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So I picked up a gearbox to replace my stuffed one last week and put it in. The box is out of a brumby build date 01/90.

The problem I've had is the final drive ratio is different from the diff ratio (3.700) the diff out of the donor brumby I got the box from is the same. So that isn't an option (clearly the box or diff in the donor wasn't origanal)

So what I need to know is what ratio could this new box be? It is slower that the origanal 3.700. I checked this by jacking both wheels on the same side off the ground and engaging 4wd and puting the box in neutral. I then marked both wheels and spun the rear one. After 5 full rotations of the rear wheel the front one ended up appox 90 degrees behind.

I believe my options are to change the diff gears once I figure out what ratio the differential in the box is (how I do this I wouldn't know?) and I find a supplier for the r160 gear ratios.

Or the other, potentially more complicated option is, to take the 3.700 diff gears out of the old gear box and fit them to the new box. The problem with this is, I have no idea how difficult this is. Nor do I want to fork out for bearings and gaskets which is why I went the 2nd hand box in the first place.

it will either be a 3.7 or a 3.9 unless the box is from and EJ car not an EA car

is it a 4 speed dual range or a 5 speed dual range?

TOONGA

If yours was a 3.7 and the new one is different, and its a 4speed Brumby box, it will be 3.9
Easiest fix is to change your rear diff to match.

It's a 4 speed dual range. I did the maths and reckoned it would be around 3.9 but wasn't sure. So now to find someone who supplies diff gears

Just go to the wreckers or ask on this site for a complete 3.9 diff, easy to swap.

MuZ wrote:It's a 4 speed dual range. I did the maths and reckoned it would be around 3.9 but wasn't sure. So now to find someone who supplies diff gears

Yep, if after 5 full rotations of the rear wheel the front one ended up appox 90 degrees behind, thats 1:20. 1/20th of 3.7 is .185, so approx 3.9

Agree, rear diff is very easy to swap if you're happy with the slightly shorter gearing (will give better acceleration & crawl ability)

If you can't find a 3.9:1 rear diff from a Brumby/MY or L series look into the gen1 liberty as they have the output stubs on the diff the same as the Brumby/MY/L series and will bolt straight in. The Gen2 rear diff requires a male inner cv joint which would mean a custom shaft to fit in your brumby.

Swapping diff gears is not the way to think with subarus in this case - it's all Lego and it is often the case of just finding the right parts to fit/match/do the job.

For instance I've got a 4.111:1 rear diff from an auto gen 1 lib in my L series, bolted straight in

Cheers

Bennie

tambox wrote:Easiest fix is to change your rear diff to match.

tambox wrote:Just go to the wreckers or ask on this site for a complete 3.9 diff, easy to swap.

NachaLuva wrote:Agree, rear diff is very easy to swap

Well I was about to say... but I guess it's already been said

Most likely there will be someone on here (maybe even close to you?) that will have a diff for you