When I change the rear brakes from drum to disc, do I need remove the original combination valve, or can I install a aftermarket (Tilton) proportioning valve in the rear brake line after the combination valve?

Thanks!

I don't know what year car you have but on a 64 thru 72 Classic Performance Products has the correct proportioning valve to replace the combination valve. Price is $59 - $79 depending on which one you need. I used their kits to convert my 71 to 4 wheel disc from 4 wheel drum. I had very few problems and those that I did have i just called their tech line and they explained it all to me very nicely. classicperform.com is where you can find them.

I used a disc/disc proportioning valve on my '85 that i bought from Inlinetube.com for about $99. It works great, and yes will have to change it order to get a properly working rear disc brake conversion. -Matt

Thanks Gents,
The combination valve is just a pre-set proportioning valve and a switch showing if the brakes fail - right?,
So if I junk it and use a variable prop valve directly in the rear line, and have the line to the front brakes direct (Im pushing this as I have already have the Tilton prop valve!), wont it do the same thing, and in addition work as a line lock if the Tilton valve is fitted so the lever is in the drivers compartment and have it adjusted (if I feel the urge to do burn outs) so there is zero braking on the rear, or vary it dependent on conditions blah blah blah..?
Just a thought..

You will also need a disc brake residual valve in the rear brake circuit. When you release the brake pedal on a drum brake system you want the brake shoes to completely retract but on a disc brake system you want a slight pressure of the pads on the caliper. I believe you can retrofit the pcorrect residual valve on the rear brake line but it might be better to replace the brake master with a proper disc/disc unit.

Personaly I don't like variable proportioning valves on street driven cars as none of them are D.O.T. approved. Get in a fatal wreck or even one with maiming injuries and the crash investigators find that variable valve, you're cooked. Besides the average person doesn't know how to adjust them correctly. My opinion, and this is only my opinion, use a proper proportioning valve and if you want to do burnouts get a real line lock.

Good point Mama, but I have had situations in which the only way I could get the car to stop properly was to install an adjustable proportioning valve. Better to have a car that you can control during a panic braking situation than a 100% D.O.T. approved car that goes out of control.

So, if I get a master cylinder designed for 4 disc brakes, bin the combination valve, install my beloved tilton for then rear, make sure its adjusted for maximum braking efficiency (or fun), that should be good to go on my '83?
(oh, and avoiding having an accident so the law doesnt get involved, although I think the examination of the prop valve is the last of my worries!)

As they say in Swahili - Asante Sana!

Sounds like a plan.