|The MGA With An Attitude
BEARING SHIMS For DIFFERENTIAL INPUT SHAFT - RA-110
I have some reported cases of strange bearing shims on the differential input shaft causing assembly problems. It is not known if this is/was an original installation or a field adjustment.
On the differential input shaft, ahead of the rear bearing there is an inner race spacer tube followed by some shims and the front bearing. The shims are used to set preload on the bearings. The bearings are different size, and the shaft is smaller diameter near the font for the smaller bearing, but the spacer tube has ID to match the larger part of the shaft. The shims need ID to match the shaft (smaller diameter) and OD to match the front bearing inner race and spacer.
Shims found in assembly have had various OD as well as different thickness. Assemblies reported have one thick shim (usually .012") and one thinner shim. If this is original factory installation, it appears they may have started with a standard size thick shim and then selected a thin shim to make up the rest of the required shim stack.
The problem found is that the OD of the thinner shim (1.220") is smaller than the OD of the thicker shim (1.370"), and the ID of the spacer tube (1.125) is somewhat larger than the shaft at that point. This leaves only a very narrow part of the thinner shim (.047" around the outside edge) to support the load between the bearing and the spacer tube. The thin shims seem to be getting crushed in assembly at this point and are giving problems with the assembly dimensions.
The apparent solution is to use a thin shim with larger OD (1.370") to match the OD of the thicker shim and the OD of the inner bearing race and tube spacer. I have checked with Moss Motors Ltd, USA, and their replacement shims all have the larger OD, so this is not a problem with current supply (at least through Moss). So this is just a heads up to watch for the small OD shims in prior installations, and if you find them, swap them out for the proper larger OD shims.