Brakes binding

[detiid]

E type FHC 1969.I took the car out recently and noticed that the brakes were binding, I returned home to find smoke from front brakes. I rang local specialist who told me it was the slave cylinder,andthat this was a common problem with after market part. I replaced the slave cylinder bled the brakes and find I still have the same problem. Does any one have any ideas. Thanks Richard

[christopher storey]

Which "slave cylinder" are we talking about ? The only thing which comes near to fitting that description is the servo cylinder, which is essentially a remotely operated second master cylinder . Did your front brakes smoke on both sides, or only on one ? If the latter , then an internally collapsed brake hose is a more likely culprit . Were the rear brakes binding as well ? Is there sufficient free travel on the brake pedal to ensure that the brakes come off when the pedal is released ? Has the car been laid up for a prolonged period ? I think we need more information to try and help you

[44DHR]

The common problem with brakes sticking or binding on is the Reaction Valve piston sticking in it’s bore and the Servo not releasing the brakes. Can be easily checked by disengaging the air hose to the servo, which will lose the power assistance, but if then the brakes no longer bind, time check the little activating piston under the white plastic Reaction Valve bolted on the end of the brake master cylinder.
A simple fix to remove the Reaction Valve from the brake Master cylinder and clean and apply red brake grease to the small piston inside the end of the Master cylinder.
Covered several times in this forum, such as post #14 in this link.

viewtopic.php?f=5&t=14620&p=122632&hili ... ng#p122632

Regards,
Dave

[detiid]

I have now replaced the master cylinder, slave, and reactor valve, still no joy. if I loosen an air pipe pressure blows out and brakes release!
I have run out of ideas.
Richard

[Tom W]

If the brakes release when you release the vacuum pipe, your problem is likely to be something to do with the vacuum circuit.

[christopher storey]

I'm afraid I don't understand how "pressure blows out" . There is no positive pressure in the servo system : it is worked by vacuum drawn from the inlet manifold , which vacuum is applied to both chambers of the servo when the pedal is NOT pressed. When you press the pedal, the sequencing valve in the plastic attachment of the front of the master cylinder admits air to the rear chamber of the servo , and this creates a pressure differential between the front chamber of the servo ( vacuum ) and the rear chamber of the servo ( ambient atmospheric pressure ), which gives additional force to push the shuttle in the servo cylinder forwards .

The diagram at page LY.s3 ( similar diagrams also exist at pages L.X.s2 and s3 of the Workshop manual , available in the knowledge base on this site ) will give you a good idea of how the system works . It is not unusual for the brakes to be held on by a sticking shuttle in the servo cylinder, and if you have tried the other potential solutions, then this is likely to be the cause of the trouble, but the account you give of instantaneous brake release when you detach the pipe is rather against this, and as Tom has said it suggests a vacuum circuit fault

[christopher storey]

I've been thinking further about this. Is it possible that what you describe as pressure blowing out is in fact air rushing in when you detach a vacuum pipe ? If so, this suggests that vacuum is not being applied fully to the rear chamber of the servo when the system is at rest i.e. with no pedal being pressed, but is being applied to the front chamber. Then, when you detach the pipe, air flows into the front chamber and pushes the diaphragm, and with it the shuttle, backwards there by releasing the hydraulic pressure in the system. A vacuum sequencing fault seems most likely

[Series1 Stu]

I would start with the reaction valve. The little piston inside it can stick and cause the brakes to hold on. It's really easy to assemble it the wrong way around.

Start by pulling the snap on cover off to see if that releases the brakes but do it under cover so the piston and spring don't disappear over your shoulder.

Regards