Porportioning Valve
 

I'm replacing the drum brakes on the rear of my stocker. I will have strange disc brakes front and rear now. Will I need a proportioning valve? Thanks Tony

Re: Porportioning Valve
 

I removed the load sensing prop valve on the Comanche - Aerospace front disks and Grand Cherokee rear disks - works fine!

Re: Porportioning Valve
 

Be sure to have the correct residual pressure valves in front and rear of master cyl.
Drums use a 8-10 lb valve and disc use 2 lb. These keep the brakes back from moving too far away to act.
Proportioning valve directs more of master cyl pressure to front or rear brakes depending where you need most braking. That may take experimentation with slicks versus small front tires.. I bet none is needed.

Re: Porportioning Valve
 

I highly doubt you have any residual ck valves unless you installed them and or your MC is lower than the calipers. I spoke to brake manufacturers and they said they haven't used a residual ck valve in MC's for years. Modern wheel cyls have little strainers or valves on the ends of the springs which prevent the fluid from flowing too far back causing a low pedal on the first pump.
I'd try without any proportioning valve and see how it goes. usually you'll lock the frt. on a drag car with skinny tires before you'll lock the rear slicks. You might end up putting an adjustable proportioning valve in the frt. brake line. You might need the next size bore larger as disc brakes use more volume of fluid than drums, you'll just have to see.

Re: Porportioning Valve
 

[QUOTE=Eman;491404]I highly doubt you have any residual ck valves unless you installed them and or your MC is lower than the calipers. I spoke to brake manufacturers and they said they haven't used a residual ck valve in MC's for years. Modern wheel cyls have little strainers or valves on the ends of the springs which prevent the fluid from flowing too far back causing a low pedal on the first pump.
I'd try without any proportioning valve and see how it goes. usually you'll lock the frt. on a drag car with skinny tires before you'll lock the rear slicks. You might end up putting an adjustable proportioning valve in the frt. brake line. You might need the next size bore larger as disc brakes use more volume of fluid than drums, you'll just have to see.[/QUOTE)
Good point master cyl usually higher in cars. I was thinking of Chassis cars with low master cyl. Thanks for reminder and update on manufacturing.

Re: Porportioning Valve
 

Tony didn't say what car he's doing this on ,or if he's using an OEM master cylinder .
Many older disc drum cars have integral residual valves ,either in the master cyl itself ,or in the factory combination/proportion valve that can cause excessive brake drag when being converted from drum to disc .
When making major system changes like this ,it's best to replace the master cylinder and the factory distribution block with parts that are sized properly for the application , particularly if the car will be foot braked .
On several of the Stockers I've built I've used Bias valves on the front brakes , not the rear,to proportion proper braking , especially at the finishline.

Re: Porportioning Valve
 

All the factory stuff is gone. Have a 1.030 strange master cylinder, I don't know if I need a bigger one. Sounds like I probably should upgrade to the bigger master cylinder also. I want to do it right, but not spend money on things I don't need.

Re: Porportioning Valve
 

Tony, I think you should go with the 1 1/8 bore MC from strange. I believe you will have too soft a pedal with your current MC.

Re: Porportioning Valve
 

What kind of a car is it? Might have to move where the rod attaches to the pedal to get better pressures with a footbrake car. Tom

Re: Porportioning Valve
 

Just got my new brakes from Lamb. In conversations with Roger he told me a few things.

1. he does not believe in reducing front brake pressure via an adjustable proportioning valve.

2. for 4 wheel discs, 4 piston caliper they recommend a 1 1/8" master cylinder.

I can tell you from my experience building cars, we never use residual pressure valves on cars where the master cylinder is on the firewall. The RPV is only used when the master cylinder is mounted on the floor.