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4WD ring & pinion in 2WD?
Posted 12 August 2003 - 06:34 AM
Thanks in advance for your help.
Posted 12 August 2003 - 08:23 AM
In looking over my books, it appears you're seeking the 1.026 reduction gear from the '83-'86 4wd AT.
I've never done tranny surgery before, but it certainly looks like you could swap the 4wd reduction gears into a 2wd diff. The part#s are as follows:
Reduction Drive gear = 31450AA020 (38 teeth?)
Reduction Driven gear = 31448AA050 (39 teeth?)
Moreover, you could probably use the ring and pinion from a 3.7:1 car.
The 3spd autos in '87+ cars with the EA82 engine had a 3.7:1 diff.
The '80-'82 autos also used the 3.7:1 diff.
It's possible that some models (XT maybe) may have even come with a 3.9:1 differential that you could use.
You will need to use the ring and pinion from a 2wd 3spd auto though, as the pinion gears are different in other trannies. (The 4wd auto has a longer shaft on the pinion gear.)
So, in summary, if I'm right about what you've got then you're starting with a total front reduction of 3.454 x 0.974 = 3.364 and you could end up with 3.7 x 1.026 = 3.796 or maybe even 3.9 x 1.026 = 4.001!!
Posted 12 August 2003 - 12:38 PM
Posted 12 August 2003 - 12:38 PM
I thought of another possibility: Will a 3.900 ring and pinion from a standard 4wd tranny interchange with the 3.700 ring and pinion in a 4wd auto tranny? I'm thinking maybe install a 4wd tranny in my 2wd car, but leave the rear driveshaft off. There should be creative way to cap the end of the case so oil won't run out. I wouldn't think there would be much of a weight difference between a 2wd and a 4wd tranny. That would give me the 4.001 reduction you're suggesting.
Thanks for your help, man. I'm getting pumped on this project now!
Posted 12 August 2003 - 01:36 PM
You can see above that there are different pinion gears for AT and MT and 2wd and 4wd. Part 1 is the 2wd AT pinion.
<img src="http://www.fortunecity.com/silverstone/subaru/1/USMB/AT_ReductionGear1.gif" style="border:0;"/>
I don't think that using a 4wd tranny would help you at all. It WOULD be more weight and you'd still need to swap internal parts to get what you want.
The way I see it, you want to get a tranny (or at least the differential section of it) with 3.7 or 3.9 gears in it. Then you can put the reduction gears (parts 3 and 9 above) from a '83-'86 4wd into it. It looks like this would require re-shimming the pinion gear, but I don't see any way around that.
Posted 12 August 2003 - 08:32 PM
Posted 12 August 2003 - 09:59 PM
That said, I just noticed that my FSM says you have to press the reduction drive gear in and out. Sounds like it'd be more of a project for a tranny shop than for a shadetree mechanic. Still, I think it should technically be possible.
Posted 13 August 2003 - 04:47 AM
I'm thinking about just keeping my eyes open for some junk tranies so I can take them apart and see what goes where.
Thanks again for the info.
Posted 13 August 2003 - 09:24 AM
Also, I was looking in my '85 hatch owners manual, and it says the 4wd Brat auto has a 1.026 reduction gear and 3.454 R&P, and the rear end has a .933 reduction gear and a 3.700 R&P, which works out to about 3.5 total reduction. Are the transmissions you're taking about actually have a 3.700 R&P? Could you scan the page you're looking up the gear ratios on and post it here?
Thanks again for your help, I really appreciate it.
Posted 13 August 2003 - 11:09 PM
#3 is 4wd 4spd
#4 is 4wd auto
My gear ratio info comes from my nearly complete set of '80s owner's manuals. I was only referring to front diff ratios since you were talking about a 2wd car. ALL 4wd automatics used a 3.7 rear diff. The rear reduction gear was used to match that 3.7 rear to whatever was used up front. Yes, I meant that the '87+ EA82 autos had 3.7 ratio front R&Ps, as did the '80-'82 EA81 autos. (From '83 on, EA81 and EA82 3spd autos are essentially the same tranny. The earlier autos had a different torque converter, but were otherwise basically the same.)
I'll scan some more stuff for you later. This sounds like a pretty cool project, and I'm happy to be helping.
Posted 14 August 2003 - 04:47 AM
Thank you Noah.
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