Rear Brakes Locking Up.

[Lemon Owner 11]

you need to bench bleed the new master! This takes some time but you absolutely have to do it.

 

x 2

[70mstang 11]

Gotta agree, if your foot is going to the floor then it sounds like air in the line somewhere. I'm sure you'd see a puddle on the floor if it was a leak.

 

I believe that if there was a vacuum leak at the booster then it would very hard to push the pedal down.

[70mstang 11]

Gotta agree, if your foot is going to the floor then it sounds like air in the line somewhere. I'm sure you'd see a puddle on the floor if it was a leak.

 

I believe that if there was a vacuum leak at the booster then it would very hard to push the pedal down.

[moose425 16]

Update. I have ensured all parts of the system are properly bled. I vented the master cylinder exactly per the manufacturer instructions. Still, my peddle was going to the floor and the rear brakes locking up no matter where I positioned the manual proportioning valve. The only adjustment left was the push rod coming out of the booster. I extended this further out, and then installed the master cylinder. I extended it out to the point where the master cylinder pistons were being displaced when I bolted the MC to the booster. However, since the car brakes lines were not connected to the MC at this point I was not pressuring the brakes lines just "pre displacing the MC pistons". Started the car up and the brakes worked great! However, after a few miles of driving the front brakes starting dragging bad. I was able to vent the front brakes at the master cylinder and relieve the pressure. I realize this may have likely been due to "pre displacing the MC pistons", but I wonder why the brakes worked great for several miles with intentional hard stops. I have a 1969 shop technical manual, and it says a "pressure impulse valve" is located at the front brake inlet of the pressure differential valve and prevents brake fluid surge back to the master cylinder resevoir. My car has the impulse valve installed, it looks just like an adapter for different size fittings but upon close inspection it is actually an orifice. Anyone have further advice? Anyone have any ideas what might happen if I removed the pressure impulse valve? Thanks so much for any help.

Moose the Mustang Guy.

[LoneWolf2U 136]

You will have to readjust the booster to master rod lenght to get the brakes to fully release properly.

Do a search here and you will find many posts on how to properly set up the braking system.

[moose425 16]

Mach1Rider is correct. I have solved my brake problem. The push rod stick out dimension from the booster is CRITICAL. Take a look at the following link, http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html. It explains how a master cylinder works wonderfuly. Look in the bottom of your master cylinder reservoirs and you will see two holes in each reservoir. A big hole towards the rear of each reservoir and a smaller hole towards the front of each reservoirl You must adjust the push rod stick out from the booster so that the piston beneath each reservoir is between these two holes, and as close to the small hole as possilbe. The closer to the smaller hole the tighter the brake peddle will be. You can actually look through the larger hole and see the piston when properly installed. If you extend your booster push rod out too far it will extend the piston beyound the smaller hole and your brakes will not be able to release pressure and will drag as the fluid heats up and expands. If you don't have your booster push rod out far enough, the piston may not go past the first hole and your brake peddle will go to the floor as mine was doing. PUSH ROD STICK OUT DIMENSION FROM THE BOOSTER IS CRITICAL! A SMALL CHANGE IN STICK OUT DIMENSION CAN MAKE A BIG DIFFERENCE.

[JTG 10]

Wow. Nice job figuring it out. You are now a MASTER of the master cylinder.

 

Sorry, couldn't resist.