Hello Mick,
There were 3 Types of differentials used with the E Type. Salisbury Type 1,2 and 3. What I was referring to with regards to not being able to determine lack lash with shims removed, referred to a Type 3 Diff used in S2 and S3 cars.
Both Type 1 and 2 used Taper Roller Bearings and both Pre-load and Back Lash adjustment was made by shims between the inner face of the Output Shaft Bearing Housing and the Differential. The main difference between Type 1 and 2 differentials is that the the Output Shaft and the mounting Flange for the Rotors and Half Shafts are a two piece arrangement for the Type 1 and one piece for the Type 2.
The method to adjust the Back Lash for Type 1 and 2 Diffs, is to install the Output Shaft Bearing Housings, as shown in the picture below (as an assembly with Output Shafts, or just the Housings) with no shims and snug the securing bolts up firm, but not overly tight.
It's best to have a circa even gap between flanges and diff housing to start. with. The correct Back Lash is then obtained by shifting the position of the Crown Wheel relative to the Pinion Gear, in or out by loosening the securing bolts for the Output Shaft Housing on one side of the diff housing and tightening the bolts on the other, When the correct Back Lash is obtained, the gap between the Bearing Housing flanges and the diff is measured and a shim stack equal to each gap, less 0.0015" each side is then assembled between the diff housing and the respective Bearing Housing assemblies. The less 0.0015" in shim stack is to result in a 0.003" pre-load of the diff centre bearings. This is a far better system for adjusting Backlash and Pre-load than with the Type 3 diff, in my opinion, for a number of reasons. 1. The diff centre side bearings are an interference fit on their journals, with backlash and pre-load being adjusted via shims located between the bearings and the diff centre. 2. Once the correct shims for pre-load have been established in the assembly, a diff spreader is typically required to assemble the diff centre with the housing; this is not the case with Type 1 and 2 differentials.
Type 3 differentials used Double Row, Angular Contact bearings, where the centre race of the bearing was in two halves. When the centre race was assembled with axial hand pressure, there exists a small gap between the inner faces of the inner race. When assembled with the Output Shaft and the nut securing the bearings was torqued up correctly, the faces of the inner race are pressed to make intimate contact and the correct pre-load resulted. These bearings haven't been available for many years and the bearing being offered is a very poor replacement. It has the same ID/OD, the centre race is one piece with the bearing having some end float that can't be adjusted. It's 2mm narrower, requiring spacers to be used. The sealing system, where the inner face lip of the seal was supposed to seal against the face of the out race is the wrong size and ends up partially on and off the bearing face.
Later differentials reverted back to using Taper Roller Bearing for the Output Shaft. The Output Shaft/Bearing Housing assemblies of the later differentials using the Taper Roller Bearings will assemble with the differential and replace the Double Row, Angular Contact bearing system without any modification to the diff housing whatsoever. Accordingly, when refurbishing a Type 3 Differential, its better to replace the original bearing system with the later Taper Roller Bearing system. Unfortunate, the Output Shaft assemblies from later differential are becoming hard to get. Accordingly, I now manufacture the Bearing Housing and as there is a "Metal On" condition with the earlier Type 3 Output shafts, an original Type 3 Output Shaft em to be re-machined to the specifications of the Taper Roller type Output Shaft; I supply these on an exchange basis.
Regards,
Bill