Porportioning Valve

[Tony Goodman]

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

[Rsmith38]

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

[Dick Butler]

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.

[Eman]

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.

[Dick Butler]

[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.

[Tom Goldman]

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.