The only difference in a standard ratio and close ratio gearbox is the pair of ‘Constant Gears’. XK120 didn’t offer close ratio gears from factory, but there is Service Bulletin offering the pair of close-ratio constant gears as spare parts, so you could upgrade your standard XK120 gearbox. If done, the gearbox number stayed the same of course, unless whoever did the mod decided to stamp in CR suffix to existing number. For XK140 you could option/specify a close ratio gearbox for new cars, and if so the factory added a CR suffix to gearbox number, on top cover as well as main body, and also on the cars matching numbers ID plate and on the factory ledgers as will be shown on a Heritage Certificate.
With a gearbox in hand the only way you can be sure is to take the top off and count the teeth on the Constant Gears.
Sorry, I was talking about Moss or Jaguar made to Moss design gearboxes as used on XKs and 3.8 E-types.
Your question is regards all-synchro E-type Gearboxes.
The prefix letters tell you. EJxxxx is Close Ratio with gear helix angle greater, and was later considered a little noisy (not in an OTS where you couldn’t hear, but more so in a FHC EJSxxxx is same Close Ratio gearbox, with an extension for 2+2 only.
EExxxx was next, now a wider ratio gearbox, still with same noisy helix angle. Only found briefly with Series 1-1/2
KExxxx for all Series 2 OTS and FHC was next, still same wider ratio gearbox, but with finer helix angle for quieter running, but at expense of less efficiency, so some loss of transmitted power. These are normal
KJSxxxx is normal for Series 2 2+2, if not fitted with Automatic.
So your EJSxxxx is a Series 1 2+2 close ratio gearbox; there was no CR suffix clues.
I’m thinking of putting this box in a 420 I’ve just acquired but having no experience with CR boxes I don’t know whether it would be good or bad with the standard 3.31 diff. The first gear at 2.68 is tall and could be a problem on steep starts. What do you think?
have a KFN box with OD so it might be a better bet.
Peter, there are 3 different ratio sets for the all synchro box (4 if you include the rare XJS box).
The 1st was standard in the 4.2 S1 E, optional in the 2+2 E, with a 2.68 !st gear.
Then you had a 2.93 !st gear for the S1 2+2, E and sedans, and then, for unknown reason they produced a box with a 3.04 !st, which was used in the S2 E and the XJ sedans.