I have just got hold of an early JH gearbox, JH1477, which would be correct for an early XK120 and am going to use some parts from it to refurbish my gearbox. The original JH gearbox in my 120 has the main shaft replaced with a JLN shaft, a Mark VII overdrive fitted and is using a JLN box top with the spacer and longer forks, all other parts being original.
I am wondering if the top on the replacement JH box I have would have been correct for a 1950 XK120 OTS with a JH box as I am getting carpet made and want to be sure the gearstick is in the correct location. The casting number on the replacement JH box I have is C1927. The top on this box has a short bent shifter which means that it came out of a FHC or possibly a saloon. I measured and the position of the shifter on the JH casting C1927 and the JLN top and they are identical.
Yes, my Mark V has box JH2210 and it is identical to my 120 box JH7977.
There were several shift levers, but they can be interchanged and would make no difference to the carpet and leather boot.
OK, I have all of the books and I am the worst at not looking at them. Urs confirms that casting C.1927 is the correct casting for an early XK120 and that all but cars fitted with radios had a bent gearstick.
The number on this box and the lower dip stick means that it could have only come from an early OTS.
Now I am going to see the clearance with the original gearbox top to see if I can ditch the JLN top, maybe be a clash with the top of the overdrive though.
Far be it from me to contradict Urs, but my DHC came with a radio and has the bent stick and I never recall any problem shifting and contacting the radio. Now, what I cannot confirm is that the car was fitted with a radio from the factory and not at a later date, although it was, from memory, the correct period unit. Interestingly, when a friend purchased the first Mazda MX5 in our area and let me drive it, the first time I shifted into 3rd my knuckles contacted the radio!
Maybe I’m reading this wrong, but are you trying to put an overdrive box in a 120? It won’t fit, interferes with the chassis cross member.
And the shifter forks are longer on the OD boxes. So unless you change them over I don’t see what you are trying to do.
And the dip stick will be an inch longer on an OD box than a JH box.
Box JH1477 could just as well have been in a Mark V, but regardless, is identical to JH boxes in XK120 and early Mark VII, same position of the gear shift lever.
The OD is already fitted, it was done a long time ago by a previous owner and the frame cross member has been professionally modified, so no hack job. To maintain full strength the steel used is very heavy gauge and the exhaust pipe hole has been removed as well. I will leave it as is, why undo all that hard work, and from what other say the OD is a very handy piece of kit.
Urs says in his book on the XK120 that the saloons at the time had a different longer shape to the knob on the top of the gearbox dipstick, which made me think that as the dipstick that was in the replacement JH box I got was the knob depicted for the XK’s that the gearbox therefore had to be from an XK. This may be in doubt now as the dipstick in the JLN cover on my existing original JH5151 box has the same knob as the XK style. This means that Urs may be wrong about the gearbox dipsticks, or simply that a previous owner changed the dipstick knob. The JLN dipstick is 1" longer just for the record.
I was going to see if it was possible to fit the JH top cover to my gearbox without the spacer, but I have since realised that it would not then have the fourth gear switch which would be necessary for the overdrive wiring. I could technically not use the 4th gear switch, but I would be asking for problems.
and may be the reason the dipstick hole covers on Mark V and alloy XK120 have a big hole in the middle, for clearance.
You occasionally see the rexine lumped up at the hole.
But it is unrelated to saloon vs XK120; my Mark V and 120 both have the shorter handled dipstick. However, a Mark V made a few weeks later than mine has the long handle. So my initial guess without more study would be that the change occurred in about the second quarter of 1950 on both Mark V and XK120.
Now it could be that the change was at different dates with SH vs JH boxes because SH boxes were coming in from Moss where JH boxes were built at Jaguar.
So the date(s) is(are) still unknown without more study and observations of known original cars.
