The GMC CCKW

Here is a strange!

1944 Chevy 1.5 ton Fire truck.

All new brakes

White Post: Rebuilt Master, Rebuilt wheel cylinders, all rebuilt shoes.

New Brake lines (complete Rubber and steel) from Vehicles of Victory.

Hydrovac nothing changed.

This is what I have done

Installed all the new brake components last summer. Bled system. When I went to put it up for the winter. No brakes. Master cylinder empty. Filled cylinder and bled.

The brakes work super. They stop great. And when holding the pedal down it would not drop (fade).

This spring take the truck out to get ready for season. No Brakes. Master cylinder empty. Inspect floor. No spots under any of the wheels or master. No brake system leaks evident. Bypass Hydrovac as I assume it is eating brake fluid.

10 days later. Go to use truck....no brakes. Master cylinder empty. Refill cylinder...bleed front brakes...all works well. No fade when holding pedal down. No spots on floor.

7 days later again....Go to use truck....No brakes. Master Cylinder empty.
No spots on ground. Some evidence of fluid leak at LF wheel. I do not believe it is brake fluid as the fresh OD paint is still on the wheel and shows no sign of peeling or bubbling. I check the pushrod on the master to make sure that is not staying engaged. There is slack so master is not "on".

Why does the master empty?

It is my interpretation of brakes that with no pedal pressure there is no outflow fromt he brake master to the system. Thus even a line leak should not allow the master reservoir to empty when not under pressure.

The hydrovac is out of the brake system loop...it can't be that.

There is no evidence of brake fluid anywhere. I removed the LF wheel and believe that is is the inner wheel seal (bearing) leaking. Took the wheel cylinder appart. It is still packed with Grease out side the aluminum cups as recommended by Dr. Deuce.

Called White Post...they have no idea.

Anybody want to venture a guess?

My plan is to replace the LF wheel cylinder with the one I have in waiting for my CCKW (if the are the same). And try it.

HELP!!!!

Bill

Bill I would have readily said hydrovac with those conditions, but you say its already been removed from the circuit. I presume when you "by passed" it, there is now NO hydraulic connection at all ? It is TOTALLY isolated ?

If that is the case I can only suggest that you clamp off the fronts, and see what happens then clamp off the rear axle and test again. Fluid don't evaporate so it gotta go somewhere!!

Karoshi,

The Hydrovac is out of the circuit...replaced by a steel splice line.

Good idea on the Clamps....I did not think of that.

While the LF wheel is apart I am going to steal the LF wheel cylinder from my CCKW brake parts (to be installed) and put it in the Chevy. I believe they are the same.

Bill

I had a similair problem and leak was a minute leak at the flex line at the front axel at the Tee. It was so small the fluid was actually dissapating before leaking to the ground. The truck would sit foir a month or so and I would go out and no fluid in the master cylinder. I finally re-;tightened every line in the system and then I noticed my master cylinder would be full after letting the truck sit for a while. The flex line was lose about 3/4 of a turn. Just enough to let the light fluids out.

Chipmunks....








I have the same problem with the chev dump

Bill, did you try pulling the master away and looking at the back? Maybe it is a little damp there. This is a common place for cylinders to leak, even rebuilts. If it is leaking a minimal amount you might not even notice it. Try plugging the line at the master and then you have eliminated the whole system. If you don't have a plug get an old line and pinch it off and screw in the fitting. Work from the master through the rest of the system. Because brake fluid is hygroscopic, it will sometimes not be noticeable in small amounts on damp concrete.
Cheers,
Barry

Barry,

Are you talking about between the Master and the frame?

I have replaced the LF hub inner seal which looked like it was leaking. I did not know whether it was that or the wheel cylinder. I left the brake drum off for 5 days while I waited for parts and there was no leaking from the exposed wheel cylinder.

Will wait 10 days and check the master.

Bill