Hi swoop and mr fixit
Arrived site on site removed the linkage from the top of the box and found that the block had jammed between the two actuator plates under the dash,freed it off truck is running fine now, but I think it was caused by partly, a heavy handed operator And worn linkage so I have advised the customer to replace the linkage as a precaution and I have a happy customer. Many thanks again for your input.
Cheers Ade

Hi mr fixit
Thanks for your input also I will check that out on Tuesday as well
Should not take long to whip the cover off I'm just hoping it's something simple as do not really want to take take the truck off site, once again thanks for input and I will let you what I find

Hi swoop
Thanks for your input, I will be back on site on Tuesday so I will see what pressures I'm getting and transmission details the serial no is B024D02265M
It does not have monotrol it's a shift stick type ( old school).
Once again thanks for your input I will let you know more on Tuesday
Cheers Ade

i'm looking in the manual for this series truck and all it shows is a powershift transmission.
can you verify this?
verify the serial number also? does it begin with C024?

if indeed this is a powershift you will have to do some pressure checking to verify what is going on in the control valve and clutch packs etc. If manual shift check the shifting linkage and make sure it is not worn or damaged as mrfixit said.
If by chance it has monotrol then there are other points to check.
If could be that it may be stuck between high/low or something like that.

first need to verify what type of transmission it is, and if it is truly manual or monotrol controlled.

Sounds like it stuck in 2 gears at once due to a bent or broken shift fork, (or worse)? Can you take the cover off the gearbox, that has the forks in it, and take a look?