Originally Posted by 6426yy
I had really soft pedal pressure before and I even called Quick Performance and they told me that some guys use the Res valves so I tried it and it cured my problems. I'm just glad there finally working. I thought I'd share incase anyone else wanted a cheap alternative to the wilwood master.
Don't take this as an argument, OK? Consider it food for thought. You might know all of this but maybe it'll help someone doing a search.
On a normally functioning disc brake system having the MC above
the calipers, there is no need for a RP valve. That's just the facts as I know them, and is backed up any number of times by brake manufacturers/distributors. If there actually IS a need, I would be looking for the root cause, rather than putting a 2 psi band aid on it.
The reason a RP valve shouldn't needed is because disc brake calipers have no retraction mechanism like a drum brake. A drum brake has springs that pull the shoes away from the drum, calipers don't. It would take 'vacuum' applied to the brake fluid to cause the caliper piston to retract- and that's what happens when the MC is BELOW the calipers and the fluid tries to run "downhill" to the MC.
The problem sometimes encountered when using a disc/drum MC on a 4-wheel disc system is inadequate volume to the rear brakes. Calipers take more volume than drums, if there's not enough volume, the pedal will bottom before the brakes are fully applied and the pedal will not be hard. The MC needs to be capable of about 1200 psi.
Providing all that is covered, to using the MC you bought you need to remove the residual pressure valve to the rear drums. The MC bore needs to be about 7/8" to 1" and the pedal ratio needs to be around 5:1.
If you have a soft pedal w/a 4-wheel disc non assisted brake system it could be due to air in the lines- bleeder screws on the bottom (calipers swapped side to side) will cause air to be trapped and a soft or spongy pedal. A too-high pedal ratio, a defective MC, or too small MC bore will also cause it.