Jim
Have you checked the transmission oil level and that it's the correct type? The older JCB 3CIII powertrain used 10w monograde oil whereas the 3CX used ATF I believe. A quick oil and filter change might be worth doing.
If it only works in reverse when cold, it's possible that the forward clutch packs are worn. Does it have much "grunt" when trying to drive into a pile of earth? If not, this again suggests that the clutch packs are worn.
I've got an old 3CIII which had a similar problem but after changing the filter and fluid, it made a difference. Don't forget that your machine's nearly 30 years old though!
Steve, September 2011
