I'm going to ultimately be upgrading my rear brakes to disc and have a proportioning valve from a 1990 IROCZ. Will there be any problem to use this in my 91 Z28 with the rear drums until I get the rear disc axle?

 

Probably will not be a problem. If it was it is easy enough to change out the proportioning valve spring to compensate in the meantime. Grainger has an array of springs lighter and stronger than stock that will drop right in. Lighter will mean less brake pressure on the rear brakes. A stronger spring means more brake pressure on the rear brakes.

 

So I couldn't just drop it in and go? If I did, it sounds like the rear brakes would be too tight, correct?

 

I would drop it in and see what happens. There is not all that much pressure on the rear disc brakes as it is with that proportioning valve. Might be just right for drum brakes. All I'm saying if there is a problem with the using that valve on the drum brakes you can buy springs and make the corrections one way or the other. Hopefully someone will chime in that has actually done what you are doing.

 

pressures for disk and drum brakes is way different. I don't remember which uses more pressure, you may have no rear brakes or a lot of rear brake with the stock disk brake valve.

 

Some members swap to discs and use their drum combination valve. According to their reports, the car stops fine; however for best brake performance, I'd swap to the correct valve as the bias is apparently different from valve to valve: disc/drum, disc/disc non 1LE, and disc/disc 1LE.

JamesC

 

Been told , discs require more line pressure.

 

Why change the prop valve before the brake change, you will have to bleed the brakes, why not do it then and eliminate any worries.