Would this work if the diff were a 3.9 unit?

DUH!!!! Yeeeaaaaaaa!!!!!

Aren't Gen 1 Brat's 4.11?

 

As mentioned here by Qman in fact:

http://www.ultimatesubaru.org/forum/showthread.php?s=&threadid=12985&highlight=Brat+4.11

 

GD

One thing to watch out for is that early Gen1s used U-joints instead of DOJs for the rear shafts. You would need to replace the stub axles in the LSD diff the Yokes from the open diff.

 

I can't remember if this change took place before or after the Brat went into production.

Would the ring gears from a gen 1 brat fit in a EA82 diff?

That I don't know - but I would try to find a 4.11 LSD from a legacy....

 

GD

Check out this post for possible donor cars for rear diffs that are going to be somewhat easy to find.

 

http://www.ultimatesubaru.org/forum/showthread.php?s=&threadid=11397&highlight=wrx+gear+ratio

my wagon has a 3.90 in the rear. It has the tag on it. Mudrat79 also said that gen 1's have 4.11's in them. I wonder what is up with this? Do they really have 4.11s or 3.90s? Maybe someone put a 3.90 tag on my rear diff if it has 4.11s in it. Strange....very strange.....

Luke Ebert ran a gen1 Brat last year with an LSD installed. I'm not sure of the rear end ratio, but I thought it was a 3.900. Just make sure the LSD you install has the same rear ratio as your current open diff.

As long as the diff is the same as the EA82 LSD's, you can switch out the open diff for a LSD diff and keep the ring and pinion gears.

I'm pretty sure that in gen 1 4WD cars the front diff and the rear diff had different ratios. I remember reading that Subaru didn't manufacture any rear diffs so they bought them from Datsun and had to use a multiplyer gear for 4WD to get the ratios to match. This would explain why some beleive Gen 1's have 4.11 (front) and 3.90 (rear) gearing. I think that a 3.90 rear will work, but I'll have to take a look at Ben's brat.

Except for the Justy and WRX STI All 4wd and AWD Subaru's in the US market use the Hitach R160 rear differintal. Also I have torn down several 4wd transmission including Gen1s and the transfer case ratio is 1:1 except the automatic. Also a former co worker of mine had a 78 brat and it had a 3.9 rear diff.

Because the the two-wheel drive Subaru has a front-drive transaxle, the firm doesn't have an appropriate rear differential of it's own. It has to buy one from Datsun which doesn't quite match the exixting front-drive ratio. However with the transfercase gearing , the front and rear ratios even out to approximately 3.889-to-1.

 

Heres the article

 

So I was wrong on the 4.11 part AND the 3.90 part!!!

so you can have an LSD in your gen 1 but you have to get it from a Datsun with the same rear end. I believe its an R160 rear end. It kinda sucks that they don't completly match the whole 3.889:1 and the 3.90:1:-\

Caboobaroo, I make 3.90 LSD rear diffs all the time, I just replace the open diff in the 3.90 with a LSD diff from a 3.70. It bolt right up to the ring gear so it if a simple conversion. There is some grinding required to the housing though.

 

I really doubt if you or anyone else could tell the difference between a 3.889 and a 3.90. In fact I bet if you count the teeth on the Datsun/Nissan you find it has the same as the Subaru. Subaru just choose to round it up, and Datsun didn't.

Cool, then I'll need to keep my eyes peeled for TWO LSDs. One for me, and one for Ben!