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Old 09-18-2018, 08:24 AM   #1
fly_25
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Member#: 467978
Join Date: May 2017
Default Deep/low aggressive vibration at certain speeds

Good morning all, my 2004 outback has a very aggressive vibration that can be felt in the seat at 80-90 km/h, not faster and not slower. It seems to get worse when I let off the gas within these speeds as the vehicle coasts. It's not engine related and I can't really feel anything in the gear shifter either (manual trans). Any ideas as to what could cause this? Also I swapped the wheels for a different set and still same problem
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Old 09-18-2018, 01:30 PM   #2
yarrgh
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Member#: 80465
Join Date: Jan 2005
Chapter/Region: RMIC
Location: Bailey, CO
Vehicle:
2001 2.5RS
Black Diamond Pearl

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Isolate the engine from the transmission. Get faster than the vibration speed, clutch in, and coast down through the vibration speed. See if anything changes. If not, it's definitely in the drivetrain. Given the observations, it's likely not the engine, this will confirm that.

One thing aside from wheel imbalance could be a driveshaft imbalance. You may have to get underneath, slowly rotate the driveshaft by hand (in neutral, rear wheels off the ground) and look for any sort of external balancing weight that's missing.

Look for any bushings in the drivetrain that are worn/missing. Rear diff, trans, and engine mounts are all I can think of at the moment.
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Old 09-19-2018, 12:27 PM   #3
fly_25
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It's definitely not engine related, I've had clutch in, out, coasting, nothing the engine does helps the vibration. Although the vibration is considerably worse when let off the gas and put the car under no load. I didn't notice any missing weights or anything unusual about the driveshaft, but what I did notice is that the driveshaft does not look like the stock driveshaft for this car. It's still a 2 piece with the carrier bearing but it just has a different design, maybe from another type of Subaru? Could the different driveshaft design cause the vibration?
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Old 09-19-2018, 02:44 PM   #4
Charlie-III
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Chapter/Region: Tri-State
Location: USA, North NJ, 07456
Vehicle:
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

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Quote:
Originally Posted by fly_25 View Post
It's definitely not engine related, I've had clutch in, out, coasting, nothing the engine does helps the vibration. Although the vibration is considerably worse when let off the gas and put the car under no load. I didn't notice any missing weights or anything unusual about the driveshaft, but what I did notice is that the driveshaft does not look like the stock driveshaft for this car. It's still a 2 piece with the carrier bearing but it just has a different design, maybe from another type of Subaru? Could the different driveshaft design cause the vibration?
Could it be?
Sure.

If it was fine before but sucks now, I will assume it was fine.
Maybe center carrier failed. In general, no decent way to fix that other than replace DS.

Stupid check, make sure DS hardware is snugged up.
Minimal play in DS (hard reach around exhaust, etc......).
Decide or check back.

A Subaru center bearing support is hard to do on your own. Really need to replace.
Yes, penny pincher hardcore may find a way, but........forget about it.
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