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Discussion Starter #1
This happened once before.....
After driving a while, my vette starts to feel like it is dragging. It feels like the brakes are always on. If I take my foot off of the brake while I am at a red light, (auto-trans in Drive), she will NOT roll like it normally would. If I am on a slightly inclined surface, and release the brake, with the tranny in Neutral, she will NOT roll downhill. If I try to accelerate up to serious highway speeds I get some severe shudder from the front end. :surprised
After letting her sit for a period of time (couple of minutes usually, 10-15 max), she feels right again, so I can continue my drive or at least head home.
I brought her into my mechanic and he made an adjustment inside the Power Booster. This was several months ago.

The symptoms have returned again....
Is this an adjustment that needs to be checked periodically? What did he do exactly? I don't recall him having to drain the brake fluid or bleeding the system, even though he had the master cylinder disconnected from the booster.
Is this something I can easily do myself, if the adjustment only needs to be tweaked again?
Any advice welcome. :lookinup:
 

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You have a good mechanic.

The push rod in the booster that pushes the piston in the master cylinder is adjustable. If set so that it is to long it will hold the piston in the master cylinder & not allow it to "seat" when the brakes are released & let the fluid back into the master cylinder.

Once the push rod is set correctly it should never need service. Has the booster or master cylinder been replaced or perhaps a brake light switch has been replaced & set to close to the pedal not allowing it to return fully.

Since the problem has surfaced again the booster may be going bad internally.

Check/feel if one wheel is getting hotter than the others when you feel the brakes are dragging. If so the caliper may be hanging up or a brake hose is going bad.
 

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I think your mechanic is full of ****!

Pop your wheels off and look at the brake rotors. The one(s) that are blue are the one(s) overheating because you probably have a piston sticking on a brake caliper. You can also take a look at the brake pads too. The side that has the thinnest is the one sticking. There truly is no other explanation for this to happen. I've never heard of a master cylinder sticking "on"...they usually blow out their seals inside and then you end up with ZERO brakes.

You will need new brake caliper(s) (rebuilt is fine) and you might as well do both sides if not front and rear. Throw some new pads on it while its apart. I recommend ceramics or graphite (they do dust).

There is a proprtional valve that feeds around 80% or so of your brake fluid (hydraulic) to the front brakes and the rears get the rest. This why it is typical to wear out 2 or 3 sets of brake pads on the front before you even have to do maintenance on the rears. But a brake caliper can have a piston at any of the positions at any given time. Its common on a old and worn brake system that hasnt had any serious maintenance in a long time.
 

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Discussion Starter #4
I think your mechanic is full of ****!

Pop your wheels off and look at the brake rotors. The one(s) that are blue are the one(s) overheating because you probably have a piston sticking on a brake caliper. You can also take a look at the brake pads too. The side that has the thinnest is the one sticking. There truly is no other explanation for this to happen. I've never heard of a master cylinder sticking "on"...they usually blow out their seals inside and then you end up with ZERO brakes.

You will need new brake caliper(s) (rebuilt is fine) and you might as well do both sides if not front and rear. Throw some new pads on it while its apart. I recommend ceramics or graphite (they do dust).

There is a proportional valve that feeds around 80% or so of your brake fluid (hydraulic) to the front brakes and the rears get the rest. This why it is typical to wear out 2 or 3 sets of brake pads on the front before you even have to do maintenance on the rears. But a brake caliper can have a piston at any of the positions at any given time. Its common on a old and worn brake system that hasnt had any serious maintenance in a long time.
I don't think it would be a single brake, caliper, or line, since there is no pulling to either side.
Further, when I had the car up on the lift the first time several months ago, I misdiagnosed the symptoms by telling my mechanic that only the front brakes were locking up. (I didn't realize the proportion was as dramatic as an 80-20 split. That explains why the front was as hot as it was.) Anyway, the first time in for this issue I came away with new front calipers, and brake lines. Needless to say, within a week I was back in the shop a little upset that I was a proud owner of new calipers that I had apparently didn't really need. It was this second trip when we put the car up on the lift and he found that all four wheels were equally locked up.
The heat that I detected from after a drive were actually coming from all four brakes. I did notice that the last time out, which represents the last time I drive it until I get it fixed, there were some small "bubbles" forming on the brake lines as if they were about the burst. The symptom of "all is well" after letting it sit for about 15 minutes included the bubbles going away.

You have a good mechanic.

Once the push rod is set correctly it should never need service. Has the booster or master cylinder been replaced or perhaps a brake light switch has been replaced & set to close to the pedal not allowing it to return fully.

Since the problem has surfaced again the booster may be going bad internally.

Check/feel if one wheel is getting hotter than the others when you feel the brakes are dragging. If so the caliper may be hanging up or a brake hose is going bad.
The MC and booster were not changed. I have had the car three years now, and the previous owner had the brakes completely redone a few months before the sale, so I was in pretty good shape.
My question about the adjustment is purely based on if it was required out of the blue last year, could it have slipped out of adjustment again? If so, is this part easily replaceable? Or would this be the time to replace the booster, assuming the push-rod comes with the new booster?
 

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The sdjustable push rod comes with the booster.

I use a depth mike for the figures to set the push rod length. I like .025 clearance between the booster push rod & master cylinder piston.

If purchasing a rebuilt unit check the mounting threads before installation to insure they are the same pitch & size as the ones you have on the booster that is being removed. The last one I took out had 8x1.0 mm threads & the replacement had
8x1.25mm threads & required 4 new nuts.

Also compare brake pedal push rod length (non adjustable). This is the rod from the booster to the brake pedal. The rods should be the same length.

Suggest replacing the brake hoses, they should not have bubbles in them.
 

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Your mechanic is NOT full of it, and you definitely should listen to DJS. I would agree that this is not common on more modern cars, and that most people would not have seen this happen before, but that does not mean for a second that it isn't real. I don't mean any offense by this, so please don't be offended.:thumbsup:

Push rod length has to be correct to both permit full travel of the master cylinder, and to allow it to return to rest appropriately. It typically takes a special measuring tool, or making a few precise measurements and calculating the length to get it just right. I also agree that it is possible that the booster has internal issues related to it's valving that make the brakes drag. Brake hoses with bubbles are not a good sign.

I found a good paper on brakes in general, that has lots of good information. It is actually part of Lexus repair training, but the basic idea is the same. http://www.autoshop101.com/forms/brake05.pdf

~wd40:buhbye:
 

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Also take a look at the replaced calipers. Look at the sliders (where the bolts on the back of the brake caliper are) They should be well greased with some heavy duty wheel bearing grease. Anything else melts out.

Check the anti rattle clip and the pads. make sure they aren't installed wrong and binding.

Make sure the caliper's piston isn't binding by pushing it back in a little.. Make sure to crack the bleeder and push the fluid out through it.. sometimes pushing a lot of fluid back into an anti lock system buggers things up.

Also if the master cylinder was recently replaced you could have gotten a bad one with the seals inside reversed. not sure of the exact internal design but some have the seals with lip on them so as no to over pressure.. and if these are reversed fluid would have a had time getting back to the fluid reservoir. No way I've heard of to verify this without taking it apart.

Sure it's all 4 and not the parking brake acting up? sometimes mine is difficult to get a full release without poping it a few times.

How old are the flexible brake lines? Have any issues with anti lock brakes acting funny?
 

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The OP states that just calipers were replaced (that should've been stated in the first post) so we can probably rule out calipers. But he also states that "all 4 wheels were locked up equally" while car was on a lift.

Since the booster/master wasn't replaced i wouldnt think that there were any issues with the pushrod being misadjusted. He drove the car home fine when he bought it.

Ive never heard of a failed brake booster causing brakes to stick on.

I would try the master cylinder first! Its the cheapest and most likely suspect. The orings are probably turning to mush and hanging up in its bore. Eventually they will fail and then NO BRAKES.

Thos brake lines with bubbles need to be replaced immediately. They are going to burst. It isnt fun when they do it either....the pedal goes to the floor then NO BRAKES.
 

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2986 c-4

Hello
I have a 1986 c-4 convertible with the rear brakes binding/sticking/ or just staying on in plain English:(
I have read that others have had this problem but I cannot seem to find out what the final outcome of the problem of rear brakes binding/grabbing holding etc.;
I know this is the first year for anti-lock brake systems.
My local mom/pop shop bled the brakes, installed new pads and the rear wheels were still grabbing, they could be turned by hand when on the lift but it was very difficult:(
The owner of the shop finally said he thought it was the ECBM but he was not sure and he said they were very expensive and maybe I should go to a chevy dealer to have it checked. He refused to charge me for the work since he said he did not fix the problem:)
I took the car to another mechanic who braged he knew corvettes in/out. Well he checked brakes and said they were installed correctly. He then adjusted the rod in the master brake cylinder and said that fixed the problem. Well driving it home it did not fix the problem. I called him back and he said well it is the Electronic Brake Control Module, he said they were very expensive and he could not find one for less than $1500 dollars. I told him I would find one and bring the car back. I felt that he was not a good choice and have since took it home and parked the car.
Please does anyone have a good educated opinion as to what is really wrong with the rear brakes locked or binding. To complicate matters it appears that the problem comes and goes:( as one poster indicated if you stop the car if the car rolls at an idle the brakes are not grabbing, if it does not roll forward at an idle it is locked up, I can tell when they locked because the transmission has to work harder.
My local transmission guy said his friend who works at the Chevrolet dealer specifically on vettes told him to install a used ebcm taken from a local 1986 corvette that was totaled out up front and the ebcm is still good?
Anyone got some ideas for me to try:) Thanks Larry in central florida:)
 

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Back when I built off road Jeep XJs I had a 1997 that every now and then did this. One day it did it and I pulled the vacume booster hose off and plugged it. They unlocked instantly. I drove it home (without power assist) and put a new booster on it and never had the problem again. Maybe you can try the same method. But I would make absolutely sure the push rod is adjusted right before replacing anything.

I will look in my service manual when I get home and see if it has a troubleshoot page for this.
 

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After looking and realizing that yours is a 84 I don't know if my service manuall will work but here are the troubleshooting steps that my manual shows. I think they would still be good to follow, and read my notes at the bottomm as well.









All of the above is good to do, but from my experience I have found that older vehicles calipers lock up for a few reasons.

1. The actual caliper is full of debree that is binding it up, usually rust from sitting for extended periods of time. This can be in the piston itself (usual culprit) or from rust on the caliper rails or guide bolts. That caliper grease that so many numbskulls have put on the pads actually goes on the smooth part of the caliper bolts after they have been cleaned good.:laughing: I have seen guys put it directly on the pad, same with the anti sqealing noise sticky. It goes on the back of the pad so it sticks to the caliper or piston and follows it when it releases and doesn't ride the rotor.

2. There are hard lines and there are rubber lines. I have found that the rubber lines build rust up right where they connect to the hard lines or at the ends where they convert into the hard line that mounts into the caliper. Yes both sides could be full of rust at the same time. I think your year has hard lines from the proportional valve to the wheel wells on all four corners then rubber lines on each wheel. I would replace them all if they have not been already.

3. Also in the system is the proportioning valve that I spoke about earlier. They can get filled with debree just like any other valve and not let fluid return as it should. You would have to check your service manual (a chiltonish one would work) and find it and replace it to be sure.

4. Lastly and probably should be first I have come across where the brake fluid was so nasty after years of running and no flush that even when replacing these parts you have continuing problems. "SO" I always required that there be a complete brake fluid flush before replacing any of the brake components if I saw it was old and nasty and not new and clean. I didn't want a car returning just because of debree in the old fluid.

I have found that if I followed these typical rules and bled the sytem good after the install I had perfectly working brakes.

I hope this helps and you get this figured out.

:thumbsup:
 
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