928S4 drivetrain vibration
 

Hi everybody,

I am slowly starting to fix all the small ailments that my 928S4 suffers from. Well, maybe I am just too picky, but I want my cars to be close to perfect.

Doing some test drives in the neighborhood I have come to realize that there is a drivetrain vibration in the 3,000 - 3,300 rpm range. The car is an automatic by the way. The vibration is engine speed related and is present in every of the four gears.

I know this is a long shot, but would anyone know how I could start to pinpoint the source of this vibration?

Thanks for the feedback,
Rik Gruwez
Brugge, Belgium

What year car? how many kilometers on it?

engine mounts? flappy operating correctly......just guessing.....

Motor Mounts - do a search for information.
Just changed mine and the vibration went away.
Good luck.
Roger

Here is some more information.

1989 928 S4 (Euro spec) with 160,000 km or 100,000 miles.

What is a "flappy", BTW?

Regards,
Rik Gruwez
Brugge, Belgium

Motor mounts are probably collapsed . They are rather expensive and often get ignored .

Can I visually inspect those motor mounts? How can I tell they are collapsed? I am prepared to buy new ones, but only if I am sure that the current ones are in need of replacement.

Regards,
Rik Gruwez
Brugge, Belgium

Put a straight edge, front to back, on the top of the intake manifold and see how much higher than the cross member it sits. Somewhere here on this site is a picture of this with good mounts....IIRC the clearance was more than 1/2 an inch....someone check me on this.....the other way is to get under the car and look with a spot light to see if the munts have collapsed.....There is also an engine rev technique where you look to see if the engine rocks back and forth a bit when you blip the throttle... fi it does not chances are the mounts are bad.....

a simple way would be to put it in neutral and slowly rev it up to the same RPM you noticed the vibration at a full stop. If it does the same thing then definitely mounts. If it happens in motion it could be a torque tube or torque converter issue even (BTW, torque tubes whine when they are on the way out)

Andy :burnout:

Rik,
I second the comments about motor mounts, that will reduce but not remove all the vibrations
Mine is a S2 model and I have been working a lot on this '3000 RPM phenomena', who seems to be 'normal' for the 928 models, but only in 4 gear
What I did: Motor and transmission (rear) mounts - This took app. 75% - Then I mounted hydraulic dampers ) front and rear) from the S model on top of the original dampers
- Today I can hardly feel when I pass the 2900 to 3500 RPM area
It seams that this phenomena is connected to the condition of the trans bearings, but I have not BTDT

Under the car, measure the vertical distance between the tips of the "J" safety hooks on the motor mounts: If there is 1cm clearance, the mounts are collapsed enough to transmit vibration to the chassis.
New mounts are 78mm high : with some acrobatics, you can also measure the installed heights (use a soft piece of solid copper wire, bend to fit - withdraw and measure!).
Search 'Motor mounts': there is a lot of data - I replaced mine recently, and many of us have reported on that.
As Andy notes, if there is an accompaning 'whine', be suspect of the torque tube/converter bearings .

I have the exact same symptoms. Releasing the pressure on the flex plate took some of it away but my mounts are bad and I have been told by Precision that this is the source of the vibration. Just dont have the spare $$ right now to do it. Re- post to let me know if replacing yours solves the problem.

Thanks for the feedback. I will put my car on my hoist and check from underneath if the motor mounts are collapsed. If they are, I know what to do one of the coming weekends.

Another question: some of articles I found mentioned the original Porsche mounts could be replaced with Ford ones, which are significantly cheaper. Is this is a safe substitute? Is there any reason not to go for the Ford mounts?

Thanks,
Rik Gruwez
Brugge, Belgium

Rik,
You may read compelling arguments for and against the 'Ford' mounts: I installed them this summer at ~15% the cost of OEM mounts. The fit is excellent, the engine now 'rocks', and the cold start-up chassis vibrations are gone: I am pleased :D . Others have had these mounts in for ~3 years - with no reported problems.

I did the same bought them from www.rockauto.com for $23 each.
Perfect fit and super smooth.

I have the Ford mounts with 20,000 miles, and no problems..! Cheap and good..! Buy them from Rock Auto on the internet, and save a LOT at $23 each...!!!