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I think my 99 Legacy 5-speed has a slipping differential--front, center, or rear.  How can I diagnose where the slipping is happening?   When my Legacy is going up a hill, and I give it more throttle, the speedometer reading increases (it's a Brighton so no tach) and the engine get louder, but the speed doesn't seem to change.  So I think I can rule out the clutch as causing the slipping.  Also, if I can't get up a hill in first gear, I can shift up to second gear and it will go up the hill better...but with some noisy complaining.    It was an intermittent problem--going months between slipping, but recently it seems to have become chronic.

Edited by edcooley

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A broken axle is a good thought--better than a bad transmission.  I drive it about 10 miles every day, but I guess it could still make that trip if it wasn't completely loose.   I haven't noticed any smell.  I will check out the axles and get back.     Thanks.

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An axle can't be intermittently slipping... It's either broken or it isn't. Also, if you've been driving with a broken axle you've roached your center diff, once you replace the axle you'll have nasty binding like driving in 4x4 on pavement. Higher gear makes sense... You put more speed into the center diff, it spins faster, heats up, and binds tighter. 

 

Does it stall if you put it in gear and let off the clutch without moving? If not have someone put it in first gear and sit with their foot on the brake and look under the car from behind to see if an axle is spinning. Do the same thing in reverse looking from the front so you can figure out which one it is. Obviously have them use the gear in the opposite direction of where you're peeking under the car... don't get run over!

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Differential don't "slip".  My money is on the cluch being worn out but can't explain why 2nd gear, not 1st, gets you up the hill.

Edited by john in KY

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If it was the clutch, the speedo wouldn't increase when the car does't accelerate. The center differential is a limited slip. so yes, it does SLIP. If you have a broken axle and abuse it enough, it'll will eventually fail and bind up.

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Clutch wouldn’t surprise me - not because it matches the description exactly but because customer diagnosis and info isn’t always super accurate.

 

That being said - it does sound ominous. I would drain the trans gear oil and check for bits, chunks and metallic flakes.

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look for a broken axle

 

any smell when this occurs?

The rear axle on the driver's side is loose at the diff and leaking oil.  That looks like the place to start.  I think I have a replacement diff and will look at the axle for damage.   This car was bought with a bad transmission, and I got a used one from a guy that (I found out later) thought I had an Outback.  I put it in and found out that the ratios didn't match up.  So I ruined the center diff on the Outback transmission not knowing what was wrong and being stupid.   I changed the diff to match the Outback transmission, but it was too late.  So I replaced some bearings in the original transmission and got by for several years.   When it went out I got another used one from a reputable wrecker and have been experiencing this current weirdness infrequently ever since.  I really don't think it's the transmission because it runs right most of the time.  I don't know why this bad axle could be intermittent, but hope that this axle/diff malfunction will fix it, and that I haven't damaged the center diff.   Back when I was having that problem, I found out they were about $900 new and there weren't any used ones.  I have had some bad experience with all-wheel-drive cars, but they really work on the gravel road we live on and in the snow.   A Vista and now this Legacy have both had issues with the transmissions.   I was pretty relaxed about keeping the tires all the same on the Vista and its center diff (in the driveline) went out, but now that I do I still have problems.  

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Yep - replace axle and/or replace/repair diff.

 

This thing got rode to hell. Previous owner hosed the trans. You installed the wrong ratio and continued driving to failure. That binding was also stressing the axles, diffs, and rear driveshaft....all that stuff was strained and probably the original cause of this current issue. Then you split the case and replaced some bearings and swapped a diff...this thing hasn’t had an easy time.

 

The AWD transmissions are fine. They’re just a FWD trans with a few more parts. There’s nothing inherently bad about AWD trans and they’re readily making the same high mileage’s of anything else when properly maintained.

 

Change the fluids and run/rotate proper tires and you’re golden.

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Next time you have a question about something acting weird, put the extended details in the first post... You left it vague and we all kinda guessed, then you told us the thing has been brutally abused. I hate to say it but... The issues you've experienced with the AWD have been self-imposed.

 

At this point, replace the suspect axles, get a good used transmission (make sure the ratios match...), and you'll be fine.

Edited by 987687

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Sorry to have misled you.  I thought those later details were not very important because they occurred over seven years ago--some 100,000 miles.  I actually think that the original transmission had a bad bearing near the rear output shaft and could have been fixed by replacing that immediately and not putting in the wrong Outback transmission which only got driven with the wrong ratio for a short time--mostly trying to figure out what was wrong.  I did get the proper diff for that transmission almost immediately--but not before ruining the center diff.  I repaired the original transmission and replaced it and the original rear diff soon after and got several years and many miles out of it.

 

I did remove the rear diff today and didn't see anything obviously wrong.  It did seem a little loose and the seal was shot on the driver's side when I reached in under the car while it was parked.  After putting it up on blocks and removing it,  nothing seems so obvious anymore.  What can I do to see if the diff or the axle is the problem.  Actually, I don't have the correct diff on hand as a replacement--it is a T2 which is apparently for a 2.5 manual transmission--mine is a 2.2 MT.

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Drain diff oil and look for chunks and metallic swirls in oil.

 

Disassemble inner axle joint and see what it looks like?

 

Attach axle to diff and try to rotate axle or diff flange with tools/leverage while holding the other side still and see what you get.

 

Just need to match the final drive ratio.

 

MTs with a 2.2 engine of that era are just about all 3.9 final drive so any 2.2 rear diff from a legacy or Impreza is an option or a 1996 outback MT (only outback that came with 2.2).

 

www.car-part.com

 

Post in the parts wanted forum here.

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I got the diff out by just disconnecting the driveline and removing the bolts holding it in place and letting it down to let the axles slide out.  Will the axles come out now by just removing the axle nut?

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I got the diff out by just disconnecting the driveline and removing the bolts holding it in place and letting it down to let the axles slide out.  Will the axles come out now by just removing the axle nut?

 

Yep, you got it.  Should be a 32mm. 

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I've had this happen on about 4 manual trans Subaru's.  The center viscous coupling will transfer light power, but when power goes to the rear with a disconnected half shaft it goes no where.  I do have good half shafts, $20 + Shipping from CO.  These are used stock Subaru axles with good used boots.

 

You can pull the strut and hub bolts if there are not frozen and then pull the hub away from the car.  Once the inner side is free you can remove the axle from hub.

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Drain diff oil and look for chunks and metallic swirls in oil.

 

Disassemble inner axle joint and see what it looks like?

 

Attach axle to diff and try to rotate axle or diff flange with tools/leverage while holding the other side still and see what you get.

 

Just need to match the final drive ratio.

 

MTs with a 2.2 engine of that era are just about all 3.9 final drive so any 2.2 rear diff from a legacy or Impreza is an option or a 1996 outback MT (only outback that came with 2.2).

 

www.car-part.com

 

Post in the parts wanted forum here.

I did drain the oil and there are metallic swirls in the oil and even some grains that can be felt when rubbing them between fingers.   Some of the metal is attracted to a magnet, but most is not.   The drain bolt has a magnet on it, and it had metal on it.

 

I took the axle nut off, but cannot budge the axle out toward where the diff was.  I hit it pretty hard using a 3 lb hammer and an oak peg.   Tire and brake drum are off.   My drawing seems to show that it should slide out.

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Yep, sometimes they are rusted in.

 

I have some drum hubs listed as well.  A little bearing noise but not to bad.

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Sounds like your diff is hosed. Time to swap in another diff.

 

I’m which case you don’t need to remove the axle right?

 

Yeah the axles can be seriously rust welded into the hubs.good job using a wooden spacer. Hit the axle too hard and it’ll mushroom, damage the threads such that the nut won’t go on and the axle can’t pull through the hub without grinding/filing down the mushroomed end. I was using a three jaw pulled and it shattered the rotor I was pulling against. Whoops.

 

The rear axle splined shafts that go into the rear diff don’t look warn do they? Never seen or heard of that happening but just checking. Subaru rear diff failure is very rare. Almost never happens, I’ve never seen a failed one yet.

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Maybe the diff problem has been festering since I briefly used the 2.5 transmission mistakenly 7 years ago.   Do you think it is repairable? 

 

I think the axle splines look good.  That was one of the first things I looked at.  The axles look good as far as I can tell.

Edited by edcooley

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Maybe the diff problem has been festering since I briefly used the 2.5 transmission mistakenly 7 years ago. Do you think it is repairable?

 

I think the axle splines look good. That was one of the first things I looked at. The axles look good as far as I can tell.

Not worth repairing as easy as they are to swap and considering they never fail a used one just makes sense. Parts will be costly or you’ll be searching used in which case we’re back to just buying another diff.

 

Also could that debris compromise the diff, ring and pinion or bearings? So repair but maybe have future issues again? If I found that in an engine I wouldn’t expect replacing the one bad part to be a good option.

 

That being said they’re small and easily disassembled. Just take it apart and look at it. If there’s that much debris it’s not like you’ll have a hard time finding the compromised parts and wear areas.

 

Ring and pinion you’ll have to set backlash.

 

If its just the diff chunk you can swap those easily and they’re not ratio specific so you can use any EJ diff chunk as long as it’s the same style axle on the receiving cups.

 

Bearings - unsure what happens then.

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I got a used 3.9 diff locally for $75 on Tuesday afternoon and put it in Wednesday afternoon.  I drove it Thursday and Friday, and it seems to be cured.  Thanks for your help.  

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