Which master cylinder for factory 4 wheel disc (2nd gen )

[1981silverz28]

I want to take the power brakes off my 81 z28 and go manual . It has factory disc front and factory 79 T/A rear disc . Does anyone know what master cylinder will work with this set-up ? I have a Wilwood prop valve on it already . Thanks

[Apogee]

1967-1976 C3 Corvette 1" bore disc/disc MC is a popular choice.

Tobin
KORE3

[1981silverz28]

Thanks Apogee , I will get one tomorrow .

[Skip Fix]

Speedway and a few others also have that MC in aluminum for lighter weight.

[1981silverz28]

Apogee, I put a MC for a 70 vette with manual disc and I’ve bled the hell out of them and still have a soft pedal and no brakes . It has a SSBC adjustable prop valve and dot 4 fluid . I bench bled the MC before installation.

[Skip Fix]

I had one of those that was bad eventhough it was new.

Big question was it really hard to cycle it when pressure bleeding it? Plug the outputs on the MC and then see if it will only go about 1/8-1/4" as it should hydraulic lock. My STrange took forever to get all the air out. If not still air or a bad MC. If it feels solid then look elsewhere.

Is the factory prop valve still there? If so just T the fronts and use the adjustable in the rear. Be sure and bleed the rear tapping the prop valve and opening it all the way also so no air hides there.

If it is all bled well and a good MC then you may need a larger one as those are some big pistons on the calipers(2.9375" front and 2.5" rears) and need alot of fluid, and the original MC was a Quick Take up aluminum on '81s for the "low drag" front calipers that had an even larger stepped bore to get more initial fluid movement for them. There is a 1 1/32 and 1 1/16 Mopar style out there.

[1981silverz28]

Skip fix , I'm going to try and take MC off today and re-bleed it .I'll post my results.

[Apogee]

If the MC is bad and bypassing fluid, then the pedal will typically sink slowly over time if you apply even, steady force to the pedal. If you just have air in the system, then it will feel spongy, but shouldn't sink further over time with force on the pedal. Sounds like you may not have successfully gotten all of the air out of the MC when you bench bleed it the first time. As noted above, with both outlet ports plugged, the piston(s) should hydraulically lock as soon as the seals clear the compensator ports internally.

Tobin
KORE3

[1981silverz28]

Apogee !!!! i removed the MC and bench bled it again and guess what ? AIR !!!! I put it back in and bled the lines and now I have brakes ! i would have bet money that there was no air in the MC . Thanks for the advice

[Skip Fix]

I also found it amazing there was still air on mine after bench bleeding it. Would feel hard,no visible bubbles then one more push and air bubbles.