A 140/150/Mk1/Mk2 close-ratio gearbox has a “CR” suffix to the gearbox
number. There is no change in 4th gear speed as it is direct drive. The
closer ratios for 1st through 3rd are nice, but it really helps to have
the numerically higher overdrive rear axle gears as the CR 1st is
somewhat difficult to live with if one has the non-overdrive axle gears.
XK150S with CR OD gearbox JLS40444CR> From Mark Stephenson:
Since my 120 has a 140 engine, there is no telling if the gearbox is original. I’m interested in determining if I have a CR box or not. I was under the car the other day and couldn’t find any indication of the gearbox number. I guess it’s on top, so I’ll have to go in through the tunnel. Unfortunately I duct taped everything to cut down on the heat.<
So, my question is, if one has the standard rear end in an XK120, what would be the speeds in mph for 1st through 4th at say 2000 rpm, for the CR box and the standard box? I should be able to tell from that, correct?<