Triumph Repair: Spitfire rear end vibration/noise, wheel bearings, vibration noise

Question
QUESTION: My 1972 spitfire 1300 has recently and suddenly started vibrating a great deal at the rear end. The vibration builds from around 40mph to 50, I daren't go faster, everything is shaking. Visual check everything appears ok, the diff does leak  but was recently topped up. On stands everything seems to move freely enough. Recent work - 200miles ago new gearbox rear mount bushes. On the 200mile trip during which this started, it was intermittent lasting for about 20mins each time, stopping 1st of its own accord and again when I stopped for petrol.
Any ideas? thanks, Marcus

ANSWER: Hi Marcus,
A vibration in the rear can be any of a dozen things so you need to put the car either on stands or on a lift and run the speed up to 40+ MPH and look to see if you can see what is vibrating. A wheel, either axle or the driveshaft???  This car has "U" joints on the driveshaft and one on each axle. You should check to see if the front flange of the differential has any play up and down or any movement in either side flanges out from the differential. Look for signs of rust at any "U" joint. Check for any free play in the outer wheel bearings. It is not likely a tire problem as you said this can come and go and a bad tire is always bad.
Let me know,
Howard

---------- FOLLOW-UP ----------

QUESTION: thank you, I'd not thought of running it on stands. 1st off, no detectable play in the front or side flanges. Running, driveshaft does not appear to vibrate - the offside wheel does vibrate up and down (possible nearside does but i'm working on my own, cant see, its ok at low speeds which the offside is not). However, this has revealed a now very noticable mechanical clunkedy clunk noise from the nearside, rather like rolling bits of iron around in a drum. As for rust on the UJs I'd previously alleviated a minor rumble at 20-30 mph by spraying the UJs with motorcycle chain lube - dont remember thinking at the time 'wow they're rusty' but cant see any now due to the lube. There is play at the wheel such that when off the ground and turned the shaft turns through a number of degrees before meeting any resistance. Ommitted to check bearings, gave wheels a good check when this happened on the road - seemed firm.

Answer
Marcus, you can't check wheel bearings when the weight of the car is on them, so your check out on the road was no good.

It is normal to have some rotational free play in a wheel as you are taking up the free play in the spider gears etc.

The odd design of the rear suspension can cause a lot of vibration and noise when a wheel is out of balance. The tests I gave you MUST be done at the speed that you are having the problem (40 to 50 MPH as you stated)

No amount of spray lube will correct a "U" joint that is showing signs of rust coming out of them, it is already bad.

Howard