Viscous Coupler Swap: WRX -> Gen II Lego

[99lego]

Howdy,

 

My Viscous Coupler is shot. Tight turns right and left at low RPM's cause for major lurching. Luckily these symptoms are limited to when I'm pulling into or out of parking spots as the Lego seldom spends time in the city.

 

So.....knowing that I'm going to have to replace this part to keep her running, currently 175k, I was hoping that someone out there had done a swap from a WRX into a Gen II Lego. It seems like it would be straight forward enough as long as the gearing was matched.....right?

 

Uh details:

99Lego 30'th aniv. edition w/ a 5MT rolling on 28's with a 4" lift.

Build thread:

http://www.ultimatesubaru.org/forum/showthread.php?t=105512

[WoodsWagon]

If the 99 is a phase 2 transmission, which I belive it is with the 8 bolt bellhousing, then a wrx center diff will fit. You can't replace just the viscous coupler on the phase 2 transmissions, the whole center diff has to be swapped.

 

The wrx has a 3.9 front diff, a 3.54 rear diff, and a 1.1 reduction in the rear transfer gears.

Make sure you use the legacy transfer gears with the wrx center diff when you swap.

 

I'm assuming you're using a wrx trans as a donor because someone ripped 2nd gear out of it?

 

You can also use a phase 1 center diff if you swap the whole transfer housing off the back of the transmission to a phase 1 version.

[99lego]

^^^^^^^^

Confused as to why a phase II tranny wouldnt accept just the viscous coupling and would require the entire center diff?

[WoodsWagon]

They changed the design of the center diff. The plates and fluid of the viscous coupler are sealed inside the carrier of the differential. The older ones had a seperate chunk that contained the vc, and it could be removed from the diff without breaking the seal.

 

It's easy to toss the whole diff in if you have a donor. Just make sure the big spring clip is still there in the back of the diff, that's what holds the cover on the VC chamber of the center diff.

 

Sometimes they pop out and get run through the rear transfer gears, but that leads to no center diff lockup, rather than binding. It also makes bad noises as the spring steel runs through the transfer gears.

[99lego]

^^^^***^^^^

A WRX center diff would be limited slip...I think. It would be fun to run a front and rear limited slip. Free Range has done it with good results.

 

I belive the gearing on the Lego is 3.9....WRX maintained the same gearing up until the 6MT....or am I totally off here.

[WoodsWagon]

All EJ 5mt's have viscous limited slip center diffs.

 

You can buy an OBX front helical LSD for $380, but that requires tearing down the whole transmission and setting up the front backlash and carrier preload. If you're going to do the work to put that in, you should put in ForesterXT 4.44 ring and pinion. They're $350 new from the dealer. A matching rear diff is easy to come by out of an Auto legacy.

 

Your legacy is probably 4.11 final drive. You don't need to mess with the final drive if all you are replacing is the center diff. Drop the rear driveshaft, pound out the roll pins and take off the shifter yoke, pull the cover off the rear transfer housing, pull one diff out, slide the other in, reassemble. Keep the transfer gears with the transmission and swap just the center diff. You don't even need to take the transmission out of the car.

[GeneralDisorder]

There is no difference between your '99 Legacy center diff and the WRX center diff. Both are 4Kg units, are 100% interchangeable and are most likely the same part number.

 

Neither are DCCD.

 

Gearing doesn't matter in the least.

 

A FRONT limited slip is another animal entirely and requires a complete tear-down of the transmission and resetting of the R&P lash. No Subaru except the STi 6 speed's has a front limited slip unless it's been added by someone. OBX sells a Torsen type-1 LSD for the front - they are about $400

 

GD