rear diff gearing swap?

[smokeythewhitewagon]

YIKES!

Just ran into a wall in my transmission swap. I was swapping out the rear diff (mine was 4:11, new transmission is 3:90)
when I realized that the half-shafts have very different ends on them, so the existing ones won't fit into the new rear diff.

So it seems my options are:
1. Get the half-shafts from the parts car and have them installed by a shop, because I don't have the tools to do that myself.
(Quite honestly, can't afford that at this point.)

2. Try to swap the gearing from the differential casings. I have no idea how this is done, or if it will even solve my problem, because my half-shafts may only work for a 4:11. :smt017

Anyone have any advice? I'm bummin' pretty bad because I probably could have finished this swap today were it not for this obstacle. :smt012
Please let me know what's the best way to proceed.

[mike-tracy]

You can in fact go either way of course, but the 2nd one involves precision measuring tools (ie. dial and feeler gauges) and power tools to break free nuts that have been together for decades.

I'm familiar with 2 types of diffs in the 90s: ones with "outie" stubs, and "innies." If you need an innie 3.9 diff, then you can get one off, say, a manual trans equipped 2nd gen Legacy or 1st gen Impreza with a 2.2.

The axle stubs aren't specific to a final drive. Just a differential casing style. If you've come this far and installed the tranny, I'd wager to say you can finish the job with the correct axles. Certain ones have a pin holding the axle to the diff stubs, just like the fronts. To get the rear axles in the outer hubs you take off the 32mm axle nut, unbolt the struts and pull the hubs towards you while slipping the (liberally lubricated) axle in. I bought an electric impact wrench and breaker bar at Harbor Freight on the cheap years ago, and between the two I can tackle any suspension! Good luck.

Also, please post your location in your "user control panel" so perhaps we can help you better.

[smokeythewhitewagon]

I have done some reading, and I should be able to just swap out the ring and pinion gears for the 3:90.

I opened up the diff housing, and can't figure out how to get the Ring gearing out. It seems like the bearings are pressed right into the casing. I don't want to mess something up.

....or maybe I do :smt027

Any ideas?

[smokeythewhitewagon]

Thanks for the information. I added my location, which is Tacoma, WA, not to far away from you.

A little background:
My car is a 98L, which had a 4EAT that went.
I'm putting in a 5MT from a 95L.
Everything so far has been manageable.

The 98's rear diff has some strange bearing support covers on the sides of the housings. They are like finned rings, held in place by a single 12MM bolt and a silly looking washer. I have no idea how to remove these.
(The 95 has some plates on the sides that seem much easier to pull off.)

[smokeythewhitewagon]

my brother pulled em with an oil filter wrench of all things. haha! i was searching frantically for a spanner wrench, and he comes up and says.. its done!

[r3v_v3ng3]

I have done some reading, and I should be able to just swap out the ring and pinion gears for the 3:90.

I opened up the diff housing, and can't figure out how to get the Ring gearing out. It seems like the bearings are pressed right into the casing. I don't want to mess something up.

....or maybe I do :smt027

Any ideas?

my brother pulled em with an oil filter wrench of all things. haha! i was searching frantically for a spanner wrench, and he comes up and says.. its done!

Your bro pulled out the ring gear with an oil filter wrench? :smt017

[Dead91silvia]

Dude, just buy a diff... I-5 Auto & Truck Parts has 4 of them for $150...

Use this link to look up your parts...
http://car-part.com/

This link might work also, this was the search I did...
http://car-part.com/cgi-bin/search.cgi

[smokeythewhitewagon]

My brother pulled the bearing covers on the sides of the diff casing with an oil filter wrench, yeah.

So we finally got both diffs and discovered that the bolts attaching the ring gears are different sizes. 95- 17mm, 98- 14mm. Everything about the 95 is way beefier. So can't swap the gears. I'll have to take dead91silvia's advice and buy a diff. Thanks for the links!
Just trying to save a little dough.

[StatGSR]

^ pics, not sure I believe you when you say it's not possible...

[Benfolio]

He probably means an oil filter cup wrench, not a strap type wrench.

https://sl-i.net/FORUM/images/imported/2012/04/41qwn4QKnzL_SL500_AA300_-1.jpg

[smokeythewhitewagon]

http://www.diseno-art.com/products/tool ... liers.html (http://www.diseno-art.com/products/tools/oil_filter_pliers.html)

Sorry for confusion he used oil filter pliers, not oil filter wrench.

Oh and I got my new diff, should be installing it later today!

[smokeythewhitewagon]

:smt013

Brand new problem.

Brought home the new differential, and it doesn't work either.

The yard I bought it from checked their computer, said it should work no problem. Supposedly, its from a 98 Manual. My axel caps will not snap in. In fact, upon further inspection, my axel caps have 23 splines and the new diff (and the old one from 95) have 25 splines.

Are the rear axels different in automatic? Or is this still a year issue? Or could it perhaps be a difference due to disc/ drum brakes?

[Dead91silvia]

All diffs and axles should have the same splines, so not sure what they are different.

If you look up on Car-part.com, it says your car is a 3.90 already...

Now I have to ask, was your car originally a 5 speed L? If so, then you rear diff should be a 3.90. There are a lot of different combos...

[Grafton]

My brother pulled the bearing covers on the sides of the diff casing with an oil filter wrench, yeah.

So we finally got both diffs and discovered that the bolts attaching the ring gears are different sizes. 95- 17mm, 98- 14mm. Everything about the 95 is way beefier. So can't swap the gears. I'll have to take dead91silvia's advice and buy a diff. Thanks for the links!
Just trying to save a little dough.


^ pics, not sure I believe you when you say it's not possible...

I'm a doubter too, but you never know. my 97 rear diff and the 05 WRX rear diff were almost identical

it's good thing you didn't try to just swap the ring gear, the pinion shaft has different tooth counts between the 4.11 diffs and the 3.9's (9 vs 13)

[smokeythewhitewagon]

All diffs and axles should have the same splines, so not sure what they are different.

If you look up on Car-part.com, it says your car is a 3.90 already...

Now I have to ask, was your car originally a 5 speed L? If so, then you rear diff should be a 3.90. There are a lot of different combos...

My car was originally an automatic. I'm converting it to manual.

The axles were not matching, I have finally discovered, because automatic and manual cars have different axles. I know a lot of you will doubt me (just like a subaru technician at the dealership) but it's true. Different part numbers even. SO I bought new axles (for a manual!). Mystery solved, my new rear diff and axles are installed!

[mike-tracy]

I noticed recently that I had an oem axle that I couldn't identify. Had the same issue as yours, wrong amount of splines on the stubs, and was physically smaller than the fronts (male & female ends, not male/male ends like most rear axles). I suspect this is what happened to you, since I have successfully used awd auto, FWD auto (the beefiest axles) axles in my different 5mt subarus over the years.

Did some digging, and found it was from my old style rear diff.

Glad you solved the problem though.