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p/t dual range binding with 3.9 diff but not 3.70

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So, as the title says, i have a part time dual range swaped into my turbo wagon. im not sure on the year of the trans.

 

the rear diff came out of an 82 gl 4spd d/r. No sticker on the diff

 

anyway, before i swapped diffs, i never noticed it binding in 4wd.. i promptly stuck it back in fwd before i drove too far.

 

after i put the new diff in 4wd binds, fwd dosn't, radda radda radda

 

3000rpm@70mph w/ 185 80 13's if it helps

well, using a gear calculator. A 3.7 (turbo, .871 5th gear) trans with 24.65" tires would be turning about 3100 rpm at 70, whereas the 3.9 (non-turbo, .780 5th) would be turning 2900.

 

 

But, if you're binding with a 3.9 diff, and not a 3.7, than I'd say you got a 3.7 trans. And if it's a PT4WD D/R. Than it's an '85-'86 RX trans.

 

 

How did the axles work out for you? Your turbo wagon would have already had 25-spline axles, and if your donor trans had been a 3.9, it would require 23-spline axles.

  • Author

it defiantly has turbo axles.. they are huge..

 

so.. there IS a part time dual range 3.70? i did not know this.

 

and at 70, its on the low end of 3000, tach says 2900 before it drops to 69

the rpm thing doesn't really make sense. but Subaru Speedo's tend to read high....so that might be it.

 

 

if you didn't have to swap axles, it's definitely a turbo transmission. And the only combination of turbo, PT4WD, and D/R was the '85-'86 RX. So yea, it's a 3.7. Also, that means it's a 1.19:1 low range and not the 1.59 of the non-turbo cars.

P/T 4wd 3.70 Dual Range with the 1.2 low range was an option on some GLs also. I have an optioned out 85 Turbo GL sedan with that trans (and an open rear diff).

 

I myself found this out when I noticed that Lo range wasn't anywhere near a 1.6 times higher engine speed for a given wheel speed ... but I didn't have an RX as it had air struts and a digi-dash.

  • 2 weeks later...
  • Author

allright, so i swaped back in the 3.70 and it works great! and yeah.. the lo range is defiantly not from a n/a d/r..

 

 

Thanks for all your help!

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