7/8" Master Cylinder and Rear Disc Brakes...

[JLsKA]

I just bought a new 7/8" MC and will be running rear disc brakes.
I have read that the check valve for the rear bowl should be removed, for rear disc applications... Is this correct?

Thanks,
James

[bertvorgon]

Check valve...???? Elaborate.

[Great_Escape]

I just bought a new 7/8" MC and will be running rear disc brakes.
I have read that the check valve for the rear bowl should be removed, for rear disc applications... Is this correct?

Thanks,
James

Residual pressure valve that is built into cylinder? If you pull the brass seat out of the out of the master cylinder you will see a rubber one way valve and a spring that holds it in place. I've found the easiest way to take out the seat is to tap it then use a small machine screw to pull it out, remember not to damage it because it goes back in.

[JLsKA]

You mean those big brass seats that look like hex nuts aren't threaded? Seems wrong to have to drill it.
Is this what Baz @ Datsport is doing to his optional MC for rear disc?
I bought mine from Troy Ermish but he hasn't replied to my same question.

[Great_Escape]

You mean those big brass seats that look like hex nuts aren't threaded? Seems wrong to have to drill it.
Is this what Baz @ Datsport is doing to his optional MC for rear disc?
I bought mine from Troy Ermish but he hasn't replied to my same question.

I was referring to the brass seat that the brake line tubing sits against. In this picture it looks like the seats are aluminum. Sometimes the seat for the tubing has a slight press fit to it. That is where the machine screw comes into play. Sometimes they fall right out. Just remember not to mess up the taper as that is where your brake line seals.

[bertvorgon]

Ah....RESIDUAL PRESSURE VALVE.

I can see taking the back one out, as it was for drum brakes, but, would it not be a bit of an issue to remove the front brake one?
If we want to minimize pad retraction, I thought we want a hair of residual pressure, to keep the pads out.

I'm just curious, so if you have any info from Baz, let us know.

I do whatever I can to minimize pad knock back and retraction. I even specified the seals in my front calipers.

[JLsKA]

Thanks, guys... I just heard back from Troy and he said the 7/8" MC he sold doesn't need any mods.
Hopefully, I won't have any problems.

[datzenmike]

Disc residual valves are only a few pounds but drum are 8-12 pounds. (give or take) When I installed my 15/16" zx master it would have had a rear disc brake residual valve in it. I just put the rear drum residual valve from my 710 master in it. I wouldn't run without one, just get one from the front of any old master. It's only a couple of pounds to keep the pad rubbing the rotor to keep it clean.