how hard is it to switch to rear disk? i know you have to change the proportioning valve but is there anything else?thr rear is out of a 86 iroc and it already had 3.73 gears and a posi.need help by tommorrow.thanks again.i didnt metion that it is a complete rear end swap.

 

ANYBODY?

 

I will be doing the same thing in a few months.

My '87 is rear drum and my '91Z was rear disc, so I'm swapping the rears. As far as I know the only necessity is the proportioning valve. I'm not positive, but you may have to swap the master cylinder as well.

And you may have to alter the e-brake cable, not sure though as I haven't done this yet.

 

You need an ebrake cable for disc brakes. It's different where it connects to the brake hardware. The prop valve you have to change, but you can keep your master cylinder as long as the threads for the prop valve match. They changed the pitch of the threads at some point (90 or 91 I think) and it's caused a nasty rumor about having to change the master cylinder.

 

couldnt you just retap the treads to match the new proportioning valve?

 

Not really.....you can't tap the prop valve because the threads have to go all the way to the bottom of the hole (plus you'd get shavings in the valve that you couldn't get out)...the line fitting you could try but I don't think it would work too well...the die would just cut the old threads off instead of cutting new ones on. I suppose it's worth a try but I really don't think it'll work too well.

 

I don't think I'd try it, but you can if you want.

 

I swapped out my old drum rear for a 4th gen disc rear into my 91z28 and I DID NOT change the prop. valve and the brakes work perfect. Some people say you have to change it and others say they didnt like me and it works fine. All I can say is change the rear and take it for a ride to a parking lot and test the brakes. Do a lot of panic stops and do some while turning the wheel. See if the car acts a lot different. if it feels like the rear wants to come around on you then you will have to change the valve.

 

The difference is that a drum brake prop valve sends around 85% of the stopping power to the front, while disc is more like 60/40. Sure it'll still work, but it's not as effective.

 

I didnt change mine and it stops like a **** I auto X too and never spin out.. the first few day I drove it the rear did lock up when stoping but it fixed itself on my car.I would wait and see what it does.. /on a side note my tires will not lock up either unless I am hitting the breaks real hard in a turn. if I am going striaght and smash the break pedel it Just STOPS the car no lockup..stock break setup too.