David
I am assuming by "hop" you mean something similar to axle wind up. If
so read on.
Years ago my father bought a Blitz (CMP F45 I think) crane conversion
(essential for a contract job, not as a hobbist, no manuals came with
it) and
had a problem with diff hop, (in Australia our terminology can get a bit
loose).
They first noticed every so often there would be "skip cum skid"
marks in the dirt. It had them baffled, but as time was money
they ignored it until one day the front diff failed (it is under the
most
load in the crane version).
Upon pull down he found the ring gear and pinion had stripped each
other.
When he went to order parts he was asked which ratio he required, this
came
as a surprise as he had assumed that WW2 vehicles were made with few
options and variations. Then he also discovered that there were major
differences between the Chev and Ford "Blitz", they just looked similar,
both vehicles were made with a choice of ~ 3 different ratios depending
upon intended use.
You guessed it, his Blitz had 1 x Ford diff and 1 x Chev diff running
dissimilar ratio gearing; it was just a matter of how long before
something broke.
In your case have a look at your diff ratios, it could be the problem,
someone might have been fiddling without the required knowledge,
if it is you will need to do your homework and find out what ratio
should be in your vehicle for your application - before something
breaks.
Regards
Doug
Australia