master cylinder ?

[LSXfan]

Do I need to use a disc/drum master cylinder for a disc/drum setup or can I use a disc/disc master?

[ROEINONDUBS]

i think as long as u have the right bore ur good. maybe a prob valve also

[LSXfan]

using an LS1 master cylinder (1" bore I think), stock style disc/drum prop valve, 8" dual diaphram booster with LS1 disc brakes up front and stock drums in the back. This is all in a 64 Chevelle

[MrQuick]

you should be fine, but why not rear disc too? its an easy swap.

just curious.

vince

[LSXfan]

budget, will do the rear conversion later

[ROEINONDUBS]

budget, will do the rear conversion later
i have ls1 rear calipers with c5 amendments that are just taking up space :idea:

[Apogee]

You can run a disc/disc master cylinder with a disc/drum configuration, however you'll want to run a 10 psi residual pressure valve in the rear circuit (if there isn't one already) to keep the rear wheel cylinders from leaking.

Tobin
KORE3

[LSXfan]

however you'll want to run a 10 psi residual pressure valve in the rear circuit (if there isn't one already) to keep the rear wheel cylinders from leaking.

Tobin
KORE3

I dont have a residual pressure valve, what's it for ? why would the rear wheel cylinders leak without one ?

[LSXfan]

i have ls1 rear calipers with c5 amendments that are just taking up space :idea:

what are you looking to get for em ?

[GenPac]

I dont have a residual pressure valve, what's it for ? why would the rear wheel cylinders leak without one ?



Wilwood ten pound residual pressure valves retain a minimum brake line pressure to help eliminate excessive pedal travel in drum brake systems. With drum brakes, a ten pound valve is used to compensate for return spring tension and maintain wheel cylinder sealing in the drums.

I ran a disc/drum setup without an RPV for a short while before I swapped to rear disc. BOTH of my W/Cs leaked and pedal hight was much lower than it should have been. IMO, you should not run a disc/drum setup without these things: A separate metering valve for front discs, or a metering section built into the proportioning valve and an RPV for the drum brakes. You won't be happy with pedal feel without the RPV.

[a67]

I dont have a residual pressure valve, what's it for ? why would the rear wheel cylinders leak without one ?

The residual pressure valve maintains 10 psi in the rear lines to the wheel cylinders when the foot is off the brake pedal. This is done to keep the wheel cylinder seals pressed against the cylinder bore(s).

Otherwise, with no residual pressure, the seals will relax and pull away from the bores. Thus causing them to leak.

Note that a metering valve for the front disc's is only to keep the wear consistent between the rear drum shoes and the front disc pads. As it holds off the front disc brakes until the rear shoes hit the drums.

I don't care for a metering valve. Two reasons:

They delay braking action to the front
It is easier to change front pads then rear drum shoes

Bob.

[LSXfan]

thanx for all the info guys

[GenPac]

Note that a metering valve for the front disc's is only to keep the wear consistent between the rear drum shoes and the front disc pads. As it holds off the front disc brakes until the rear shoes hit the drums.

I don't care for a metering valve. Two reasons:

They delay braking action to the front
It is easier to change front pads then rear drum shoes


I don't want to debate this with you but a metering valve has more purpose than just brake wear, it has a part in braking balance as well. By allowing the rear shoes to touch drum as front pads engage rotor, this will improve rear braking stability on wet/slippery surfaces.

[a67]

I don't want to debate this with you but a metering valve has more purpose than just brake wear, it has a part in braking balance as well. By allowing the rear shoes to touch drum as front pads engage rotor, this will improve rear braking stability on wet/slippery surfaces.

If you didn't want to debate, then why address my post in this fashion.

Having driven a front disc, rear drum car without a front disc metering valve for years on end in all kinds of weather, I have never had an issue with rear braking stability.

Bob.

[LSXfan]

i would think the stock style prop valve has the front metering valve built in.Would this be a false assumption ?

[a67]

i would think the stock style prop valve has the front metering valve built in.Would this be a false assumption ?

Factory disc/drum combo valves (not the prop valve) typically have a metering valve built into the front line section. Again, this is to even out the wear between the front disc pads and rear drum shoes.

This is done for the average consumer that doesn't like to keep replacing front pads more often then usual. Under light braking without a metering valve the fronts do all of the work. So the front pads will wear out at a faster rate then the rear shoes.

To further bolster my claim that this is the only reason for a metering valve I checked Wilwoods site. They DO NOT SELL aftermarket metering valves.

However, they do sell 10 lb residual pressure check values for drum systems (and 2 lb for disc systems). And they also sell proportioning valves (NOT combo) for both disc/disc and disc/drum (same valve for both apps).

So if a metering valve was so important to braking stability in wet conditions, wouldn't they sell one? Lots of races are held whether it is sunny or raining.

Bob.

[ROEINONDUBS]

what are you looking to get for em ?

Umm 105 shipped how does that sound

[LSXfan]

Umm 105 shipped how does that sound

sounds like a hell of a deal, wish I had the dough...thanx for the offer

[ROEINONDUBS]

sounds like a hell of a deal, wish I had the dough...thanx for the offer
no prob bro they will be just sitting so pm if need them