Disk/Disk proportioning valve

[87 Grey T]

Well i just got done running all new stainless brake lines and hoses with my four wheel disks. My prop valve is most likely original and set up for disk/drum, would there be a problem running that or is it best to swap to a disk/disk. If so any recommendations? Ive seen many on amazon, ect. that look almost identical. Im trying not to cut and reflare the brand new lines for an adjustable one. They're C5 ZO6 front and rear. Thank you.

 

[pontiacgp]

the problem using a disk/drum proportional is the valve has 10 lbs. of pressure on the drum brakes to keep the springs from pulling the shoes too far back from the drum. The disk brakes need a 3 lbs residual valve to give you a nice pedal height. If the residual pressure is to high the brakes will drag

 

[87 Grey T]

So my best bet would be to keep the disk/drum prop. valve and plumb in an residual valve for the rear between proportioning valve and rear? I was hoping to not have to do that. Ive seen Wilwood has 2 or 10lb. Apoligize for the lack of knowledge about this. First time doing rear disks. Would 2lbs be to little pressure?

 

[Bonnewagon]

No, the stock combination valve Steve is talking about has a RESIDUAL pressure feature. That means it keeps the 10 lbs in the rear line at all times and the drum brakes never relax all the way. You want a true 4 wheel disc combination valve that only has a LIMITING feature. Stock 4 wheel disc valves are biased to the front just like disc/drum because when the brakes are applied all the weight is thrown forward and the fronts need more pressure than the rear. The limiting valve keeps the rears from locking up as weight is removed. A stock Camaro/Firebird from our years with 4 wheel discs has the right factory combination valve that can be used on our cars.

 

[87 Grey T]

No, the stock combination valve Steve is talking about has a RESIDUAL pressure feature. That means it keeps the 10 lbs in the rear line at all times and the drum brakes never relax all the way. You want a true 4 wheel disc combination valve that only has a LIMITING feature. Stock 4 wheel disc valves are biased to the front just like disc/drum because when the brakes are applied all the weight is thrown forward and the fronts need more pressure than the rear. The limiting valve keeps the rears from locking up as weight is removed. A stock Camaro/Firebird from our years with 4 wheel discs has the right factory combination valve that can be used on our cars.

Ok so its as easy as swapping out proportioning valves from the same model year F-body as long as its a disk/disk.

 

[87 Grey T]

Im going to try PV72 and see how that works out. Thanks for the helpful info.

 

[pontiacgp]

The PV72 is $100 on amazon.ca. The F body proportioning disk/disk valve is about half of that..

 

[565bbchevy]

You can use the factory disc/drum proportioning valve but you would need an adjustable valve in the rear line.
I have Wilwood rear disc on my Monte and a Wilwood adjustable proportioning valve knob style mounted to the frame just before the rear tire and the stock valve up front, what I like about this set up is you can adjust the lockup on the rears something you can't do on a factory style disc/disc valve. On my car with front runners I rely on the sticky rear tires to help stop me so I need the adjustability

 

[87 Grey T]

The PV72 is $100 on amazon.ca. The F body proportioning disk/disk valve is about half of that..

Thanks. I believe it was $52 through summit.

 

[87 Grey T]

You can use the factory disc/drum proportioning valve but you would need an adjustable valve in the rear line.
I have Wilwood rear disc on my Monte and a Wilwood adjustable proportioning valve knob style mounted to the frame just before the rear tire and the stock valve up front, what I like about this set up is you can adjust the lockup on the rears something you can't do on a factory style disc/disc valve. On my car with front runners I rely on the sticky rear tires to help stop me so I need the adjustability

Thats what i originally thought i would have to do but i didnt want to cut and rwflare brand new lines. Maybe i will go that route later if i want to fine tune them. Thank you.