On 6/14/2012, Simon Terry wrote:
"Is there a way to evaluate backlash without pulling the thing apart"?

Apply hand brake. Select neutral. Turn propshaft by hand. If it will rotate back and forth 1/4-inch (about 8 degrees rotation), it will likely have a clunk with reversing torque, on and off throttle. Then replacing differential thrust washers will most likely remove a lot of that backlash.

Excessive backlash between ring and pinion gears is very unusual. The ring and pinion gears are about the most robust parts on the whole car. These commonly run a quarter million miles with no problem.

Badly worn bearing, races out of plane.

If the differential oil was not changed for 30 years or so, or it was allowed to run low on oil, then the ring and pinion gears might wear. They won't break, but the would whine like crazy until you get perturbed enough to fix it. Also running contaminated oil or without oil, it is more likely that the large ball bearings in the differential carrier will wear out before the gears. That also makes it whine loudly before anything falls apart.

See tech session for changing MGA and early MGB differential gears and thrust washers at
http://chicagolandmgclub.com/photos/a_diff

On 03 December 2012, M.J. Moore in Cheshire, UK wrote:
"The flat thrust washers are 2.5" OD and 1.5" ID. The bronze ones I took out of mine were 32 to 34 thou thick and I replaced with fibre ones measuring 36-37 thou. The convex washers were 1.5" OD and 23/32" ID; thickness on the old ones was 31-32 thou and on the new ones 35 thou. The backlash on my axle at the input was around 4 degrees and I estimated that over a quarter of this was due to crown wheel/pinion backlash and there will be more due to wear in the half shaft splines plus differential sun/planet gears. I estimated that approx. one third of my backlash will be removed by replacing the thrust washers. I will measure it again after traveling a few hundred miles after giving the cup washers a chance to bed in. I remember looking around at the time for material from which to make bronze washers but without knowing the metal specification I concluded it would be risky venture".