What about the following post by a 944/968 owner about solid motor mounts? Does any of this rationale apply to the 928?

Harvey
=====
"Solid mounts are a TERRIBLE idea in a street car, especially if you don't also run a solid tranny mount. Two big problems top be concerned about. First, the increased vibrations are a major concern, especially for the plastic oil pickup tube, which get old and brittle and will crack, causing you to lose your oil pressure. Race tracks are generally have a much smoother surface than streets, so its not nearly as big a concern for track only cars.

Secondly, and at least just as importantly, if you run solid engine mounts, you HAVE TO (repeat that as many times as you need to until it sinks in) run a solid tranny mount. The driveline in a 944 is designed to "float" at the three points. If you remove two of the three floating mounts, ALL the movement gets transferred to the third and the whole thing will act like a pendulum, which will result in damage and unpredictable behavior."

Regards,
__________________
Scott

Reading what he says makes me think they are discussing mounting the engine solid to the chassie and the need for doing the same with the tranny.
Hard to say without reading the rest of that thread though.
It doesn't seem like a solid rubber versus hydraulic motor mount dicsussion to me.

/Peter

The hydraulic mount is clearly fitted to the post '83 cars as a means of managing vibration - for a variety of reasons: the early cars, like my '80 have solid mounts; however, they do employ a mini shock absorber in tandem to diminish transmitted vibration.
What are the impacts of transmitted vibration beyond that of discomfort to occupants? I'm not certain, but the rational presented from the 944 forum of a transaxle coupled by a TT is an interresting one and cannot be dismissed. The 928 oil pick-up tube is metal, so not one to lose sleep over.
The reality experienced by nearly all who have replaced collapsed OEM hydraulic mounts is a near universal claim of a far smoother, vibration free engine. This is true regardless whether the replacement mounts were OEM or the #2698 HYD. It would be of interest to hear from those that choose to replace with the #2698 solids .... as to a before/after result.
Having noted this, then the must be corollary must be evaluated - for all these 928s that have been operated (for possibly several years) on collapsed mounts, we were effectively running on solid mounts: namely, we were experiencing varying degrees of higher transmitted vibration .... up to the point of operating on solid mounts. The worst case would be having enough collapse to allow the engine/oil pan resting in contact with the crossmember - that's vibration at its best.
Have any of our cars been damaged by operating on these collapsed ( aka - 'solid') mounts?? I'm not aware of any reports other that that of discomfort due to transmitted vibration.

What Garth S said.
Solid is not solid in this instance. The solid mass of rubber still flexs and absorbs vibration and movement as per the hydraulic.
I believe the cavity inside the Hyd unit is very small so the rest of the MM is solid rubber.
If I get the chance I will cut one in half and see the extent of the cavity.

My new motor mounts are the #2698 HYD type fitted ~ 1 year ago. Major differences are the height of the engine and the rockin' it has when revved both of which were not there before with the collapsed OEMs. The collapsed mounts transmitted a vibration through the car @ approx 2.5/3k rpm which is also gone with the new mounts.

I assume that if one was to never do the MM job ever again the solids may be an option. I'll deal with potentially collapsed 2698s +10 years from now..............unless I get that 'GT'.