Transfer box in neutral for brake rollers?

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sierrafery said:
Mine passed every MOT since the beginning without any involvment of the transfer box. If the stand has the regulated right/left rotation function dedicated for 4x4 vehicles on that setting the wheels are spinning in opposite directions with the same speed and the propshaft rests. I've seen that every time and nothing bad can happen. I agree with @discool, maybe some MOT testers dont have the proper equipment

here's an example of such equipment https://www.maha.de/cps/rde/xbcr/SID-8C73D582-0301A6E0/maha_de/AMZ_Allrad_EN.pdf
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I would suggest that MOST MOT testers do not have the dedicated 4 wheel drive counter rotational special brake testing systems.
Which is why they do the safe thing and test with a Tapley meter. They also brake and use their brains to see if the brakes pull to one side or the other.
No magic in it.
It is not the tester's job to test a brake system to destruction.

And yes, as another poster mentioned, a rolling road is very different from brake testing rollers. In the former, the car provides the rotational force, in the latter the rollers provide it. Not rocket science. The first is designed to test the drive provided by the engine and transmission, the second is only designed to test the brakes.
 
Stanleysteamer said:
And yes, as another poster mentioned, a rolling road is very different from brake testing rollers. In the former, the car provides the rotational force, in the latter the rollers provide it. Not rocket science. The first is designed to test the drive provided by the engine and transmission, the second is only designed to test the brakes
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but what are the other 2 wheels doing and how is the center diff coping:eek:

J
 
Disco1BFG said:
Find and watch the video I referred to by Ashcroft :)
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why?
I know how a diff works.
If 1 wheel spins then you have the axle diff spinning against a stuck wheel and in a 4x4 case you also have a center diff spinning against front/back wheels also stuck.

so please excuse me if I don’t understand “spinning a wheel” on a brake tester for a few seconds.
J
 
marjon said:
but what are the other 2 wheels doing and how is the center diff coping:eek:

J
Click to expand...
Your Q is a bit ambiguous.
If you take a car to a rolling road to tune it, you need to have all the driving wheels on the rollers. I have only ever done this with a two wheel drive vehicle. The car's wheels drive the rollers and they in turn have to fight the resistance of the rest of the equipment. The machine measures how much power is being exerted on the rollers and translates this into bhp. If you tried to do this on a 4x4 one axle would push the whole vehicle off the rollers!
On a brake tester, the rollers turn the wheels with the car in neutral so that when braking force is applied, the rollers sense this resistance to their being turned and this is measured.
If you stick a 4x4 on the latter, the front wheels are turning, they in turn turn the prop and this then tries to turn the centre diff. If both the transfer box and the gear box are in neutral, then the gears should just spin, but they get very hot very fast. This is what the Ashcroft video is all about.
With a specialised 4x4 set of rollers, they spin one wheel clockwise and the other anti-clockwise and like that the prop shaft isn't turned at all. So the centre diff, tranny box etc have no problem. You just have to hope the diff on the front axle is able to cope, but they do.
and this is what the MOT testers say on their own forum!;););)
https://mtaeta.info/thread/3194/4x4-brake-test
 
Stanleysteamer said:
Your Q is a bit ambiguous.
If you take a car to a rolling road to tune it, you need to have all the driving wheels on the rollers. I have only ever done this with a two wheel drive vehicle. The car's wheels drive the rollers and they in turn have to fight the resistance of the rest of the equipment. The machine measures how much power is being exerted on the rollers and translates this into bhp. If you tried to do this on a 4x4 one axle would push the whole vehicle off the rollers!
On a brake tester, the rollers turn the wheels with the car in neutral so that when braking force is applied, the rollers sense this resistance to their being turned and this is measured.
If you stick a 4x4 on the latter, the front wheels are turning, they in turn turn the prop and this then tries to turn the centre diff. If both the transfer box and the gear box are in neutral, then the gears should just spin, but they get very hot very fast. This is what the Ashcroft video is all about.
With a specialised 4x4 set of rollers, they spin one wheel clockwise and the other anti-clockwise and like that the prop shaft isn't turned at all. So the centre diff, tranny box etc have no problem. You just have to hope the diff on the front axle is able to cope, but they do.
and this is what the MOT testers say on their own forum!;););)
https://mtaeta.info/thread/3194/4x4-brake-test
Click to expand...

oh wow

”If both the transfer box and the gear box are in neutral, then the gears should just spin,“

Who cares about the gears? Oh, if the transfer box is in neutral the gearbox won’t do anything actually.

it’s diff damage we are talking about.

J
 
marjon said:
oh wow

”If both the transfer box and the gear box are in neutral, then the gears should just spin,“

Who cares about the gears? Oh, if the transfer box is in neutral the gearbox won’t do anything actually.

it’s diff damage we are talking about.

J
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If the car is in neutral but the engine is running, whcih is normal for an MOT then the gears in the gearbox WILL be spinning, they just wont be engaged and doing anything to drive anything. If you then engage a gear but the tranny box is in neutral then the tranny box "won't do anything"
If we are talking about diff damage we are also talking about centre diff damage too. Which is what the Ashcroft thing is about.
 
if front axle can have one wheel spinning one way the other the other way center diff wont turn,if only one wheel can turn center diff will spin if transmission is in neutral either or ,not in neutral rear axle will try and turn, unlike ashcroft i dont find the center diff that weak as my disco and all landies ive had the center diff spinning shifting trailers and driving around my yard and fields,ass anyone else will have thats had a wheel spinning
 
So, to recap, that's a NO, YES, DON'T KNOW, PROBABLY, PROBABLY NOT then?
I'll drive it onto the ramp and go and chat to the other mechanics and leave Ian to it :)
 
Find a serious tester who has equipment for 4x4 vehicles and you can stay calm and wait.... normally those who dont have the tools should not have authority to test 4x4s. As long as the customer is paying why woult he remove propshafts or stay stressed?:mad:
 
jamesmartin said:
if front axle can have one wheel spinning one way the other the other way center diff wont turn,if only one wheel can turn center diff will spin if transmission is in neutral either or ,not in neutral rear axle will try and turn, unlike ashcroft i dont find the center diff that weak as my disco and all landies ive had the center diff spinning shifting trailers and driving around my yard and fields,ass anyone else will have thats had a wheel spinning
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Sounds like this could be Ashcrofts trying to cover their backside!;);)
 
jamesmartin said:
i think so,i believe they had a few center diffs bust and rather than blame yourselves you blame the driver, though some worn out old units are near the edge
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...question of driving sympathetically to the vehicle. If syncro on second is gone, do you just crash it in or double-declutch? You double-declutch! Although you wouldn't, you'd rebuild the box. lol!:D:D:D
 
Stanleysteamer said:
...question of driving sympathetically to the vehicle. If syncro on second is gone, do you just crash it in or double-declutch? You double-declutch! Although you wouldn't, you'd rebuild the box. lol!:D:D:D
Click to expand...
exactly crashing the gear will chip away at the gear and synchro hub dog teeth,meaning a vastly increased priced compared to a new baulk ring
 
Stanleysteamer said:
...question of driving sympathetically to the vehicle. If syncro on second is gone, do you just crash it in or double-declutch? You double-declutch! Although you wouldn't, you'd rebuild the box. lol!:D:D:D
Click to expand...

we are talking about diff issues?
How did it move to gear change methods;)

J
 
marjon said:
we are talking about diff issues?
How did it move to gear change methods;)

J
Click to expand...
We were talking about driving sympathetically to the vehicle, driving sympathetically to a Disco with diff lock means engaging it when off road to avoid the sort of problems you could possibly incur through not doing this. That is a diff issue. :rolleyes:
 
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