Clunky Rear Drive Bevel Box

Hi All, some advice for a Newbie please : bike is a Le Mans MK II, 1979, unknown mileage.

Bike on main stand, spin rear wheel and we hear ( me and Elsa the collie) a light clunking noise. Drive box fill plug removed and we can see the pinion gear is the source. I can move the pinion a couple of millimeters (max) with the end of a screwdriver; I can’t imagine that it is supposed to be anything but tight on it’s bearing ??

Having said that, the oil contains no metal debris and the teeth contact patches look perfect. Any comments folk ?

Hi and welcome.
It is quite normal to have a bit of backlash in the gears. It would be worthwhile dropping the rear wheel out to check and grease the spline that goes into the bevel box from the rear wheel. Then drop the whole bevel box off (4 nuts where it attches to the shaft) and grease the splines and collar where it connects to the drive shaft.
Keep the open end of the bevel box tipped up, or the oil will flow out.

Don, you are indeed a star, many thanks for your wise words !! Thats me for the weekend then !!

Do you mean the crownwheel? I don’t know that the pinion is visible.
Which way is the movement? As Don says, a bit of backlash is normal - I’ll check mine but maybe 10-15mm at the wheel rim.

Sorry, of course it’s the crown wheel ! I can move it a mil or so in it’s direction of travel ( and back) which from what you guys say is normal so I’m happy ! I will do as Don suggested and grease up the various splines, thanks for your input :smiley:

Hi Dave,
If you remove the bevel drive box from the swing arm just make sure that when you come to re-assemble it that you put the rear wheel axle through the bevel drive and opposite swing arm leg and then nip up the pinch bolt before you tighten the four nuts holding the bevel drive to the swing arm. This ensures everything is correctly aligned. The ultimate test is that the axle passes easily through the bevel drive, the wheel and the swing arm upon final assembly.

Hope this all makes sense.


Many thanks for that Phil, great stuff !!

The wheel splines were well greased and as a bonus, the wheel bearing looked pretty new and the cush rubbers were in perfect condition.

The drive shaft splines had a little bit of grease on, but I could see no wear marks at all on the teeth.

We check the compression a while ago, 155 and 160 PSI !!

All in all this must be a low mileage bike , its a MK II dressed as a Mark I so the mileage is unknown. The history I have goes back only a couple of years; she made the front cover of Classic Bike Guide a couple of months ago.

Anyone recognise the plate CEB 163 V ??