Some random thoughts on the speedometer problem.

First, we probably have a match that never existed in "stock" form, at least not in the US market... I'm guessing a 4.10 diff, matched to a transmission speedo drive that "wants" a 4.56 rear gear ratio to work accurately. Therein would lie an approximate 10% inaccuracy from the get-go. ((Not that early 140 speedometers were all that accurate to start with... IIRC, they didn't even tell you which part of the "slash" on the ribbon was supposed to be the accurate part!))

Having said all that, my 1972 140 parts catalog has very clear references to the existence of many different drive gears for the M40, M41, and BW35's, well outside the 18 to 20 tooth range. The M40 part numbers are:

380164-4 (16 teeth, 142 & 144 excluding USA & Can)
380166-9 (17 teeth, 142 & 144 USA & Can, 145 chassis #9200 and up)
380168-5 (18 teeth, 145 up to chassis #9199)

The same catalog lists 13, 14, and 16 tooth gears for the BW35, to wit:

670131-2 (13 teeth, 142 & 144 various chassis numbers)
672886-9 (14 teeth, 145 various chassis numbers)
380164-4 (16 teeth, 142, 144 & 145 various chassis numbers)

Since there is a crossover part number (the 16 tooth in both tranny's), I would therefore assume that all M40 and BW35 speedo drive gears will physically interchange... but I don't know this for a fact.

Unfortunately though, when you get to the M41 (at least WRT to the 1972 140), there is only one drive gear listed, and it seems to be unique to the M41. Interestingly enough, there is NO gear tooth count for this part number, 380753-4. Prolly the 20 tooth? In any case, no clue as to whether it will physically interchange with any of the above 13 to 18 tooth gears above.

So the 20 tooth drive gear you are currently using came with the M41, yes? Do you still have the speedo drive gear from the automatic? If so, the obvious questions... how many teeth on it, and will it physically fit in the M41?

And finally, a comment on your 142E, as delivered new. A rompin', stompin', 10.5 to 1 B20E, with a stinking automatic????? That had to be a pretty rare combination, I would think? I can honestly say I have never seen one. Of course, they were also slipping (no pun intended) automatics into a few high compression (1970/71) 1800E's at that time, so I guess the '71 142E auto would have to have been a distinct possibility.

Gary L.

--
1971 142E ITB racer, 1973 1800ES, 2002 S60 T5