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Rear Diff, Bearing, Transfer Case?

13K views 11 replies 5 participants last post by  jg1891 
#1 ·
Hi new memeber here.
I have a 98 Outback Wagon limited AWD with 148,000. I have a problem which I have been unable to get a correct diagnosis.

I am getting a mild "grinding" or whining noise when I let off the gas. It sounds like it is coming from under the passenger side wheel well. Initially it just happened at higher speeds(50 and up). Now it is becoming more noticeable at lower speeds. If i give the car gas the noise stops instantly. Let off the gas and it is right back. It is as instant as flipping a switch.

Tonight I put the "2wd" fuse in to try to isolate the problem, and the noise was gone.I Put the fuse back in and it came right back.

I have an appointment to have a third diagnosis done in the morning and was wondering if anyone has had this problem before.

Thanks in advance for any and all replies.

JG
P.S. Tire pressure,brakes,etc all are good
 
#2 ·
Sounds like throw out bearing in the manual transmission is failing. You didn't say if it was AT or manual but given my MT 5spd did this same thing when the bearing started to fail seems right about dead on with your description I'm going to put my money on it that you have a manual transmission and thats what your hearing. Mine surfaced at 144K
 
#5 ·
The AT has a front diff which is totally isolated from the AT it is not uncommon to discover owners who serviced the AT but never serviced the front diff- you can see where thats headed. Enough miles down the road the front diff starts to fail given it was never serviced.

That could be your worst case situation. The wine could be a dry diff ie diff with no gear oil in it- higher speeds generate noise first given what little oil is left gets whipped up and thinned out by the spinning gears.

Have the front diff serviced with a good quality gear oil and you might have avoided an expensive repair.
 
#6 ·
doesn't sound good - front differential is seemingly likely.
check the oil level in the FRONT DIFFERENTIAL
change the gear oil and look for junk in the oil
changing the oil may help.

also - the front DOJ's (inner CV axle joints) can make noises that are load dependent as well, typically on acceleration. yours doesn't sound exactly like they typically do when this happens but have the axles ever been replaced?

if they're aftermarket axles then they are more likely to have issues.
 
#7 ·
Thanks for all the replies so far.

So, on a Subaru there is a front, middle, and rear differential right?

Like I said in my initial post the noise definitely sounds like it is coming from the rear passenger side of the car. Near the rear passenger wheel well.

Would the front differential make a noise in the right rear of the car?

I am getting ready to drop the car off this morning. Will report back.

Thanks again for the help!!
 
#8 ·
When the FWD fuse was installed, the noise disappeared. Seems to me that if the noise was from the transmission or front differential, it wouldn't change, at least not much when the fuse is in place. Instead, this suggests that the noise is coming from the rear drive train, and disappears when there's no power being applied (transfer clutch is disengaged by the FWD fuse).

Same possible causes as were suggested, such as old or low gear oil, or a differential pinion gear issue, still apply, but for the rear differential.

I'd also consider a worn/failing U-joint or CV joint in the propeller shaft, which is silent when torqued, but exhibits it's "sloppiness" when the gas pedal is released. This also would apply to the rear axles.

A detailed inspection of the rear drive train is the first step. Then perhaps driving the car while someone else listens, perhaps from the rear seat or even in the cargo area, or while the car is on a lift.

So, on a Subaru there is a front, middle, and rear differential right?
Not exactly. There's a front and rear differential on all AWD Subarus. The "center" differential is found in the manual transmission, and automatics that have the VTD system (primarily the 5-speed automatic). The front differential is inside the overall transmission case near the front, but with the automatics, is internally separated from the rest of the transmission. The rear differential is clearly separate and visible at the back of the car. The center differential, where applicable, is inside the transmission, toward the back of the case. Your 98 would have a front differential and a rear differential.
 
#9 ·
Thanks for the information Plain.

Yeah, I think the problem is definitely related to the rear portion of the drive train. In 2wd the noise was completely gone.

I just wanted to be able to provide as much "help" for the third mechanic who was looking at this today. The first two mechanics had some pretty laughable theories.

Aamco drove my car for 10 minutes and never even put it on the lift.
They suggested a complete transmission rebuild. Quoted me $3600 at minimum.
Wilmington NC Aamco. Stay AWAY. Maybe the shadiest place I have ever seen.

Second guy told me it was the fuel pump going bad because of the location of the noise(under rear passenger seat). He almost had me believing him until I thought to put the 2wd fuse in and that put his diagnosis to rest.

Anyway I hope by giving this 3rd guy a little more to go on he might be able to get an accurate diagnosis. He said he has never seen a problem in the rear differential in a Subaru however he did mention "transfer case".

Again thanks for the help everyone and I will post results this afternoon.
 
#11 ·
AMCO historically is known as the king of rip off. So right off I would consider their advice with a grain of salt.

Subaru AT has a front diff and a rear diff thats it. They do not have a traditional transfer case they have a very basic clutch system that transfers power to the rear.

Probably the smart move is to just do a basic diff service front and rear with proper gear oil.

The rear end is pretty **** simple all you have is a diff - a drive line and two axles with CV joints. A wheel bearing in the rear wheel will make some noise which could be what your hearing. A cv joint when it gets loose and worn etc clunks and clicks very different than a constant gear noise or noisy wheel bearing.

My advice take it to a subaru shop and AVOID AMCO like its a case of the herpes!
 
#12 ·
Thanks again for the help everyone.

The problem was solved today.
This is the quote from the invoice: We found the rear differential cross member was "grounding out" on the right chassis bracket. The bracket was bent, so we straightened it as best we could.

$78 dollars and the noise is now gone.

He said the only way it could have gotten bent was from my previous mechanic improperly putting my car on the lift.

However, while doing their courtesy inspection they gave me an estimate of well over $1600 for a bunch of totally unrelated stuff that I wasn't aware of and my previous 3 mechanics this month most of overlooked as well.

I really do need to find a good mechanic in my area. I think the guy I went to today is at least knowledgeable but he quoted me $171 just for new spark plugs so I doubt he will be my guy.

I'd like to go more into this guys other estimates but I think I will do that in another thread.

Thanks again for your help every one!

p.s. Subie, I did a little research on Aamco after they tried to !!!! me and I found tons of people who had the same thing happen to them. They also have class action lawsuits against them and entire websites devoted to people unhappy with them. The guy I dealt with even went as far as to tell me about "short term no interest loans" that he would have "available later in the month" for customers like me. Like me? WTF is that supposed to mean? LOL
 
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