I NEED HELP - BAD ! Brake troubles on 99 Silverado

[63SW]

I have a late 99 Silverado 1/2 ton ext cab with a 5.3 .

we put new ROTORS and PADS on all 4 corners - No big deal right ?
WRONG.
Heres the problem and i cant figure it out.

Front brakes work fine.

REAR BRAKES - Both side are continually applying pressure and causing the Rotors to get EXTREAMLY HOT .
( Naturally , as they get hotter the pressure is greater and it will slow the truck down by itself )
I've only made test runs !

Everything was fine befor , just worn and time for maintenence.

We didnt release any lines , just droppen in pads and slid on new rotors.

Greased all the slider pins too.

WE JUST REPLACED THE CENTER REAR BRAKE HOSE from the frame to the rear diff ( thought maybe a colappsed hose) but SAME THING.

ANYONE GOT A CLUE THAT WOULD HELP ME OUT !
I'll put you on my Christmas Card list if you can help me figure it out ...LOL

[63SW]

Anybody !

[TonyL]

Sounds like the wheel cylinder is dragging. you may need to lube them. happened to me.

[63SW]

I dont think it has wheel cylinders ... Its DISC !

BTW , IT IS NOT A PROBLEM WITH THE EMERGENCY BRAKE SET UP , Its the main Braking system dealing with the Pads & Rotor.

i dont think it the calipers either because they compressed ok , and you can see them compressing & decompressing when we test them.

Besides , i wouldnt think that BOTH sides would go bad at the same time .

THANKS FOR TRYING THOUGH

Im still confused .

ANYONE have knowledge of the ABS system ?

[dhardison]

Try pulling the ABS fuse and see if it repeats. It's going to throw a trouble code when you do, BTW.

[Steve68]

The rear calipers have phonalic pistons and when you pushed them back in they now are sticking, the pistons are not true anymore, round, try that,

friend had a 99 Blazer had the same problem, we screwed around with it, took the piston in and out, ended up with new rear calipers, worked great, just reuse the copper crush washers because the others are junk!

Let us know what happens.

[Steve68]

I read that the pistons are moving in and out, but are they moving back in enough?,

did you put a clamp on the lines and break the bleeder screw loose when pushing the pistons back in??

if you don't, you can back flush the ABS unit with trash, very common with GM trucks,

[TonyL]

piston is what i meant to say. Usually when they crush them back in they use C-clamps. this can bend them and make them less than round. or worse, the cylinder that the piston rides in can be come gouged. Or the piston itself can become cocked or cracked. This causes dragging, and will cause the pads to not let off enough to give you freewheel.

[63SW]

Thanks for the info ... I have a GM tech aquaintence comming over with a scanner to check...

No , we didnt open the bleeder when we pushed the piston back in .
We did use a C-Clamp ...

I dont think its the piston / calipers but i undersatnd the thought behind that...
Only because its BOTH side on the rear ...

We did the same thing on the fronts with no problem...

Yes , the calipers are moving in & out , ENOUGH , i dont know...

If i go for a test drive around the block , by the time i get back , THE REAR BRAKES ARE EXTREAMLY HOT !

If i hit the Bleeder screw , it releases pressure and the brake are ok , TILL I HIT THE PEDAL.

I am leanning twards the ABS system and for some reason it is NOT releasing the pressure...

THANKS FOR THE HELP , I'll try a few more things!

[BonzoHansen]

I with the bad piston theory, but it is very important to break the bleeders open when pushing pistons in. I would not be surprised if that damaged something.

[Steve68]

Your giving me all the signs of the Phonalic pistons out of round, The Blazer did the same thing!!!!!!

ABS I think you'd get a SRS or what ever light,

[DeepBlue68]

I may be way off base here, but could it be something with the F/R brake bias? I know nothing about newer GM trucks, but could it have gotten adjusted somehow when you were doing the work?

Edit: Ehhh, now that I think about it, I guess that wouldn't explain why the calipers are still applying pressure to the rotors when the brake pedal is released. I guess I defeated my own theory :screwy:

[David Pozzi]

Did you remove the master cyl cover to release any possible pressure?

[63SW]

Yep , we did remove the master cyl cover , and it has maximum fill line .
The fluid was higher than that so i removed some till it was at the line.

Guy came by with the scanner and ran a diagnostics check --- NO CODES SHOWED UP.
he went ahead and bled the ABS system ( i dont understand that because you dont have to bleed anything like you would think - its done internally with thie scanner)

STILL DOING THE SAME THING...

He checked the rear calipers and YES, they move in & out ...

Going to replace them anyways ( there goes another 100+ )
thinking that they may be "OUT OF ROUND "
or that since they were out so far the there may be debris ( rust , dirt , what ever ) in the piston cyl thats just enough to allow it to be compressed with a clamp but not with line pressure.

THANKS FOR ALL THE HELP AND IDEAS TO TRY ...i'll let you know.

[Steve68]

That's exactly what I'm trying to tell you, the pistons were out to far, the phonalic is now out of round and it's hanging up in the body,

[63SW]

I know , thats why i put it in parenthasise ..i was giving you credit ..LOL

It was a last resort , because it seemed as though the calipers were working and they did collapse ok when we installed the new pads.

the other contributing factor was that with the aluminum calipers ( rather than the cast they used to use , onece they are out so far the build up corrosion and causes the same thing...

BUT AFTER REPLACING THE CALIPERS - I NOW HAVE PERFECT BRAKES!

Thanks for the help!

ANOTHER CRISIS OVERCOME!

[Steve68]

I was being addiment about the calipers, because this was the exact problem we had and after 3 hours of screwing with them and talking to my friend who owns a shop, new calipers fixed it and home they drove,

Glad I could help,

[68nate]

I've seen alot of problems with this design calipers sticking after pushing back in for a brake job. As far as not opening the bleeder to push the pistons back causing ABS problems, I have not seen it in 14 years as a master tech. I agree that is the "CORRECT" way to do it, and yes you could push crud back to the ABS motors. But in reality, not opening the bleeder would rarely if ever cause a problem like you were having. Strategy Based Diagnostics- always start with the basics. Glad to hear you got your problem solved.

[PRO TC]

check the rotors you may have the wrong rotors. 99 was the change over year and there are two different rotors. i have ran into this problem. just never left the shop
barry

[Steve68]

Hello!!!!!


Did you read "after REPLACING the caliper" he's got great brakes!!!!!


Hello!!!!


WTF?? did you read any of this post??????

[PRO TC]

well i guess i missed the last couple post. but thanks for being a tool!! i was just trying to help.
barry

[Steve68]

Sorry Barry, I just assumed that everyone had read through and had personally analized the problem at hand, no disrepect, I'm Sorry for coming off like a dork, Steve

[PRO TC]

no problem my fault. i should have read the post a little better.
barry

[Steve68]

Peace to my fellow GM mechanic!!!

[63SW]

The Guy i had come over and run the scan on the truck is a certified Tech too and he said " opening the bleeder is the correct way " but in 6 years HE HAS NEVER DONE IT EITHER ---LOL

I made sure to tell the parts guys the this was a LATE 99 truck , Knowing that they split the year ...Funny enough , they said it didnt matter ...Only mattered if it was a SILVERADO ...it is , But i dont know why that would make a difference.

I appreciate all the advise tips - the trucks great now...

I think I'll stick to my old cars from now on !

[MonzaRacer]

OK Im gonna chimein here and hope this posts as i havent been able to get on the site since thanksgiving, keeps giving me server is too busy.
so for therecord the pistons are actually called phenolic resin pistons.
and a few things will cause problems on these brake systems.
One if you dont open the bleeders to push the pistons back the trash (black gunk and rust debris) that collects behind the pisons will go back up the lines and destroy things if it gets in wrong places(ie ABS or between the piston and caliper bore) and the fluid gets contaminated by air, moisture and other contaminates and will cause bad braking characteristics.
Now as a rule I rarely have seen a phenolic piston go out of round (did see a fella wire wheel one, really messed it up haha) if you happen to have aluminum calipers on a truck they can deform under heavy braking (friend built a drag Silverado and we had to find better caliper in rear as they kept warping, we finally found a company that stainless steel sleeves them for reliability)as I have found since they became common. After tearing a few down and measuring them I believe this is the common problem. Another thing I have notice is that using c-clamps cause them to have more problems and a simple plate with one or two bolts and some nuts welded to them and an old pad work much better to push the pistons back in. WE had a bad run on having to replace calipers upon combacks, even had company quality assurance coming in and questioning how we did brakes and who had most combacks.
I am not saying some may have bad pistons its just not all on the phenolic pistons as millions of cars run them with no problems at all.
Oh and as for codes being present, if the light is off you would only most likely pull history codes.
As for ABS causing dragging brakes , never seen it unless someone trashed it by pushing garbage back up into the valve assembly or you have a system sending false signals to the EBCM activating the ABS.See ABS has several enabling criteria one is over a preprogramed speed and then the only thing that it reads are the Vehicle speed and all 3 or 4 wheel speed sensors, then if it clculates one or more wheel sliding(ie no movement) it will cycle the piston in the control assembly in a manner to control slippage from that wheel so as to allow you to NOT lock a wheel and slide.
Now one of the big problems with olderdrivers is that if they actually learned how to modulate(ie vary the preasure on the brake pedal with your foot to aloid lock up) the brakes to avoid lock up they will need to learn to allow the system properly operate as it is built in the assumsion of the driver mearly locking the brakes and the system then regulates the brakes.
And if it activets you should hear the pump and the modulator assembly operating.
Oh and to deactivate ABS if you dont like it is to simply unhook one of the wheel speed sensors and ignore or remove/coverup the light. BUT if you have traction control too it deactivates that too,,, oh andsome vehicles actually read vehicle speed off computations from the VSS and one or more of the WSS so it can cause problems in soem vehicles.
most likely the reason you had problems was that you needed to open the bleeders to allow the trash to come out rather than back intot the brake system. The old problems preABS was that people would go have front brakes done and then a feww days/weeks later the master cylinder would go south with no warning and it was just attributed to well the brakes were worn out so I guess the master cylinder was too.
Another thing to remember to do is also spread a thin coat of the same silicone grease on the back of the pads on top of the shims(if equipt) as this will quell any vibrations (ie squeal) I also have a product avaiable for purchase that you can spray directly on pads or shoes to aleviate annoying squeal and it works much better than that silver crap sold to spray on rotors, and the product I sell will work on drum brakes too.
hope some of things I related help others,
Lee

[Steve68]

Here, here!!!!