Hi I have googles this to death and tried to search the forum but can't find the answer.
We have a Hymer A class and I notice that 5th is like an overdrive ratio and if your tootling along at 60 it won't pull 5th uphill or into a strong headwind, you have to rev it quite hard in 4th before it will pull 5th.
I noticed on a very old post from 2016 that someone had changed the 5th gear to a lower ratio and I have been trying to find more information and part numbers etc
Can anyone point me in some directions to look please?
I was faced with the same problem.
I was aware of the possibility for the lower ratio 5th gear for the 2.8Jtd. You do not say which year your engine is since the position of the 5th gear changed from being external to internal.
I solved the problem in another way, by having the engine re-mapped, not just with a chip, but done to my requirements through the engine management.
If you decided to go for re-mapping as an alternative to changing the ratio of 5th, I would recommend two things about operating - firstly, which is actually applicable to 5th gear on any 2.8Jtd, is to wait till engine is up to operating temperature before changing to 5th, to ensure the spash lubrication is reaching 5th, secondly not running in 5th below 2200rpm, to avoid over-torquing the drive train including the clutch.
With those two caveats in mind I would say that after 25,000 miles the re-mapping is a good alternative.
Although I did not ask for better mpg it does seem to produce 1-2mpg better, because one can sustain 5th for longer.