porsche928guy

Hey guys...have been doing work on my 82 US Auto for the last couple of months in prep for SITM (now I don't think I'll be going). Got the car done early this week and dialing it in. Here is a partial list of what I've done in relation to this question.

1) Rebuilt TT from Roger/928 Intl.
2) Edge upgraded TC
3) New converter bearings
4) New tranny mounts
5) Cleaned and repacked inner CVs
6) Tranny swap from low mileage 80

The car is running great as usual but I'm now getting a good amount of vibration around 3100 to 3500 rpms from the rear end. It then goes away for the most part after 3500. This happens in park, neutral and going down the road in every gear (haven't tried reverse ).

Any thoughts?

pcar928fan

Well, it has to be something rotating even when the car is not moving so you are looking at TT and maybe the converter... I think you can rule the rest out, but I guess it could be the tranny mounts. My money would be on TT though...

James

Bill Ball

So, I gather this was the same before the rebuilt TT and TC, which would have been the most likely candidates.

Hmmmm.... Have you uncoupled the TT from the flywheel to see if it is forward of the drivetrain. Bad harmonic balancer maybe.

nosnow

Check your green wire and if you know someone close see if you can swap the ignition box on the passenger side. Supposedly those don't go bad but the one on my car was bad, there was extensive corrosion around the plug and on the internal components. It would cause an intermittent mis at ~1800 and 3200 RPM and the engine would produce no power over 4K. They are VERY expensive so I suggest trying one out before committing to a purchase.

porsche928guy

Hey guys thanks for the advice thus far. Let me add to the story to hopefully make it clearer.

Bill- This was not the case before. The car shifted fine and drove fine but had some bad "droning" bearing type noise in the rear. I thought I had burned up the bearings in the transaxle portion as I was leaking fluid badly and didn't know it. I don't drive the car much but moved and had to drive it about 800 miles. (all fluids were changed before the trip so it was full when I left) Once I got to Cincy I noticed noise and got to investigating to find that all I had in the diff. was about 1/4 qt of 80/90. The original tranny was leaking out of the pump o-ring and had some miles on it so when I found the low mile 80 tranny I thought I would just swap them (in hindsight maybe not the best idea...verdict is still out).

So "while I'm in there" I decided to do the TT and TC ugrade. Now I fear something is wrong with one of those. Let me emphasize that the vibration is felt coming from the rear. Engine is running well.

Oh...and Paul my 82 is the same color. LOVE IT!

Bill Ball

OK, it's a bit confusing. So, this was NEW after the TT and TC?? Always look at the last thing you did before the symptom appeared.

If it does it in sitting in park, then you know it is TC forward, so TC or TT.

porsche928guy

Sorry for not being clear..a lot of things running through my head.

No...this was not happening before...new condition after TT/TC. Happens in park (not quite as bad as in gear though). I've been thinking TT but want to be as open as possible to the advice of the gurus on this forum.

What do you think about driving it in this condition? If I keep it under 3k rpm (the vibration point) do you think I'd be doing any damage?

ROG100

I'm with Bill look at what was changed last - TT is a rebuilt unit from a top source - could be bad but I doubt it.
How was the TC bearing install - did you get them all the way home in the housing.
Can you get underneath and listen with a stethoscope for unusual areas of noise.
I know the vibration is at high revs but this may tell us something.

dr bob

Some depends on how the trans was installed to the TT. It's really easy to 'hang' the trams n the TT and vice-versa during installation, before the bolts are into the flange. That would possibly bend the end of the TT. Next suspect is the converter and the drive plate for same. You can get a dial indicator into the drain vent at the bottom, and watch the runout on the converter housing as you have someone rotate the engine from the front. (do this with the plugs out...) A converter housing that was dropped or damaged in shipment might be bent. It doesn't take a lot to get it out of balance.

You may want to put the car on tall stands or a lift so you can look under the teher with the engine spinning at vibration speed. Might give you a bettr clue.

Mrmerlin

Its a possiblity that the harmonic damper was left out of the new TT thats exactly where the vibrations are and so it was fitted to stop these vibes

porsche928guy

Roger - I agree on the TT I'm doubtful as well but everything else is new in there too so I'm trying to start with the most likely candidate. I took the converter housing to a machine shop and had them do the work on pressing them out and in. I inspected it before installing and everything looked good.

Dr Bob. I'm not sure I entirely understand what you are saying. I installed the TT onto the tranny out of the car then installed as a complete unit. I guess I don't know what could get hung up. Is there any harm in leaving the plugs in while rotating the engine?

I'll go down and get the car in the air and inspect a little further based on your suggestions.

Thanks - Jeremy

dr bob

Jeremy--

TT to trans before install is just fine. No chance of bending stuff while trying to support one while lifting on end of the other before the flange bolts are in and snug,

Having the plugs out makes it a lot easier and smoother to turn the engine by hand.

porsche928guy

OK thanks that is what I thought... I've been turning it over with plugs in and haven't had too much problem.

So...what do you guys think of driving the car? As long a I keep it under 3k rpm it is smooth as glass. My original plan was to go to SITM from Cincy then to Oklahoma. I'll be in Oklahoma for 3 months and would have time to take care of the problem then. Otherwise the car will sit for 3 months in Cincy as I really don't have time to deal with it before I leave on Thursday.

I have access to a trailer about 5 hours away so I am now thinking of driving it there and trailering the rest of the way.

Your thoughts?

porsche928guy

OK...coming back for more help. Since I last posted I've mounted the flex plate to the TC at all three positions. The vibration changes each time in that it happens at different RPM ranges but never completely disappears. Does this rule anything out in your minds?


I've been thinking about this issue and wondering... do the positions of the front and rear flex plates to each other make a difference?

Bill Ball

The flexplate/clamp units are balanced. You will see balancing scallops on the arms. If you detached the clamp from the plate and rotated it to a different position, then you could have a balance problem.

Since it does it sitting in park, you know it's either the TC or TT. You need to change one of them. I vote something that happened to the TC to throw it out of balance.

Did you try detaching the TT shaft and spinning it to see if it spins true, on the outside chance it's a bent TT shaft?