This ones got me kinda stumped.Go to pump the brakes to set the line lock,and after a couple pumps,the pedal is rock hard and won't go down at all...it's stuck at the top.It's very intermitent,but it's happened more than once...even happened at the stripe tryin to tighten a race up.Went to drag the brakes and the pedal was hard and wouldn't go down.Every time it happens,I let off and then the pedal's fine. Still running drums in the rear,but switched to wilwoods up front with a mopar aluminum master about 5 years ago.Everything has worked fine up until recently.Any ideas?

Hey Jeff - are you running a proportioning valve? Have you checked the pressure to the fronts?

Yeah Bill,got a wilwood prop valve in the front brakes.It's always been cranked open.10 lb.residual valve to the drums.Have never checked brake pressure(I know,I should though).

It sounds like it's building pressure and not releasing it - that should be indicative of proportioning valve. You should put a gauge on the fronts and check them while Steph pumps the pedal.

When this happens , do you have brakes? if not I would look at the brake rod, it might be about to fall out of the master cylinder!!!

That could very well be.It's one of those things where it won't do it in the garage,only when it matters.

I'll bet the problem is your M/C, If you can get it to recreate in the garage have someone crack the lines loose at the M/C when the pedal goes hard and see if it drops as soon as they get cracked.....If not then you know it is in your linkage or M/C

I don't believe I have brakes when it happens,as it didn't slow at all the other week when I tried to drag them on the big end.The pushrod is fully seated into the rubber grommet in the master.Already checked that.

We had a similar problem and found a twist and tight bend in one of the flexable lines,straightened it out and no more problem.