Front Brake Problem 1985 C4 Help Please

[wildbill85]

Hi, need help with the front brakes sticking on a 85 c4. I had a earlier post with the same problem and I thought I had it fixed. I replaced the front brake pads as the old one's where shot. I can drive the car one time with on problem at all,but on other times the front brakes start to lock up and get really hot and start to smoke. I was told by someone on this site that it sounds like the master cylinder was going out. If you were to look at my master cylinder it looks in really good shape.(new looking) My one question before I go and replace the master cylinder can you bleed the master cylinder??? or should i just go a head and replace it. Any tricks or help on this brake problem would be very appreciated. Thanks. Bill

 

[kim]

You may have a bad caliper.

 

[wildbill85]

c4 front brake help

both sides are locking up in the front!!!!

 

[John Robinson]

Here is another possibility when you bleed the brakes you also have to bleed the modulator valve.

It has to be done first before bleeding the brakes themselves. Now this raises the question is the modulator valve needing to be bled or does it have a problem with not releasing the pressure to the front brakes when the brakes are used. This valve is used to insure that in the event of a leak lets say in the rear brakes then the valve shuts off the hydraulic fluid to the feed line for the back brakes leaving you with at least front brakes. So it is possible that when you put on the brakes the valve is holding the pressure to the front brakes by shutting off. This would then allow the brakes to remain on or dragging.

 

[wildbill85]

c4 brake help

Here is another possibility when you bleed the brakes you also have to bleed the modulator valve.

It has to be done first before bleeding the brakes themselves. Now this raises the question is the modulator valve needing to be bled or does it have a problem with not releasing the pressure to the front brakes when the brakes are used. This valve is used to insure that in the event of a leak lets say in the rear brakes then the valve shuts off the hydraulic fluid to the feed line for the back brakes leaving you with at least front brakes. So it is possible that when you put on the brakes the valve is holding the pressure to the front brakes by shutting off. This would then allow the brakes to remain on or dragging.

Ok how do you bleed the modulator valve.Plus where is the location of the valve. Thanks

 

[John Robinson]

It should be in the compartment behind the drivers seat and there should be a bleeder fitting on it. At least that is were it is shown on my 93



I HAVE JUST LOOKED AT ANOTHER REFERENCE SOURCE AND IT APPEARS THAT YOU DO NOT HAVE TO BLEED THE MODULATOR VALVE ON YOUR YEAR CAR. HOWEVER THERE IS SPECIFIC INSTRUCTIONS ON THE SEQUENCE TO BE FOLLOWED FOR BLEEDING THE BRAKES. AS FOR THE BRAKE FAILURE CLOSING OFF THE FRONT OR BACK BRAKES THAT IS DONE IN THE MASTER CYLINDER.

 

[Bronze85]

No abs on an 85, I would examine the master cylinder carefully. Does fluid come out of the front caliper bleeders when this occurs? It sounds more hydraulic related than mechanical i.e slide sticking,piston sticking in bore etc.

 

[wildbill85]

1985 c4 Brake help

No abs on an 85, I would examine the master cylinder carefully. Does fluid come out of the front caliper bleeders when this occurs? It sounds more hydraulic related than mechanical i.e slide sticking,piston sticking in bore etc.

Ok if the pistons are sticking in the bore's on the front brake's in your best guess would this be a Master Cylinder Problem????

 

[John Robinson]

As you said both brakes drag and smoke so your problem is not a caliper. I f you had a caliper problem it would pull one way or the other and the odds of both calipers failing at the same time are very slight. That only leaves the master cylinder and since it is the front brakes that further isolates the problem to the proportioning valve. If you can open the bleeder valve on one of the front brakes when this happens and the fluid squirts out that says the valve is holding pressure even with the brakes not being pressed.

 

[wildbill85]

c4 brake help 85 corvette

As you said both brakes drag and smoke so your problem is not a caliper. I f you had a caliper problem it would pull one way or the other and the odds of both calipers failing at the same time are very slight. That only leaves the master cylinder and since it is the front brakes that further isolates the problem to the proportioning valve. If you can open the bleeder valve on one of the front brakes when this happens and the fluid squirts out that says the valve is holding pressure even with the brakes not being pressed.

Thanks John, i have another question what are the chance's that it could be the front brake hose's breaking down inside and making the front brakes stick or would you think its just the master cylinder. Thanks.Bill

 

[John Robinson]

Thanks John, i have another question what are the chance's that it could be the front brake hose's breaking down inside and making the front brakes stick or would you think its just the master cylinder. Thanks.Bill

I don't think so again because both brakes are acting in tandem