Have a 1968 122S coupe with 4-spd M40 transmission. Vehicle did not come with an owner's manual, so I am hoping that someone will be kind enough to tell me: what the gear ratios are, what the max. speed is in each gear, and what shift points to use with a stock B20 (dual SU's) for best performance.

Thanks.

-=Bob=-

Hello Bob! I just wanted to give you some adding information about m40 gearboxes(useful or not, had nothing to do right now).
After 73`(140-series) they changed the ratio on first gear to 3.54:1(if i remember correctly)and gave it a stronger reverse gear(longer bearing).
Also there is a m42 gearbox with 2.60:1 on first gear and also longer second gear(i don`t remember the ratio), that was very popular for racing many years ago.
But the m42 was only used in military 4x4 Volvo "valp"("puppy") and 4-track snowmobile(had a low compression b18b engine).

DE. Sweden.

Gear...Ratio..incl Rear axle
1st.....3.13...12.8
2nd.....1.99...8.16
3rd.....1.36...5.57
4th.....1.00...4.10

In very general terms, shifting at 5500 rpms is a pretty good shift point for a stock B20 in normal tune for good accelleration. Probably 4500 rpms in normal use is better.

Speed in gears (approx - varies based on tires, speedo error, etc)
Gear...4500...5500
1st.....27.......33
2nd....43.......51
3rd.....60.......74
4th.....84.......101 (not a shift point - unless you have an OD???)

Funny to see the numbers worked out.
When tachs were a luxury, 30-50-70 were the typical shift points, unless the guy with a 283 Chevy in the other lane was trying to make a point.
Then you just drove it til it ran out of breath.

John,

Thanks very much.

Have saved your message for future reference. ;-)

-=Bob=-