I have an XK120MFHC with the JL transmission. While it is cold and during warming up it shifts fine. However, when it is fully warmed up the transmission will not shift. Any attempt at selecting any gear (with clutch fully depressed) is met with grinding. I know the clutch is operative and disconnecting the engine from the trans as you can depress the clutch (when cold - engine running) with the trans in gear and the car does not move Double clutching doesn’t help. Will rebuild and replacement of all synchros solve the problem? Could even the 4th gear synchro be that bad and, if so, why don’t they grind when cold? I want your opinions before I launch into a rebuild so I make sure to address the actual issue. Thank you very much. Scott

 

Hello: I am not an XK120/140/150 guy, but since you have not received any replies, I'll mention that I had a somewhat simliar condition in my 1980 Triumph Spitfire that was resolved when I chenged the gear oil in the transmission. I repeat, I have no knowledge of your JL transmission, but it might be worth a consideration/further investigation before tearing into the tranny.

Good luck.
Chris

 

Basically, you have what is called "clutch spin". The clutch is not releasing fully, so there is some slight drive going to the gearbox when you press the clutch pedal. When the gearbox is cold, the drag of the oil means this slight drive input doesnt make the gearbox move much but when its hot, movement is easy, so you get the crunching. I suggest you check out the clutch hydraulics, and try bleeding the clutch line. Have you checked for leaks at all ?

There could also be contamination on the clutch friction surfaces.

Can you also tell us what you mean by "JL" gearbox. Your car should have the Moss gearbox that has no synchro on 1st gear anyway.

 

Fraser -

Thanks for the reply. The “JL” is a Moss gearbox. They had the JL, JLE, and JH, and, I think, a JBN versions. The JL is the one used in maybe all XK’s. The clutch is a mechanical linkage instead of hydraulic and is adjusted properly. I think I am going to pull the trans and have it rebuilt. While out I can inspect/replace the clutch parts and see if that works

 

My '52 XK120 had some shifting issues using 10w-30 engine oil(straight 30 wt. oil a bit hard to find in some areas), did find some straight weight oil and I used 1 qt. of 30wt. engine oil mixed with 1 pint of Lucas oil conditioner additive, made a large difference in shifting with this car. Still kinda like driving a trash truck, but it does not grind nearly as bad.

 

Mark -
thanks for response and relaying your experience. I had straight 30wt oil with additive in the box and it not only would grind a little bit, it was nearly impossible to shift. The box was sent to a specialist to be rebuilt (probably due anyway) and with a fresh clutch should work ok. Fingers crossed. Scott S

 

Keep us posted, hope a trans refresh will do the trick!

 

Hello Scott,

I am having the exact same problema with my clutch. Please let me know how you've proceed, please.

 

I drove MK7s for 17 years and did have an XK120 for a year or so in the 1960s.
It is a clutch problem and not a fault in the gearbox.
It is either the friction plate sticking on the splines or the clutch plate and throughout bearing not doing the job or not properly adjusted.
cheers

 

Reactivated a '49 Ford pickup crash box and with the engine riunning it would creep forward even in neutral, because clutch disk was stuck on the transmission splines and would not slide away from pressure plate. Generous squirting of carb cleaner into the bell housing got things working normally..