I havea 2wd drive 91 s10 blazer with the rear lowered 4 inches (3 inch leafs and 1 inch block).DoI still need to shorten the driveshaft so Idon'tbreak thetransmission?How doI knowwhat the correct length of driveshaft is needed afterlowering the rear like this. Please help. I already have atransmission leakfrom the output shaftof the transmission. The seal wasworn out because thedriveshaft is pushed too far into the transmission. thanks,

 

Lower your front end!!!!!! There is no need to shortin your drive shaft if you lower your front end!!! It will be cheaper to lower your front then to get a new shaft made!! Replace the leaky seal lower your front and you will be fine!!!

 

I would remove the driveshaft and slip the back of it into the diff and bring the front up beside the trans tailshaft. Then you can measure how much you need to shorten the shaft so that the front slip yolk will be about half way into the tail shaft.
There are a few places around that will shorten and balance drive shafts at a reasonable price.

 

you no doubt have a wear ring on your rear driveshaft. mark where the driveshaft currently sits inside the tranny tailhousing. Pull the driveshaft out and see how much further it went intot he trailhousing by comparing your mark to the old wear ring. Lay the shaft up next to the tailhousing and see how far it goes inside the tailhousing. Being a 2wdr, you have lots of space in there for it to slip.

I would guess your leak is due to the crude ont he driveshaft that is now inside the and past that seal. Clean up the driveshaft, replace the seal, and you should be fine. You may have to whack some off the end of the driveshaft, but I doubt it. You should have like a 6" tailhousing, tons of room for slippage. I am guessing your new mark and old mark are about 1" of so of each other.