Thought I would share this. Been having a heck of a time finding this info. I bought a Wilwood 260-11179 adjustable proportioning valve for my 90 IROC. The threads on the IROC are all metric. After several attempts I have all the correct adapters to fit this. Was able to get them from Summit Racing.

2 each Edelmann 262010 adapters for front brake lines
1 each Edelmann 262011 adapters for line from master cylinder to proportioning valve
1 each Edelmann 262012 adapters for line from master cylinder to proportioning valve
1 each Edelmann 262015 adapter for rear brake lines

 

You can get by with just 2 adapters if you're willing to bend your own brake line.

Post #584, https://www.thirdgen.org/forums/ltx-...ml#post6074511

 

Thank you. I thought i had the adapters figured out. I just got the M12 x 1 adapter yesterday. I believe it is a M12 x 1.5. Probably going to bend it up. So the above adapters i posted are not correct.

 

Both my 4th gen and the '89 3rd gen master cylinders used the same fittings. Front brake line was M11x1.5 and rear brake line was M12x1.0 at master cylinder. I couldn't get that info from this site so I ended up measuring it myself with a thread pitch checker tool.

I originally had stainless Brakequip fittings but that turned out to be a constant headache of chasing leaks. I later switched to softer Edelmann fittings and it's been leak free ever since. Here are the Edelmann p/n's I used when switching back to the 3rd gen master cylinder. My prop valve is now different than yours but you'll see the Edelmann p/n's I used at the master cylinder, Post #1178, https://www.thirdgen.org/forums/ltx-...ml#post6293639

As you already know, the aftermarket prop valves have fittings sized for 3/8" line, but the stock lines were a combination of 3/8" (front) and 6 mm (rear). 6 mm tube nuts are very expensive and hard to find with very few choices. 1/4" tube nuts are close enough such that it is okay to substitute; you'll just notice it fits a little loose on the original 6 mm line. I got my info from an actual engineer that designs tube nuts so no worries about that.

The only locations needing any kind of adapter is where you want to transition from 3/8" line up to 6 mm (or 1/4") line. Those two locations are the rear brake port at the master cylinder, and the fitting at the flex line to the rear axle. Everything else can stay 3/8" line with no special adapters. I've done it both ways where I stack up adapters at the prop valve and run 1/4" line all the way to the rear; or run 3/8" line out of the master and then transition to 1/4" line somewhere under the car. Choose your poison. Personally, I better like it under the car (easier to work and access).