Rear drum to disc conversion question, Do I need to do anything with the master cylinder? Options

[GriffGirl]

Someone told me he thought I will need to do something with/replace my master cylinder when I convert my rear drum brakes to disc brakes; something about the proportioning valve.

Here's what he said:

In regard to your brake swap, I could be wrong, but I'm almost positive that you'll need a different proportioning valve...When you do it, though, you should see about swapping the proportioning valve and
master cylinder (if it's different on the GTs)... Drum brake wheel cylinders and disc brake calipers use different amounts of fluid (typically) and if you swap from the former to the latter, your rear discs brakes won't be doing as much work as they should.

This is all greek to me. Help? Is this something I should look further in to?

[alltracman78]

I've done the drum to disk swap on 2 cars and neither needed a different valve.
The GT and ST master cylinder are the same.
All of your ST stuff will work fine except you need (GT) the backing plate w/e brake assembly, rear disks/pads/calipers, the rubber lines, and the cables to the e brake handle (all GT stuff).

The GT and ST master cylinders are NOT necessarily the same.
With ABS is the same, and without ABS is the same.
If you have a GT w/out ABS and an ST w ABS the master cylinders are different.
Most likely the difference is the size of the piston, just like in the 5th gens.

Also, rear drum and disc brakes DO require different pressures to work correctly.
This is why there are different part #s for the different P valves.
It doesn't mean your brakes aren't going to work if you don't use the correct valve, but most likely they will work better if you do. Toyota didn't design them different just to spend extra money....

^I have all of that stuff you listed. It was the proportioning valve that came into question; it's my understanding that it is not something that is required for the conversion, but if swapped, will increase braking efficiency.

Exactly