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Driveline issues - Updated!

1044 Views 5 Replies 4 Participants Last post by  pneff23
Hey all, been lurking here for a bit but first time posting. I have been scouring all these boards hoping to find a solution to my problems, but no luck. Heres some background info. I have a 2001 5spd L Forester, with about 128k on it. Starting last fall I was getting some off and on scraping, clunking, and rubbing noises under the car (I was initially thinking bad u-joints). I took it into a local shop, they didn't hear anything and said everything looked good.

This went on for a while, until eventually one day I got a bouncing feeling in the back end when I first started driving in the morning. If I put the car in neutral the bouncing stopped. This would only last for about a half mile then smooth out. Took it in and was diagnosed with a bad rear differential (they said they see it all the time?). Shop replaced it with a used one, then found that my u-joints were seized and super crunchy, so they swapped the driveshaft for a used one as well.

I still have the bouncing in the back end first thing in the morning, though goes away after pretty quick and its not nearly as bad. However, ever since that work was done I have a vibration at highway speeds, but it only starts after I have been cruising at 50+mph for at least 5-10 minutes, and I feel from the middle/back of the car. No shake in the steering wheel, and no wobbling feeling. Just vibration. Before that everything is perfectly smooth. I brought it back to the shop that did the work, but they didn't take it for a long enough test drive on the highway and were unable to find anything wrong.

Just recently brought the car into another shop to get some fresh eyes on it. They took it for a long test drive, felt everything I was talking about. They check the u-joints on the driveshaft and said they were pretty notchy and most likely the problem. I pulled the driveshaft out last night, and they were right, all the u-joints were pretty rough feeling. Put in a new aftermarket, no changes at all in the symptoms. Bouncing from the back end still first thing in the morning, a vibration after driving on the highway for 5-10 minutes, but drives perfectly smooth other than that. Not sure where to look next. Could the replacement rear differential be causing this, or did something completely different start showing symptoms at the same time the work was first done.
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First thing in the morning thing has me thinking maybe cold tires?
^ agree - maybe the tires are flat-spotting overnight?

G'day & Welcome @pneff23 What PSI? Do you have quality tires?
it was bad u joints and carrier bearing , it can damage differential pinion if bad enough the drive shaft need to be able to flex slightly as angles of stress vary under load, check your motor and transmission mounts now too
@pneff23 "If I put the car in neutral the bouncing stopped." Is this still the case (I missed this point initially)?
Its been a while but figured I would reply now that I think I have things mostly figured out. Turns out it was a couple of things (maybe), u-joints were definitely less than ideal on the driveshaft, cold pavement and snowtires not getting along (first winter parking on pavement ever, never experienced flat spots before this), and a real bad alignment (thrust angles were pretty off). Alignment wasn't showing any of the usual symptoms, but apparently when driving at highway speeds for longer periods of time something must have been getting stressed. I still don't want to fully accept that its fixed, but I'll take it for now.
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