915 Line boring required?

[dentist90]

I have to replace the final drive housing on my 915 (1984 = 915/68) as the pinion bore is toast. I have a lead on a good used housing. I am wondering, though, if I bolt my existing gear housing to the new diff housing is there a problem with the front and rear bores lining up? Not sure if housings have to come in matched sets.

Also: the races in the middle (gear) housing that are retained by c-clips... are they supposed to be able to turn? If they were a press fit, why the retainer clips?

[Porsche84]

I have mixed cases on the 915 with no problems You don't need to line bore them. The bearing races in the middle case (actually all of the races) must be tight. They have c clips to keep them in place when they loosen up. I have rebuilt many 915s and about half of them have issues with the races in the center case, only a couple in the front case. I have a local machinist who has fixed the problem cases in two ways. Early on, he bored out the case about 1 mm larger, interference fit a piece of aluminum-bronze, then bored them for proper fit on the race. On the last couple of repairs, he purchased bearing material and made a replacement bearing race with a larger outside diameter. He bored the case to true it up and re-center the holes and installed the new races. We heated the case and cooled the race to drop them in instead of pressing them in. I've attached a photo of the front case I use in my car. This has the bronze sleeve. I also use the Guard bearing retainer to add strength to the assembly. This has been in my car with a 3.6 for about 3 years. I rebuilt the trans this year and this fit is still perfect.