FJ40 MC Replacement

[mikeglenn]

My stock MC has died, so I decided to change over to a dual reservoir system and continue to cruise around with the stock drum brakes for awhile before I change out to disc brakes. So I fabricated a bracket to mount a GM MC. The problem is that I can't seem to find a MC that pushes enough fluid to actuate the brakes. I tried a newer MC that is set up for front discs, an older design for all wheel drums, and most recently a Corvette MC designed for all discs. The best I've been able to get is that it takes 8 or more pumps to get the brakes to actuate, and then they don't totally engage. I realize that the stock 8 cylinder system is designed by a demon on steroids, and bleeding the lines is tough, but still I'm (reasonably) sure the air is out of the system, and the drums are adjusted properly.

Is there any possibility that GM manufacters a non booster MC that will work?
Should I go with a Toyota mini truck booster system?
Is the MC not the problem?

 

[chuglife]

Why not stick with a stock MC? I screwed around with mine for awhile, considered putting a mintruck MC in (before i knew about this site ) for my planned disc conversion... turned out to be a bunch of trouble and just went back to a stock MC, which i bought from the local dealer at retail (before knowing about this site ) and all my problems went away.
what i'm trying to say is what was wrong with the stock MC before it busted? why not just put a stock one in? it seems like more trouble than its worth...

 

[3_puppies]

brakes are something I don't want to take chances on, as they are kinda important. stick with stock until you go disc

 

[Degnol]

The stock mcyl has residual valves for the drum brakes, this keeps the return springs on the shoes from compressing the wheel cyl and pushing fluid back into the master. Any dual circuit that was intended for disc/drum will/ may not have the residual valve, so that's why you have to pump.
Go with a stock setup from a later model '40, you can use them unboosted.
GL
Ed

 

[Pin_Head]

The best I've been able to get is that it takes 8 or more pumps to get the brakes to actuate, and then they don't totally engage. Is the MC not the problem?

If the brakes were adjusted, you wouldn't have to pump them to get them to engage.

 

[foxfab]

residual valve for drums should be @ 11 psi

 

[snailwagon]

Maybe you checked this, but did you look at the push rod clearance between the booster and the master cylinder. Most MC's have different push rod adjusmtments. A small space between the rod and the MC is amplified quite a bit. I imagine your GM MC is a 1" or even a 1.25", so it shouldn't take a humongous amount of pedal travel to actuate the brakes.

 

[mikeglenn]

Thanks guys for your input. I'm going to stick with a stock MC that will later facilitate a jump to disc brake system.