driveline clunk and slight vibration over 100km/hr

[Divano Veloce]

Hi All,

I am at a loss to remedy a somewhat minor driveline issue on my twinspark Berlina. After replacing the trailing arm bushes and tightening the diff pinion nut I now have noticed a clunk that occurs on the transition from engine braking to hard accelleration and back. It does not occur on the transition from engine braking to acceleration under most normal circumstances though. It feels like it is coming from the tunnel adjacent to the seat mount. I didnt notice this before, probably because the play in the trailing arms was absorbing all of the torque reaction.

There is also a slight but noticable vibration at speeds over 100km/hr.

So far i have replaced the gearbox mount. No improvement.

I have the tailshaft out and the the center support and bearing feels good (which is annoying as i have already purchased replacements). There is a tiny wee bit of play in the universal joints, not enough to explain the clunk but perhaps the vibration

Otherwise the car is running superbly.

Any suggestions?

Cheeers!

[LaStregaNera]

Hows the Donut look?

[Divano Veloce]

Most of its still in there



This guibo was replaced a while back with a new one which still looks brand new.

[AikenDrum105]

How soft is the centre support bearing rubber bushing ?   My Super clunks on transitions like that but my centre support bearing is very old and saggy. 

Another one that makes them clunk are the two conical bushes holding the diff to the trunnion arm - the diff rotates forward / back on accel /decel and clunks up there if the bushes are stuffed or loose.

Vibration can be the uni-joints on the driveshaft incorrectly phased - mine are wrong at the moment and cause a vibration but haven't had the spline joint apart to correct it yet.  I suspect you've already checked those.

Sandown sprints coming up Matt - got the Berlina entered ? 

Cheers,

[LukeC]

Most of its still in there

Not enough though! 

While you have the propshaft out, check the spherical end on the rear of the gearbox mainshaft and the mating female "Top hat bush" in the front of the propshaft section. Few mechanics regrease this area when replacing the propshaft. The result is that wear appears and the propshaft is not held concentrically with the gearbox - causing an imbalance at higher road speeds.

The top hat bush is replaceable and available new from Classic alfa. Unfortunately, the rear of the mainshaft is only repairable by stripping the gearbox. I use the centre section of a Alfetta propshaft centring bearing pressed onto a machined spigot.

I have done two repairs as such this year.

And: Worn splines in the rear propshaft section....

[Divano Veloce]

Thanks guys for your advice.



I had to put the tailshaft back in last night as the Berlina is a daily. Still clunks of course as i changed nothing. I will check the conical bushes at the diff/trunnion tonight.

If i can get this and a couple of other minor things sorted it should be good for Sandown.

Scott, if you want to upgrade your center support to the later type, i have the support and bearing new and surplus to my needs.

[Craig_m67]

Scott, if you want to upgrade your center support to the later type, i have the support and bearing new and surplus to my needs.

I always wondered if the later type bearing was a straight fit to the 1300/1600 prop shaft?
Or is there no difference between them other than the flange bolts at the diff.

I've got one to do as well.

[LaStregaNera]

I'm not sure about the driveshaft side of it, but the upgrade does involve some reworking of the mountings I believe - bit of precision required in the welding (certainly not a job to be performed lying under the car)

[Craig_m67]

Ah see this is what I was afraid off. Without wanting to hijack this thread further I wonder what the differences are between the transmission tunnels of late and early cars?

[LaStregaNera]

Early cars have a bolt on shifter tower, late cars have it integral I believe? (as well as the different centre bearing mounting)

[Divano Veloce]

The trunnion/diff conical bushes are fine.... I'm now suspecting the LSD clutches; theres about 1/16th of a rotation of the tailshaft to get the rear wheels turning (this is not free play at the C&P).

the car remains "nearly sorted"....

[cjheath]

I'm now suspecting the LSD clutches; theres about 1/16th of a rotation of the tailshaft to get the rear wheels turning (this is not free play at the C&P).

I thought this was normal - I noticed it the first day I put an LSD in my '69 GTV, a slight clunk when you roll on and off the accelerator. Hugh told me it was normal and to ignore it, and that was 15 years ago.

I'll be interested to hear what people think, and whether you find something that needs fixing.

Clifford.

[Divano Veloce]

Thats funny, Huey told me it was the LSD and to pull it apart and shim it!

I think it will suffice as is for Sandown on the weekend

[cjheath]

I guess it depends how big the clunk is. It seem unlikely that Alfa would have shipped them without being properly shimmed, so the "problem" must have emerged, but I don't think mine has gotten worse while I've had it, and I haven't really treated the car gently .

[Colin Byrne]

The LSD clutch plate splines are pretty fine, both internal and external, so I'd be surprised  if your getting a "Clunk" out of them.  Did you check the backlash of the pinion while the driveshaft was off?  As has been said before the pinion nuts have a habit of losing torque and causing excess backlash
Just one other point I don't think I've seen brought up (and a pretty basic one so I'm sure you've checked it) but if the tail shaft flange bolts aren't tight enough the flanges can slip against each other and cause the type of clunking noise your describing.