AAU3052 Layshaft Bearings – B series 3 synchromesh gearbox, 3 hole layshaft

Currently, the needles in the AAU3052 bearings are .004” undersized, which will result in incorrect meshing of the gears.  An alternative is to use needle roller 8G2404 in this application.  These are the correct diameter, and are longer so have more bearing area.  Although they run over the unused circlip grooves, this has not proved detrimental, and over the long term this arrangement has given better bearing life compared to the original bearings.

To fit these needles:

  1. Use 20 x 8G2404 each end
  2. Shorten the spacer inside the laygear from 3.850 to 3.372”
  3. Retain the innermost circlip at the front end of the laygear.  Fit the shortened spacer up against it from the rear as usual.
  4. Add a front spacer inside the laygear, to seat down on the above circlip,  width 8.0mm.  The offcut from step 2 can be used for this, it is a good idea to cut this second spacer first before shortening the main spacer to its final length.
  5. Use adapted end thrusts/locators from the original needles at both ends of the new needles  Adaption needed may include grinding off the lip (though this might fit between layshaft and circlip if the thrust is assemble with the lip away from the needles), or reducing the OD a little on the front inner one.
  6. Retain with circlips
  7. Cut down the old layshaft to the length of the laygear to provide an assembly tool.  It is worthwhile making it sufficiently longer to help align the front thrust as the laygear is lowered into place    Grind a radius or taper on one end of this dummy shaft to facilitate its exit as the new layshaft is fed through.

Note that although the new needles are longer and extend over the circlip groove, experience with high mileage gearboxes with this modification has shown it gives no reliability issues.

Acknowledgement to Garth Bagnall for developing this alternative

Recent Posts