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Differential Side Shim Thickness Determination from Initial Backlash Measurement

September 23, 2010 | Troubleshooting & Repair

By Larry Coreth

[This article also available as an Excel spreadsheet]

The following data and charts are intended for those who are equipped with the necessary measurement tools, shop manuals and the desire to setup the ring & pinion having swapped out either the differential carrier or said ring & pinion set. The use of these tables (right) and graphs (below) are straight forward in that you can use either the tables or the graphs since the graphs are made directly from the data tables.

Once you have assembled the intermediate plate with all the gears, shafts and bearings and inserted this assembly into the trans. housing, then the differential with bearings and shims (estimated) and finally bolting all this up tight you are ready to do the backlash measurement per the manual. If as usual this measurement is outside the spec. of 0.15+ or ñ .05mm you need only look up the measured backlash on the X ordinate and read up or down to the curve and then over to the required shim thickness change required to bring the backlash in spec.

For Example

Backlash measured = .010" / .25mm
Required thickness change = .0049" / 0.12mm


All this is based on data I got from Mike Robbins who has been doing transaxles for some time, read decades! For those with interest the "predicted" curve is a regression analysis done on Mikeís data in MS-Excel and the fact that it crosses the X ordinate right at .006" /.15mm , the backlash spec, is a an indication of good correlation with the data.

[This article also available as an Excel spreadsheet]