Vanishing Brake Fluid
 

So the rear half of the master cylinder slowly loses fluid until empty. I suspected that the front wheel cylinders might be leaking, but I pulled back the rubber and they were dry inside. I see no evidence of leakage inside the drum. I have looked and can’t seem to find a leaking line anywhere.

It’s a 69 K25 with PB and drums on all 4 corners.

I’m stumped. Ideas? Pump the fire out of the pedal and keep looking, I guess.

Re: Vanishing Brake Fluid
 

its leaking out of the rear seal of the master into the brake booster

Re: Vanishing Brake Fluid
 

Thanks, brother!

Re: Vanishing Brake Fluid
 

Did you also check your rear wheel cylinders? I'm assuming you see no leaks under the truck either. If not, then I suspect what Volksworld said is probably the case. Disconnect the master cylinder from the power booster and see if you see any fluid there.

Re: Vanishing Brake Fluid
 

All good advise. I have a truck that would suck the fluid through the vacuum hose and burn the brake fluid, with very little evidence. There was an internal hole/defect in the seal/bladder in the vacuum canister of the power brakes. Just an idea if all other sources check out okay, Bruce

Re: Vanishing Brake Fluid
 

Rear cylinders are good. Replaced a couple months ago. No leaks, other than motor and t/c. :lol:

Re: Vanishing Brake Fluid
 

X2, I couldn't find mine either as I never looked up underneath there. New master which was surprisingly cheap and easy to install, no problems since.

Re: Vanishing Brake Fluid
 

Correct, Sir! Ding ding ding? $60 for a new one. $30 for reman.

Re: Vanishing Brake Fluid
 

Do NOT EVER buy a reman master cyl!!!

Re: Vanishing Brake Fluid
 

I know. I don’t buy much reman because I prefer to only fix a problem one time. Had already gotten a brand new one.