The Stovebolt Site Forums The Parking Lot Big Bolts 1964 c-60 brakes

having a problem with loss of brake fluid. when in use during the summer master cylinder stays full, during the winter it sits. when spring comes master cylinder is empty. where is the brake fluid going?

Hy joek3167, check all your backing plates for wetness, if you don't find any evidence of leaks, then remove the drain plug from your Hydrovac and see if that is where the missing brake fluid is. When you top up the brake fluid in the spring and bleed the brakes do they function properly?

haven't checked the hydrovac, but everything else is dry and yes when I fill mastercylinder back up everything works fine. its just when the truck sits over the winter months that it loses fluid

I have the same issue every Spring with my 'T.F.'55 6500. Time to replace the hydrovac,and replace all of the (rear) lines,(flex/steel) as well. The brakes work great,but not taking any chances. I'm going to re build the M.C.,as well as the rear wheel cylinders. the front cylinders were replaced,(along with the front flex/steel lines),two years ago.

everything on this truck of mine was replaced brake wise and still have this issue every spring time

I have the same problem with our '72 c-50. That thing can stop on a dime, but in the spring the master is empty, I just fill it up and all is well again.

where does the fluid go

I don't know either.

It's in the hydro-vac....the secondary master cylinder thats mounted to it always has a vacuum on the end of it and eventually the brake fluid gets drawn into the vacuum chamber....I've been trying to remember to pump the brake pedal after I shut the engine down to release the vacuum to prevent this,
Scott

Thanks,Scott! GREAT tip!!

48 big trucks you are right , I was told the same thing by another guy who also told me to hit the brake pedal a few times to release vacuum