Cracked 915 Diff Housing- Toast?

[dentist90]

I am in the process of refurbishing 1st and 2nd synchros on my tranny when I noticed that the race for the pinion shaft was spinning in it's bore ( a common problem I hear). As I was mulling over whether to Loctite the race back in, I took a close look at the wear inside the bore. Dang! Noticed this crack, which apparently goes thru to the input shaft bore as well.

Pinion bore, race out:


Input bore, race still in and tight:


Top view of case between bores... not cracked thru yet:


Need advice from anyone who has been here. Can I possibly get away with this for a couple more years? The diff wasn't making any noise. I caught this before it became symptomatic. The race still fits in snugly, but can be removed by hand. I realize it is a matter of time before it's all over. If this final drive housing is a ghost now, any recommendations on where to source another one? I wasn't planning on dismantling the diff, but if I can fix it properly now I guess it's worth it. I don't know where I'd have to send the tranny to get the ring and pinion properly aligned again. Anywhere in Canada?

[Dadofour]

I had a similar issue a few weeks ago. I decided to choose between having Wevo fix and reinforce the case, or buying a replacement bell housing.

I chose to buy a bell housing from Gary Fairbanks. He knows these cases and was able to evaluate the quality of the case for me before selling it.

Link to my 915 spun race post

[Tinker]

Than,

What does Gary charge for a replacement bell housing?

Was it a mag or aluminum housing?

Thanks.

Tinker

[dentist90]

... and how can I get hold of him? Any pics of what WEVO does to repair these would be helpful too.

[Dadofour]

I have Gary's number at work and will post it tomorrow if someone else on the board does not beat me to it.

Gary had two housings that met my needs. One aluminum and one magnesium. I chose the 85 aluminum case as it was changed by porsche to prevent these failures. It seems that in '85 Porsche made the bearing smaller which allows more meat in the case to support the bearing.

Wevo's site has a very good explanation of what they do (which is leaps and bounds better than OEM, but much more expensive as well.

Wevo's Case upgrade

As a side note, I really might go the extra mile and get Wevo's internal shift gate. I have found all of their products to be top, top notch.

[Dadofour]

Gary Fairbanks (203) 866-2466

Good Luck!!

[RarlyL8]

You might just use the WEVO bearing plate. If your motor is not high torque it should hold.

[Gunter]

As part of my SS 3.2 engine swap, I decided to do an overhaul of my 915 with LSD because it felt a little tired.
I have an extensive background in machinery but...................
If we didn't have JW in Seattle, I would have undertaken it.
I made an appointment with JW, cleaned the 915 thoroughly, drained the oil, packed it in my Civic, drove to Seattle, JW applied his magic and his trained eye, and experience, found more than I would have.
One night in the Motel and back home. PM me if you want to know how I made it through the border.
The parts are expensive whoever does the rebuild and it is just too much work and effort to install it and find that it isn't working right.
Anyway, with his expertise, and the jigs required, it felt it was worth the trip.
Consider contacting JW in Seattle about this, he may have a housing?

[dentist90]

Thanks Gunter, Than and Brian. I am shopping for a good used final drive case right now. The Wevo machined insert looks like an excellent upgrade, but I'm hoping a used case will be cheaper. I hadn't planned on touching the diff as there is no way I will even attempt to set it up again myself. I want to do it right, but it is tempting to try to get a few more years out of this one. I have no idea how long this crack has been growing. If I have to swap cases I will definitely be looking for someone experienced in fine-tuning the ring and pinion. Rebuilding the gear shafts is easy enough, but not the final drive.

Brian: when you replaced your split bearing retainers with the one-piece Wevo were you able to use the same shims again, or do you have to get the rear end 're-indexed' again? I hadn't tought of it, but that would reinforce the crack a bit without having to do a complete teardown.

Gunter: I have already used Mr Walker to obtain un unavailable part for this project. He would be my first choice if I decide to go for a complete rebuild. I'll definitely give you a ring if I have to cross the border.

[RarlyL8]

Nothing changes when you simply tear down a tranny and put the parts back together. The number of shims remains the same and therefore so do the tolerances.
Unfortunatley (for me) the WEVO upgrade did not fix my problem but in your situation it would reinforce the cracked area very well. You would not have to re-index anything.

[dentist90]

Yeah, I didn't have the growlies before I took it apart and the casting isn't cracked right thru yet. I'm hoping that the one-piece retainer would at least hold things together so I wouldn't have a catastrophic failure and munch up the differential gears. This is certainly worth considering as it is a much simpler repair (bandaid) than a new diff housing.
I was thinking that if I do simply Loctite the race back into the bore I would place the pinion shaft in place and torque down the retainer plate with the shims in place to make sure I get the proper alignment of the race. Make sense?
I haven't heard back from any of the recyclers that I've enquired about a final drive housing yet. Anyone have a ballpark idea on what these might go for?

PS: thanks for your input Brian. I read your R&P Whine thread and the experimental measuring of the backlash, preload (whatever that is), etc. I plan to keep the car so I'm not averse to doing it right, but I wasn't planning on my DIY gear repair turning into a total rear end re & re, with the prospect of having to crate it all to the States for JW to finish. I'm just afraid that if we try to relocate these otherwise fine, but used, differential gears into another housing we will never get them lined up right again.

[dentist90]

Another question: the roller bearing (NOT the ball bearing that the retainers clamp) on the input shaft has some minor scoring. It should probably be replaced. If I pull the race out of the input bore and replace it will that affect alignment of the shafts enough to worry about? I would think not. I think I should be more worried about worsening that crack by pounding and pressing.

[Gunter]

Since you'll be spending money and time on this, go one step further:
Have you considered a Limited Slip? You'd like it!
Call JW and discuss your options, he might come up with a fresh idea.

[dentist90]

Worth considering if I have to re-do the diff. I must admit I haven't had too much trouble with spinning a tire under heavy accel, even accelerating out of a corner. I guess I must be babying the thing too much, eh? I would much prefer at present to stay out of the diff all together if possible. I've got rear T-bar bushings and a realignment/ corner balance on my list of things to do next year if I don't spend $$$ on this.