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1986 GL front and rear diff questions


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10 replies to this topic

#1 hellosubaru

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Posted 22 November 2010 - 04:12 PM

I recently picked up a 5spd d/r trans from a wrecking yard to replace my old 5spd d/r. The car is a 1986 GL sedan 4wd. The old (original) trans was 23-spline, and the new one is 25-spline for the front axles. My question is, what gearing do the 23 and 25-spline trans have? 3.7, 3.9, something else? I'm pretty sure my rear is a 3.9 open (I was under there a few days ago and just glanced at it). I do not know what the new 25-spline trans came out of, it was already pulled and on the shelf at the wrecker.

I'm sure that I need to match the gears front and back, so what are my options, assuming that the 25-spline is geared differently than the 23-spline?

I also have a 1992 Legacy auto, would that diff work for me? Anything I'm forgetting?

Bottom line is, if I need a new rear diff, where can I get one (or the gears to put in it)? Price is not too big of a deal at this point, but the less money, the better!

Thank you for any help you can provide!

#2 ruparts

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Posted 22 November 2010 - 06:02 PM

hi,
its hard to say for sure but , i was thinking the 25 spline d/r was a turbo car unit and would have 3.7 front diff. you do need to find out for sure somehow. main thing is, if it's 3.7 you can get an open rear diff cheap , there should be plenty of them around that area, even the ea-81 rear units will work in your car. the front diff should (Only) be 3.7 or 3.9 as far as i know. the 25 spline front axles are the same as 23's other than the inner doj, happy hunting.

#3 hellosubaru

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Posted 22 November 2010 - 09:23 PM

hi,
its hard to say for sure but , i was thinking the 25 spline d/r was a turbo car unit and would have 3.7 front diff. you do need to find out for sure somehow. main thing is, if it's 3.7 you can get an open rear diff cheap , there should be plenty of them around that area, even the ea-81 rear units will work in your car. the front diff should (Only) be 3.7 or 3.9 as far as i know. the 25 spline front axles are the same as 23's other than the inner doj, happy hunting.


Awesome, thanks. Do you know what the '92 legacy rear diff is geared?

#4 MilesFox

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Posted 22 November 2010 - 10:01 PM

92 legacy would have a 3.9 gear.

sounds like you got a turbo RX trans, turbo being 25 splines, and dual range with the lever makes it rx. There will also be a vacuum diaphragm to lock the center diff.

you indeed got the most desireable transmission available! go find a lsd 3.9 rear diff and turbo 5spd axles and you are good to go. also, you can use the vacuum solenoids of pushbutton 4wd dl's and gl's for the diff lock.

otherwise you could sell that trans and buy 2 of the correct ones!

#5 capn_r

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Posted 22 November 2010 - 10:04 PM

It could also be an 85-86 RX dual range box. 25 spline axle stubs and part time 4WD with the 1.19 low ratio.

#6 hellosubaru

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Posted 22 November 2010 - 10:15 PM

92 legacy would have a 3.9 gear.

sounds like you got a turbo RX trans, turbo being 25 splines, and dual range with the lever makes it rx. There will also be a vacuum diaphragm to lock the center diff.

you indeed got the most desireable transmission available! go find a lsd 3.9 rear diff and turbo 5spd axles and you are good to go. also, you can use the vacuum solenoids of pushbutton 4wd dl's and gl's for the diff lock.

otherwise you could sell that trans and buy 2 of the correct ones!


Now this would be awesome! Did you mean find a 3.7 lsd, or 3.9? Also, where do i connect the vac solenoid to the trans if it really does have diff lock? You've got me excited now! :D

#7 ruparts

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Posted 23 November 2010 - 10:25 AM

92 legacy would have a 3.9 gear.

sounds like you got a turbo RX trans, turbo being 25 splines, and dual range with the lever makes it rx. There will also be a vacuum diaphragm to lock the center diff.

you indeed got the most desireable transmission available! go find a lsd 3.9 rear diff and turbo 5spd axles and you are good to go. also, you can use the vacuum solenoids of pushbutton 4wd dl's and gl's for the diff lock.

otherwise you could sell that trans and buy 2 of the correct ones!


hi, i have an original 88 RX and the diffs are 3.7 , i also had a fulltime awd turbo sedan and it had 3.7 , i think the trans you got probably is also.
sure wish i had another RX trans to put in my xt.

#8 MilesFox

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Posted 23 November 2010 - 11:14 AM

Now this would be awesome! Did you mean find a 3.7 lsd, or 3.9? Also, where do i connect the vac solenoid to the trans if it really does have diff lock? You've got me excited now! :D



whoops, i meant 3.7 rear diff for the lsd turbo

#9 hellosubaru

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Posted 23 November 2010 - 11:23 AM

Where does the vac solenoid hook up to the trans? Is it an electrical connection or mechanical?

#10 Caboobaroo

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Posted 23 November 2010 - 02:10 PM

Posted Image

The vacuum diaphram is on the driver side above the front diff, seen in this pic. There's a cable that goes from it to the center diff near located in the tail section of the tranny.

If it doesn't have it, then its going to be a '85 '86 RX/GL-10 part time dual range 3.7 tranny.

#11 hellosubaru

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Posted 24 November 2010 - 03:13 AM

Does anyone know where to get all of the vac diaphram components to make the locker work? Being how I had a 23 spline 4wd trans before, I have none of this.

Thanks!




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