How to tell diff ratios....???

lincolnthemod · Post by **lincolnthemod** » Fri Jul 16, 2010 2:28 pm

Hey all,
I own an '83 Subaru Wagon and want to put in a dual range gearbox, as the one fitted to this is from an '81 and single range:(, my question is how do I tell the diff ratio of my gearbox. If it helps the rear diff I have (with the sticker thing still on it) is a 3.7 ratio.

Thanks in advance,
Lincoln

Post by **Alex** » Fri Jul 16, 2010 2:40 pm

rear diff matches your gearbox. therefor your gearbox is a 3.7 ratio.

AlpineRaven · Post by **AlpineRaven** » Fri Jul 16, 2010 9:48 pm

Thats correct above.
Sorry to sidetrack... Some Subarus have 1.0:1 or 1.1:1 reduction ratio, RS Liberty had 1.1 reduction where about the front diff was 3.9 and rear diff had to be 3.545!
Cheers
AP

spike · Post by **spike** » Sat Jul 17, 2010 2:58 pm

mark your wheel.............
get under the car........
rotate the drive shaft 4 times the wheel should go around once and a bit

lincolnthemod · Post by **lincolnthemod** » Sun Jul 18, 2010 11:06 am

I know that the gearbox that is fitted to it must be a 3.7 but what about the dual range box I want to fit to it, how do I tell what this is?.

Some Subarus have 1.0:1 or 1.1:1 reduction ratio, RS Liberty had 1.1 reduction where about the front diff was 3.9 and rear diff had to be 3.545!
............Wow that's kinda confusing.

Cheers,
Lincoln

steptoe · Post by **steptoe** » Sun Jul 18, 2010 11:21 am

Some Subarus...my L Series GLTA 4WD sedan with its 3 speed auto no low ratio 4WD box had rear diff at 3.7:1 with front 3.45:1 ...yeah, weird brain teaser as to why???

If box is still in donor car, obvious to check rear diff, but if it is out well the diff oil drain plug gives access to the crown wheel to one side, clean a toof and mark with corrector and turn front drive stub . Did this yesterday with WRX box, we got 39 teeth. Then if the other cog has ten teeth we get 3.9 diff ratio. cannot see the divider cog, so then divided by eleven to get 3.54 something which is not a subie ratio, divide by 9 and got a bigger 4.3 or close, also not a subie ratio so assume it is 3.9 that way. L series box were only in manuals 3.7 or 3.9 as far as I know. MY models like yours - all I ever seen is 3.7:1

lincolnthemod · Post by **lincolnthemod** » Sun Jul 18, 2010 9:26 pm

Wow thanks heaps everyone, great info, will have her on the road in a couple of days hopefully.

Cheers,
Lincoln