The Stovebolt Site Forums The Shop Area Engine Shop Brake residual valve question

I just bought semi-Kevlar shoes for my horse,and the people at Praise brakes recommended 2 pound residual valves for both the front and rear axles. Later I looked at the Master Brake website and they recommend 10 pound residuals and say that 2 pound are for discs only, to prevent flow back. They say 10's are needed with drums to keep the shoes close to the drum and give a firm pedal. Has anyone tryed any of this? What do you guys think is best? I really appreciate this site and each 'bolter...you guys are really great help, and gentlemen too.

I've always installed 2 lb in the front and 10 lb in the back.

Use 10 lb valves for drum brakes (if they're not incorporated into the master cylinder) and 2 lb valves for disc brakes.

The misconception that the purpose of residual valves for drum brakes is to keep the shoes against the drum is a common one, but I'm very surprised to hear that Master Power's site is repeating it. They know better.

It takes around 70-80 lbs of fluid pressure to overcome the tension of the brake shoe return springs. There's no way that residual valves can even begin to affect the position of the shoes. That's determined by the regular shoe adjustment procedure.

The residual valves prevent air from being pumped around the wheel cylinder cups by the action of the master cylinder return spring during brake release. That's all they do.

In disc brakes, the 2 lb valves prevent siphoning from calipers to master cylinder. They are most important when the master is mounted low, as under the floorboard in a stovebolt.

The type of friction material is irrelevant to the residual valve question.

Joe

Chevy1, that's the setup MP described for disc fronts and drum rears..I guess I'll just keep my drums at all four corners till $ are available for disc conversion. Joe, the dual master cylinder conversion kit I got from Chevy Duty says to use an early to mid seventies Chevy "mid-sized" master clyinder. How do I know if the residual valves are built in? I thought I'd just go to the local parts place and get a master for a 70 - 73 pickup with all drums. Do ya think that sounds like a good plan? Thanks guys..

I'm sorry Gobsow.........I thought you were running a disc/drum setup. I convert everything I own to disc/drum so that's why I was saying 2 lb for front disc and 10 lb for the rear drums.

The easiest way I've found to determine if the residual pressure valves are in the master cylinder is to take my very expensive high tech tool....."a tooth pick or similar" and insert it into the outlet port of the master cylinder. If the residual pressure valves are installed, you feel a rubber plunger that will retract into the port further with slight pressure. The residual pressure valve is just a rubber plunger that is backed by a small spring to seat against the opposite side of the outlet brass nipple. The springs give you the required line pressure by keeping the rubber plunger against it's seat.

Thanks Chevy1 - I'm off to the parts store, armed with your aforementioned high tech residuality determinator.

I am doing this this week or next, all I need to find is a master cylinder. Did you find one with the valves already in? If so what did it come from? Thanks for the help.