[quote name='raydog' post='63109' date='Nov 14 2008, 04:33 PM']Roland what kind of problems were you getting from the other mounts?[/quote]
It actually happened while I was "inspecting" the car while I considered purchasing it. If I remember the history correctly, the PO had some work done on the car, and had something like 2-3 larger repair bills in the prior months, and I think that was one of the reasons he decided to sell. So when I went for a test drive, it had just come from the shop with new engine mounts. I noticed a shaking, or rumbling, almost like it was running rough or missing, but it wasn't. I seem to recall there was almost a binding effect in the drivetrain, as if this weren't lined up correctly. Just some type of shaking at idle. So I told the PO that this wasn't right, that something is wrong. He said he would take it back to the shop, and the result was they replaced the engine mounts with the part for the Tip car. When I went back for the "real" test drive this symptom was gone. So I can't even say 100% for sure, maybe they found some other problem that was the real source, maybe the alignment is sensitive so that this symptom only appears on some cars. Wish I knew more about it, but the reason I expressed caution is this symptom of binding/shaking that I thought I felt in the drivetrain at idle.
Other than drivetrain alignment issues, the only thing I can think of is the torque converter. Perhaps with this part, at idle, the torque converter is (in a way) sending backward torque to the engine (like a braking effect on the torque tube at idle). So the engine is trying to turn normally and because of the torque converter there is some "back pressure" (rotational force) contradicting the rotational direction that the engine would like to turn, and perhaps this means additional forces on the engine mounts (I am making this up and throw it out there for discussion!).
And come to think of it, when I release the brake, the car moves ahead fairly well. I wonder if Porsche uses a more aggressive torque converter compared to other cars to enhance performance (compared to the '63 Pontiac I once had). If it is an aggressive torque converter I can see that maybe it causes more force on the motor mounts. Maybe that is why they are more heavy duty motor mounts (again, a guess...)
Roland
