Rear diff problem, I think

[Huffer]

Over the last couple of weeks the car has begun making odd noises on full-lock low speed turns (think parking manuvers). Specifically a juddering/clunking noise that FEELS like the tires are scrubbing on the pavement.
(imagine trying to push your car sideways at low speed with the tires skipping)

I have a "FWD" fuse holder in my car (98 Legacy GT, 4EAT). When I put the fuse in, it makes the car "front wheel drive".

When the car is in FWD mode, the juddering goes away, and the car is sweet again. Which leads me to believe there is a specific problem with something toward the rear.

I have no problems at speeds above 20mph on sweeping turns, or in straightlines. Accelerating out of a turn causes some judder.

When in FWD mode - what is it doing to the transmission at this point - does it lock/unlock a differential?

I drained and refilled the rear diff fluid yesterday (using 80w90 as per owners manual), and the problem diminished some. The magnet was pretty thick with shavings... the diff fluid was black.

At this stage I'm finding some quotes for rear diff replacement units... factory is 4.44.

[shazapple]

Im thinking its more to do with the torque converter or transfer clutch (Subaru AT's dont use a center differential)

[Huffer]

Tell me more. I can't find jack schitt about differential problems on a 4EAT.

[Huffer]

Ok, found some answers at bbs.legacycentral.org.

"Torque-Bind"

By Dave

This has been a hot topic of late, as more and more older Subaru Legacies reach high mileage and drivetrain wear becomes a factor. One of the most common problems in AWD 4EAT automatic transmission equipped cars is the dreaded "torque-bind".

The most common symptoms of this problem are a shudder throughout the whole car, but more pronounced beneath the seat, when accelerating in a low-speed turn. The shudder will stop if power is removed and disappears when speed goes beyond the threshold of most tires or the wheels are straightened out.

Recently i've found out that the early model Legacies don't actually have the wear problems listed below, but frequently have a malfunctioning solenoid in the same area that causes pressure problems and very similar symptoms. Replacing this should fix the problems in pre-95 models.

The solution to the problem is relatively simple and comprehensive but first you should know what causes this problem.

The evolution of the problem and the solution were shown to me by a Master Technician at Subaru of Ogden in Ogden, Utah.

In the rear of the transmission is a watermelon sized aluminum housing that contains several valves, bushings and seals. The rear driveshaft that couples with the rear differential. The problem occurs in here, and the replacement of this cures it.

Inside of the housing the rear shaft spins and has teflon bushings and fluid seals for the AWD system. This is where much of the rear power is transferred. The problem occurs when these bushings wear against the aluminum. For some reason Subaru, or the transmission manufacturers, decided not to have a bearing or liner in lieu of using the housing itself as the wear surface.

This is where the problem and solution lies.

The bushings and seals wear the aluminum down after time. This allows the pressurized ATF to leak from one chamber to the next. The torque meant to be transferred to the rear ends up being greatly reduced and the fluid transaction causes the shuddering.

Thankfully the fix is relatively inexpensive and doesn't require the transmission to be removed.

At Subaru of Ogden i got to see a 95+ Legacy in the midst of this operation. The rear driveshaft and exhaust rear of the Catalytic Convertor have to be removed and the rear transmission housing needs to be removed.

The housing is completely replaced with a new one. New internal components are included and apparently the bushings and seals on the driveshaft are also replaced. The most important piece of the solution is the addition of a steel liner to protect the aluminum housing against wear. This should ensure that this problem doesn't occur for the remaining life of the car.

The procedure was quoted as $750 by Subaru of Ogden.

An updated case with the steel liner was put into prodution and installed in all new cars in mid-1997.

You may never have this problem but if you do, there is a relatively easy and inexpensive solution to a more and more common problem.

So if the problem doesn't go away after I flush the AT, then it's likely to be a malfunctioning solenoid in the rear housing, right before the rear diff.

You don't have to pull the tranny or the pan. You need to remove the rear extension housing, and the solenoid is in there.

There's a good posibility the clutches need to be replaced if the solenoid is toast.

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Ok, so now the worst case scenario is (I like planning this way, that way I'm pleasantly surprised):

1. Transmission is toast. (It isn't, but it's not exactly "butta", so it may need a rebuild, or a damn good cleaning)
2. Clutch packs and "duty solenoid C" are toast. Likely. Very. Replacing them, might as well find a remanufactured transmission.

In the meantime, it's off to NAPA to get some Lubegard and ATF fluid.

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Last night I went and had the wheels balanced at Walmart (who did a better job than a dedicated wheel/tire shop). They did take an hour longer, but that's the tradeoff for $30 balance.

I also drained and refilled the AT with Quaker State DexronIII ATF, about 3.75qts and added a bottle of Lubegard's ATF Protectant.

Went for a quick drive around the neighborhood. Backing out the driveway, the transmission felt "heavier", like it was sloshing. Heading down the road, I made a 90deg right turn (the "good" side) with no major issues. Got to the end of the road, made a left 90deg. turn. (Cringe time)

Where was the shudder? There was a little there, but it was greatly reduced! I kept driving for about 10mins, taking every left, right turn I could, and going around some 25ft dia. roundabouts (left turns). MUCH better.

I have to drive to work now, so we'll see how things go. Perhaps this weekend I'll install the new tranny mount to see if that helps cut down on some of the vibration.

I'll post a followup in a couple of days, but the $20 I spent last night on fluids may have postponed a $700+ bill.

PS. The wheel balance had nothing to do with the torque bind. I had torque bind prior to the wheel balance issue.

[Huffer]

Ok, seeing as no-one actually cares... :P

Two days after the AT drain and refill, + lubegard, the car is still performing pretty well.

I can't make full lock <5mph turns, but I can make 75% lock <5mph turns with just a touch of torque bind.

I also sorted out the freeway speed vibration issue, found that the shop that had mounted the wheels back onto the car had:
1. inflated tires to incorrect pressures
2. mounted the wheels without sitting the lugnuts totally flush.

Mental note to self - essential tools you must have in your arsenal:
1. lightweight racing jack
2. impact wrench - cordless
3. torque wrench
4. assorted impact drive sockets

[shazapple]

so many stories of shops doign everythigns wrong , this is why i do stuff myself!