Got that lovely howling sound...

[Kilroy]

I've posted this in uklegacy.com, but I'm hoping to get a little more information from this side of the big pond. My vehicle is a 1994 JDM BG5 GT Auto with a 2.35L Hybrid.

First post:

It now looks like I will be needing to replace/repair my rear differential as it is howling like a beast. I replaced the original differential oil a few weeks ago (tiny shaving particles on the drain magnet) with full synthetic 75w90 and I don't think it liked that very much. About a week after changing it, I noticed it howling on the way home (25 minutes of driving at ~120 km/h) and crawled under the car to put my hand on the differential and it was so hot I couldn't keep my hand on it. I drained the synthetic oil (no particles on the drain magnet) and added Lucas to see if it would make any difference, it did not. I swapped all of my tires (they were ~1/2" different in diameter between the largest and smallest) and put on a set that were only 3/16" different in diameter, but still had the howling and hot differential. It seemed to be hotter towards the front of the differential, where the drive shaft is connected. I am thinking that perhaps the bearing is no good. I'll be taking it for a drive today and using a laser temperature gun to find the hottest part of the differential housing, this may help me determine if it is the bearing or an internal problem.

How difficult is it to remove the rear differential for a replacement bearing or a rebuild?

Second post:

After about a 15 minute drive, I backed the car up on ramps and slid underneath with my laser digital temperature gauge. The rear of the diff was 95F and the front of it was 110F. That would seem to indicate that the bearing on the drive shaft side was failing. Then I aimed the temperature gauge at the rear drive shaft and it was at 130F, towards the front of the drive shaft it was at 160F! Perhaps the issue is actually with the center differential and the heat is being transferred down the drive shaft to the rear differential. At 160F I was able to keep my hand on the drive shaft, but when I checked my rear differential last week it was so hot I couldn't keep my hand on it which would indicate a temperature of 180F+. If the rear was that hot, I can only imagine how hot the front differential must have been (assuming the heat was being transferred).

I'll need to take it for another short drive and get the front up on ramps to verify that the center differential is indeed getting as hot as I suspect.

Anyone have an idea why it would suddenly be getting this hot after a fluid change? Suggestions for a fix?

[Legacy777]

Do you hear any noise without the car moving? What about with the clutch depressed vs. not depressed?

Not sure why you started having the noise after a fluid change. My Impreza trans is pretty noisey and it started doing it after I put a synthetic trans cocktail and then went to dino oil. It's been like that for a couple years now. I'm just going to keep driving it untill it dies.

[Kilroy]

No noise when the vehicle is stopped, it gets noisier as I pick up speed. At first I thought it may be a wheel bearing, but the hot diff seems to indicate otherwise. It did sound like the rear end originally was the culprit, but noise travels through the drive shaft.

Automatic transmission.

[Legacy777]

If it's automatic you do not have a center differential, but rather a clutch pack setup.

Try inserting a fuse in the FWD fuse holder and see if that changes anything about the noise.

[Kilroy]

Tried the fuse thing as I originally had a 1990 Legacy Wagon EJ22 N/A and knew about it. Unfortunately, this JDM unit LOCKS the diffs with the fuse in. Surprised the heck out of me when I got into the car and there was a "DIFF LOCK" in bright red showing up on the instrument panel.

This makes me wonder if my solenoids have finally packed it in completely. I am having trouble with the transmission as follows:

Due to the substantially increased horsepower, I am having an issue with the automatic transmission at this point as well. When on the highway at cruising speed, everything is great. When I put my foot in it (with no kickdown to a lower gear) it picks up great until the secondary turbo spools up at ~4000 RPM. At that point the torque converter can't handle the sudden increase in power and the RPMs immediately spike to over 5000 RPM, it doesn't seem to lock up quick enough or solenoid B is failing.

[Legacy777]

Hmmm....that's odd.

Can you give any more detail on the car? Is the trans the original auto trans that came with the car? Everything else original mechanically besides the motor?

[Kilroy]

Hmmm....that's odd.

Can you give any more detail on the car? Is the trans the original auto trans that came with the car? Everything else original mechanically besides the motor?

Everything else is original on the drivetrain. See the post above your previous post.

[Legacy777]

Did you drive the car at all with "diff lock" light on?

Unfortunately, I don't have any JDM manuals for the 2nd gen legacies.

Whats your trans fluid smell and look like? Smell burnt at all?

I'm not sure what to tell you. Hopefully someone else can provide some additional input.

[Kilroy]

I did drive the car a short time with the "diff lock" light on, but there seemed to be no difference to the sound. I would actually like to try it on the highway to see if it gets rid of the RPMs spiking when the secondary turbo comes on.

Transmission fluid was recently replaced as well and looks great with no burnt smell.

I'm seriously considering having the transmission rebuilt or at least the Trans-go kit installed. Word is that these transmissions are only good to ~350HP and I am hovering around that mark at this point, but I'm also considering upgrading the turbos (primary is starting to whistle, may just be a simple air leak though) while we are installing the 3" downpipes. It has to be torn down to the turbos for the downpipes anyways, I might as well take care of any issues I am currently having all at the same time.

[Kilroy]

Well, I put the fuse in again and had my brother drive the car slowly back and forth while I watched the drive shaft. Normally this would put the vehicle in FWD mode and the drive shaft shouldn't turn. This is usually for towing purposes.

Sure enough, the drive shaft rotated. Apparently the fuse on this particular JDM AWD vehicle is not installed for towing purposes. To be honest, I have no idea why one would want to "DIFF LOCK" the vehicle and I'm not sure how it would apply here unless it is now sending a signal to the solenoid B to lock up the torque converter at all times.

Anyone else have an idea what it could be doing?

[Legacy777]

The drive shaft is going to turn. The reason it is going to turn is because the rear wheels are turning, and spinning the rear diff gears, which in turn spins the drive shaft.

To perform this test, you need to jack up the car off all four wheels, insert the FWD fuse and see if only the front wheels turn. The rear wheels may spin a little, but it shouldn't be anything like the front.

Then repeat the test with the fuse out to see the difference.....

[Kilroy]

Thank you! I knew there was something I was missing with my troubleshooting, it was so obvious. I told my brother that what you described is another way to test it, but it was just easier at that time to have him drive a little.

I have 2 jacks and 4 jack stands, I'll give it a shot tomorrow.

[93forestpearl]

You could remove the rear section of the driveshaft leaving the carrier bearing in place. This would be the right way to do the test, since there will always be a little drag on the transfer clutch.



Are you absolutely sure it's not a wheel bearing?

[Kilroy]

You could remove the rear section of the driveshaft leaving the carrier bearing in place. This would be the right way to do the test, since there will always be a little drag on the transfer clutch.



Are you absolutely sure it's not a wheel bearing?

I've considered the wheel bearing quite a few times, but it keeps coming back to the temperature of the rear differential and the drive shaft. There is no heat in any of the half shafts to indicate a transfer to the differential. Of course, there may be two separate issues (a wheel bearing AND a drive line issue).

If a wheel bearing is causing the sound, it should heat up the hub more than the other 3. I'm going to take it for a drive later this afternoon, I'll shoot the laser temp gauge at the hubs once it's back in the shop.

[Kilroy]

I put the car up on jackstands yesterday and tested to see what the fuse under the hood would do. As it turns out....absolutely nothing when on jackstands. All 4 wheels turned with the fuse in AND with the fuse out. I had a friend try to stop each wheel from rotating when I applied a light throttle. The front ones would each stop with just one hand lightly applied to them, but the rear ones required a good grip with both hands and some force to keep them from rotating. This is with both the fuse in and out. So it would seem the fuse does something that I don't understand (it certainly doesn't put it in FWD mode) or something is messed up within the system that doesn't allow it's signal to read correctly and all I get as a result of putting it in is the light on the instrument cluster that says "DIFF LOCK".

I also drove the vehicle home and to the shop twice since yesterday, each time I stopped I used the laser temperature reader to check the rear differential and the hubs (in case a wheel bearing was causing the sound). This is the same drive that I originally found my rear differential so hot that I couldn't keep my hand on it and figured it was ~180F. This time the laser read ~110F in the center of the differential, but hotter (up to 170F) as I went to the bottom of the differential. I noticed that the bottom of the diff was considerably closer to the 3" exhaust pipe than the center, so I am convinced that the heat from the pipe (220F) has been causing the heat build up. I imagine the original 2" exhaust was far enough away that this wasn't as big of an issue. My question now is, how hot is too hot for a differential to be?

As for the temperature of the wheel hubs, they all seemed to quite normal. The front ones are about 25F hotter than the rear ones each time I check, but they also do most of the braking and heat up quicker.

So now where does this lead me? What is the cause of the howling I am hearing? I think I will have to check the carrier bearing in the middle of the two drive shafts next for excessive heat build up. I'm running out of things to check on.

EDIT: I just did some reading and it seems that anything under 200F is fine for everyday driving, up to 240F if you are towing. At ~240F, the paint will start to bake and peel off of the diff cover. The flash point of 75W-90 gear oil is 400F+, depending on what brand you are using.

[douglas vincent]

Have you tried putting it on jack stands and just driving it and listening for sounds?

[Kilroy]

Have you tried putting it on jack stands and just driving it and listening for sounds?

I'll keep that suggestion in mind, I may be able to do that tomorrow. I just don't feel comfortable having the wheels spinning at highway speeds when all four wheels are off the ground.

"Sh!t happens."

[Legacy777]

Do you have the original owner's manual for the car? Does it talk about the FWD fuse at all?

On the north american cars, there is a FWD specific light that will come on. It's possible the overseas cars didn't have that feature, but I've never seen anything documented one way or another.

[Kilroy]

JDM vehicle.....guess what language the manual would be in if I did have it.

I mentioned further up that I had expected to see a FWD light come on when I inserted the fuse which is why the DIFF LOCK light shocked me.

[Legacy777]

Hmm. Only thing I can suggest is to scan through this overseas Liberty Manual. It is likely to be similar to the JDM models.

http://www.main.experiencetherave.com/s ... SM_-_FULL/

Section 3 is the trans.

[Kilroy]

There are two types of Subaru Automatic Transmission.

The ACT4 type, commonly fitted to lower-spec and USDM vehicles. 90F: 10R default torque split. The fuse puts the transmission into Front Wheel Drive Mode.

The VTD type, commonly fitted to higher-spec and JDM vehicles. 35F:65R default torque split. The fuse locks the centre differential.

The issue regarding the hot rear diff is interesting. I've heard of a couple of SVXes where brand new replacement diffs have caught fire within a few thousand miles of being fitted. Unfortunately there was never any firm conclusions about the cause.

I raised the car on jack stands a couple days ago and had my brother listen with a mechanic's stethoscope for any indication where the sound was coming from. It seems that the rear passenger wheel bearing may be the culprit. It isn't bad enough yet to cause any additional heat, thus my failure with tracking it down with the laser temperature gun. I pressed out the bearing last night and the hub side did feel rough when I spun it with my hand, so I'm hoping I'll be on the road today with the situation rectified.

On another note, I soaked my brake rotor in vinegar (5% acetic acid) last night to see how well it would get rid of the rust build up. I'll try to post the results within the next couple of days

UPDATE: So after all this fkin around, it turned out to be a wheel bearing. It hadn't worn bad enough yet to produce additional heat, so the laser temperature gun wasn't showing anything out of the ordinary.

I soaked my parts in vinegar over night and now they all look brand new. I have the photos on my camera at the shop, I'll post them up next week when I'm there.

No more howling, what a relief.

[Legacy777]

Good deal!