Brake pedal stuck

[clazar]

I have a 70 RR with factory frt power disc brakes. Yesterday after stopping at a stop sign, the car didn't feel right after pulling away. I noticed the brakes didn't release. The pedal had stayed down. A quick tap tap of the pedal released them. What would cause them to not release??? That was the only time it's happened.

Chuck

 

[clazar]

bump

 

[clazar]

Bump x2

 

[69Runner]

does this help?

 

[clazar]

does this help?

I'll check the service manual.

Thank You
Chuck

 

[clazar]

Service manual didn't help much. Any other ideas ?????


Chuck

 

[Dako]

I would guess the piston in the master cylinder stuck. Things like this can happen with a vehicle that gets driven occasionally vice regularly.

 

[barnfind]

spring or shoe hanging up in the rear brakes, wheel cyl with contaminates in the fluid (if old)

 

[clazar]

I would guess the piston in the master cylinder stuck. Things like this can happen with a vehicle that gets driven occasionally vice regularly.

That's the area I was thinking. It's only happened one time. Should I rebuild the m/c ???

Chuck

- - - Updated - - -

spring or shoe hanging up in the rear brakes, wheel cyl with contaminates in the fluid (if old)

Newer springs & shoes. Wheel cyls are new, as is stainless brake lines & new fluid last year.

Chuck

 

[Cranky]

What's the fluid look like in the MC? Do a flush and see what comes out of it. Just a simple bleeding could/would show signs of rust etc in the system....

 

[Yatzee]

Did you ever consider that the binding might be at the pedal arm? Pull the pin to the booster at the arm and move the rod out of the way sideways. Move the arm through it's full stroke noting smoothness and side play. OK? Then lube the pin and put it back together. I doubt (unless there is a positive connection between the bulb on the end of the push rod of the booster to the master, which there isn't) that the master would hold the brake arm down. There exists a certain gap here to prevent accidental application of the brakes. Now the booster rod could as it's rod is securely fastened to the diaphragm or most are with a plastic bulb retainer and the other end fatened to the brake arm via the pin.. Perhaps the filter or orifice that vents the diaphragm to atmosphere temporarily became blocked ( dirt, debris, moisture,oil fumes etc.) and would not bleed off vacuum. Or perhaps it's time to test the vacuum booster for cracks, leaks and such. It may be just on the cusp of needing rebuilding and this is the first sign of it's condition. If you believe it's the rear brakes causing this issue, and you have a dual master, temporarily block off that port at the master and give it a try to reproduce the situation. Rear brakes only account for about 20% of stopping power so you will still have a lot of braking. Don't forget that proportioning valves have a tendency to bind if let sit for a long time, especially if there's any moisture at all in the brake fluid the spools will rust slightly and seize. They can usually be removed and cleaned using 2000 wet/dry sand paper soaked in brake fluid on the spool and it's bore. Good luck and I hope this post has been helpful.

 

[clazar]

What's the fluid look like in the MC? Do a flush and see what comes out of it. Just a simple bleeding could/would show signs of rust etc in the system....

Last year everything except the m/c was changed. New rear wheel cyl's & new stainless steel lines & new valves in the system. Master cylinder has not been changed or rebuilt. Also new silicone fluid (dot 4).

Chuck

 

[Cranky]

Did you flush the MC with the silicone fluid and how old was it before doing the change over? It will not mix with glycol based DOT3, DOT4, or DOT5.1 fluids (can create a gel, damaging braking system if mixed). I thought silicone was DOT5?

 

[clazar]

Did you flush the MC with the silicone fluid and how old was it before doing the change over? It will not mix with glycol based DOT3, DOT4, or DOT5.1 fluids (can create a gel, damaging braking system if mixed). I thought silicone was DOT5?

Entire system was flushed with the new fluid. I'm at work & only guessed at the dot #. I'm thinking either m/c or power brake booster.

Chuck

 

[clazar]

If the booster needs rebuilt. Who does it ???

Chuck

 

[clazar]

bump

 

[Yatzee]

You'll have to check around locally for a service/rebuild shop. If you do rebuild it make sure the shop bench tests it thoroughly after rebuilding. There's a procedure for this that you can find in a manual or online that requires a hand vacuum pump. If the shop you choose doesn't do this your probably at the wrong shop because just changing parts on the booster doesn't guarantee it's integrity. There are also online vendors that do direct swaps using yours as a core exchange and you might even get lucky and find your exact booster at a local parts store like Napa, Car Quest etc. You will of course need yours as a core exchange.