Using brake fluid

[Stinky]

On my '86 swb 720 pu...i have to add brake fluid every 2-3 weeks or so.

 

I can't find anywhere it is leaking it.

 

I have changed the master cylinder and the booster from my parts truck.

 

Last time that I worked on it.  The pu was out of use for 2-3 weeks and it seemed like it took at least a month for it to start using BF again.

 

Any ideas?

 

 

Edited June 16, 2020 by Stinky

[Stoffregen Motorsports]

Disappearing brake fluid is a sure sign that the booster is bad and the fluid is getting sucked into the motor. But you say you replaced the booster.

 

Hmmm....

[datzenmike]

Did you take the rear drums off and look at the wheel cylinder(s)? It may be so small it just gets burned off on the brake shoes and isn't visible on the backing plate.

 

 

 

[jagman]

I noticed the same phenomenon with my chrysler ans found it to be a pinhole in the rear brake line. It only showed when the brakes were applied and then only as a drop which was swept away by the wind when moving leaving no telltale trace on the car or the floor of the garage. I ended up replacing all the lines because of the internal rust in the lines.

[grannyknot]

Sometimes it will pool in the bottom of the booster and not leak out.

[datzenmike]

8 hours ago, Stinky said:

 I have changed the master cylinder and the booster from my parts truck.

 

 

Maybe they were both bad.