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My 95 manual trans Legacy has a bad vibration that occurs when releasing the clutch.  It feels like the drive training is 'bucking'.  If clutch is released carefully it is smooth with no vibration, but if a bit more torque is applied I get the bucking.  I think it might not actually be the clutch since when released carefully it is totally smooth with no vibration.

 

It's been tough to pin down since it only does it excessively when actually driving, more when starting from a stop, but also when shifting gears if motor speed is not matched to next gear. 

 

I've tried blocking the car or holding the brake while letting the clutch out to slip a bit under torque and I don't get much doing that.

 

I'm imagining this might be a motor mount but haven't seen good access points to check that.

 

It seems particularly bad when starting in reverse, especially if backing up a hill a bit.

 

Any ideas on how to troubleshoot this or check the mounts without having to tear it all down?

 

Thanks.

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A faulty knock sensor can cause rough running and bucking until a certain rpm. Those often fail after a long time.

 

But  yeah it sounds like mounts. Although when I had a faulty engine mount, it helped my car to dump the clutch asap.

I would get shaking when slipping the clutch, but after taking off there was no more shaking, even shifting into 2nd at 5 or 10 mph

Edited by sparkyboy

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Also check the 'dog-bone' that connects the rear-top of the engine to the bulkhead, just below the windshield.

It's unlikely that this part would fail, but it would only take 10-seconds to do a visual check.

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With all the brakes on, try engaging the clutch slowly in first gear.

The engine will move around a bit, but not much.

If you can see the engine moving a lot (upwards or side to side), it could mean failed engine mounts.

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Well I finally got a chance to follow up on this.  I blocked it up on ramps, chained it to my truck, and looked at the mounts as clutch force was applied.

 

I didn't see much but it seemed the passenger side front differential mount had a bit more movement than the right side.  (The one right in front of the rear wheel)

 

I took the bracket and bolt out and the mount looked intact, but when I looked closer I saw a good portion of the rubber was cracked away.

 

I cut some 1/4" thick fiber reinforced rubber washers from some heavy duty radiator hose and sandwiched them above and below the mount to keep the diff mount from being able to move far enough to hit the frame.

 

This fixed the problem.

 

Seems a mount swap is pretty simple here, but how do you get the old one out?  Seems some high force press is needed which probably means disassembling the entire differential and mount from the car.  Not worth it.  The rubber washers I made should last a fair while.

 

If one were to want to change the mount bushing, is there a way to get it out without removing the whole diff mount?  Maybe some special tool?

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