Noise from Diff

[CG901]

The Elan S2 diff was completely rebuilt last year but I am noticing a clunking sound when accelerating and decelerating. It is a single 'clunk' which I initially attributed to a loose mounting. After careful inspection, all bolts are secure. The propshaft bolts are also secure. If I place the g/b in first and rock the car, I hear the same sound, possibly coming from inside the diff. I don't recall hearing this after the diff was rebuilt last year. Anybody ever hear a sound like this? Any ideas about what would cause it?

[seniorchristo]

Was the diff ok after the rebuild and then started clunking all of a sudden? If it's internal then maybe too much clearance between crown wheel and pinion. Maybe improper pinion depth or preload on pinion bearings. I'm in the process of rebuilding my diff right now. Apparently setting pinion depth using the crush washer can be difficult and deceptive. There is a lot to learn about this basically simple mechanical device.
Chris

[CG901]

Chris - I believe the sound came on gradually as I don't recall exactly a start point. The rebuild was done by a very well known guy who is a know Lotus Specialist. He does a lot of them. Of course, that doesn't mean it was done correctly in my case.

[bill308]

I would also carefully inspect the torque rods, both the bushing pack and frame mounting bolt. Also inspect the metalastic housing to frame mounts (Fustacones) and associated hardware.

Bill

[nmauduit]

did you check the exhaust tube clearance with the chassis or gearbox? depending on how your exhaust system is hanged, a gradually getting loose exhaust mount may cause some acceleration/deceleration knock noise, as engine tilts in its mounts.

[nigelrbfurness]

If you can get the rear end safely up in the air, put it in top gear and lock the handbrake on one side by adjusting it up tight. Then get someone to rock the free wheel backwards and forwards to see if you can reproduce the sound - look for anything that moves when it shouldn't - mountings etc as others have said.

If all the other checks don't reveal anything and you still have doughnuts check one of those hasn't broken - I've had them make clunks and clicks when they've failed and its not always immediately obvious. Except when they disintegrate, of course. That's generally obvious.

Nigel F.