Brake Residual Valves

Will they help with braking? i bought the hermtheoverdriveguy dual reservoir unit for disc brakes yesterday and a friend told me that these valves will improve the braking, so you don't have to pump to slow down. what do you think?

i will be running disc up front and drum in the rear. the valves go for $15 on speedwaymotors.

 

The residual valves should already be in the master cylinder he gave you. Different residual valve pressures are used, depending on whether disc, or drum brakes are used. Confirm with Herm that the residual valves in the master cylinder you received are for disc in front, drum rear.

 

ok i will, i know it comes with a proportioning valve built in but unsure on residual valves. i see they run 2psi for disc and 10psi for drum.

 

spoke with herm and they are built in!

 

Proportioning valve and residual valve are different.

 

If there in the MC, there should be no pumping to get the brakes to work unless you still have air in the system. Never seen a MC with a prop valve built in.

 

is the size of the reservoir's different on the master cylinder? will this act as a prop valve?

 

Reservoir size won't matter. Typically the disk brake pistons hold a larger volume of fluid than the drum cylinders. The disk-side reservoir is made larger to accommodate the larger change in volume with wear.

Without a proportioning valve, the only difference in braking force comes from the sizes of the pistons. All the master cylinders that I've seen have the same size cylinder for both halves of the master cylinder. The sizes of the wheel cylinders are chosen to balance braking between the front and rear.

Jeep claims that its proportioning valves (when present in the combination valve) hold off some of the rear wheel brake pressure to prevent rear wheel lockup under severe braking. When you brake really hard, the weight of the car transfers mostly to the front wheels, and the rear wheel contact lightens. The proportion of force front-to-back due to the difference in cylinder size is always going to be the same, regardless of how heavily you are braking. So the proportioning valve adds another degree of control to prevent front or rear lock-up under all conditions.

 

Chris,
Don't you still have the original MC for your '70? It should have been a dual reservoir. If it is the original Lockheed Wagner MC it would have stepped bore sizes, with the smaller bore for the front brakes. This will give some proportioning in the braking force front/rear.
Think of it this way:
x amount of force applied by your foot on the pedal is applied to both MC pistons. Now if one piston is larger than the other, the larger surface area of the piston face will produce a lower psi (x force / piston area) than the other smaller piston. That combined with the different sized wheel cylinders puts more of the braking force to the front wheels. I think it is kind of an elegant solution the engineers came up with to solve rear wheel lockup.

If you experience rear wheel lockup with the new MC from Herm, you can get adjustable proportioning valves from Summit Racing as weill as other vendors. Install it in the rear brake line, and experiment with the adjustment untill the brakes apply closer to evenly. You will still want the front to lock up first if you like being able to steer in a heavy braking situation. When the rear brakes are locked and the front wheels still turning, there is nothing to keep the rear end of the Jeep behind you.

Don

 

You dont 't want any residual presure with disc brakes. Residual check valves are used with drum brakes, with drum brakes the the residual presure is not enough to overcome the resistance of the return springs. With disc brakes any presure in the system will cause the pistion in the caliper to apply, causing the brakes to drag. Also with disc brakes the hydraulic system needs to be open from the caliper to the master cylinder when the brakes are not applied. There is a second hole in the bottom of the master cylinder reservoir for the disc brakes this is the compensation port, as the brake fluid gets hot it will expand the compensation port allows the expanding fluid to to escape back into the reservoir (when the brakes are not applied) this way the system will not build presure causing the caliper pistion to start to apply. Not only will a residual check valve cause the disc brakes to drag it will not allow the funtion of the comensation port.

 

Not so, with any system that has the MC lower or at the same level as the brakes, you use residual pressure valves, that is what the 2lb units are specifically for, disk brakes, the 10lb unit is for drums. All you have to do is read the Wilwood page and it will give you all the info you need.

 

Additoionally some disc brakes are set up as a drag style. Such as the S10 calipers I have on my rear D44, I'll need a residual valve on the rear lines.

 

i did have a problem with braking before. the rear would lock up on me. and i had to pump like crazy. i figured since i was going to a dana 30 up front with disc that a new MC would make sense. Herm's unit has residuals built in, but as for proportioning valves i wasnt sure if i needed them or one. with my new power i want to make sure the brakes are perfect! if i run 3/16 line up front and stock line in the rear with herm's unit will i have to add or take away anything?

 

Chris,
Do you have existing lines to the front brakes? If you do, the original lines should be 3/16.
If you ordered your MC from Herm and told him it was for Disc front and drum rear he would have set it up with the proper residual valve setup.
I would give it a try before going to the expense and trouble of a proportioning valve. If you have rear lockup problems, then get the proportioning valve and plumb it in

Don