ok i have a brake proportioning valve off a 1989 trans am gta had a 9 bolt PBR rear brake setup .well my camaro is a 1992 rs i have a built 9 bolt now with 94 bpr brake setup on it now ...well my ? is i really about that there was alot of info out there i know they changed the threads on the rear line but when .was it from the swap of the 88 iron brakes to the newer 89 pbrs or did they change it again after 89?? and help is a big thanks bc there seams to be alot of wishy washy info

i have pix if any one wants them it has marking MB on a tag and MB 35KH 270 9 marked into it

 

From Dan Burke's page concerning the combination valve:

1st design: M1.0 tube nut threads (for 1982 to early 1989 applications)
2nd design: M1.5 tube nut threads (late 1989 through 92).

Either of the valves can be purchased below:

http://www.flynbye.com/catalog/c1_p1.html

You may also find the 10-Bolt FAQ useful:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC