what diffs are there in a JDM 6 speed gearbox. and is it only a UK 6 speed that will match a uk 3.9 diffs

 

i think so

 

Most jdm 6 speeds have 3.9 front diffs 1:1 transfers so need 3.9 rear diffs

Most uk 6 speeds have 3.9 front diff 1.1:1 transfers so need 3.545 rear diff.

Steve, your car will have come with a 3.545 rear diff originally.

 

ive supposedly got them all , but i was hoping it would fit with out the rear diff so i could sell it on

 

I reckon there's no reason why you couldn't change the step off gears [transfer gears ] from the UK box to the JDM box and vice versa. Thus you could have the benefit of the better 5th and 6th ratios of the JDM box and run the 3.5454 Uk rear diff.

ALL 6 speeds so far seen by API are 3.9:1 ratio front diff. US Forester may be different but you'd need the US guys to advise.

That help??

David APi Engines / APi Impreza

 

I did just this. Had a JDM 6 Speed box 1st, so had a 3.9 rear diff (quaife atb) and then went to a UK 6 speed, just swapped the transfer gears over, and kept the 3.9 rear diff.

I know Steve has changed his box before, so dont know what rear diff he has.

Steven

 

mine is still the uk rear diff

 

you will need to either change the rear diff, or change the transfer case then.