Odd brakng issues... '74 FJ40

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Apr 18, 2011
Mentone, Cali
So after a full day off roading, I started to notice a slow degrade in braking performance (still running all drums), basic problem was the pedal was slowly going to the floor with little to no actual braking. When we stopped to have a few adult beverages, I looked at the master cylinder, and noticed a lot of brake fluid around the rear reservoir and on the cap, and of course the master cylinder had brake fluid on it.

I did notice when I really didn't have pressure for stopping, if I pumped the pedal once, I would have full brakes again, of course this made the brakes very touchy, but it worked every time.

I was talking to my off roading buddy, and he thinks there might be air in the system (not sure how that would have happened), I haven't had a chance to bleed the brakes again, and not sure if you can only do it with one person.

Any advice or suggestions that I should look for?
I think you need a new master or rebuild it. mushy usually means air in the system, but slowly going to the floor is a leak or bad master from my experiences.
sounds like its pushing past the front cup and pushing the fluid into the rear.

is the front fluid level much lower than the rear...is the rear over full?

is it leaking from the back of the master cyl?

pics would probably help
The front fluid level is perfect. The rear fluid level is low, I can't really tell right now if it's leaking from the rear of the MC, since it's covered in fluid and dirt, and I haven't had a chance to clean it yet. I can get pictures later today when I get home.
Well before this weekend, the brakes worked fine, only after off roading for a few days, the problem started.
So, after looking online for the Master Cylinder, I found this one and this one, I'm not sure which I need. Everything tells me the second one, but all the pics I've found, show the first one.

If I do a search for a 1974, it shows the second one, if I do a search for a 1975, it shows both. :idea:
I would clean up the master so you can tell where its leaking from. And also go around and adjust all your drums. Lots of info on here about setting your drums...basically tighten till the wheel locks then back off a couple few clicks.
Master can also leak inside the truck (look under the dash).
Yeah, I'm planning on doing that today when I get home. I haven't messed with drum brakes since high school (a long time ago), so I'll have to read up on it.
I decided to buy a new MC, so that should be going in tomorrow, it was cheap enough, and who know when / if it was every replaced.

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