Vibration at 4000rpm - gearbox??

[sidewaysalfa]

Problem:
Alfetta GT. Severe vibration in the shift linkage at 4,000 rpm and up, ONLY in 5th gear. 4th gear, same rpm range no vibration.

I have another trans, with a shattered differential that I could swap.

Are there any ideas as to what may be causing this vibration??

[keith_h]

How are the donuts holding the tailshaft together?? If they are cracked and/or a piece has fallen out you'll get a vibration. Check the rear one first.

[sidewaysalfa]

Donuts OK.
It vibrates only in 5th. Same RPM in 4th and now I remember checking in 3rd also, no vibration.

[BigSwede]

What happens if you rev slowly through the rpm rang in low gear?

Have you checked your tires for imbalance? CV-joints on the halfshafts? Wheel bearings?

[mjr]

Dip the clutch at worst vibration, and keep the revs up to the same rpm. if the vibration remains, its not the transaxle.

[sidewaysalfa]

Mats:

I did creap up on the rpm. It vibrates at exactly the same place, 4,000 rpm and up, 5th gear only.

It has new rear wheel bearings, and I "think" I had the CV joints repacked recently.

Because of time trials I have rotated the tires several times.

New center support (converted from a new 78-79 version) and the front and back guibos are pretty OK: No cracks or missing chunks.

MJR:

I remember that I did this test with the clutch not engaged and 4000 rpm and no vibration.

the car is in pieces right now. I am swaping motors to my old Time Trial motor because my neighbor Norm is getting closer to me on the track!! and I may need a little help.

obtw: I am having the drive shaft balance checked this week, just to be sure. It's only about $80.

This is focusing on 5th gear as far as I see. I recently had 2nd gear synchros changed. And the gear fluid was OK at the time of the vibration.

I noticed this at a JanuaryTime Trial. It was Ok at the begining of the day and the vibration developed later.

Any more questions or ideas??
I just noticed that this conversation is happening on 3 continents. Wow!

[sidewaysalfa]

Update:
No driveshaft balance for a couple of weeks. The guy, Mike at Wenco in Van Nuys, went on vacation. He's the owner and seems to be the only person there who knows how to bolt up the Alfetta driveshaft to his machine.

[mjr]

If the vibration goes away with the clutch dipped at same rpms, its not the propshaft, its the transaxle. You already have your answer, if the 2nd synchros were recently changed. look at the last thing disturned ,i.e the trans. or as mats says, half shafts too. its a bit strange that its only in 5th gear though. can only guess that you maybe are getting some sort of harmonic going on from the output shaft or clutch flywheel at that particular 5th ratio and rpm? I can't see how you could put the output shaft or a gear out of balance though, unless damage was done during the syncho swap. when u say 2nd gear synchros changed, do you mean new? i.e presume you threw the old ones out, you didnt re-use the old synchros in any way.

check the transaxle alignment too since its been out.