to the pulsing you get with a warped rotor.

I experienced the ABS unit issue a few years ago when I replaced the master cylinder & booster on my 96, never could get that truck stopping properly again. This doesn't feel the same to me but I'll keep it in mind to try to cycle it next time I'm out driving. The reservoir never went empty and i swapped the wheel cylinders out pretty fast so I'd hypothesize the ABS never went dry.

Thanks for all the help folks. I really hope I can get this resolved soon. Taking a break on wrenching tonight but may put it up on the stands again this weekend.

 

[Ironhead]

Drums have a maximum diameter spec, and rotors have a minimum thickness spec.

Years ago, when I did not have much money, I drove an older Buick Skylark with aluminum brake drums. When they reached 90 thou over sized, they needed turning again, and the shop would only do it if I signed a waiver, as 90 thou over was the maximum allowed by the factory specs, and they noted on the bill that the drums were turned to 120 over because the customer insisted. Having said this, I have no idea about the size of your brakes, and am not implying that you are deliberately compromising safety.

Those drums went out of round pretty quickly. That old Skylark would haul a$$ in a straight line, but it would not turn or stop worth a damn.

Brakes are pretty important, especially when they are fairly marginal as they are in the GMT 400 light duty trucks, so it's important to get them working as well as possible. Good luck on this one.