Rear Disc,,, What Master Cylinder ?

jakedog

Frequent Racer
Apr 10, 2009
606
0
16
Upstate NY
Hey I am gonna convert the rear to disc, My question is what master cylinder should i run ? Mine is now leaking and i need to change it. A friend of mine suggested one from a 70's Vette cause those had 4 wheel disc. Any thoughts ? Also will i still need a proportioning valve ? And do i need to change my metering block on the frame ? Any input would be great ! I plan on piecing it all together with the speedway brackets and such , so i can save a few bucks !
 

dwkohout

Frequent Racer
Sep 25, 2004
529
0
0
Albany,MN
I used a stock master. I removed the prop/combo valve and installed an adjustable prop valve.

008.jpg
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
A stock MC won't give the proper pressure or volume of fluid for rear disc calipers. Also, the stock combo valve isn't biased or metered properly for rear discs. Using an adjustable prop valve instead of a combo valve eliminates metering & if you have the right MC, causes early rear disc lockup. I used an 1-1/8" Vette disc/disc MC & a disc/disc combo valve from Master Power Brakes. They're both a direct bolt-in.

Tommy
 

axisg

Frequent Racer
May 13, 2008
407
0
0
YYZ ( Toronto )
I use the stock MC with LS1 rear disks and Blazer Dual Piston up front. I notice the pedal is a little softer then when it was Disk Drum but stops great nontheless
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
axisg said:
I use the stock MC with LS1 rear disks and Blazer Dual Piston up front. I notice the pedal is a little softer then when it was Disk Drum but stops great nontheless

I bet you can't lock up your rear tires. That's why your pedal is softer. The brakes will still work & the car may even stop shorter with the better front brakes, but the rears aren't getting the proper pressure to work right.

Tommy
 

dwkohout

Frequent Racer
Sep 25, 2004
529
0
0
Albany,MN
With a few turns of the prop valve I have no problem locking the rears.
 

axisg

Frequent Racer
May 13, 2008
407
0
0
YYZ ( Toronto )
LS6 Tommy said:
axisg said:
I use the stock MC with LS1 rear disks and Blazer Dual Piston up front. I notice the pedal is a little softer then when it was Disk Drum but stops great nontheless

I bet you can't lock up your rear tires. That's why your pedal is softer. The brakes will still work & the car may even stop shorter with the better front brakes, but the rears aren't getting the proper pressure to work right.

Tommy

you may be right. Once the fronts lock then my brain takes over and I back off, modulate, and steer. Once they are "broken in" I will try again
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
15,847
1
38
North Jersey
dwkohout said:
With a few turns of the prop valve I have no problem locking the rears.


Without the combo valve locking the rears isn't a problem. Removing it actually makes it too easy. There's no proportional modulation going on to back the rear pressure down under heavy braking. What the aftermarket calls an adjustable prop valve is not really a proportioning valve. It's a front/rear bias adjustment valve & it's not intended to replace a combo valve. It's a fine tuning tool to be used in conjunction with a combo, proportioning or metering valve.

Will your brakes work without a combo valve & just an adjustable valve? Sure. LOTS of people run that exact setup. Would their brakes work better with the proper combo valve? Most likely. A full on race car runs without a combo valve, but it's a completely different animal. It has two separate masters controlled by an adjustable front/rear bias rod & an adjustable bias valve on top of that for fine tuning.

Tommy
 

MalibuRacing.com Gear

Stickers & Shirts!!