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Help! Rear brakes sticking

jjaymoore

Member
Joined
Nov 14, 2012
Messages
10
Location
Navarre, Florida, United State
Corvette
1986 Yellow Coupe
I just got my '86 a few months back and am in the process of fixing everything that the PO either rigged up or didn't fix on the car (which is a lot!). Anyways, my rear brakes are dragging. I can shift into neutral at like ten mph and the car will come to a complete stop as if the brakes are applied. I tried bleeding the rear brakes and they will not bleed at all unless the car is running. I do not have an ABS light and the fronts are working fine. Has anyone experienced this in the past? I have never messed with ABS systems so any advice would be greatly appreciated.
 
Just for grins, did you check that the hand brake is fully released?
 
"Won't bleed unless the car is running?" You can get no fluid out of the bleed screw, with the motor off, and the pedal depressed? Something not right there...

When bleeding, make sure to loosen the screw ONLY A LITTLE, almost so that NOT ALL LINE PRESSURE IS RELEASED. If pressure is totally released, sure, you can get more air out, but also it can get BACK IN.

You're sure that the e-brake linkage isn't binding anywhere also?


Better be REAL careful too, if they're really binding. They'll get toasty, and if too toasty, you'll need a LONG stick, and some of these:


RoastingMarshMellows.jpg
 
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They are definatley not bleeding with the engine off. I suspect that there is something going on in the ABS module. It seems like they are holding pressure and just real slow to release. if i stop on a slight slope i can feel them release and let the car roll back after a few minutes. Like I said I don't have much experience with ABS, I have read a few threads on various sights about the ABS troubleshooting, but nothing really seems to address this particular problem.
 
Job of ABS, in short, is to RELEASE pressure, created by pedal pressure. ABS doesn't create line pressure.

Failed ABS doesn't create pressure. If pedal is depressed, and ABS doesn't work, it doesn't do ANYthing, including HOLD pressure, created by pedal.

Binding brakes blamed on ABS is the MOST COMMMON brake myth. Probably originated with unscrupulous mechanics offering to replace in -
"I can replace the ABS, and we'll see if that takes care of it"

And he frees sticking wheel cylinders, or caliper pistons additionally (or other problem), to fix the problem...
 
When your cars slows to a stop:
1) does it pull to one side?
2) is one rear rotor hotter than the other?

What "bleeding procedure" did you use to determine that the rear brakes will not bleed without the engine running?
 
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Take the lines lose at the callipers and see if they release. The brake lines sometimes peal inside and block full flow.
 
Take the lines lose at the callipers and see if they release. The brake lines sometimes peal inside and block full flow.

smiley4.gif smiley4.gif smiley4.gif

Loose worn out wheel bearings will make them hang up too!~!:thumb:thumb:thumb


:beer
 
Typically

The E brake doesn't release properly...
Junk has a valid point about rear wheel bearings....
Do you know how to check rear bearing play?
You could also inspect the U joints / 1/2 shafts...

So here are the painful questions
How many miles?
What area ( state ) was the car before....CA... NYC... NC ??
How rusty is the exhaust at the muffler area ?

Mike
 
The parking brake does not work, there is no way that it is sticking.
I attempted to bleed the brakes by having someone apply pressure to the pedal while i opened the bleeder. just like i have on every vehicle I have ever serviced brakes on.
I have not checked any bearing play or u joints, but that would not explain why my brakes are sticking, Yes they are definately sticking and no, the vehicle is not pulling one way or another.

I had a problem once with another vehicle that would not bleed and it ended up being the ABS module (it was a GM but not a Corvette.) It stands to reason that if there were something wrong with the ABS that it would cause the system to hold pressure. What is occuring is not as if the brakes are slammed on, but you can definately feel it with the vehicle in nuetral and rolling at around 5mph. If i stop on a hill it will hold the hill in neutral and the vehicle in neutral. I was hoping that someone else on here had seen this in the past. These vehicles are old enough that sometimes it is easier to pose a question on the internet vs. troubleshooting blind.
 
The parking brake does not work, there is no way that it is sticking.
I attempted to bleed the brakes by having someone apply pressure to the pedal while i opened the bleeder. just like i have on every vehicle I have ever serviced brakes on.
I have not checked any bearing play or u joints, but that would not explain why my brakes are sticking, Yes they are definately sticking and no, the vehicle is not pulling one way or another.

I had a problem once with another vehicle that would not bleed and it ended up being the ABS module (it was a GM but not a Corvette.) It stands to reason that if there were something wrong with the ABS that it would cause the system to hold pressure. What is occuring is not as if the brakes are slammed on, but you can definately feel it with the vehicle in nuetral and rolling at around 5mph. If i stop on a hill it will hold the hill in neutral and the vehicle in neutral. I was hoping that someone else on here had seen this in the past. These vehicles are old enough that sometimes it is easier to pose a question on the internet vs. troubleshooting blind.


In response to your question about someone with experience with these cars giving you there input. Many of those who have responded with suggestions have been working on these cars for a long time. Among all who have responded GMJunkie has more experience because he is in the business of repairing Corvettes and building high performance cars and has been doing so for over 40 years. Whenever He has suggested something for me with my car no matter how far fetched it may have seemed it always pointed me in the right direction. As for the others they two have been able to help me and others. Sometimes because of there experience they ask questions to narrow down the possibility's. After all if you called your doctor and said you did not feel well he would ask you some questions like are you having chest pains or are you running a fever etc. Obviously you are mechanically inclined and I look forward to your input on this forum in the future. I just hope it is not because I am having a problemm with my car:chuckle
 
The parking brake does not work, there is no way that it is sticking.
I attempted to bleed the brakes by having someone apply pressure to the pedal while i opened the bleeder. just like i have on every vehicle I have ever serviced brakes on.
I have not checked any bearing play or u joints, but that would not explain why my brakes are sticking, Yes they are definately sticking and no, the vehicle is not pulling one way or another.

I had a problem once with another vehicle that would not bleed and it ended up being the ABS module (it was a GM but not a Corvette.) It stands to reason that if there were something wrong with the ABS that it would cause the system to hold pressure. What is occuring is not as if the brakes are slammed on, but you can definately feel it with the vehicle in nuetral and rolling at around 5mph. If i stop on a hill it will hold the hill in neutral and the vehicle in neutral. I was hoping that someone else on here had seen this in the past. These vehicles are old enough that sometimes it is easier to pose a question on the internet vs. troubleshooting blind.

Parking brake is 100-% different thru cables that have little to do with the brake pedal of the fluid. Parking brakes live inside the rear drums/hubs and operate with all cables. And yes, they DO DRAG.

Not gonna help the parking brake with the pedal or resevoir. it needs to be cleaned and adjusted.
 
Rusted shut

If the wheel bearings are bad the rotor will not sit 90 degrees in the caliper.. depending HOW bad the bearing is.
The cables for the E brake can rust / corrode internally so you have enough leverage to engage ( via the handle ) but the internal spring cannot release tension when the cable SHOULD be slack.
Well based on your feedback the caliper needs a rebuild...
Is your feedback based on disassembly and inspection ?

Mike
 
Today I disconnected the brake lines at the Master Cylinder and had an assistant press the brake pedal there was excellent flow from bith lines. I also disconnected the rubber hose form the caliper and had an assistant press the brake. The line barely leaked anything, maybe a drop or two. Correct me if I am mistaken but the ABS Module is the only thing between the MC and the Calipers. Does anyone know where to find a good schematic of what is actually going on inside of the module?
 
Random Thoughts

I have been sitting hear thinking about all that has been tried or suggested and there are some things I would check if it were my car. You indicate the car had poor maintenance and you are in the process of sanitizing the bad work and neglect. Did the car sit for a few months before you bought it? On my 93 when I bought it it had been on the lot for a few months and the rear brakes were dragging. Because of the mileage on my car I had the rear brakes replaced within a week after buying it and we found that the caliper piston had a ridge of rust around it. Also the piston was fully extended because the pads were totally worn out. So while it was not being driven the rust developed around the caliper piston and would not allow it to retract fully. That caused the brakes to drag. The other problem I had was the piston had been pushed out so far it would not go back into the caliper without some gentile pushing to get it started back into the sleeve it slides in inside the caliper. If you have not already done so you might start by cleaning everything up on the piston and calipers to make sure it is functioning properly and if the pads are mostly shot replace them and see if the brakes don't work then. You might also inspect the front brake pads to see if they have more pad on them then the rears. If they do that would explain why they are working because of the above mentioned problem I had. I know my 93 could be a lot different than your 86 but in looking at my manual I see a brake bias valve in the system. If the problem is still there after you have made sure it is clean etc. you might think about how that valve switches pressure between the front and rear brakes and if it is malfunctioning it could be not releasing the pressure to the rear brakes when the pedal is released.
 
Bias Valve

I was reading your post and it hit me that I dont have a warning switch installed on the master cylinder. It looks like this monitors the bias valve? Could having it removed cause this problem? I will remove the bias valve today and check it out. I think the Master cylinder was replaced by the PO. But, so far with this car everything that has been "replaced" has been done so incorrectly or half a$$.
 

I was reading your post and it hit me that I dont have a warning switch installed on the master cylinder. It looks like this monitors the bias valve? Could having it removed cause this problem? I will remove the bias valve today and check it out. I think the Master cylinder was replaced by the PO. But, so far with this car everything that has been "replaced" has been done so incorrectly or half a$$.

Took a quick look on eBay. There's a few miscellaneous ABS components including a control unit up for sale. Seems like you've narrowed it down to the ABS control unit, so there are options, now.

Good luck... :thumb
 
Today I disconnected the brake lines at the Master Cylinder and had an assistant press the brake pedal there was excellent flow from bith lines. I also disconnected the rubber hose form the caliper and had an assistant press the brake. The line barely leaked anything, maybe a drop or two. Correct me if I am mistaken but the ABS Module is the only thing between the MC and the Calipers. Does anyone know where to find a good schematic of what is actually going on inside of the module?

Take the other end of that hose off and give it a try, any fluid? Then throw it away and put on a new one, both sides if you get fluid or not. You can't believe how much trouble Ive had over the years by those hoses not releasing pressure.
 
Some pressure

OK, I disconnected the rear line at the T, before the rubber hoses and there is some fluid flow. Oddly enough, there is suddenly fluid at the calipers too!! I think they are still dragginf some, but i went ahead and ordered new stainless hoses for all four corners. I am about to completely overhaul my suspension and install C5 front brakes anyways. I may as well do all of the repairs/upgrades that I can while I have the car torn down.
 

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