On or around Fri, 10 Jun 2005 22:35:22 +0000 (UTC), "SimonJ" <
[email protected]>
enlightened us thusly:
>>
>> Someone who knows how diffs *really* work once expplained to me why
>> the two wheels driving the diff is not the same the diff driving the
>> two wheels. But it was a while ago, when our 7.5 tonner needed a tow
>> after it broke down and the recovery block took the rear prop off,
>> which was apparently the correct thing to do.
>>
>That's nowt to do with the diff, removing the prop doesn't stop the wheels
>driving the diff. The prop is removed to stop the gearbox being damaged (on
>commercial vehicle gearboxes, there is very often an oil pump driven from
>the input shaft.
same's true of land rovers with LT77, R380 or auto boxes.
>If you tow the vehicle with the prop connected, the gears
>are spinning, but the oil pump isn't, hence oil starvation, and a buggered
>gearbox.) The alternative method is to remove a halfshaft, slightly messier,
>as oil escapes, but sometimes you cant get to the propshaft, for e.g. on a
>tri-axle tractor unit.
>
However, there is a point about the diff, too. having one set of wheels
turning and the other not for extended periods or at high speed is not what
it's intended for; the whole diff is on bloody great roller bearings,
whereas the planet gears, which while going straight ahead do nothing at all
and on normal cornering only turn slowly, are not; they are, typically, as
was said, just on a plain shaft. Spinning the diff (especially if under
power on a rolling road) with one axle stationary is working those much
harder than they should be.
As regards suspended towing, in the case of the LRs with a neutral in the
transfer box, you can put the main box in gear (P on an auto) and the
transfer box in neutral. That stops the main box from turning at all and
the only stuff that turns is the lower half of the transfer box, and since
that's old-fashioned splash-lube, it should be fine. Suspended tow on 2
wheels does run the diff as mentioned above, but it's only driving the T-box
internals and therefore not under load, and I doubt it'd be a problem for
shortish distances - for long distances, I'd pull the prop anyway, to be on
the safe side.
--
Austin Shackles.
www.ddol-las.fsnet.co.uk my opinions are just that
Appearances: You don't really need make-up. Celebrate your authentic
face by frightening people in the street.
from the Little Book of Complete B***ocks by Alistair Beaton.
