Hello everyone,

I am new to the board and have read many of the awesome tech articles on here but I just want to make sure I have all my information correct. I have just bought a 9 bold borg warner rear end in great shape. My car is a 1990 corvertible Iroc with factory rear drum brakes. To my understanding to make the conversion I will not have to replace the master cylinder, but I will have to come up with a new combination valve. The rearend I purchased is out of an 87 Iroc. Being that I am swapping an older pre 89 rearend into a 90 model car I am to assume I would use the older style combination valve? Or do I have my information backwards? Main question being is should I use an 87 style combo valve or should I use the 89 and up? Will my lines all fit properly? And most of all UUGGG why did GM put a ragged 2.73 drum rear end in the covertible anyway?

 

Welcome to TGO.

If the rear end was from an 89+ car with PBR's (or if you'd swapped the latter in), you'd use a the second design 1LE combination valve. A problem arises when you try to use a rear with the old style Delco-Moraine calipers, as the standard disc combination valve for those brakes has different threads than your 90 (M1.0 tube nut threads vs. the M1.5 tube nut threads in your car). You may also have issues with the parking brake cables as well since the early cars have an adjuster in the tunnel above the drive shaft and your 90 may not.

JamesC