Triumph Repair: 1972 triumph spitfire rear-end noise, shaft vibration, pinion bearings

Question
Hi Howard, just a follow up question re vibration from rear end 1972 spitfire when i let off on the gas (ie coasting) , I removed the drive shaft, U joints are good, however should there be any Play in the drive pinion coupling flange when i turn it, It seems to turn about half inch before it engages. Could the front pinion bearing be bad?  Thanks  Wayne...

Answer
Hi Wayne,

The pinion bearings can be bad but you don't check them by rotational movement. It should not have any up/down right/left movement at all. The rotational movement free play is the "Backlash" which is measured by the ring gear movement not the pinion movement. The rotational movement of the pinion seems a lot but that is due to the swiping action of the pinion gear so it must be measured at the ring gear free play with a dial indicator. Without looking it up it will be about .005".

It is very rare for a vibration to be from the differential unless there is a large amount of movement from a completely destroyed bearing and more often be a bearing on the carrier assembly. Most differential vibrations are in the form of a whine noise. If you feel a vibration in the car you need to ID the frequency to separate it from wheel speed or drive shaft speed. Drive shaft vibration is a frequency of about 3 to 4 times as fast as wheel speed. Rest your hand on the shift lever when you back off the throttle to see if it is in the drive shaft or even the rear transmission bearing.

Put the car on a left and run it on a lift while someone is under the car checking for the vibration.

Howard