Jaguar 4 speed and o/drive gearbox Mk2 Jag

I have a very good Jag gearbox in my Mk2 but occasionally it is difficult to get across the detent into the reverse plane. Yesterday the car got a little hotter than usual in a traffic jam - it has an additional fan so no problem with the engine. I drove it a bit further and tried to park it but this time it was impossible to get the lever across into the reverse plane. After letting it cool off for a bout ten minutes it reluctantly moved across and was not the slightest trouble for the rest of the day. i have known other old Jag boxes very difficult to engage the gears when hot, but this is a different problem. all the gears including reverse engage very easily - it is just the detent that baulks. Any help or advice would be welcome. Bryan D

It would be good to know if your car has the Moss gearbox or the newer all sychro unit. Also might be good to add your location to your info in the forum.

It is the Jaguar box, not the earlier Moss box.

A lot of the linkage is external on top of the box, may be worth trying to spray some chain lube up and over the top of the box or go down from the gear lever gaiter hole, also make sure the gearbox oil is up to level.

Thanks for the advice. It is a strange problem because otherwise the gear shift has a really sweet, light action. I had an Austin Maestro once where the gear linkage repeatedly got crudded up with dirt and it affected all of the movements all of the time until it was cleaned again. This box has the best shift action of any I have tried but just once in a while it baulks on the cross plane movement.

Fortunately, on the manual cars, you can access the top of the gearbox in situ, so could remove the top cover to inspect. It’s an unusual problem, and it may be that the actual selector has come adrift on its shaft, so will not move into the slot in the selector forks. These are held in place with square headed grub screws which are lockwired; may have worked loose\ been assembled without lockwire, perhaps. Doesn’t sound like a difficult fix, YET, hopefully. If grubscrew drops out completely, you may be unable to select other gears if it’s in reverse.

Far more likely to be crud or burrs on the external selector quadrant or rods or spring detent plunger. If the selector fork was loose on the shaft I’d expect constant poor or impossible selection.

A misaligned quadrant assembly with the Tufnol washers and flat spring on the wrong side places the selector off line. Once it starts catching the tendency to cause burrs or rough contact surfaces gets worse the more you force it.

Don’t take the cover off until you have a gasket handy…

You can see the reverse detent position here, could be dry, gritty or similar,

Thank you for that. I did not expect to be able to actually see the part - very helpful. It is odd though that the next time it slotted through quite normally and has been fine ever since.