My wife's Outback XT has developed what can only be described as a shudder under load. I noticed it a couple of months ago at full throttle. Now, any time that there is a load on the engine it shudders.. Smooth idle, smooth cruising. Terrible acceleration or maintaining speed on a hill.

 

When was the last tuneup?  I.E. Plugs, Wires, PCV Valve, Air Filter, Fuel Filter, etc....?

How many miles?

 

Check engine light on? Blinking?

If not, probably drivetrain related. The u-joints on the rear driveshaft should be checked.

No check engine light, new plugs at the time of the head gasket replacement 5,000 miles ago.

It feels mechanical, not like a combustion problem.

have the axles ever been replaced?  new/aftermarket axles are suspect.

 

vibration under load - according to my definition i almost always:
1.  aftermarket axles (even brand new ones - brand new would be a red flag actually) - the inner joints particularly.  a very bad OEM axle could do it as well - but it would have to be exposed/deteriorated substantiall

 

2.  front differential.

 

3.  driveshaft ujoints

 

other things could be described as "vibrations under load" - but would typically have other symptoms/descriptions associated with it - so that's why i qualify my statement as ""according to my definition".  if what you see is true, complete, and as i'm accustomed to seeing on Subaru's then #the above are the usual culprits.

Axles are OEM, cv boots are great and the CV joints are quiet.

I'm thinking u-joints. Taking it into the driveline shop tommorrow.

Again, I am going to put my money on the torque converter.  Classic symptoms if the engine is running correctly.

 

http://etereman.com/blog/transmission-care/diagnosing-torque-converter-problems-procedures-for-all-vehicles

 

Emily