I haven't posted in a good while but I had to log in for some advice. I brought the rr to be tested today and I wasn't paying too much attention with 2 mad kids running round, but I saw that the tester drove the car onto the 2 rollers. I assumed he was carrying out a visual test or something (as it shouldn't be tested on 2 wheel rollers?) and I'm not sure if they actually tried to brake test it on the rollers but I did notice the back wheels studdering and shaking. The whole car shook. Is that normal in these tests? Or I s that what would happen if u put the rr onto a 2 wheel roller and try to brake test it?

It passed the test and i was happy enough but after getting home and thinking bout it shaking and back wheels struggling I thought I'd look into it.

Any advice appreciated.

I didn't think RR are suppose to go on the rollers, unless its a four wheel one, It won't have done the centre diff much good.

 SC 4.2, 2012 face lifted, 25K miles, 1 previous owner
Triumph TR6 1973
Triumph Bonneville 1970
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what he said^^

they should have a deceleration box they use to test the brakes on the car, thats what they do over here on cars with permanent 4wd. I would make a written complaint to the testing station. It will not have done the centre diff any favours at all! There is nothing that can't be fixed with a hammer😜😜
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Not good

I had this argument at a local test centre with my Defender.

I told the "engineer" the only way it was going on the rollers was if he stood between the Defender & the wall in front of it.

He backed down. Diesel - Just Say No!

2000 110 4.6 V8 (mmm Megasquirt)

Thanks but I'm wondering if they even did try to test it as I can just imagine me complainig and them saying they didnt put it on the rollers. Surely the fact of the back wheels shuddering was them
Attempting to test it?

what should I look out for now regarding damage?can I test myself or have to get a mechanic to check?

i recently had nct, for braking they dod with a meter

it went on the rollers but i don't think they did a break test, think it was doing like suspension type testing

yep that would be it.

there isn't many ways to test that it hasn't done damage. RRphil has striped one of the centre diff/transfer boxes, maybe he can offer assistance on what damage may have occurred if any.

though it isn't good to do it you may have been lucky and avoided damage. There is nothing that can't be fixed with a hammer😜😜
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Permanent 4WD doesn't mean it can't be tested on a single axle roller.

For the purposes of an example lets take a bog standard 300Tdi Defender (i.e. one that doesn't have traction control). It has three diffs: one in the front axle, one in the rear and one lockable one in the centre.

An open differential splits torque equally between both sides - when one side loses traction then less torque is required. Because of the 50:50 split then less torque is applied to the wheel that has traction, this torque may be less than required to spin the wheel therefore what happens (assuming the power output from the input / pinion gears remains constant) then the wheel with little traction spins faster.

In the case of an unlocked centre diff then when one wheel loses traction you can spin that wheel leaving the three with traction stationary. Extrapolating this example then two wheels can lose traction (say rear axle) and the front stop spinning.

If you lock the centre diff then this means that you are guaranteed not only 50:50 torque split (inherent from the differential design) but also 50:50 power distribution. Therefore you will have 50% of power going to the front axle and 50% going to the rear axle. In this situation you can still lose traction completely as you can have one wheel at the front and one wheel at the rear spinning through loss of traction.

If you add a one more locking diff (say rear) then you can at worst end up with 3WD as one of the front can still spin freely leaving the opposite with no power. Three locked diffs is the only true way to get continuous 4WD.

So... the summary is that it is safe, assuming a bog standard Defender with bog standard diffs, to run a vehicle such as a the Defender on a single axle rig provided the centre diff is unlocked.

Now the full fat... The issue gets complicated by the traction control / terrain response such as in the Full Fat. Unfortunately in this situation the system kicks in and either locks the centre diff automatically or potentially simulates a locked rear diff by applying the brakes to the wheels. Without knowing what "off" means in terms of the DSC or Terrain Response I wouldn't like to make a call as to running it on a single axle roller rig. In this case it'll be a case of RTFM.

Hope that helps clear up a few things?  Ed

I note what you say but when I had my manual Disco 1, which has the same drive train as a bog standard Defender, in the 16 years I owned it it was always the decision of the respective tester not to use the single roller but to go for a drive and use a Tapley meter instead. This was at a number of Mot test stations over the years. The only time a tester was considering using the roller, imo in ignorance of the possible consequences, he changed his mind when I asked him if his insurance was up to date before testing my car.
Nothing to stop you testing the Disco handbrake on a roller other than the possibility of shearing the bolts holding the drive shaft to the transfer box flange should the handbrake be in really good working order.
As to the FFRR there is no way a tester is testing my cat on a roller irrespective of the theory, fortunately to date I have never come across the situation, testers generally seem to have sufficient common sense not to be so foolhardy.
If I happen to ever come across a tester about to test my FFRR on rollers I would simply terminate the test before he could.

Slight update to my post above as I (stupidly) missed out an important bit of information.

Driving the wheel on a single axle rolling road won't be an issue. However (and here's the important bit) if you hit the brakes then you can in effect simulate a limited slip diff and thus make the 1 or 2WD drive potentially become 4WD and then catapult the vehicle off the road.

The other unique aspect with Defenders / Discos is the transmission brake - not good to apply that when under motion, either on a rolling road or not!

So the theory of how a diff works still holds up but above is just a description of how a differential set up works. Ed

The man said it right above... Fine on a two wheel rolling rig, right until the point where you apply the breaks then It all goes wrong

Most likely what you saw was the suspension and side slip test being performed one axle at a time.Thats the reason why you saw the vehicle shaking around.The suspension test plates are right beside the rollers

It doesn't cause any issues at all on a FF, the traction system will only work if you are using the engine to turn the wheels, and you are in drive or reverse, the vehicle will be in neutral. The rollers are turned by an electric motor, therefore the car thinks it is coasting and will not lock the center diff or use the brakes on any spinning wheel.

It won't cause any damage to any part of the FF and it won't fly off the rollers unless you put it in drive and accelerate. Pete

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My MOT he took the car for test drive with a compass type box in the passenger footwell

an extract from the WM,