Hello group,I am experiencing all four brakes binding after a short run of 8 miles or so.Brake master and booster and all vacuum and rubber hoses were changed in 2017.Problem is intermittent making diagnosis difficult.Vehicle is a 1970 2+2..When I am able to replicate the problem,I raise the car on a lift so that all four tires are off the ground ,engine off,and all four brakes rotate but are tight.I think the problem lies in the slave cylinder sticking and not returning.Cannot see the booster causing the problem because the problem still occurs with engine off.After a few minutes of rest,the brakes release and all wheels rotate properly.Also possible is a sticking master but the pedal feel seems ok.I intend to change the booster with the slave .And then the master if that does not work.I understand that this is a common problem and hopefully someone has experienced this issue and was able to fix.Any and all help is deeply appreciated.Thank you.Ted

 

All the hoses have been replaced, but could one or more be defective? Sometimes internal rubber degrades and creates a flap that blocks the flow and return of brake fluid. Odd though that it affects all four, so perhaps the issue is closer to the master and or booster, as you are surmising. Are you using silicone BF? On my 69, the rear brakes did not work at all and it turned out that the silicone had degraded the rear's circuit. The master was replaced, system flushed and standard BF put in.

 

Since I assume all four wheels are locking up in unison I agree with Valerie that it means that this is not a problem with an individual caliper and is likely near the master cylinder and/or booster. I have a series 3 so don't know exactly how your braking system differs from mine but in general check for a sticking master cylinder (does the pedal come up all the way immediately, with no play?) and if you have a vacuum booster like my series 3 is the booster releasing pressure correctly when you let off the brake pedal? It sounds like the system had a good flush when the new hoses were installed so I would focus on the master and booster as the likely cause.

 

Hi,just to clarify,the brakes don't lock up,they just drag a little once they are driven..The drag is not bad,If you are on a modest incline,the car will roll on it's own when put in neutral and releasing the brake.I am sorry to say that a new servo did not fix the problem ,so I will replace the master and hope for the best.I did remove all rubber brake hoses and they are good..Thanks for the replies.

 

I'm no brake expert, but could it also be that the pistons are not retracting into their 'pots'?? Have you done any caliper work? I believe the original E calipers are not stainless and so would it be possible that the pistons are sticking? When you bleed the brakes, do the pistons seem to retract? BTW I HATE brake work, mostly because of the fluid and the damage it can cause to ancillary areas.

 

This is the toughest problem to diagnose, because the system is a bit Rube Goldberg. I believe most of these problems are related to a vacuum leak in the servo or reaction valve. The servo is activated by the reaction valve on the front of the master. The reaction valve, in turn, is activated by a tiny piston at the front of the master cylinder. Very often, this small piston is the problem: it can stick and cause all sorts of problems. What I would suggest is to first remove the reaction valve, it's just a matter of removing a few screws. It attaches to a plate that's bolted to the front of the master. There will be a small hole in the center of the plate. What you want to do is to poke a nail through the hole and push the piston in as hard as you can. Then have someone press on the brake. You should find that you can't keep the nail pressed into the hole, because the piston is pushing it forward. Once the brake is released, it should push in smoothly. if there's any sticking, remove the two bolts. Then hold a plastic bag over the end of the master and have someone press. The little piston should pop out into the bag. Inspect it, clean it, wipe it with brake grease, and reinstall. Then reassemble and see if there's any improvement.