rkhall

Hey All, I am new to this forum and need help. I'm hoping someone here is an expert that can help figure this out. Frankly, I don't trust the dealers or independent shops anymore since I just get lip service and another expensive repair bill. I apologize in advance for the novel I am about to write!
I have a 2001 Silverado 1500 2WD with a 5.3, automatic, 4 wheel disc brakes and factory tow package. I am easy on the brakes and went nearly 85k miles on the factory installed brakes. I never had any issue up to that point and felt they were the best brakes I ever had on any vehicle outside my Corvette. At 85k miles, Les Schwab told me I needed new everything, calipers, rotors, pads, the works. I went along and within 2-3 months, I had pulsating brakes. Also, the pedal feel was never the same after the new brake install. It felt squishy like there was air in the system, although they insisted that they bled it properly and actually did it again to be sure. Their excuse was "GM Soft Pedal" like it was a common problem. I figured I got lucky with the factory brakes since I never had that issue. Ultimately, they turned the rotors telling me that I had overheated them and they were blue although I never drove any different than the first 85k miles. Within 6 months, the same pulsation returned. They talked me into replacing the rotors (since they were now too thin to turn again) with slotted rotors to help with the issue. Again the problem returned.
I have now gone through this exercise several times, with several sets of rotors/pads. Still the pulsation returns. Also, as a side note, I made a panic stop in freeway traffic, which activated the ABS and the pedal was nearly on the floor. Scary stuff. Immediately after that, the pedal feel was better although after a time it began to fade again. At a stop light, I pushed the pedal to the floor and again the pedal feel was better for a time before returning the squishy again.
Another clue is that the pulsating brakes have been either front end (felt in steering wheel) or rear wheel (felt in the seat of your pants) before progressing to the overall truck shake.
I wonder if this has something to do with the brake balance, as it always seems to occur at one end or the other first? I asked the tech about the proportioning valve and he blew me off. I also wonder if the ABS might have something to do with it.
Before all of this happened, the brakes were very strong and positive with a tight pedal feel and no brake fade even when pulling a heavy trailer.


Thanks in advance for any help you might be able to offer. This is driving me nuts, and costing thousands. Even though I love this truck, I am considering selling due to this issue.


Thanks again, RK Hall.

tech2

Are you saying the problem goes away when new parts are installed but returns after a period? If yes, sounds like cheap line parts.
I have seen low quality rotors have runout right from new cause a pulsation. I don't install cheap line rotors for customers anymore due to the problems they induce. That's the reason oem parts are expensive...they are much better quality.

For the spongy brake issue. Have someone with a full function scan tool perform an automated system bleed.


A bad proportioning valve would not cause a brake shake. The abs system will not cause a brake shake. However an abs signal fall out will cause the system to activate and the pedal will drop with increase braking distances.

rkhall

Thanks for the response. I understand the cheap parts issue and spent for good quality slotted rotors this last time. Also, I apologize, as I forgot to mention that they did do an automated system bleed. The pedal feel never improved. I also know the ABS wouldn't cause the pulsation by itself. So for arguments sake, lets assume the parts were okay to begin with. I guess I am curious to know if there is some way the system could activate the front OR rear brakes out of balance with the other? My thought is that if this was possible, the brakes being applied more heavily might overheat and blue to rotors while the other side was barely applied, then leaving me with warped rotors on one end (rear end shake). I just wonder if it is all related that the truck doesn't stop as well, the pedal feels spongy and after 2 or 3 months of use on the new brakes, it develops a pulsation again. I am now on my fourth set of brakes in as many years. Thanks again for your time.

tech2

post a picture of the front of your master cylinder. I want to see if it has the proportioning valve built into it. If it does, a special tool is required to open the valve to bleed the rear brakes.

rkhall

Will do. Thanks!

therewolf

Hi rkhall, Welcome to the Chevy Forums.

If you didn't have "GM soft pedal"(which is some BS I have

NEVER heard of) in the first 85K miles, why now? The clues

all seem to point to improper bleeding and improper adjustment of

the proportioning valve. Just because someone "bled" your brakes

does not mean it was done right.

IME, the major failing on every brake job I have ever had done

by flat-rate mechanics is a poor bleed job at the end of the service.


If I were you, I would take this to a well known brake specialist in

your area, who has a Power Bleeder, and test drive it when they are done.

The brakes should be as good as new, or better.

rkhall

Here is the photo of the master cylinder. Thanks!

rkhall

Hey Super and Tech 2, I really appreciate the help. I am of the same opinion that they were not bled properly, or there is something else going on to cause the fronts and rears to apply out of balance leading to one set or the other working too hard and causing the bluing and warped rotors. Just cant seem to get a straight answer from the dealer or Les Schwab. Frustrating!


By the way, I know just enough to be dangerous as I have been a car guy all my life, but the "new" computerized stuff is beyond me.


Thanks for you help.

tech2

I don't see the combination valve so yours may be different...sometimes the lines coming out of the m/c go to a combination valve that houses the pressure differential switch and proportioning valve.

rkhall

So do you think its possible that this valve may be causing a problem in the brake balance leading to overworking one side or the other?