Hey all, back again with another question.

On my newly acquired 75 F600, there was absolutely no brakes when I bought it. I recently replaced my master cylinder and all 6 wheel cylinders and now the brakes are working (perhaps a little too well). It seems like I have 1/2'' of pedal travel where there is no brake engagement, then another 1/4'' further and the rear wheels are locking up. Is there a common problem/fix for this ''all or nothing'' type of braking issue or is that just the way these trucks are? I have been reading that contaminated shoes can be the cause or potentially the surface rust on the drum? All of the cylinders were leaking quite badly, I attempted to get as much fluid off the shoes as I could with brake parts cleaner and they appeared relatively clean when I reassembled them. I haven't had a chance to go for a long drive yet to see if they would settle in on their own but I'd rather get a bit of insight before I have to take them completely apart again

If I drive with my foot on the brake lightly for a couple clicks would that help in clearing the rust off the drums and burning off any brake fluid that might be in the shoes? I've read that baking the shoes in the oven would work but I don't have access to an oven that I can use for that purpose. Also, if I adjust the shoes further away from the drum would that be of any help?

Thanks for the replies!

**edit - I also have not replaced the rubber lines yet. I have them on order and will be swapping them when they arrive.

 

I've never worked on a big truck before, but on my highboy, yes, adjusting the rear brakes down (away from the drum) can have a dramatic effect on premature rear-wheel lockup.

One thing though, I've always been one to completely replace brake shoes when they get contaminated with brake fluid.

 

No that is uncommon.
I do not recall fresh brake fluid or rusted drums causing brakes to grab. However a slow long term axle seal can cause build up in the drum that will cause that. It would be uncommon for both sides to do that at the same time.
Brake companies recommend replacing any shoes that have had oil on them. Commercial companies I have worked for steam cleaned and reused them. Gas works pretty well but all of the build up must be removed. Yes oil can still be in the pores and leach out. While the brakes may not be 100% I never saw a problem you describe from that. Loose brake adjust can cause grabbing. Tighten them down until you cannot turn them. Then back them off 3 through clicks until the wheel can be rotated.
Some master cylinders have different depth holes where the brake pedal plunger goes into them. That can cause stuff like you describe.