I recently pulled the engine on my 2004 outback and replaced the head gaskets along with other items including the clutch, pressure plate, throw out bearing, and idle bearing.  All new after market parts.  Once the engine is warmed up when letting out on the clutch it has a vigorous shake.  The one thing I did not do that I wish I had done is to have the flywheel machined.  Could it be the flywheel causing this?  If so why would it not do it when the engine is cold.  When the engine is cold the clutch is very smooth.

Unfortunately this is pretty common with aftermarket clutches. The flywheel isn't typically the cause but a non-flat flywheel can contribute.

 

I've had good luck with Exedy clutch kits. Exedy/Daikin makes the original clutches for Subaru. Lots of people recommend them, and they're typically trouble free.

 

Another consideration with the clutches on these cars has to do with the release bearing. The bearing rides on an aluminum quill on the transmission, which is prone to wear. When the quill wears it causes the bearing to twist a little sideways when it is pushing against the fingers of the pressure plate. This causes uneven engagement of the pressure plate with the clutch disc, and causes part of the pressure plate to heat up and get "grabby", and causes a shudder as the clutch disc grabs and slips between the pressure plate and flywheel.

 

If the release bearing is a loose fit on the quill on the transmission, there are sleeve kits available that are slid over the quill, and a slightly larger diameter release bearing is used to fit over the sleeve. This prevents the bearing from twisting, and helps maintain even engagement of the pressure plate surface.

 

I would recommend getting the flywheel machined at this point. Once shuddering starts happening, it will wear the flywheel unevenly and possibly cause the same problem with another new clutch.

Thanks for your reply.  What is the easiest way to replace the clutch.  Pull the engine, or pull the transmission.

Hands down pull the engine !

I've done both and it mostly depends on what tools you have access to. If you have (or can get) an engine lift, that's much better than lying on the ground with a floor jack to raise/lower the trans.

 

It is slightly more work to pull the engine, but if it needs any other work such as oil seals, valve cover gaskets, separator plate seal, etc., pulling the engine gives much better access.

Thanks guys.  I have already pulled the engine once so I a familiar with it.  I have access to an engine hoist so pulling the engine is the way to go.  Because it does it only when it is warmed up and most of the time it is back and forth to work I am going to put up with it for now.  If it gets worse I will tear into it.  I want to get as much as I can out of the new clutch I already put into it.  I wish I would have checked this forum before I put an after market clutch in it.

 

By the way fairtax4me I put a sleeve and over size throw out bearing on when I put the new clutch in.  So it has to be either the clutch plate or the flywheel causing the problem.  I will either replace or machine the flywheel and buy a reputable clutch plate.  Thanks again for your replies.