kru911

Recently had replaced at the same time: clutch (incl flywheel, IMS, RMS, et al) and engine mounts (OEM replacement). I now notice ever slight vibrations that I don't recall feeling before. Seems to be via the seat, not the steering. The shake varies with speed and surface. And nothing unusual at idle.

I brought it back to the shop, and was told that the car drove fine. The tech thought perhaps I'm feeling more of the road and suggested I could lower the rear tire pressure a little (currently at 44psi).

With new motor mounts, should I expect to feel the road more? Perhaps I simply need to appreciate the car is "tighter"?

Pcar is MY03 Cab w/ ROW M030 (suspension 4.5 yrs old).

Silk

Could be that some engine vibrations particular to your car are now transmitted different to the chassis with the new mounts. Before you did not notice them due to different attenuation characteristics of your old mounts. I would suggest to drive and see if it changes in the short term. No idea if new mounts need to settle a bit.

Does the vibration disappears after a while? Lets say that it goes away after half an hour driving after cold start?

Driving seat vibrations are sometimes related to rear axle tire unbalance. But that seems not very logical because you did not change anything there. Check again tire pressure and see if there is any uneven wear on the rear tires.

Maybe old vs new mounts cause a slight difference in weight distribution in the rear. which cause a slightly altered tire alignement, which needs some miles to wear off the tires till they are properly set in. Anybody can comment on this one, if it is really possible?

gnochi

Speed and surface tells us that motion is the cause, not the engine. As it is, your tire pressure is almost certainly way too high. Depending on model/tire size/etc I've seen 32F/34R recommended most frequently.

Silk

Unless it is a semi-track tire, which has extra stiffness in the sidewalls, I would not go so low for the rear. I think 34-36F/39-41R is a better range to start and see if it helps.

kru911

Much thanks for the replies. At least nobody's suggested a mount is not bolted down or I the new flywheel is unbalanced (though the latter would be obvious at idle, I think).

It's been less than 2 weeks since the re&re, and I've only driven the car 3 times (totaling some 45 minutes). I'll just give it some time.
Regarding the tire pressures, over the years I've had 35-37F/43-45R. Though it's always been a firm ride, the post re&re vibrations are new. If the "vibes" still bother me after a while, I'll try reducing the pressures.

dporto

Porsche's pressure recommendations for 18" wheels are: Front - 36 psi
Rear - 44 psi... I know they seem high, but that's what they are...