I have a BW disc brake rear that I want to put in my car. My car currently has drum brakes. I know the master cyl or prop valve was different on the disc brake rear cars, but can I swap it in without changing all that? Has anyone tried this before?

Also, if I can't, can I put the drum brakes from the 10-bolt on the 9-bolt rear?

Thanks

 

What if I just get a new proportioning valve for a disc brake rear?

 

ttt

 

the master cylinder and pro. valve both have to be replaced

 

Was the RPO code for the BW rear disk's also J65? That's the rear disk code for the regular 10 bolt 7.5 or 7 5/8" axle.

If it IS code J65, and your current master cylinder is the J50 rpo (will be stamped on the bottom side of the body, not the reservoir, of the m/c), then you could keep your J50 disk/drum master cylinder. Apeiron (on the Suspension/Chassis/Brakes) board found an old GM service bulletin that said the J65 m/c was only used to give better "pedal feedback", typically required by a performance driver. But people with new cars complained about the pedal being too hard, so GM said the "fix" was to put a J50 m/c on the car.

But the prop valve is different.

The early master cylinders were cast iron; and can rust... later models are aluminum. You might want to replace yours just for that fact. Beware: Bleeding the m/c is a first class pain in the butt.