2 replies to this topic

[jef]

HI,

 

Changing out my current diff gears and have picked up a set of 3.45 from a BA ute that are m78, and want to know how much i need to machine off the pinion bearing seat for the gears to line up. The housing is a R31 with true track.

[76lxhatch]

Well in theory the difference in crownwheel size is 0.3" (7.8 - 7.5), so half that is 0.15". However its probably a bit more trial and error than that, the pinion bearing is designed to be shimmed to get final install height so you'll need to check tooth pattern for the end result.

Unless of course you happen to have the housing that the M78 set came out of, then you could take an accurate measurement of depth to machine to, this would be my preference. I've always wanted to try this, not sure if the M75 housing has enough material to safely remove this much or not.

[myss427]

Can be done with a little grinding of the carrier and housing.They use to do this with the early A9X's, my brothers old car has a 4 pinion conversion which was done in the early 80's with 3.55 gears from a M78.