Power Disc Brake Master Cylinder Help
 

I’m currently working on a power front disc conversion for my 1969 GMC 1/2 ton 2wd. When I bought it last year, it included some new parts including this brake booster. I used the PN to determine that this is intended for a 1967-1970 C20 ¾ ton truck. I looking to determine if I should try to make this setup work or just buy a different booster/master/prop valve that is intended for a c10.

To make this booster work, I am guessing I would need a C20 master/proportioning valve? I’ve read in the forum that these differ from the C10 parts. I’ve read that the masters are ‘reversed’ in terms of which reservoir is intended to go to the ports on the prop valve, so the lines must cross. If this is a better booster than the C10 parts, I would prefer to utilize it.

Can anyone point me towards a C20 master/prop valve combo that would bolt right up to this booster that I already have? I see some of the aftermarket companies sell master/prop combos but I cannot determine which one would match this style of booster.

If this ends up being too much of a science project, I could just sell it and buy a booster/master/prop valve intended for a c10 from CPP as I have purchased all other CPP components so far. But would like to keep it if C20 parts are a better/stronger product.

Thanks,
Jacob

Re: Power Disc Brake Master Cylinder Help
 

I may be wrong, but I believe you can put a 71-72 C10 master cylinder on there. You need the power brake version.

As far as I know all proportioning valves for disc/drum will interchange. "PV2 proportioning valve" is a search term. Same prop valve is used on GM disc/drum trucks and cars for a long time. I would try to use the prop valve for the donor brakes if you have it.

Re: Power Disc Brake Master Cylinder Help
 

Interesting.. I thought I had read that the pushrods were different lengths and not compatible. My original plan was to use 71-72 disk master/prop valve until I read that the stuff is different. Can anyone help to confirm?

Good point on the prop valve being common, I guess what I'd be looking to buy is a master/prop valve combo that will go straight to this booster (assuming the master is different; I have found plenty of MC/PV that are intended for c10's).

I don't have a donor, the brake components are all new CPP parts.

Re: Power Disc Brake Master Cylinder Help
 

C20 and C10 master cylinders are different, but I was under the impression that the boosters interchanged. Could be wrong.

Re: Power Disc Brake Master Cylinder Help
 

The 1/2T booster is easy to come by.
My friend with a 72 3/4T had a heck of the time finding a replacement 3/4T booster when his failed. I am mentioning this as it is likely you could change from the 3/4T to the 1/2T and possible break even or even make a few $.

Re: Power Disc Brake Master Cylinder Help
 

Yeah the rod from the back of the pedal is different between the two boosters. I have a C30 but I believe it was a chassis cab originally. It has the flatter C10 style booster, and when I went to install a new one I got the same one you have. The rod from the pedal is shorter. I believe you can actually get the rod on, but the brake pedal is on the floor by the time it's all said and done. No worky.

Re: Power Disc Brake Master Cylinder Help
 

Good point - if I just sell this one and find a 1/2 ton I'm in the same spot. I had read the below link that made it seem feasible, but I don't really want to start a science project and have it be a pain to find replacement parts in the future.
http://67-72chevytrucks.com/vboard/s...d.php?t=223436

Thanks - I hadn't thought about the geometry on the back of the booster to the pedal, I'll measure to confirm but that is yet another reason to go with designated c10 parts..

Re: Power Disc Brake Master Cylinder Help
 

I used a new master for7–72 1/2 ton and it works fine with the ‘70 booster and pushrod. I bought a used prop valve from the parts board.

Re: Power Disc Brake Master Cylinder Help
 

Thanks for the info, was your '70 booster originally for a 1/2 ton?

Re: Power Disc Brake Master Cylinder Help
 

Yes, but I bought it from the parts board over 10 years ago. There are two styles of half ton boosters, a Delco Moraine and a Bendix. Mine is a Bendix. I can take some pics of the set up and post them later tonight if you want.

Re: Power Disc Brake Master Cylinder Help
 

Thanks - yeah I've seen the different style of 1/2 ton boosters out there. I'll end up buying one and selling the 3/4 ton one I have most likely