Vibration on deceleration... wheel bearing, transmisison mount, clutch/flywheel or?

Getting a noticable vibration on off throttle, in gear (usually lower gear like the unappreciated 4th) vibration through the car at deceleration from 90 or so mph. It can possibly be in a lower gear and lower speed (like 2nd and 45 mph) but I haven't tested that yet. The vibration seems to be originating at the rear (possibly passenger side, but not positive on the actual left/right part). No vibration accelerating to 90 mph or more. Car is only on 2nd wheel bearing since new. Clutch has about 55-60k miles, which is frankly amazing because in the past, i've not gone more than 40k miles on a clutch. What could it be? the 'Guibo' is original too.

I recognize your name from Quattroworld..I am Swordfish on there. When was the rear diff last serviced ?

If it's only off throttle, I would keep testing it and see what gears it happens in. It could be the "coast" side of a gear is starting to fail. As swordfish states....you could always change the gearbox fluid and see what kind of foreign material comes out, if any. If you have metallic particles, something is letting loose. Jyoteen and swordfish.....know you both. Too funny.

I just had the Guibo (flex disk) replaced on my 2004 C4S and it got rid of a similar vibration that I had. It was done at the same time as replacing a leaky front differential seal, so it seemed the perfect time to address it. When I purchased the car a little over a year ago there were notes in the service history that the flex disk was cracked and needed replacement (going back to 2010), so I decided to have it done as a preventative measure. It turns out that the disk was is bad shape by the time it was finally changed about 3 weeks ago, and there was a noticeable reduction in vibration when letting off the gas - at all speeds. I didn't really realize how much vibration was there until it was gone, so a noticeable improvement and worth the $80 part. If you can see cracks in the flex disk, replace it. As my Indy says, 'it didn't come from the factory that way'.

Interesting - I have a vibration on decal in my C4S as well. It's rpm dependent rather than speed dependent. 2nd, 3rd, or 4th gear on throttle to 5k rpm or higher and the vibration kicks in on decal at about 4600 rpm and goes away at 4200 to 4000 rpm. Of note is that it only happens when the engine is at operating temperature. Also seems to originate from passenger side rear and is felt through out the car. Very consistent and easily replicated. Replaced motor mounts no change. Having the Guibo disk replaced later this week.

Now that I looked up Guibo disc, I see that would most likely be a common issue. I would recommend performing a detailed inspection or potential replacement of them. Looks easy.

Worn transmission mount? If you're going to go through the trouble to pull out the old guibo, spend the extra half hour and junk the FWD stuff. Lose some weight, and get a hearty helping of that "OVRSTEER" your license plate mentions. I'll never go back.

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I actually just saw your AC woes thread on the D3 board a few days ago..

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Paul: Is that something you'd need a microscope to do? jyoteen: If you haven't changed your motor mounts in the past 5,000 miles, the conventional wisdom on here is that they are overdue and will dramatically improve all aspects your life.

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Just like we have a IMS tool loaner program setup, Paul really needs to get on the ball and setup a Microscope loaner program. IIRC, the model he has can even one up Blackstone Lab's...

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The car's fluids (all of them that aren't motor oil or brake fluid) I have religiously purged all fluids every 2 years. So transmission, coolant, etc are all new regardless of mileage due to track use.

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Hi Paul, I sure hope it's not the transmission, except I wouldn't be totally surprised since I have 152k miles on it with a lot of track miles with the transmission never been rebuilt. I don't have difficulty shifting up or down. Still smooth, but just maybe the coast gear as you indicate. Will swap fluids first, of course.

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Actually, I just changed my motor mounts last year, if I remember correctly. However, I have heard that the motor mounts do not take kindly to jacking up the car from the center seam right behind the engine case as I have had to do to get jack stands under the car. So maybe they're prematurely toast? But I don't get any other indication that the motor mounts are on the way out.

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Please post your update, as my suspicion is the gumbo, only because everything else really on the car has been replaced and all fluid service is also pretty current. Porsche does not sell the guibo flex disc by itself (have to replace the shaft too), so let me know of the costs if you do find the guibo disc by itself and part number. I know people have suggested using a BMW part but that is different. If it is the BMW part, I get that at cut throat work related discount.

Pelican Parts - 10-2539-005-M57 $94.75 1 $94.75 Driveshaft Flex Disc Brand: O.E.M., Brand: O.E.M. It may be the same as a BMW part, but not sure.

Having the guibo disc replaced tomorrow a.m. and will let you know if it solves the issue. I did purchase the disc from Pelican, tech is fine with just replacing the disc and was actually happy to hear that a source for just the disc is available. Fingers crossed.

Guibo disc installed - not the solution to the vibration on decel. Although it was worth doing as the old one was much worse than originally thought and other small vibrations at cruising are now gone. So we know what doesn't fix the issue: New Motor mounts New Guibo disc The tech and I keep assuming it is vario cam related but we ran full diagnostics; including me driving with the tech and his portable brain in the passenger seat. He could feel the vibration on decel but diagnostics show everything is fine. A tad technical for me but cam timing, deviation, angle... all as should be. If anyone else stumbles upon the solution I would be most appreciative to hear about it.

Thanks for the update. I think my course of action is going to be 1. wheel bearing 2. guibo 3. transmission mount 4. removal of the front diff/halfshafts (easy enough to reinstall) 5. inside the transmission. I have 152k on the odometer and it's time to do the IMS bearing again (current is LN Engineering) and basically redo the engine anyway. Need to save just a tad bit more and now, instead of the daily driver status, it's a weekend car so I can extend it a bit.

Mine has 49k miles on the chassis and 12k miles on the Porsche reman engine. In my case wheel bearings, trans mount and front diff all ruled out. Sort of focused on the vario-cam since it is replicated in 2nd, 3rd, 4th, (and yes 5th) gears and consistently occurs at the same rpm range each and every time. Although the tech confirms the vibration exists; diagnostics show nothing amiss. Been down that road before and know that nothing fixes itself, it will reveal itself at some point, just hoping the 1 year extension on the warranty is still in play if indeed it is engine related. Reiterating that it occurs only when engine is at full operating temperature, anything below full op temp is either very mild or non-existent. I rarely drive the car in a manner that has me decelerating under full compression so it's not the end of the world, just something that I know will plague my brain until it gets sorted out. Hope you get it figured out and keep us posted.