Can MOT testing damage transfer Box?

Looking at my fuse box cover... it reads... "A single axle roller rig may be used for speeds up to 5km/h. The centre differential lock must be disengaged. For roller tests over 5km/h, either all four wheels must be rotated at the same speed or if only a single axle roller rig is available, the centre differential must be locked and the propeller shaft to the stationary axle must be removed." Was it a 4x4 specialist garage? Hope this helps.

Wolverine Big Red 110CSW

There are similar warnings about suspended towing;

I wonder if someone could explain the damage mechanism? As I see it a single roller, or suspended tow is not a lot different to the situation where one pair of wheels on the same axle are spinning in mud and the others are stationary. (without the centre diff locked). Surely this is not going to damage things?

Regards Jeff

However, the initial question was about applying the handbrake while on the roller. A very good question indeed when one reads the driver manual of def's specifying that one should not apply the handbrake before the car is stationary.

Fred

On or around Fri, 10 Jun 2005 12:39:00 +0100, "Jeff" enlightened us thusly:

depends. You don't spin the wheels at e.g. 40 mph for extended periods. In other words, the speed difference across the diff is not very large and is only maintained for a short period.

God! I forgot about that one. Did it by accident once whilst pulling into the drive. The steering wheel still has the impression of my teeth in it!! :) Wolverine Big Red 110CSW

I'm absolutely not casting any aspertions on the MOT tester's abilities, but yanking the handbrake on when on the rolling road (as most do fro the MOT) can buckle the brake back plate. I'm saying no more....

Richard

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.

Richard

Richard

Is this likely to cause the problems that I have 'transfer box oil seal failure and therefore oil contaminated brake shoes"?

Regards

In message , Dunga writes

It is the wrong procedure to test a Landrover handbrake on a rolling road. Due to possible damage to brake backplate and prop UJs.

The act of having two wheels on the brake testrer. spinning with the others are stationary will do NO damage at all to the transfer box.

If you were underpower on a Dyno then a two wheel rolling road would damage the diff in the transfer box.

When under load on a two wheel rolling road the diff is having to pass all the power via the planet gears. These have no real bearings so to speak and soon die.

This is why if you get stuck and sit spinning your wheels you will knacker your axle diffs over time.

I imagine the diff and the UJ's in the propshaft would be subject to quite a bit of torque, which wouls also apply to the front axle via the transfer box and centre diff. Though if it bust an oil seal I expect said seal was about to go anyway.

had a double-system brake failure on a 110 once (sabotaged) and in panic I used the handbrake rather earlier than I should have (should have used the gears first), was on gravel at the time and managed an impressive but brief 4-wheel skid. No damage done (beyond the obvious sabotage). (don't worry nige, it wasn't the 110 you are currently driving).

Regards. Mark.

I had to have my centre diff replaced because it had been damaged due to excessive speed difference across it, I can't remember what the damage is but they're certainly only designed to take a fairly limited speed differential between the two outputs. Hence the warnings about towing in most 4x4 vehicles, including my old Audi 90 Quattro.

Its a possibility, but it would need careful examination to reach that conclusion - I'm treading very carefully on this as my wording could be misinterpreted.....

Richard

I wouldn't think so having driven some distance with the handbrake inadvertently on only to see the thing smoking away merrily which cannot have done the brake much good but my transmission is in tact. Of course my handbrake is not what it was and will need sorting before the MOT I suspect.

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. 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.

On or around Fri, 10 Jun 2005 22:35:22 +0000 (UTC), "SimonJ" enlightened us thusly:

same's true of land rovers with LT77, R380 or auto boxes.

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.

In message , Austin Shackles writes

Yes Austin I would pull the prop because the speeds involved are much greater than a rolling road.

Why not just disengage 4WD oh forgot you can't do that in modern land rovers can you :)

No but you can put the transfer box into neutral so only the diff with the wheels on the ground and half of the transfer box is turning...

I'm not up enough on how diffs work let alone throwing in a transfer box to know if that helps at all... I must look in a toy shop as some point to find some model diffs to play with. B-)

In message , Larry writes

No thankfully they have progressed !