Vibration at 3000 RPM decelerating

[BertEverhart]

Car s 2006 Boxster S with 10200 miles. US Spec, 6sp m, Black/Black, Borla exhaust. This is my 5th P car, but first Boxster, so some noises are new to me and may be nothing. But because of the mileage, and original IMS Bering, I am nervous about vibration. I put the Borla exhaust on shortly after I bought the car in December, but don't remember if I had the symptom before. Love the sound of the Borla, but if this vibration is from the exhaust, I'm OK. If it is engine, I am worried. It seems to happen in all of the lower 4 geers at 3000 RPM. Please tell me others have this and its not impending doom.

[rwc94303]

Engine vibration, off throttle especially, is a sign of the front motor mount failing, not a catastrophe impending. The front motor mount accommodates a lot of vibration in a vertical direction by large holes in the rubber above and below the central through bolt. When this space is taken up by the rubber losing its strength and the engine weight pushing the center bolt (and tube it goes through) against the thin rubber on the bottom of the motor mount (off throttle torque on the engine/transaxle adds to this force) you feel the characteristic vibration at 3100 rpm. Solid motor mounts do this and stuffing the holes in stock motor mounts with anything (in hopes of reducing movement of the engine and it's effect on shifting) may also lead to feeling this vibration.

[BertEverhart]

Thank you very much, that eases my mind. Is it a DIY to replace the front mounts and will stock do for an old geezer who mainly drives and autocrosses?

[rwc94303]

There are DIY tech articles on this motor mount change at Pelican Parts, and other places I’m sure.

Pelican’s conveniently fails to point out their simple procedure is done with coolant lines disconnected and out of the way. I’ve done this only once and can’t conceive of how it could be done with the lines in place, but have read other people’s account indicating it is possible. 

So, if you are ready to change your coolant and maybe water pump and thermostat at the same time this whole job will be longer but easier to complete from a difficulty standpoint.

( I welcome a video of how to remove the motor mount with coolant lines in place. A $10 donation to renntech.org will follow)

Edited April 27, 2018 by rwc94303
typo correction