legacycentral bbs

I have a 99 AWD Brighton that is getting a significant amount of work. One item is a disc upgrade on the rear. I have a 91 AWD parts car I can pull anything out of. One item I am unsure of is the proportioning of the master cylinder from a rear disk ABS car to a rear drum non abs car.

The 99 has no ABS, the 91 parts car has ABS. Both AWD. From what I have read, this is a fairly simple swap. Only of all the articles there is nothing about the master cylinder proportioning ?

Typically the MC bore size is different between non-ABS & ABS equipped cars. The ABS MC is typically larger. Also, cars with rear drums typically have a slightly smaller bore size master cylinder.

The proportioning valve is a separate item from the MC, and from what I've seen really doesn't change between drum & disc brakes. It's more geared towards the brake size.

What I'd recommend is just leaving the MC & prop. valve alone. Drive the car after the swap, see how it brakes compared to before. If you have excess brake pedal travel, you can upgrade your MC to a larger bore MC. Likewise, if you have issues with too much or too little rear bias, you could look into swapping proportioning valves.