JPrevost

So I'm stumped on this one. Where is it? I thought GM put it into the master cylinder but the part numbers are the same for both drum and disc rears! So where is it and if it's built into the combination valve then okay, why are the disc and drum combination valves the same part number... I'm loosing my mind trying to figure out what should be common knowledge. Also, I already did a search for "residual valve" and came up empty handed.

RBob

iTrader: (1)

Jon, I checked the '92 Helm manual and there is no mention of a residual check valve. No-where, no-way. Surprised me too. The master cylinder is a quick take up design which may make up for the lack of the pressure check valve. A quick take up M/C supplies a lot of fluid at low pressure during the initial actuation of the stop pedal.

OTOH maybe the wheel cylinder seal design is different and diesn't need the residual pressure to hold the seals against the bore. Dunno'

As you mentioned GM used to put the valve into the M/C outlet. Could check for it by inserting a toothpick into the outlet fitting. If it only went in about a 1/4" and stopped the valve was there.

RBob.

P.S. C4 brakes rock.

Grumpy

The *quick takeup* seal designs took away the need for residual pressure valves in most applications. Some GM cars used them up until ABS. Since ABS, I haven't seen any, but I haven't been into many late model cars.

*Generally*, the iron master cylinders were for the old design seals and would most likely have the residual pressure valves.

According to I think it's Wilwood they only suggest them when the M/C is lower then the calipers/ wheel cylinders, anymore.

JPrevost

Ah, so the quick takeup seals are built into the wheel cylinders? That makes sence considering they're size compared to other older drum brake cylinders I've seen.
The residual valves are used to keep the shoes out near the drum. The 10psi is enough to overpower the return springs but since there is only 10psi the pads eventually get "kicked" off the drum surface staying in limbo. I wish I could find more about the wheel cylinders because that is very interesting.
It makes sence that the brake components mounted on the chassis would be the same no matter what the brakes were. This is a normal procedure done to save money when things like brakes and drivetrain/suspension components are out sourced.
I plan on bypassing the combination valves proportioning part and just didn't know if the residual valve was in it or not.