Technical Residual Pressure Valves

I have a drum/drum braking system (F100) with the GM master cylinder high up on the firewall. There is no servo. I will be fitting a proportioning valve.

Do I need to use residual pressure valves? If so, how many and where is best? I ***ume it is 10lb valves needed with drums.

 

If its a drum/drum master, chances are the residuals are in that master. They pop into the ports

 

I would say no,only needed when master is below bleeders. Just make sure your cylinder is for manual brakes,and prop valve is for drum/drum.

 

Thanks chaps. I will check the master cylinder.

 

Depends on if your master is for drums and if it has built in residual valves. But probably not unless its a disc drum then you will have to make up the difference between discs and drums which is going to be about 5 lbs.

 

Hopefully your proportioning valve has a section that is a metering valve, the metering valve is there to make the take up happen on the drum section before the disc section clamps down. I have a car without it and everyone notices the pedal has a two section feel every time it is pushed. Residual valve may not be necessary, but, the systems that have it seem to be less prone to slave cylinder leakage when they age.

 

All vintage drum brakes up to the early/mid '70s used/needed residuals, (regardless of master cylinder location) but they will also help pedal feel/travel even on later drums. Add 10 lb. aftermarket residuals close to the master outlets [if the master has no internal residual(s)] and upstream from the prop valve.

 

Stay away from the wilwood valves, I had good luck with the SSBC products. Check master with a paperclip, will be behind the tube seat. 10lbs for drum, 2 lbs for disc as close to the master as possible. A lot of masters that SHOULD have them get rebuilt and not put back in (I have had two of the exact same masters from the same company, one without the res valves).

 

What ramifications will be present if the residuals are after the proportioning valve?

 

Probably none, but possibly causing the prop valve to malfunction. I've never seen or worked with OE residuals down stream from a prop valve, but know they won't cause any PV problems upstream.

 

Ok thanks.
I have a tight space issue, and they will be after the proportioning valve.

 

You can locate the prop valve at the rear axle line drop if necessary, which should provide room for the residual upstream.

 

Ok, I just looked at the packaging for the SSBC res valve and it says "Note: residual valve should be installed BEYOND an adjustable proportioning valve, if used."

 

Really helpful - thanks very much.