Cascade Crew

[Al Hasse]

What's the consensus on the proportioning valve for 4-wheel disc vs rear wheel drums? I've heard I need to change it when converting to disc in the rear, I've also heard otherwise for cars after a certain year, but I forget what year.

[Alphius]

Hey Al, I had to do the disc brake swap boogie and prop. valve fun time a month or two ago myself... with my LS1 rear end on an '84 Z28.

As far as I know, all cars with rear drums at least need a new prop. valve from a thirdgen with disc brakes. You will be able to stop with the old disc/drum valve, but it will stress your front brakes and the rears will sit there and do nothing basically. I ran like this for about two weeks. Also, AFAIK, there were exactly three (four?) kinds of prop. valves in thirdgens. Here they are:

1. disc front/drum rear
2. disc front/disc rear
3. 1LE disc front/disc rear
4. 1LE disc front/drum rear (not sure if any 1LE's had drums, i don't think so. this valve probably doesn't exist.)

So, your '89 will have option numero uno, correct? stock single piston 10.5" disc brakes on the front, stock drum brakes on the rear. Since that is the case, and your new rear came from an '82 F-bod (option 2 above,) then you have a couple of options...

First option being to beg, borrow (permanently), steal, or buy a prop. valve from a non-1LE thirdgen with 4-wheel disc brakes. Easiest option.

Second (and better) option being to purchase yourself an adjustable proportioning valve and install it yourself or pay (threaten) somebody to do it for you. Not hard, just have to procure yourself a double flare tool to reflare your stock brake lines to get the right size fittings on the end of them.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG3905&N=700+4294918718+115&autoview=sku

That is the piece I had to buy, since no thirdgen ever came with dual-piston 12-inch disc brakes, I had to do my own prop. valve install and tuning. Again, easy, only took me two hours or so to do it all beginning to end, and I can stop on a dime now. Just need to get some LS1's up front too! Looks kinda funky with 10.5" front/12" rear brakes...

Anyway... back on topic.

http://www.thirdgen.org/propvalve

This link is awesome, take a look at the picture there. That looks basically like my setup, except for one small difference... I left the stock PV in place, and capped off the two fittings that the rear brakes went to. Altogether a cleaner install to use the T-fitting like that gentleman, but my way is quick and dirty. I pulled the rear lines apart, left the front lines alone, and reflared my rear lines to attach to my PV. There is a little rod thingy in the PV that comes out the front when you remove the brake line there... I removed it and left it out. I now believe my fronts get full pressure (pretty sure anyway,) and the rears get whatever you dial in with the valve. Works amazingly well, and it is the suggested option from me to you, as I have done this swap already.

I guess for you the whole "buy a new one from a thirdgen with discs" would work, but it all depends on how much you want to work on it. Me, I like to build everything myself, like to know how things work, so I did it all myself.

There's your options:
1. Buy valve from thirdgen with 4-way discs, but not 1LE.
2. Buy Adjustable PV and have some fun

Now that I'm done rambling... which I'm sure this is way too long... but whatever. It's late, I can be excused, right?

I'm tired, so anything not making sense, get back to me and I'll try to be a little more clear... Goodnight...

[83Z28BlackBetty]

go with the adjustable valve from wilwood. I got mine on ebay for like 55 with shipping. that way if you ever step up the brakes again, you won't have to get another new prop valve.

~JAKE

[Twilightoptics]

If you're going to go through the trouble of replacing the propvalve... you might as well get an adjustable one, and ditch the stocker all together.