'41 Chevy Brakes Help

I'm having a real battle with the braking system on my '41 and wondered if anyone here can help me out PLEASE!

The truck runs a stock '41 Chevy MC and the rest of the system is stock (1/4") apart from the rear axle, which is a 12-bolt with smaller diameter (3/16") hard lines running along its width. I adapted the end of the flexi line where it meets the axle from 1/4 to 3/16, but I can't see any reason that it should cause a problem with pressure build-up?

The problem is that over a medium to long journey the pressure builds up in the system resulting in the brakes coming on (all round) and when I pull over the brake lights stay on and the drums are all warm. If I leave it parked for a few minutes, the pressure backs off and all is well again.

I originally thought the fault was the adjustment on the brake pedal, but backed it off a long way and it just meant that I could drive it longer, but the problem still came along eventually. Then I decided it must be the return spring not being strong enough and causing the pedal to 'vibrate' whilst travelling and 'pumping up' the pressure in the system. I now have a really strong and positive return spring, but still the problem persists.

I rebuilt the MC and bench bled it before installation. I have bled the whole system many times and have really good brakes with no trace of 'sponginess' at all. They just get a bit too good!

Can anyone help to shed any light on this problem for me please? It's spoiling the enjoyment of my newly finished motor, 'cause I can't drive it as far as the drags! For once it's not engine troubles shortening my journeys at least!!!

Cheers,
Mark

 

I had the same issue and it ended up being a faulty residual valve in the M/C. Did you put a new one in when you rebuilt it? Changed mine and the problem went away. Al

 

Residual valve? Never even heard of it, let alone replaced it! I'll look into that and get it changed.

Nice truck by the way!

Thanks for your help.
Mark.

 

Is that the gold coloured thing in the bottom left of this kit?

 

Yes it is! Thank you for the nice comment! Al

 

Make sure the piston is returning far enough that it clears the smallest hole you see through the filler opening. I have seen crud built up in the open end of the bore that kept the piston from fully returning,also too thick of a stop washer there ,when used. Do you have a hot exhaust pipe close to the MC ?

 

John,

Thanks for the advice. No exhaust next to the mc. There shouldn't be any crud in there as i rebuilt it on the bench recently and got it nice and clean. I will check though.

Mark.