The Classic Machinery Network

It might just be that the Bowden cable from the dash lever to the shuttle spool is worn, they can go stiff with age. Also I think their should be some kind of detent to find neutral but I remember ours was worn.
Check the convertor/shuttle fluid by running on fast idle for a few minutes from first start up. Either check whilst running or immediately on stopping the engine. Add fluid down the dip tube (near the bulkhead in front of the screen under the bonnet). Add fluid carefully in small quantities as it is easy to overfill. The gearbox is a separate unit although all bolted together. That has a level plug on the side.

As this a power train you should not put ATF oil in at all, the shuttle (long dipstick ) it should have 10/30W oil in the gear box has HD90 gear oil in (fill through level plug in side of box) it sounds to me that you have damaged the clutch plates by running with the wrong oil in.

ATF fluid is specially designed for torque convertors, been using it for years and no problems. Torque converters are based on fluid wedge theory so using a denser fluid can be more damaging than using a less dense one. While using too dense fluid can cause sever mechanical damage to the converter, the use of not enough dense fluid can only cause drive slip and this causes overheating of the converter (same as if you put it into gear and increase throttle while holding down the brakes). As for transmission, if you do not have the torque converter linked to it than yes, don't use ATF in transmission. I have a greycab 3cx and mine has the torque converter and transmission linked so it uses same fluid (JCB special transmission fluid = ATF, it's the same stuff), but the principle is the same.

Try to get the manual, probably it's here on this site, there you can find exactly the amount and type of oil/fluid to use and where to fill/check it.

For more info though:

jcb 3c3 powertrain

JCB boy you have got it wrong your m/c does take atf powertrains do not, they take 10W engine oil

I used to use the JCB torque fluid or whatever they called it (20 odd years ago) and I recall it could double as a light engine oil. We have an old Sanderson with an identical (or very similar) borg warner soft shuttle + spicer g/box, I have used either the JCB oil or another dedicated transmission oil. Surely the t/con is combined with the shuttle and that requires an oil suitable for wet clutches?

Phil is spot on
This could be useful, although there are mistakes/overlaps if you are looking at a specific model


http://www.q8oils.co.uk/applicationdatabase.aspx