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]

Awesome, glad to see you got it sorted out.

also, i don't mean to hijack the thread, but seein as there are a few people online, in reference to the conversion from drum to disc with abs, is it any harder than without? also, my ABS isn't functional at the moment..

Lines in the rear are the same either way, the difference is in the stuff up front.
The only potential problem I can see is if you need different knuckles, you'll need to make sure they're for ABS so they will hold the sensors. I'm assuming you can use your old wheel bearing assy, if not you will need ABS ones for those too.

I don't actually have ABS, although I don't think it would be any harder than without ABS. I imagine you would use the sensors that are on your car already. They actually detect wheel speed, so it stands to reason that they control the application of the brake regardless of being drum or disc. However, I don't know this for a fact. It could also be that ABS on an ST only has wheel speed sensors on the front wheels, since that's where the majority of your braking load is anyway. Do GTs have wheel speed sensors on all 4 wheels? It seems like I read on here they do. . . IDK.

All Toyota cars have 4 wheel ABS, only some early 90s trucks have 2 wheel ABS.

This post has been edited by alltracman78: Jul 13, 2008 - 5:29 PM