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Diff-locks to engage or not to engage.

G

Guest

Guest
The oil tanker came to our house yesterday and they (new supplier)
didn't send the small lorry requested, but rather an ordinary large one
"to see if it would fit". So it got stuck, and I had to haul it up the
drive with the LC80.
I was a bit worried about pulling this much weight uphill, and bearing
in mind the comments about breaking diff-locks - especially the front -
under heavy loads I decided just to use the centre locker. We made it,
with some wheel spin, and I was glad about this because I felt that it
limited the loads on the transmission a bit.
However it got me thinking: is it better to engage the diff-locks or not
in this sort of situation? I suppose in favour would be that it
distributes the loads equally on each half shaft, and against that it
puts more load on the locking mechanism.
Ideas anyone?
Christopher Bell
Devon, UK
1996 1HD-FT
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Guest

Guest
Christopher,
Locking the diffs does not balance the half-shaft load, just the
opposite. When a wheel is spinning and you lock the diff that wheel still
has no traction, all of the torque is on the other wheel. There is a
possibility of putting all the engine torque on to one wheel if all the
diffs are locked. This could break a shaft.
My answer to this problem would be to let the oil company get the
vehicle towed out, that way they would remember next time.
Regards,
Clive Marks
Home: +44 1293 514600
Mobile: +44 7821 491897
Crawley, West Sussex, UK.
 
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Guest

Guest
Clive
You're quite right of course - after I posted that I realised that leaving the locks off would be more likely to give even loads (so I think it was the right thing to do). I think engaging the centre lock was probably right thing to do given the viscous coupling, after all in the original Toyota setup this would happen automatically in low range anyway.
As for leaving them to tow it out ... well, it's a single access lane which would be blocked while it was there. Pulling it out backwards would be tricky because there is a 90 degree bend to negotiate; getting round the top is tractor access only via the fields, and at this time of year that in itself would be tricky; finally - crucial point - my tank was dry (don't ask) and I wanted that oil!
CB
Christopher,
=A0=A0=A0=A0 Locking the diffs does not balance the half-shaft load, just the opposite. When a wheel is spinning and you lock the diff that wheel still has no traction, all of the torque is on the other wheel. There is a possibility of putting all the engine torque on to one wheel if all the diffs are locked. This could break a shaft.
=A0=A0=A0=A0 My answer to this problem would be to let the oil company get the vehicle towed out, that way they would remember next time.
Regards,
Clive Marks
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Guest

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One of the Mercedes Trucks we have is an 8 wheeler with a crane that weighs
24 ton empty. Our 100 series v8 has happily towed it home when there was
fly by wire throttle failure.
Our Farm is on a pretty steep 1/2 mile gravel track. From experience with
the weaker Land Rover axles I have found it safer no to put the axle lockers
in because it can lead to a lot of load on 1 shaft. The 100 series only has
the centre lock but has never failed to tow anything. The Police man did
just shake his head is disbelief and looked the other way as we trundled up
the motorway.
Cheers
JOhn
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of Christopher Bell
Sent: 22 January 2009 10:44
To: [Email address removed]
Subject: [ELCO] Diff-locks: to engage or not to engage.
The oil tanker came to our house yesterday and they (new supplier)
didn't send the small lorry requested, but rather an ordinary large one
"to see if it would fit". So it got stuck, and I had to haul it up the
drive with the LC80.
I was a bit worried about pulling this much weight uphill, and bearing
in mind the comments about breaking diff-locks - especially the front -
under heavy loads I decided just to use the centre locker. We made it,
with some wheel spin, and I was glad about this because I felt that it
limited the loads on the transmission a bit.
However it got me thinking: is it better to engage the diff-locks or not
in this sort of situation? I suppose in favour would be that it
distributes the loads equally on each half shaft, and against that it
puts more load on the locking mechanism.
Ideas anyone?
Christopher Bell
Devon, UK
1996 1HD-FT
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses
 
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Guest

Guest
John
| 24 ton empty. Our 100 series v8 has happily towed it home when there
was
| fly by wire throttle failure.
That's reassuring.
Though it was not, I suspect, in low range 1st gear on a motorway! That
was what was worrying me as there is *so* much torque going through the
transmission.
There is a final irony: I've since discovered that the same lorry failed
to make its next fuel drop 3 miles down the road because its gearbox
broke. Judging by the mess he made in our yard by driving around with
his diff-lock on I rather suspect that "gearbox" should actually read
"rear axle".
CB
____________________________________________________________
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Guest

Guest
Hi,
I would say should not make much difference if you had the diff locks on,
providing the surface is slippery? As all torque/bind would get wasted once
the wheels slip?
Keeping the rear/front diff locks off is probably the better option if it's
likely to bind due to the surface you are on.
I guess the centre lock is best to lock up or you may do the Viscous in, or
possibly find most of the power going to the rear which will probably leave
you spinning and going nowhere as the viscous tries to shove power to the
front and back to the rear.
You certainly have the risk of putting too much strain on the gearbox, if
you had it all locked up and the surface is not slippery,not sure if that
would bind the gear box with open diffs (I don't think it would as bind can
be released by either wheel when the rear/front is unlocked?).
Open diffs are much better on slippery side slopes as locking the rear would
tend to send the rear of the vehicle sliding down the slope...
Sorry I am pulling this information out of my head, and there are far more
knowledgeable people on this list, who are sure to point out my errors :)
Suppose the rule of thumb for this, is to try the diff locks if you are just
spinning, unless you have dug yourself a hole already of course in which
case it's too late.DOH! :)
So it looks like you done the correct thing...
Martin.
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of Christopher Bell
Sent: 22 January 2009 11:38
To: [Email address removed]
Subject: RE: [ELCO] Diff-locks: to engage or not to engage.
Clive
You're quite right of course - after I posted that I realised that leaving
the locks off would be more likely to give even loads (so I think it was the
right thing to do). I think engaging the centre lock was probably right
thing to do given the viscous coupling, after all in the original Toyota
setup this would happen automatically in low range anyway.
As for leaving them to tow it out ... well, it's a single access lane which
would be blocked while it was there. Pulling it out backwards would be
tricky because there is a 90 degree bend to negotiate; getting round the top
is tractor access only via the fields, and at this time of year that in
itself would be tricky; finally - crucial point - my tank was dry (don't
ask) and I wanted that oil!
CB
 
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