Rear Diff question...

[Kilroy]

I have been getting a mild 'fluttering' type feeling throughout the car when driving at highway speeds for the past couple of weeks and have been trying to track it down. The steering wheel seems to be rock solid and I more feel it through the seat (very little to feel really, but there is something there). It is not a vibration, but more of a feel that something is loose and fluttering in the wind. I have checked the external body of the car (found a missing screw in the grill and replaced it, thought I had nailed down the fluttering) and everything is securely in place. On the way home tonight I thought it might be in the rear of the car as I felt it through the seat and not the steering wheel, so I crawled under the car as soon as I got home from work (25 miles on the highway @ ~70 MPH). I put my hand on the rear diff and found it to be quite hot. Not hot enough to have to remove my hand, but very close. The temperature outside was about 55F, but with the air moving past the diff it would be quite a bit cooler.

 

Should the rear diff be this hot?

 

Has anyone encountered this type of 'fluttering' feeling throughout their vehicle?

[idosubaru]

is this on a 1990 legacy? what vehicle and how many miles?

 

there are a number of options but my first guess is a ujoint in the driveshaft. check the ujoints for any play. if it's very light and "flutter" like you said, you might not notice any problems unless it's removed or you have a really good eye for spotting seized ujoints. the joints could be seized instead of having play in it and in those case they are very hard to diagnose without actually dropping the driveshaft down.

 

before going through that you might want to make sure it's not a wheel out of balance or a bad/old tire as well.

 

i'm doubting it's your diff, but it's not impossible. they normally like to make noise, not just vibrations. there are a couple other things to check but i think they are less likely so im going to stop there.

[Kilroy]

1990 Legacy Wagon 4EAT with 106,000 miles. I agree that the rear diff would be making noise if there were a problem with it. I wasn't concerned that it was the problem, I was just concerned with how hot it was.

 

I had the car up on ramp on Monday and did a thorough check of the driveshaft and it is solid from front to rear. I looked at the U-joints, but I don't think I would be able to tell if they had seized.

 

I have ruled out the problem as anything related to a tire/wheel due to there being no shake/vibration in the steering wheel.

 

It is quite hard to describe this 'fluttering' that I feel. It is like I am feeling it through my body, like super low bass on a good subwoofer. At first I was not even sure it was there, but after a period of 2 weeks I am very sure of it. I also thought it could have been my rear spoiler 'fluttering' in the wind. I checked it and it is solid and tight. It isn't a spoiler like on the newer Subarus, but an aluminum fin type that creates a downdraft over the rear window.

 

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