master cylinder/combo valve
 

I'm nearing the end of the brake mods (as part of a whole vehicle rebuild ) and am sorting through my master cylinder cores. The upgrade to LS1 front calipers (from a 2000 Camaro) and PBR rear calipers (from a 1991 Camaro) is finished with the exception of shimming the rear caliper carrier for centering.
Lots of information in these pages makes it helpful sorting out the details so I thought I'd go over what I think I've learned and whoever wants to straighten me out, please go ahead.
I've read that any master cylinder will work with a disc brake upgrade. I believe the two relevant codes are J50 and J65. The primary difference between them is the amount of pedal effort needed to operate the brakes. The J65 being the "sportier" of the two. Sound right?
In my previous car (86 IROC), I upgraded to rear discs and scooped the master/combo from a 4 wheel disc junker. I recall the disc/disc master cylinder piston diameter being larger than on the disc/drum master. Would that be the difference between J50 and J65?
As far as combination valves go, I understand that the J65/1LE valve is the only one that will work. And it seems exclusively available only from Flynbye/Ed Miller.
Another question. What's the prefered method for shimming the carrier/caliper? I've seen both axle flange shims (between the flange and the backing plate) and shim washers (between the carrier and backing plate).
Any correction or insight is appreciated.

Re: master cylinder/combo valve
 

Yes.

Yes, or perhaps from the classifieds.

The OE method was to place the shim between flange and backing plate. You can see the position and shims on the floor in the following link:

https://www.thirdgen.org/forums/atta...s-89-shims.jpg

http://www.andyz28.com/catalog.htm sells a shim kit. If you're interested, I have the three leftovers that I'd make you a deal on.

JamesC

Re: master cylinder/combo valve
 

I'll have to determine the amount of shim required. The only drawback I see to the flange style shim is that it doesn't allow for adjustment of the carrier if it isn't parallel to the rotor. I can't say for certain at this point if I have a misalignment in that regard, however if I do, I'll have to take the shim washer approach.
For the record, your FAQ page and threads have been invaluable in the build process.