My 1984 Trans Am has disk brakes front & drum rear + prop valve. If I were to install a rear disk brake kit, do i keep the current prop valve, remove it or replace the current prop valve with an adjustable prop valve?

 

Either get an 84-88(?) prop valve or put in an adjustable one. If you're using a stock disk brake system I'd get all the stock disk parts. If your going the through the trouble I'd consider the MC if it's original. The adjustable is unnecessary if you have stock parts. Also, if you remove the stock prop valve for an aftermarket one I think you get a light on your dash. There's a sensor/ground in the stock prop valve to detect brake line failure.

I put a wilwood adjustable in my 82. But I also put big wilwood brakes on. I don't think it's necessary on a stock system.

 

I swapped the spring in my stock valve ('87 disc/drum) to the 1NCR5 job recommend here. Running Wilwood four pot calipers on all four corners with a 2002 master cylinder and it stops like a modern vehicle. With it up in the air, off, and someone in the driver seat it's possible to prevent the front wheels from rotating by hand and the rears still spin without issue. It required a totally reasonable amount more to stop the rears. Best part is I was able to use all stock hard lines.

 

The early factory rear disc brakes ('82-'84) really aren't very good. Unless you're going to use the later model brakes, you might as well stick with the drum brakes on the rear...

 

Yeah, true. They're really hard to get working properly and the e brake mech is miserable. I assume this is more about a period correct setup vs performance.

 

I am going to leave well-enough alone. Tkx for the information.