I have learned this is not a easy swap with a 672 carrier. Who has overcome the issues?

 

#672 = 3.42 & anything numerically higher, 31 spline 1967-1968

Biggest issue will probably be finding a set of 3.90 gears and the axles if you don't have them.
What issues did you hear off?
If you have a complete differential with a 4.33 gears and it has a 672 carrier, the 3.90 gears should swap right in.

 

The rear end is complete and in solid shape. Just want to change to a higher gear. 3.90 or even a 3.42. I have been told by someone who know the Olds rear ends the if using a aftermarket gear like Richmond the gear will need to be machined .100 off the flat surface or .100 off the carrier mounting surface. If that is my only option then so be it, I guess thats what I will do.

 

yOUR NOT GOING TO GET THE GEAR MACHINED...wE DID IT ONCE IT WAS crazy EXPENSIVE AND THE RING GEAR IS very hard....so good luck with that.
The carrier will be a better choice ...but you are weakening the strength of the carrier so be careful .
YOU just need to find a good used set of 3.42 or 3.91 gears.

Yukon does sell the 31 spline 3 series posi carrier.
expensive BUT will solve the issue and be a rebuild able unit way down the road too ....I fthe car is a keeper and handed down through the family.

 

FYI - the gears you are looking for are out there. Probably can find some 3.42's also.
391 3.91 Gear Set From 1968 TO Axle OLDS originals

OLDS TYPE "O" 3.90 RING AND PINION Sorry, missed that these were aftermarket gears.

 

Thank you, will do a search.

 

FYI - the gears you are looking for are out there. Probably can find some 3.42's also.
391 3.91 Gear Set From 1968 TO Axle OLDS originals <<<<< these will work they are GM BUT for 750.00 Welll ......


OLDS TYPE "O" 3.90 RING AND PINION <<<<<<<<<< These WILL NOT fit the 672 ior 588 carrier so that is a NO on that purchase . All aftermarket gears are 3 series...YOU need the 4 series gear . sorry will not fit.