Anyone have experience putting the R&P out of a 79/80 or other 3.9 rear into an 84 lsd rear. Mazdatrix says the 79-85 are the same pinion and racing beats sets all say 79-85 I believe.

 

Yep, just put the LSD into the 79/80 pumpkin. I say "just" but the whole process is about as tedious as an engine rebuild.

There's a spacer pressed under the pinion bearing that's matched to the differential housing, so you'll want to keep them as a set.

If the older differential is known to be in good shape (no noises), use gear marking paste on it before taking it apart so you can replicate that pattern on reassembly.
Used gears don't always follow the teeth patterns in the guides.

 

thanks for the input. My situation is I have an 84’ lsd rear end in the car and all the parts from an 80 rear end on hand. I am Assuming only the R&P are transferrable ( I know I have seen minute differences somewhere in the pinion shaft diameter somewhere ). Obviously the driveshaft flange from 84 will be reused. Just curious if people have done that and if a different pinion bearing is needed… even if minute difference. Good to know I saved my 80 pumpkin and that is an option.

I also would like to completely do away with the crush sleeve and know the measurements/part needed to do so……

 

Don't know about different pinion diameters, at least within first gens.

It's not installed yet, but I put together a diff with a solid spacer from Weir Performance. Phone is the best way to order.

 

i just looked at my sheet, and the only difference between a 79 and an 84 is the companion flange and the diff side gears. if the 84 has a limited slip that would be too