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Join Date: Mar 2004
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944 vibration (motor mounts?) advice?

My 86 944 na w 45,000 miles has a vibration that seems to resonate thru shifter and gas pedal above 2500 rpm. just had balance shaft belt checked. My mechanic thinks that maybe it is the motor mounts but my experience with previously owned 84 944 is that when the motor mounts go the vibration is at idle and not at higher rpms. Could it be motor mounts or? Thanks.
Old 03-21-2004, 04:48 PM
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Unfortunately, it's more likely to be the rubber center clutch beginning to go... However, it could as simple as shifter pin wear allowing the shifter shaft that goes back to the tranny to vibrate. The mounts have a different failure mode...

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Old 03-21-2004, 05:43 PM
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Jup, probably not the motor mounts.

I had the same problem (And still have) with my 88 Turbo.

A lot of vibrating at about 3000 rpm or at high loads on low rpm. My mech just ripped everything from the drivetrain out and noticed the driveshaft bearing (hard to explain, but it holds the main driveshaft in place at the clutch) was completly wasted.

So, we replaced it with a second hand one. Most of the annoying vibrations and drivetrain noise was now gone. But, still the vibration in the stick remained. I replaced a couple of rubbers at the gearstick which reduced the vibration a LOT. But, it's wearing out again pretty fast as there is still vibration.

And, i think i know why:
The gear linkage for a 944 is very long (tranny in the back) and this linkage is probably sensitive for some vibration in a certrain frequency range. Of course, the engineers designed the car in a way that the frequency of the engine, driveshaft and gear linkage would not go in sync.

They did this with the balancer shaft in the (very unstable) 4-cyl engine, special bearings on the driveshaft and some rubber dampers all along. But when stuff starts to wear out, frequencies will strengthen each other.

Solution: replace all the dampers and rubbers in your gear linkage etc. It will keep out most annoying frequencies.

PS: Scuse me for my terrible english, but i'm trying
Old 03-22-2004, 01:30 AM
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Quote:
Originally posted by arnebret
...

And, i think i know why:
The gear linkage for a 944 is very long (tranny in the back) and this linkage is probably sensitive for some vibration in a certrain frequency range. Of course, the engineers designed the car in a way that the frequency of the engine, driveshaft and gear linkage would not go in sync.

....
I wouldn't give the 1970's engineers credit for doing FEA on the 924/944. Didn't have the easy to use CADD and mechanical design software we have now. Any vibration dampening was done after the car was built and test drove if not a year or two into it's production runs.

As to 944 vibrations; if the engine will vibrate with the clutch in and in gear then look at the pulleys on the balance shafts. One (or both) is off by 170 degrees. The difference between the two keyways. You can notice this at idle by putting your hand on the engine. Has a high frequency vibration. Could also have the balance belt off a tooth or two.

As the drive shaft turns with the engine rpm by having the car in gear and the clutch pushed in you eliminate the drive shaft, clutch disk and trans as any potential source of vibration.
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Old 03-22-2004, 04:26 AM
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Well, in my case it's a bit of both. The engine itself is a bit unstable at 3000 rpm, but barely noticable. As soon as i let the clutch in, the driveshaft just amplifies the vibrations. And i'm pretty sure the driveshaft and clutch are ok, as they have been replaced by a pro porsche mech and really cleared up most of the really annoying vibrations and sounds.

By the way: i agree on your point that in the late 70's it wasn't that easy to filter out any unwanted vibrations, but i hearded that the 944 and 951 have both been tested on stuff like vibrations and that they made great advances there compared to the old 924. I can tell you, if my 951 vibration where stock, i would NEVER want to drive 924 But they weren't...
Old 03-22-2004, 04:47 AM
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Old 03-22-2004, 04:47 AM
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