Master cylinder id

[truckeroy]

I have a 66 that already has the disc brake conversion up front. Has mid 80s style. The master cylinder is non power with a proportional valve. It's very hard to stop. The mc looks like a 67-72 style with the deep rod. No numbers on it. Could this be for a shoe brake setup? I can't figure out how to post a picture. When I do, I'll send it

[truckeroy]

Trying to upload a picture

[theastronaut]

I have the usual squarebody disc swap on the front of my '66 C10 with stock rear drums. I used a 1" bore master cylinder without a booster and it stops great with plenty of braking power. The larger the master cylinder bore is the less hydraulic pressure it makes for the same input force, you might have too large of a bore. 1" is just right for me, you might want a 15/16" bore if you want an easier pedal, but without ABS and easy pedal makes it lock up too easily in a panic stop situation. 1" makes it easier to modulate near lock up.

If you have ceramic pads, they have a lower coefficient of friction and will make it harder to stop, you'll want to make sure it has semi-metallic pads with manual brakes.

New pads/rotors need to be bedded in or they won't stop nearly as well/as easily. If you've swapped pads but never gotten them hot enough to bed them in it will be harder to get it stopped.

[truckeroy]

Thanks for the reply. The mc bore is 1". The pads are not new. This mc looks like a 67-72 style that was for shoe brakes? I don't know if the disc brake mc looks different?Plus, I have found leaking at some fittings. I'm in the process of running new lines.

[rbruno68]

Shouldn't the front reservoir be larger for the manual disc brakes? I will be hunting for a MC for disc/drum non power set up soon. At least for, me there seems to be a lot of confusion for which one is right.

[truckeroy]

If both reservoirs are the same size, usually it is for disc/drum or disc/disc. The earlier ones had a large bowl for disc and smaller for rear drum. Since mine is equal size,I'm assuming it's the correct one.

[theastronaut]

Did you use the tool to lock the pressure differential valve in the center position while bleeding the brakes? If not it’ll move and block off the circuit you’re bleeding, then that circuit won’t get any pressure to it.

This article explains it-

https://mpbrakes.com/proportioning-v...v6mlNxUmLcCC7_

[truckeroy]

I have to admit that is new to me. Thanks.

[Agv63]

When i converted mine to disc brakes ,i swapped out control arms and spindles from a 87 g10, that uses the 2" lca shafts.
I used a 1" master and stayed with manual pedal, it brakes but i do have to step on it, making emergency stops a bit of a worry. Did a dual diaphram 8" booster and drilled pedal to suit, staying with the 1"master. Made a worlds difference,my knee dont suffer anymore and no worries about stopping in time. Mine stops really quick and not locking up wheels. It is on the touchy side but i got used to it and prefer it that way.

Adriaan.

[truckeroy]

Did you use the manual mc you had with the booster?

[Agv63]

Originally Posted by truckeroy

Did you use the manual mc you had with the booster?

Yes. This master is dual application has ports both sides and can be used manual and power. There is a small insert that looks like a bullet, goes into the piston to work with booster.