brake master cylinder

[scott johnson]

My home computer died so I'm doing his from my phone so don't hate me for not using the "search ".

I have a 72 fj40. With 79 axles. My brakes are holding pressure. When I start out I have about 1.5 inches of travel before the brakes engage. After a couple of stops I have no travel and the brakes drag.
Should I get another 72 brake master or swap out another master cylinder. The one I have was adapted to have the right residual pressure foe the front disc brakes.

Will the later model master bolt up to my 72 booster? I have heard of people swaping in a mini truck setup. Just need something that will work safely and not kill the budget.

Thanks.

 

[LAMBCRUSHER]

check the plunger between the master and booster. If it is too far out, it will not disengage the master, after a while, pressure can bleed back down and feel like you have pedal again(the next day), but as you start using it, it will build back up and not open. the plunger should be just under an 1/8" or so from contacting the plunger of the master when they are bolted up. you can put a dab of grease on the end of the booster plunger, set master, then remove master to check to see if there was grease transfer from end of rod to master cylinder plunger. If the grease transfers, you will need to turn the booster plunger in some....You did remove the residual pressure valve from the front circuit of your master cylinder to work with the disks, right?(I think you said you did that part....)

 

[Pighead]

The one I have was adapted to have the right residual pressure foe the front disc brakes.

Are you sure it's the correct residual valve? Try running without that residual valve. If the problem persists, it's the pushrod between the master and booster is too long...

 

[lostmarbles]

Are you sure it's the correct residual valve? Try running without that residual valve. If the problem persists, it's the pushrod between the master and booster is too long...

In my opinion it is a common misconception to believe that "residual valves" leave any permanent pressure in brake lines.

I believe they leave this pressure there only while the wheel-cylinder pistons are returning to their pre-brake-application positions (with the purpose of keeping the lips of the seals on drum-brake wheel-cylinder-pistons firmly held against cylinder walls, thus preventing fluid leakage, at this time).

So I'd go straight to the pushrod-length solution if it was me.



PS. This residual valve info is certainly true for the type that's used in my 1979 cruiser anyway:

 

[Pighead]

So I'd go straight to the pushrod-length solution if it was me.

Probably me too...but the residual valve is easier to check first.

 

[scott johnson]

I'll check the push rod. The residual presure valve was removed when we put the disc brakes on.

 

[scott johnson]

fOUND A REPLACEMENT MASTER AT PARKS AUTO PARTS FOR $25. WONT HURT TO REPLACE IT ANYWAY. HOPEFULLY IT WILL SOLVE THE PROBLEM.

 

[LAMBCRUSHER]

since yer in there...check that there is clearance betwixt the pushrod and master...