hb4

I think I know the answer, but would like some perspective from anyone that's been down this road.

I've been working with Thomas (Supercedar) chasing down a vibration on his car and now his car is now smooth as silk. His experience has been discussed on the List recently. My part has been to 'hold the light HERE', and Thomas' has been everything else. We're now starting on mine and here's where we are:

The vibration starts showing itself around 2800RPM, peaks at 3000, and drops off at 3200 or so. The vibration was much stronger (higher amplitude?) during a dyno run.

So far we've:
Replaced the fuel injectors (earlier, as part of Sharktuning)
Looked for fireflies
Replaced the motor mounts.
Ran the motor with the front flex plate disconnected and NO vibration.
Replaced the transmission mounts.
Checked the exhaust for contact
Measured the front TT bearing distance (it was OK)
Found two loose bolts on one of the three arms of the rear flexplate.

Torqued the loose bolts and checked; the vibration now seems a little more 'defined'; as if it was more of a square wave than a sine wave (forgive the EE background).

Spoke with Constantine and his feeling was that a TT vibration would be all across the RPM range, although post 27 on this thread indicates otherwise in one case.

The next step we're considering is to remove the torque converter and inspect it for anything that might cause an unbalance, and while we're at it inspect the TT (and probably replace the bearings to save doing it later).

In addition, we'll change the TC bearings, seal, and Pump O-rings.

Doing some research into the repair history of the car (I've had it a year and it was previously owned by a RLer, 'Pappy'), I find that he had a stall converter made which ended up at about 1800 RPM and then sent back and remade to the 2400 stall that he had asked for. Finally, he had a 2700 converter made by Auto Trans in Canada. This was apparently installed with the last transmission rebuild that included Mercedes planetary gears from Germany. An old RL thread by the PO at time he was selling the car listed a stall convertor for sale. Since the current TC acts like a stock configuration, I assume he changed the stall convertor out for the sale, but I have no record of its purchase or installation.

I've found a local TC rebuilder that will rebuild mine for $150.00, and I'm considering just going ahead and doing that if there are no apparent balance issues from the outside. According to an email from Steve Cattaneo that was included with the records, the torque converter is 'where contaminated parts from the transmission like to hide' - which I assume could be a cause for unbalance. We'll find out when it's taken apart. The TC rebuilder does not have the fittings to check the balance on the 722.3 TC.

In my RL research, some have advised to separate the rear flexplate from the TC and see if that points to the TT or something aft. It seems to us that there's not enough clearance and too much possible in/out movement of the TC to make that safe, but if anyone's done it and can suggest a technique to do it while the trans and TT are in place, please let us know.

I'm really hoping that it's not internal to the transmission or diff, and have no idea how to check while the trans is out of the car. Anyone tried this?

We'll replace the TC bearings, TT bearings, and rebuild the TC in one move and if we don't see anything wrong with the pieces we took out but the vibration goes away, I don't think we'll ever know what it was.

If it doesn't we'll be back here looking for ideas.

jcorenman

Bill,

Didn't read somewhere that someone fixed their vibration by re-indexing the torque converter on the rear flex plate? (That is, remove the bolts, rotate the TC 120-deg and re-attach). Of course I know nothing about automatic's and may have misunderstood completely.

Cheers, Jim

hb4

Jim,
Thomas and I did that on his car; After his MM, Trans Mounts, TT bearings, and TC bearings were replaced, he had nearly zero vibrations, but you could still feel them. We rotated the flex plate once and it seemed about the same. We rotated it again and also noticed that the cats were rubbing, which we cleared. After that, the vibrations were GONE. We think the small vibrations were the cats rubbing rather than the final rotation, but we really don't know.

I am assuming that the flex plate is balanced by itself. The logic seems to be that the TC collects debris that is somehow self balancing (for the conditions at the time) and stays there. That implies, I guess, that _something's_ out of balance to begin with but I don't know what. In Thomas' case, the mechanic that last had the trans out said that he couldn't be sure that the flex plate was replaced in the same orientation to the TC that it was when disassembled and for this reason it is something to try. What's more logical to me is that neither the TC or the flex plate is perfect and there is one orientation that is optimal. Note that everything above is heresay and inexperienced conjecture on my part.

CraigL

The front bearing on my TT had migrated waaaay down the tube. 25" to be exact. My symptoms were a significant vibration only in the 2500 - 4000 rpm range. It was easy to mehasure the distance by shoving a stiff piece of wire (coat hanger) down the TT via the front and rear inspection plugs.

supercedar

We will know as soon as I rotate the TC back to original setting. It is good to see you have history about the trans debri hiding in the TC. Might be more than a myth.
Thomas

odurandina

what's next ? a phone call to Constantine (of course).

the stock driveshaft leaves much to be desired.

Black Sea RD

Thanks Odurandina for the vote of confidence!

Bill did call me and we had a pleasent conversation and discussed a few possibilities with the focus for me being the transmission and probably the torque econverter after asking many questions.

Really a bit hard to diagnose over the phone without being able to drive and feel it yourself. However with all the work that seemed to have been done to the transmission in the past, a remanufactured "blue" TC in place, and no evidence of the front TT bearing unit having migrated, I really have the TC in mind to be the possible culprit. The vibrations were also at too small of a RPM range to me to be a bad TT. But again this is all a long distance guessing game at best.

As far as the flex plate orientation causing vibrations, we have never noticed it to be so. The flex plates, both front and rear, are balanced units and it should not make any difference as to how they are bolted back onto the TC or Flywheel. No mention of this in the WSMs IIRC either.

Good luck with the diagnosis Bill!

NC928S4

I am experiencing the exact same vibrational phenomena as hb4. New MM, wires, coils, plugs, caps, rotors. I fixed a bent and out of balance RF Rim that dramatically calmed the vibration but it is still there. Steering Rack and bearings are very worn too which may be contributing and are on my list. Cats were rubbing/vibrating on heat shields and remounting exhaust and bending the heat shields helped noticeably. But at 2800-3100 ish you can hear the rattle of the Cats on the shields and feel vibrational energy throughout car.

The AT Mounts are next and I remain hopeful this will help. However, after helping NCGrowler with his TT replacement, I suspect one or more vibration dampeners/bearings have migrated towards the rear. As newbie, I was shocked that the dampeners just float in the tube via a press fit. I will be checking this soon since I learned the “coat-hanger” measurement method in this thread.

A call to Constantine is in my near term future in between college tuition payments.

Speedtoys

Ive got this as well.

New 928Int TT, fresh bearings, new flat front flexplate, NEW tranny mounts, NEW motor mounts...

Vibe from 28-32..quite annoying.

hb4

Speedtoys,
I'll have replaced everything you have soon; the only difference will be the TC rebuild. Since I'm doing the TT, TC bearings, and TC rebuild in one move, if the vibration goes away I'm hoping I can find a defective part to point to. I believe you changed your transmission as well; or was that just the differential? I assume you've had the vibration all along.

NC928S4,
Do you have vibrations in Park and/or Neutral? Have you tried disconnecting your flex plate to see if it's engine related?

So far only two data points of those with a 3K peak vibration that have replaced all those parts:

Speedtoys: NFG
Supercedar: Success!

Anyone else?

NC928S4

I’m traveling and the next couple of weeks are crazy so I won’t be able to provide feedback for a while. I look forward to other RL’s progress.

Mrmerlin

see if your TT has the damper installed there was a TSB from Porsche about its use,
and it was installed to cure a vibration from 2600 to 3200 RPM

Speedtoys

Ive had the vibration in both tranny setups.

Speedtoys

What is the damper?

Gonna go look at parts diagrams..

hb4

Speedtoys, Mr Merllin
Here is a thread I just found posted by Vilhuer from 2006 that has the excerpt below from the Porsche '82 yearly changes document (Post 87). The vibration peak is a little different, however.

Porsche says that there is 'residual unbalance', that this corrects. It looks like the damper(2) resists the unbalance through the rubber springs(3).

If you don't have any residual unbalance I guess you don't really need a damper.