Can MOT testing damage transfer Box?

>
> A front CVJ locked solid and the tyre got a flat spot on it.
>
> I was not in the workshop while the test was being conducted, but I saw
the
> large dials rotate to something like 80%. Then on the second axial, the
> dials only went to about 10%, and the engine revs reduced much quicker. I
> assumed that it had failed.
>
What have engine revs got to do with it, the test is done with the vehicle
in neutral?

> But it passed.
>
> My service man and the VI person I spoke with at first, agreed that the
> tester had put a massive force on the transmission.
>
> The first journey after the test was when the wheel locked.
>
> The VI man told me that the tester was at fault. But after a written
> complaint, I their story changed.
>
> It was suggested to me that the centre diff was on during the test.
>
Assuming that you mean diff lock, had that been on it would have shown
itself imediately the rollers had started turning.

> The big question. Why did the dials on the second axial only go to such a
> low level. The only answer that makes sense is that the tester remembered
> that he was doing it wrong.
>
Or perhaps that the brakes on the rear axle aren't as effective as the rear
(front= discs, rear= drums)


> There was also a minor problem with the need to change bushes on the rear
> shocks, which did not need changing. Clearly the tester had no idea how
to
> test Land Rovers.
>
The rear shock bushes on a land rover are no different to any other vehicle.

On or around Mon, 13 Jun 2005 16:10:23 +0100, Marc Draper
<[email protected]> enlightened us thusly:

>In message <[email protected]>, Austin Shackles
><[email protected]> writes
>
>
>>>There is no way that damage to the centre diif you cause your vehicle to
>>>swerve into on coming traffic.
>>
>>Inclined to agree, there. Mind, *rear* diff, I've had one of them cause
>>interesting effects.
>>
>
>
>Yes Austin.
>
>Wheel bearings, CVJ, front or rear diffs, bushes and ball joints could
>all cause it to swerve and none of them can be damaged by a brake
>tester.

aye. Discounting the possibility that something was on the verge of failing
anyway, I spose, and the act of braking with the transmission brake
overloaded something already-weak in the transmission. But that's a very
long shot.

--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Quos deus vult perdere, prius dementat" Euripedes, quoted in
Boswell's "Johnson".

On or around Tue, 14 Jun 2005 00:12:45 -0000, "Alan Morris"
<[email protected]> enlightened us thusly:

>> Please give details of how you feel you vehicle was damaged by the test?
>>
>> AS we have discussed at length the only possible way to damage it would
>> be by applying the handbrake on the rolling road.
>>
>
>A front CVJ locked solid and the tyre got a flat spot on it.

was this the incident on the road?

If so, then the CV joint was worn/damaged beforehand, very probably. Front
brake test doesn't load the CV joints. If the diff lock had been engaged in
the centre diff, then the brake tester would have immediately showed this.
Could have damaged the diff or the difflock, but not likely the CV joint,
IMHO. The CV joints are pretty tough.

>But it passed.
>
>My service man and the VI person I spoke with at first, agreed that the
>tester had put a massive force on the transmission.
>
>The first journey after the test was when the wheel locked.
>

I'd not actually rule out the possibility that the CV joint was damaged, but
it is, IMHO, extremely unlikely. Nor would damage to the centre diff or
difflock affect the CV joint.

The only brake test that can damage things in the rear half of the
transmission is the handbrake, which is of course a drum on the gearbox.
Thus the REAR half of the transmission is put under (possibly excessive)
load by hauling on the handbrake. Front brakes, however, work on the wheels
and put no load on the transmission, UNLESS the centre diff was locked,
which there would be no need to do. Still, I doubt if such loads would
damage a CV joint unless it was already weak, more likely to damage the
centre diff or the difflock.

CV joints in "straight" position are pretty strong.

--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"Quos deus vult perdere, prius dementat" Euripedes, quoted in
Boswell's "Johnson".

"SimonJ" <[email protected]> wrote in message news:[email protected]...
> >
>> A front CVJ locked solid and the tyre got a flat spot on it.
>>
>> I was not in the workshop while the test was being conducted, but I saw
> the
>> large dials rotate to something like 80%. Then on the second axial, the
>> dials only went to about 10%, and the engine revs reduced much quicker. I
>> assumed that it had failed.
>>
> What have engine revs got to do with it, the test is done with the vehicle
> in neutral?
>
>> But it passed.
>>
>> My service man and the VI person I spoke with at first, agreed that the
>> tester had put a massive force on the transmission.
>>
>> The first journey after the test was when the wheel locked.
>>
>> The VI man told me that the tester was at fault. But after a written
>> complaint, I their story changed.
>>
>> It was suggested to me that the centre diff was on during the test.
>>
> Assuming that you mean diff lock, had that been on it would have
> shown itself imediately the rollers had started turning.
>

Normally when the vehicle is placed in the rollers both rollers a run together to
straighten up the vehicle if the diff lock had been in and the hand brake applied
then yes the dials would have shot up or if the roller not being run locks (some
do to help you get out) again this would have had the same effect
But as SimonJ said it would have shown itself imediately the rollers had started
turning
The question is who put the diff lock in? A chap tried this on me because he
had a faulty rear brake that wouldn't show itself on a tapley (decelerometer)
test but did on the rollers




>> The big question. Why did the dials on the second axial only go to such a
>> low level. The only answer that makes sense is that the tester remembered
>> that he was doing it wrong.
>>
> Or perhaps that the brakes on the rear axle aren't as effective as the rear
> (front= discs, rear= drums)
>

Or there is a pressure limiting valve on the rear brakes

--
Andy

SWB Series 2a ( dressed as a 3) "Bruce"
It's big, it's mean it's really, really green

>
>A front CVJ locked solid and the tyre got a flat spot on it.
>
>I was not in the workshop while the test was being conducted, but I saw the
>large dials rotate to something like 80%. Then on the second axial, the
>dials only went to about 10%, and the engine revs reduced much quicker. I
>assumed that it had failed.
>
>But it passed.
>
>My service man and the VI person I spoke with at first, agreed that the
>tester had put a massive force on the transmission.
>
>The first journey after the test was when the wheel locked.
>
>The VI man told me that the tester was at fault. But after a written
>complaint, I their story changed.
>
>It was suggested to me that the centre diff was on during the test.
>
>The big question. Why did the dials on the second axial only go to such a
>low level. The only answer that makes sense is that the tester remembered
>that he was doing it wrong.
>
>There was also a minor problem with the need to change bushes on the rear
>shocks, which did not need changing. Clearly the tester had no idea how to
>test Land Rovers.
>
>Alan
>Alan.
>
>

The wheels are not driven by the engine during the brake test !

The front axle should be a lot higher in reading than the rear !

If the centre diff was engaged then the front wheels would either not
turn because the hand brake was on or it would just pop out of the
rollers because the rears would turn as the fronts were driven by the
rollers.

I find it very hard to believe that the rolling road can but the
transmission under more load than the car can itself when under general
usage especially a Discovery. The CVJ are hugely strong.

The reason your tyre was flat spotted is because your CJV locked up
other wise the other one would have had a flat spot too !


If the bushes have play in them then they need changing

I do think your failure was more bad luck than MOT damage.

To make a comment as you did regarding the death of his son was
unnecessary on a public forum !

--
Marc

The vehicle handbrake is for holding the vehicle when parked, but it is
also an Emergency Brake.
As such, it needs to be tested to prove it is capable of bringing the
vehicle to a halt when required.

The transmission handbrake can be tested on rolling roads. There is a
procedure outlined in the MOT Inspection manual to perform this test.

Both rollers must be run together.
The handbrake must be pulled up very s-l-o-w-l-y while holding the
release trigger in.
The tester will know what readings to expect to see, and as soon as
these readings are attained, then the brake should be released.

The readings are 16% for dual circuit brakes, and 25% for single
circuit.
Using a vehicle of 2000kg as an example, this equates to:
16% = 320kgf (or 160kgf per rear wheel)
25% = 500kgf (or 250kgf per rear wheel)