%&$# drum brakes! (1 Viewer)

[dc8ups]

Alright, my rig is a 67 40 with the stock single circuit drums at all four corners. My master cylinder had a slow leak (paint peeling on the firewall) but not anything too concerning. Anyway, I had to park the truck for a couple of months and when I got back to it, sure enough, pedal goes all the way to the floor. Order a new master cylinder from SOR, bench bleed and install it. Problem is now it takes 3 or 4 pumps to build any pressure. Adjusted all 8 of the cylinders, re-bled the entire system, still no joy. Same thing every time, pedal goes all the way to the floor on the first pump, same on the second and then on the third pressure is fine and truck brakes normally. Release the brake pedal, however, and same problem pops up. WTF!? I am leaning towards off the shelf failure of the M/C but not sure. There are zero leaks in the system, like I said I adjusted all eight wheel cylinders, and bench bled the M/C. I have built a couple of kit cars, restored a Vette, and have done a body off resto on this rig and I feel pretty comfortable with brakes but this friggin thing has me at wits end. I have read every post on this forum as well.....what am I missing? Thanks gang

 

[huminajumina]

mine was like that with 2 single circuit MC and I converted to a mid 70's MC with dual circuit and booster, it was still soft, but better, went to a 80-series master clinder and it locks up the brakes everytime... The only other thing that changed is my occasional brake adjustment and I blew out a wheel cylinder so I rebuilt it....but my pedal was always soft too, and with the first MC it required 2-3 pumps.... Not saying they are junk, but I could never get one to work either...

 

[bj40green]

Pumping to get it working means that you're compressing air.
There is still air trapped somewhere in the system.

Or.... the volume of the new MC is not big enough to handle 8 cylinders.
Compare the old and the new one to see if the cylinder chamber volume is the same.


Rudi