74 c15 no brake pedal.

[Swampyankee74]

About a year ago this truck got a completely brand new brake system not one old part was used. Originally it was what I believe would be a jb1 (1-1/4 front rotor with rear drum, manual brakes). I ended up converting to vacuum power brakes. Truck might have 200 miles on it with the new brakes. Started having a problem with the brake pedal taking a couple seconds to return after depressing. I ended up replacing the master cylinder and brake booster with tuff stuff master cylinder and booster combo 2132NA-2 dual diaphragm 1" piston master cylinder.  This is the one tuff stuff said was for my truck.

I Bench bled the master, installed in the truck, and then proceeded to bleed the brakes the old pump and Crack the bleeder method. I end up with a pedal that gets good and firm about halfway down. But when you start the truck goes to the floor. So I went wheel to wheel vacuum bleeding over and over again. Still the pedal is trash. Bench bled the master cylinder again and then pressure bled the entire system. No air at all in there. Pedal is still trash. I take the truck for ride, the truck will stop but I believe it's about 90% back brakes doing the work. The back brakes are smoking hot and the fronts are warm. I'm at a loss. I have days invested and about 6 quarts of brake fluid. Has anyone had any experience with that master cylinder? Do I have the wrong part? A defective part?

Link to the part I used.
https://www.tuffstuffperformance.com/i-24485898-brake-booster-w-master-cylinder-11-in-1-in-bore-dual-diaphragm-w-pn2018-dual-rsvr-master-cyl-10x1-5-metric-studs-3-8-in-16-pedal-rod-threads-chrome-2132na-2.html

[VileZambonie]

Make sure the parking brake cable isn't pulling on the shoes. Check the pushrod length, pop the master off and make sure it isn't depressing the master while driving. Put an OE master cylinder on and see what happens. I've had a lot of trouble with those master cylinders.

[Swampyankee74]

My parking brake isn't hooked up. As far as the pushrod goes I believe it is non adjustable on this vacuum booster, if there is such a thing.  I couldn't see a way to adjust it? I don't believe it is pushing on the master piston. I can slide the master cylinder back to its mounting spot on the vacuum booster without having to depress the piston.

[VileZambonie]

The rod attaching the booster to the brake pedal arm is threaded and adjustable. It needs to be adjusted once the booster is installed with the pedal in the return position.

[Swampyankee74]

I gotcha. Way it is hooked up now the pushrod is fully retracted actually holding the pedal slightly from all the way back. Should I run the pushrod out til it just makes contact with the master cylinder piston?

[VileZambonie]

With the booster installed and the brake pedal in its returned state, adjust the rod so that it fits. It should not be acting on the pedal in anyway (neutral adjustment). Are you using JB1 or JB5 Master?

[Swampyankee74]

I'm not sure what the tuff stuff master cylinder was. But I just picked up a what I believe is a jb5 from napa I'm going to try out.
https://www.napaonline.com/en/p/NMCM2072

[Swampyankee74]

I can confirm the master cylinder was bad. Put in a napa master cylinder like vz recommended and my problems went away. What a struggle over something that should be simple. But that's part of it haha! Thank you again VZ!

[VileZambonie]

I went through 2 or 3 of them as well on my 74. I'm not sure if I'll keep it on there either. It looks cool though 

[Swampyankee74]

Yea, I liked the idea of the chrome with brake fluid being involved. I guess I'm just going to end up painting this raw cast iron master cylinder.

[Shifty]

Might give it a bit of contrast.   

Save your chrome one, and either hone it, and throw new cups in it, or send to Cardone, or some other re-builder to do so. 

[Swampyankee74]

If I end up stuck with it I will possibly go down that road. Otherwise i'm gonna try and return it.