I have a 2000 Legacy GT manual transmission, over the past several weeks my car has this horrible shudder/vibration when going from a stop or slow roll. It stops once I hit 20 mph. It is getting increasingly worse and no matter how slow or fast I take off it still does it. What do I do and what could it be?

bad clutch??

Sounds like bad bushing on the driveshaft carrier bearing.

Could also be an axle problem.

I's suspect the driveshaft/carrier bearing /u joints first and the the clutch. 

The clutch seems to be fine...I was just worried it was the transmission. I just had to rear transmission seal done a month or so back.

Did this start right after the seal was replaced?

yes actually, Id say 2 weeks at most

Loose inner CV joints can cause a vibration w/accellerating.

Check them for play.

Sometimes they are bad w/o detectable slop.

Had one once that required axle replacement to finally diagnos.

Pull down the heat shield in the middle of the car and see if the center support bushing is messed up.

The shop could have bolted the support bearing bracket on upside down and thrown off the driveshaft angle which will wear out the bushing very quickly.

 

Also check the 4 bolts that secure the two halves of the driveshaft together at the flange by the support bearing, and the 4 bolts that secure the driveshaft to the rear differential flange. Make sure they're all tight.

It sounds like "chuckle" to me, usually it happens in the 25-18 MPH range, It is caused by a worn side gear shoulder, usually the the case and gears must be replaced