lucid_door Posted April 18, 2010 Share Posted April 18, 2010 I recently swapped a used AWD auto trans/diff assembly into my 1990 Legacy wagon non turbo. The trans came from a 1994 Legacy, not sure of any other details on the donor. After finishing installation, I went to drive it, and the driveline was binding pretty bad; felt like I was dragging a boat anchor around. Now silly me didn't do my homework thoroughly enough to realize some of these cars came with different gear ratios in the differentials. I tried tossing the FWD fuse in but it didn't help at all. I removed the rear drive shaft, and the binding is gone (and that used tranny shifts awfully nice too, whew!). The tag on the rear diff states a 4.11 ratio. I guess what I'm wondering is, where could I look to find the ratio in the front diff? The old one had the drain plug exiting on the passenger side; new one exits to the driver's side. Is that useful in identifying anything? Would there be a part number or tag on it somewhere like the rear diff has? I've been looking online pretty hard to find something but have come up empty so far. Thanks for any help you can provide! Link to comment Share on other sites More sharing options...
edrach Posted April 18, 2010 Share Posted April 18, 2010 I recently swapped a used AWD auto trans/diff assembly into my 1990 Legacy wagon non turbo. The trans came from a 1994 Legacy, not sure of any other details on the donor. After finishing installation, I went to drive it, and the driveline was binding pretty bad; felt like I was dragging a boat anchor around. Now silly me didn't do my homework thoroughly enough to realize some of these cars came with different gear ratios in the differentials. I tried tossing the FWD fuse in but it didn't help at all. I removed the rear drive shaft, and the binding is gone (and that used tranny shifts awfully nice too, whew!). The tag on the rear diff states a 4.11 ratio. I guess what I'm wondering is, where could I look to find the ratio in the front diff? The old one had the drain plug exiting on the passenger side; new one exits to the driver's side. Is that useful in identifying anything? Would there be a part number or tag on it somewhere like the rear diff has? I've been looking online pretty hard to find something but have come up empty so far. Thanks for any help you can provide!You probably have a 3.900 front diff. But you can be sure by looking up the transmission number using the chart in the USRM on transmission information. Your transmission number is on the VIN plate in the engine compartment; something like TY752V1AA. Or you can find the label on the tranny bell housing near the starter motor. IGNORE everything I just said; I re-read your post and you have an automatic tranny. My info is for a manual transmission. Although if the diff states it's a 4.111, you likely will need a 3.900 rear diff to go with the transmission you just installed. Link to comment Share on other sites More sharing options...
johnceggleston Posted April 18, 2010 Share Posted April 18, 2010 (edited) it could simply be torque bind in the transfer clutch. since the FWD fuse did not cure it that would be the first place to look. oor it could be both, the transfer clutch and mis-matched diffs. but you have the parts in the old trans to fix the transfer clutch. BUT, there is a process to check if your front and rear diffs match. i have written it up and posted it a couple of times. search for "diffcheck" and read up. found it under "diffcheck". http://www.ultimatesubaru.org/forum/showthread.php?t=109760&highlight=diffcheck WARNING: the process for checking if the diffs match is potentially dangerous, please be careful and take the proper safety precautions. Edited April 18, 2010 by johnceggleston Link to comment Share on other sites More sharing options...
edrach Posted April 18, 2010 Share Posted April 18, 2010 BUT, there is a process to check if your front and rear diffs match. i have written it up and posted it a couple of times. search for "diffcheck" and read up. found it under "diffcheck". http://www.ultimatesubaru.org/forum/showthread.php?t=109760&highlight=diffcheck WARNING: the process for checking if the diffs match is potentially dangerous, please be careful and take the proper safety precautions. This should really go in the USRM for easy referral. Nice write-up. Link to comment Share on other sites More sharing options...
MilesFox Posted April 18, 2010 Share Posted April 18, 2010 I've got a 3.9 rar diff laying around if you can use it. good luck and welcome to the forums. see you in wisconsin! Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 18, 2010 Share Posted April 18, 2010 Don't know if it works on the auto's or not - but on the MT's you can count the ring gear teeth through the gear oil drain plug hole using a flashlight. That will get you the ratio. It's probably 3.9 though - the early Legacy MT's were 4.111. Auto's are typically the higher geared of the two. GD Link to comment Share on other sites More sharing options...
lucid_door Posted April 23, 2010 Author Share Posted April 23, 2010 Just an update: Located a 3.900 rear diff at Badger Motors Auto Salvage in Wisconsin Rapids for a measly $90 (they even threw in a radio bezel for free, how awesome is that??), drove the 260 miles round trip yesterday, threw it in tonight and all is good Those little buggers are awfully heavy to hold over your head while lining up the cv shafts and getting a bolt started LOL Thanks for all the suggestions and information everyone, I sincerely appreciate it My Legacy is back on the road! Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 23, 2010 Share Posted April 23, 2010 The trick is to unbolt the knuckles and swing the axles outward so you can mount the diff without having to put the axle shafts into it first. It's like two bolts on either side for the knuckles. GD Link to comment Share on other sites More sharing options...
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