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?

[DEATH]

They [PV and MC] are the same. The only difference is the regular and 4 channel ABS setups. Just going from nonABS ST to nonABS GT there is no difference.
Griffy will be along to confirm this shortly.

This post has been edited by DEATH: May 6, 2008 - 1:45 PM

[alltracman78]

They [PV and MC] are the same. The only difference is the regular and 4 channel ABS setups. Just going from nonABS ST to nonABS GT there is no difference.
Griffy will be along to confirm this shortly.

So because this didn't make sense to me, I don't trust most aftermarket stuff, I was curious [and work was slow today], I checked this.


There are three different P valves.
1 for all GTs, 1 for the STs without ABS, and 1 for the STs with ABS.
I couldn't check without using VINs, and I'm not as familiar with the 6th gens as I am with the 5th gens, but I'm assuming all GTs have 4 wheel disc, and all STs have rear drum?
If that's the case, they are different depending on rear disc/drum.

If that is true, I would suggest changing the proportioning valve along with the rear brake components.
If you don't it's not the end of the world; I'm currrently using a FWD P valve on my Alltrac, and it brakes just fine. Also, I'm sure others that have done the swap are using the valve with no problems.
But, it will most likely improve your braking quality a bit if you do, and make your rear wheels less likely to lock up.

I didn't check master cylinders. Maybe one of these days I'll dig through it.