Gearbox

[Acco6x6]

      I have been carting some gravel for my road in the last week. The gearbox is jumping out of gear on the over run or going down hill.  I have been told it could be worn selectors and am wondering if others agree or have had other problems. I suppose it means gearbox out to fix the problem does it?

            Cheers

[GGG]

Gearbox or transfer case?
Geoff.

[Acco6x6]

     Geoff. It is the gearbox

[Chazza]

It could also be the detent-spring being broken, or weak, for that selector rod.

Have a read of a workshop manual and see how the box is made, which should give you an idea on whether or not it has to come out,

Cheers Charlie

[Acco6x6]

   Thanks for the reply Charlie  If I can get my hands on a workshop manual I will  do that 

       Regards
             Stewart

[Ravvin]

Here you go.

https://www.dropbox.com/sh/okfo5y3ixjwn4x1/AABsPQtZxKslQDZRjnPDpClea?dl=0

MK3 Service Manual, so slightly different gearbox, but should be better than nothing.

I've never seen a copy of a service manual for the F1's.

[Acco6x6]

    Much appreciated Ravvin and by the way I have been enjoying your posts on your rebuild
         I wonder has it damaged the gears from changing in low range.  I t is very hard to get them in when crawling along.  Wonder how the army drivers were taught to do it

[GGG]

Stewart, we used to change gears in low range as it was all in the drivers' course at RAASC Centre. They are not normally all that difficult as crash boxes go so unfortunately it sounds like you have a problem. Sorry about the happy thoughts. I asked which box originally as the transfer case tended to jump out of low range on the over run to the point where the co driver spent a fair bit of time sitting on the engine cover holding it in. Descending a steep slippery hill in low range was not a nice time to suddenly find yourself in angel but it was all good fun.
Geoff.

[Bluebell One-eight]

Stewart, the most common cause of a box jumping out of gear is excessive end play in the mainshaft. It could be a selector problem too, so a complete inspection is in order. The transfer case was actually designed to select low range without front axle drive if the trigger was NOT pulled.It would then return to neutral under overrun. This feature was introduced when the 6X6 was released. The Mk 3 did not have the feature when released, but the Mk4 did. When cases were overhauled, they were modified to the later standard. If low range was selected and the dog teeth for front axle drive did not line up then the detent mechanism didn't lock the case in low range and it would jump into neutral on overrun as above. It was best to select low range while the vehicle was moving, that way it would lock in low almost always. Any sort of fault in the locking would produce the fault too. hope this helps.

[Acco6x6]

     Thanks gents.  It is the main gearbox which is jumping out of gear 1st 2nd 3rd so this would have nothing to do with the transfer case would it

[john.k]

there is a manual online for the 6x6 gearbox,look at Fuller 5W43.which is the proper designation for the box.In my experience,the commonest cause of these boxes jumping out of the lower gears is gear damage caused by incomplete engagement,which is common in accos,commercial as well as army.I do have a little experience,with 50 years spent repairing truck components.Incidentally,these are one of the best 5 speed boxes ever fitted to a truck.

[Acco6x6]

    I think you might be on the money with this one John K.   It is pretty hard to get 2nd and third into gear perfectly when crawling along loaded when going uphill or in boggy ground etc  Thanks for the manual info
   Stewart