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By checkmate1996
#80675
So after getting some miles on the euro, I am noticing a vibration in the shifter that occurs precisely at 3900 rpms and goes away at 4200 rpms. Torque tube bearing is my first guess. Other than that, she shifts perfectly into every gear and no other weird noises. She drives and rides very smooth.

Thoughts?
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By worf
#80681
checkmate1996 wrote: Sun May 16, 2021 11:17 pm So after getting some miles on the euro, I am noticing a vibration in the shifter that occurs precisely at 3900 rpms and goes away at 4200 rpms. Torque tube bearing is my first guess. Other than that, she shifts perfectly into every gear and no other weird noises. She drives and rides very smooth.

Thoughts?
Tell us about your motor mounts.
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By checkmate1996
#80686
Don’t really know. I have no prior maintenance records to indicate they have been changed. That being said, I know many of the cam , front main and oil pan seal were all replaced at one point. I am guessing they were changed as well. Again, everything other than the specified rpm range is fine. She idles super smooth...
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By checkmate1996
#80697
It seems after doing several google searches - TT vibration dampner is the leading suspect as this keep things in check....
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By worf
#80727
checkmate1996 wrote: Mon May 17, 2021 7:49 am It seems after doing several google searches - TT vibration dampner is the leading suspect as this keep things in check....
You wrote “shifter” in thread title. I assumed 5-speed. Auto has a (mode) “selector.”

When the vibration damper goes really bad, you can hear it sliding back and forth on the shaft.
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By checkmate1996
#80748
No you are correct. It’s a 5 speed. I feel the vibration in shifter.
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By worf
#80774
checkmate1996 wrote: Mon May 17, 2021 12:01 pm No you are correct. It’s a 5 speed. I feel the vibration in shifter.
IIRC, No vibration damper in 5-speed T-tubes. 3 bearings. Damper in auto T-tubes. And why GB has bone with Constantine about replacing damper with bearing.

You can measure 1st and 3rd bearing carrier locations for migration. TT rebuild won’t hurt (well... you’ll hurt) but it is a WAG right now.

Are your motor mounts flat? Volvos? Or Porsche?

When did you discover the vibration? What work was done just prior? If volvo, Has the engine sat on the mounts and been disconnected from u/l bell housings for any length of time.
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By checkmate1996
#80776
Ahh ok- yeah it’s a CF With Greg vs Constantine on that one. I’ll get car back up in the lift and check the motor mounts. The car sat for 11 years game but my understanding is that the transmission was the last thing being worked on when LSD was added ...
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By linderpat
#80963
following. I also have a drive train vibration in my 85. It's a 5 speed US spec though. It is a steady vibration, low level, at all speeds. some modulation with rpm's detected.
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By checkmate1996
#81000
It’s independent of gear and more rpm consistent. So, in essence, in any gear at 4000 rpm the vibration in the driveline peaks and then drops off after 4200ish rpms like it was never there. Also if I push the clutch pedal down right at the point of vibration it also disappears ...
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By Geza-aka-Zombo
#81016
linderpat wrote: Tue May 18, 2021 10:34 am following. I also have a drive train vibration in my 85. It's a 5 speed US spec though. It is a steady vibration, low level, at all speeds. some modulation with rpm's detected.
How are the trans mounts? Transaxle touching the aluminum crossmember? New trans mounts solved my driveline crudeness/vibration.
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By Geza-aka-Zombo
#81019
checkmate1996 wrote: Tue May 18, 2021 12:35 pm It’s independent of gear and more rpm consistent. So, in essence, in any gear at 4000 rpm the vibration in the driveline peaks and then drops off after 4200ish rpms like it was never there. Also if I push the clutch pedal down right at the point of vibration it also disappears ...
So, if I understand correctly, driving along in any gear at ~4000rpm, vibration in gear shift lever is present. Pressing in the clutch at this point makes the vibration go away.

If this is the case, disconnecting the engine from the driveline stops the vibration. The driveshaft is still spinning in the TT at ~4000rpm back driven by the wheels, so it's most likely not the TT/driveshaft or transaxle/mounts.
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By checkmate1996
#81031
The drive shaft would still be spinning in an automatic but not a five speed.
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By 3.2 Targa
#81047
These were the exact symptoms of my failed TT when I had my 1981 928. The definitive test for me was:
1. Bring up to speed in 4th gear, press in the clutch, let the RPMs fall .... Rev the engine in the 3800-4200 range. Is the vibration present?
2. With clutch pedal down, pull into next lower gear and then slowly release the clutch while bringing up the engine speed to match..... You should feel the TT spin up and the vibration will appear like it is "spooling up".

I would do this from a 4th - 3rd around 70 MPH. The trick is to release the clutch relatively slowly
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By Geza-aka-Zombo
#81048
Driveshaft is directly bolted to the engine on an Auto, thus always spins at engine RPM. Driveshaft is direct bolted to the transaxle on a manual, thus always spins at its speed. Thus, depressing the clutch, disconnects the engine from the driveshaft, but the driveshaft continues to spin at whatever the tires, thru the transaxle are directing it to spin at, no?
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By Geza-aka-Zombo
#81051
3.2 Targa wrote: Tue May 18, 2021 2:42 pm These were the exact symptoms of my failed TT when I had my 1981 928. The definitive test for me was:
1. Bring up to speed in 4th gear, press in the clutch, let the RPMs fall .... Rev the engine in the 3800-4200 range. Is the vibration present?
2. With clutch pedal down, pull into next lower gear and then slowly release the clutch while bringing up the engine speed to match..... You should feel the TT spin up and the vibration will appear like it is "spooling up".

I would do this from a 4th - 3rd around 70 MPH. The trick is to release the clutch relatively slowly
While traveling at fixed speed (~70mph), and depressing the clutch, just the act of shifting from 4th to 3rd (via the syncros) spools up the driveshaft and clutch plate near instantly.
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By 3.2 Targa
#81063
This has been 15 years since I did this.... Thanks for reminding me of a key piece.

1. Get up to speed in 4th gear..... kick car into neutral and coast..... This isolates the TT
2. Depress clutch and rev-match.... Pull into 3rd gear and you will feel the TT spool up.... gently release clutch and the vibration should appear.

It may take a few times but you will find it.

Ignore my prior post.
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By worf
#81092
checkmate1996 wrote: Mon May 17, 2021 2:17 pm I’ll get car back up in the lift and check the motor mounts. The car sat for 11 years game but my understanding is that the transmission was the last thing being worked on when LSD was added ...
Obviously look to see that you've a nice gap between the oil pan and the engine carrier.

Then look to see if the mounts are Porsche or not. Look at the locating pin for the bottom of the mount. If it's the same size as the locating hole then it's a Porsche mount.

If it is not a Porsche mount, then you need a couple of strips of rubber that are as wide as the oil pan and as 'deep' as the cross member and 2 to 3 cm thick (total, you shouldn't have more than 3 cm carrier clearance.) Two sections of old tire tread stacked, cut from an old tire work well. Raise the engine enough to stuff those rubber sections between the cross member and oil pan.

Then go drive again.

Regardless of whether or not you use this 'speed mount' the next time you test:
- drive past 4200 rpm and then let it coast down to 3500 - through this vibration zone - in gear, clutch engaged.
- do the above but this time coast down, in gear, with the clutch pedal to the floor - clutch disengaged - engine idling.
- and again, in neutral, the clutch pedal to the floor - clutch disengaged - engine idling.
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By worf
#81096
I'd didn't parse through all the posts on the driveshaft. Remember that the clutch pressure plate is attached to the flywheel, that the clutch disc is attached to the driveshaft and that the driveshaft is coupled to the gear set.

Clutch engaged the driveshaft spins at engine speed.
Clutch disengaged the driveshaft spins at 'gear' speed (tire speed x gear ratio x math) independent of engine speed.
Clutch disengaged and gear box in neutral, the driveshaft will spin down - but not all the way to zero if the road speed is not zero as viscous coupling from the gear box oil may spin the shaft a bit. But, close enough for vibration work.
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By worf
#81100
The *reason* I posted directions on using the "speed mount" is that the non-Porsche motor mounts can be damaged if the engine is disconnected from the bell housing and allowed, for an extended period, to 'droop' forward (which it will do since the carrier isn't at the center of mass for a dressed 928 engine.)

Since this car has had 'transaxle work' and/or an otherwise unknown history, it may be a candidate for this failure mode.

The 'damage' is characterized by resonant vibrations at certain engine speeds.

I do not know if Porsche mounts have the same failure mode. Nor do I know if all non-Porsche-brand mounts have this failure mode. I just know that this failure mode can happen.
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By checkmate1996
#81110
Makes sense!

First test- measured 1” gap between oil pan subframe.
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By checkmate1996
#81495
Ok - I am 75% sure I have found the problem. After jacking the car up on the lift - I was going to check the torque tube pinch bolt by the transmission - while I was doing that I reached up and checked the rear shifter coupler. It had EXCESSIVE play in the coupler. Something is way off but I can’t see it because it covered with some duck tape hack job. This also explains while the shifter felt a little sloppy on neutral. This is my primary suspect at this point ... more to come
Last edited by checkmate1996 on Thu May 20, 2021 9:51 am, edited 1 time in total.
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By worf
#81530
checkmate1996 wrote: Wed May 19, 2021 11:10 pm... way off but I can’t see it because it covered with some duck tape hack job...
Yeah, that ain’t gonna be factory duct tape.
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By checkmate1996
#81536
:roflmao: :roflmao: ^^^^^
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By checkmate1996
#81618
Well here’s what I pulled down over the rear shifter coupler along with one of the bushings. I am now 99% sure this is why it was vibrating.
Image
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By checkmate1996
#81619
Image
Image
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By worf
#81640
That’ll do it.

And you say it vibrates at *only* 3800 rpm :roflmao:

checkmate1996 wrote: Thu May 20, 2021 5:58 pm Image
Last edited by worf on Thu May 20, 2021 8:28 pm, edited 1 time in total.
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By worf
#81641
Oh, was going to mention the glove too!
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By checkmate1996
#81658
Just saw the glove!!! Hahahah
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By checkmate1996
#81679
worf wrote: Thu May 20, 2021 8:27 pm That’ll do it.

And you say it vibrates at *only* 3800 rpm :roflmao:

checkmate1996 wrote: Thu May 20, 2021 5:58 pm Image
I would say the top three symptoms were:
  • Neutral feeling sloppy
    1st gear to far to the left
    3800-4200 rpms seemed to be point of crescendo for the vibration
Best,
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By Constantine
#81707
[/quote]
IIRC, No vibration damper in 5-speed T-tubes. 3 bearings. Damper in auto T-tubes. And why GB has bone with Constantine about replacing damper with bearing.
[/quote]

After 1980 and after Porsche stopped bolting the TT to the rear mounted battery box, Porsche started using the vibration dampener (VB) in both manual and automatics TTs. They even have a patent on their VB and it helps explain in great detail why they designed and used it .

As for GB's "bone" with the Super Bearings, and ultimately me, he does not believe using three (3) of them to rebuild the TT suffices to remove the VB from the TT as was the specific design intent for the Super Bearings. And before this turns into a thread hijack, I will leave it there.

Glad the source of the shifter vibration was found. Usually when the TT bearings are causing vibrations they are also felt in the chassis, not just the shifter and usually get worse as the RPMs climb. The main failure for 928 manual TTs is the front bearing unit walks back into the TT which causes a long length of unsupported drive shaft to vibrate during operation.

Cheers.
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By worf
#81712
Constantine wrote: Fri May 21, 2021 12:29 pm After 1980 and after Porsche stopped bolting the TT to the rear mounted battery box, Porsche started using the vibration dampener (VB) in both manual and automatics TTs.
Thanks for the correction C. I can't get the TT lore to stick to my brain.

So, while you're here, what are the basic differences between the Auto and 5-speed TT assembly?

This is what's in my head:

Auto: much longer driveshaft, protrudes from front of tube. Shorter tube. Four bolts at each end.

5-Speed: driveshaft slightly shorter than tube. 6 bolts at rear, four bolts on front.

What else?
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By checkmate1996
#81721
Constantine - thanks for chiming in! Always great to hear from you!

I put Rogers replacement bushings in and holy cow. It’s like my shifter had viagra. Tall and stiff! :roflmao: :roflmao: :hiding: :hiding: :hiding: :hiding: :bigok: :bigok:
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By checkmate1996
#81722
Pic for reference
Image
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By Constantine
#81758
Hi Dave,

The TT stuff is hard to keep straight at times and you have enough on your plate to keep up with servicing all the 928s for your clients. Instead of going deeper in this thread about the 928 TT stuff, I will make another thread just for this purpose. In this way, 928ers would have an easier time to search for this information in the future and others can chime in with their own experiences and knowledge.

Perfect solution Brad! It is amazing what you find sometimes in these 928s as quick and dirty fixes.

Best to you both.
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By Sazerac
#81949
@ Checkmate: glad the problem was solved!!!

@ Constantine: I would really appreciate such a thread from you about the super bearings. I have to date purchased 2 torque tube rebuilds and one bearing set. I'm a happy customer, but I'd like to understand what's going on. This is a new datum of information: I did not know that the specific design was also done to avoid the VB. Very interesting.
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By Constantine
#81977
Sazerac wrote: Sun May 23, 2021 11:42 pm @ Checkmate: glad the problem was solved!!!

@ Constantine: I would really appreciate such a thread from you about the super bearings. I have to date purchased 2 torque tube rebuilds and one bearing set. I'm a happy customer, but I'd like to understand what's going on. This is a new datum of information: I did not know that the specific design was also done to avoid the VB. Very interesting.
Great to hear about you being happy with your purchases from us!

This is explained in good detail on our website about why we believe the 928 Super Bearing's design takes away the need from re-using the VB. The Super Bearings evolved from their initial offerings and this became a specific design parameter from just focusing on fixing known problems areas of the OE bearings units.

I am hesitant to do such a thread specifically about the Super Bearings here since there are others who believe differently, and although I enjoy a healthy discussion about such topics, it turned into a harsh debate replete with personal character attacks and ridicule on that "other" forum.

And I would be viewed (rightfully) as promoting my products on this still new forum where I am not classed as a vendor and currently debating being one after the bad times of being one on that other forum.

To me the ultimate proof of the Super Bearings performance is from owners like yourself who have reported back on how well they work in their 928s for the years they have been available. If they weren't working, I would not sell them.

With kind regards,
Constantine
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By checkmate1996
#84788
Quick Update: After fixing the rear shifter coupler, the vibration diminished greatly. However, you still "feel" it spool up at 3800-4000 rpm and then drops off quickly. So I do think it's TT bearing but since it's "almost" insignificant, I'm not going to worry about it till it becomes a real issue. That being said, it also felt like the more I drove it, the less it got...I could be imagining things but that's where its at...
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By Constantine
#85154
When TT bearings, or the OE vibration dampener, go bad enough to give you vibrations in the cabin, it isn't in such a narrow RPM range. They are usually felt across the RPM range and the higher in RPMs, the more pronounced they feel.

This sounds more like MMs, TMs, engine dampener or rough running engine.

HTH.

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