92RS_Ttop

iTrader: (3)

I will be upgrading my 92's rear drums to discs at some point in the near future with PBR's either from a later thirdgen or and early fourthgen. I've started hunting for parts so I can find the best possible deals available, and I found a wrecked IROC in a local junkyard. The entire rear axle was gone, but the combo valve was still there. I grabbed it figuring I could use it for my rear disc swap. However, from what I have read on here its the early style one with the coarse threads. My 92 should have the later style with the fine threads which obviously creates a problem.

The 2 valves look the same externally so I was wondering if it was possible to swap the internals between them? Basically take the internals from the one I found at the junkyard and put them in the one in my car?

JamesC

iTrader: (5)

Apparently there is a mod, but I can't venture a guess as to what it might be or how it's accomplished:

http://www.flynbye.com/catalog/i160.html

JamesC

92RS_Ttop

iTrader: (3)

Yeah, I've seen that before and I searched all over that site and on the other one listed in the tech article but I haven't been able to find out what the mods are.

From what I have read, the main difference between disc and drum rears is the amount of fluid/pressure being sent to the rear. This would require the internals for the rear circuit to be different, but the front circuit should be the same. I would suspect the internal passages to the rear circuit are the same since the pipe connections are the same size, just different thread pitch. If that is the case, I would think all the regulation is handled by the internal mechanism which should be easily swapped. That's my reasoning, I just want to be sure before I tear them both apart and end up with 2 useless valves.

As for flynbye.com, that's not a bad price at all, but I would still prefer to do the work myself if possible. I'm not knocking their work as I've never bought anything from them yet and I've only ever read good things about their work. I just hate to pay someone else to do something that I can do. Especially since I have both styles of valves already and it would save me the wait.

JamesC

iTrader: (5)

I wonder what the pressure differences are between disc/drum, disc/disc with Delco-Moraines, disc/disc with PRB's, and disc/disc with 1LE's?

JamesC

92RS_Ttop

iTrader: (3)

That is something I've been wondering as well. Seems like every post I read on here has a different answer. I've yet to find any hard/confirmed numbers, but I've read 1100-1400psi for fronts and 600-1000psi for rear discs. That was on a non-1LE I believe. I'll have to see if there are any numbers listed in my shop manual when I get home tonight.

JamesC

iTrader: (5)

Found nothing in mine--but I did find the following for whatever it's worth:

Do not attempt to disassemble the combination valve. If any portion of the combination valve is defective, it must be replaced with a new combination valve.

And a bit later: The combination valve is not repairable and must be serviced as a complete assembly.

JamesC

92RS_Ttop

iTrader: (3)

I've always translated that and similiar text to:

"This can be done with the right tools by a person of average or better intelligence, but we don't want to get sued by the idiotic masses so we're saying it can't be done."

Kinda figured it would say something like that as its really not worth a GM tech's time to diagnose and rebuild one. Probably just sent them back to GM to be rebuilt and then sent back to dealerships as "new" parts.

I'm surprised it doesn't have the line pressures listed though, even if only for diagnostic purposes.

JamesC

iTrader: (5)

Probably so .

If you find anything, I'd be interested in knowing.

JamesC

92RS_Ttop

iTrader: (3)

No problem.

RBob

iTrader: (1)

IIRC there are some threads here where folks pulled the proportioning valve portion out. This was done for rear disk systems.

RBob.

92RS_Ttop

iTrader: (3)

Yeah, I've spent most of my spare time at work today reading through some of those threads. I've read and subscribed to several in the past as well. I'm coming away with some mixed answers though. Some like the idea of gutting the valve, some don't. I haven't really seen any good, hard evidence that its safe and works as well as using the correct valve.

Right now, I'm leaning towards modifying the one that came in my 92 with the one I found if possible. Its the easiest, cheapest, and probably the safest way to do it.

If I can't do that I'll probably go with the adjustable valve on the rear and splitting the fronts directly off the master. I must admit that the opportunity to run my own lines and route them the way I want adds to the appeal of this option.

I'm not really inclined to just "gut" the valve as I'm not entirely sure its going to be safe. If it was just me in the car I wouldn't care, but my daughters(5 & 9) love riding in the backseat.


JamesC - I did find that on the early disc rears(Iron calipers) line pressure is 600psi.