NCT brake testinig a 4wd car on rollers

gn3dr

Quick question for anyone that might have experienced it.

I took my wifes car for NCT today - a '00 Audi A6 1.8T Quattro. I told the guy before the test at the reception that it was 4wd . Of course someone else tested the car and the stupid P***k did the brake test on the rollers. I knocked on the window to stop him but they didn't hear me knocking. As it is permanent 4wd they are supposed to do the brake test outside with the accelerometer.
I complained to the guy in charge and asked for a complaint form. They just tried to fob me off saying it was OK because it was non permanent 4wd (not true of course) and it would flag on thier system if it wasn't OK (which it wouldn;t because their system only pulls info from the log book) etc etc..

Has this happened to anyone else before?
If so what did you do to follow up if anytihing?
I think the car is probably OK but I want to follow up in case there is an issue with the gearbox / diff down to line.

Anan1

I brought an A8 quattro in a while gack, and they tested it outside with a decelerometer. What exactly did they do - ie were the front wheels on the rollers with the rears stationary? If so, I can't see that being good for the centre diff.

lazy-biker

yup my dads outlander

the monkey snaped something under the car and then the refused to pay the damages and they failed it because of it

the car was then parked in the middle of the testing area and walked out of the place

the soon payed up to repair the car

Top Dog

I've only ever brought one 4WD car to get an NCT. I was sure to tell them that they couldn't do the standard brake test because of it, and sure enough the tester drove around the normal rollers and took the car outside to test it with the decelerometer (?).

I'd lodge a complaint with them anyway, and also mention that you'll be taking it to your local dealer to make sure that no damage was done to your center diff as a result of them not paying any attention to what you'd told them.

felim

Forgive my ignorance but why can they not brake test a 4wd on the rollers?

Ferris

felim wrote: »

Forgive my ignorance but why can they not brake test a 4wd on the rollers?

I might be wrong but......

Because all 4 wheels are connected by driveshafts each axle is effectively 'locked together' with the other axle via a centre differential and driveshaft. Rotating one axle without rotating the other put huge stress on the centre diff and will break either diff or driveshaft within seconds.

There are different types of diffs that might take more punishment in comparison to others however (not sure - Haldex?).

gn3dr

Anan1 wrote: »

I brought an A8 quattro in a while gack, and they tested it outside with a decelerometer. What exactly did they do - ie were the front wheels on the rollers with the rears stationary? If so, I can't see that being good for the centre diff.

Yeah they put front wheels on rollers with rears stationary AND then put rear wheels on with fronts stationary (while I was knocking on the glass in the waiting room).

I have an S6 quattro myself and I always put a sticky note on the steering wheel saying not to be tested on rollers but this time I didn't do that - I just told the guy when giving him the keys thinking that would be enough.
I'm a bit mad with myself in that I should have maintained my assumption that these guys need step by step directions.

omega man

I was driving my wifes 4WD (grand vitara) in heavy snow yesterday and realised very quickly that there was only power going to the rear axle. Its not a permanent 4WD but had its NCT a few weeks ago and the wife said they did not take the car out. Should i assume they knew to ensure it wasnt in 4WD mode or does this matter?? Its gone to a Suzuki garage today on a seperate issue but they will check it out for us. I would never have thought of this until i saw this post.

Anan1

I'm surprised the car stayed put!

Top Dog

Ferris wrote: »

I might be wrong but......

Because all 4 wheels are connected by driveshafts each axle is effectively 'locked together' with the other axle via a centre differential and driveshaft. Rotating one axle without rotating the other put huge stress on the centre diff and will break either diff or driveshaft within seconds.

There are different types of diffs that might take more punishment in comparison to others however (not sure - Haldex?).

Thats pretty accurate.

Its also the reason that its recommended to never tow a 4WD with just one end raised, either flat-bed or tow with all 4 wheels on the ground if its only going a short distance.

Farls

I've never taken a permanent 4WD to the NCT but I'd be very surprised if no damage was done OP. I would call back in and look for a manager tell them that you will be getting it checked out at your dealership for damage and forwarding them the invoice. Any trouble get your solicitor involved.

Are these people even mechanics?!?! :rolleyes:

peasant

I'm not sure, but I seem to remember having read somewhere that the Torsen differential on the later Quattro models can indeed be tested on the brake rollers without damage.

I know for certain that the viscous coupling on my Syncro can't.

kayos

Whats the bets they have an any damage caused bla bla bla is not their responsibility clause.

galwaytt

..my last TT, when they put it on the rollers: front wheels on rollers, rollers started turning. As soon as they turned, the car 'climbed' out of the rig - driven by the rears!

They guy just didn't get it - repeated it twice. Only the other guys in the hall shouting "4 wheel drive" eventually got through to him.

Never affected the car, though. Bear in mind - that's a situation that could happen in real life - reversing out of a snow bank........??

Robbo

kayos wrote: »

Whats the bets they have an any damage caused bla bla bla is not their responsibility clause.

It's sufficiently negligent for them to have no way out.

Thinking back, I wasn't aware of this when I had an A4 quattro and had it tested.

peasant

galwaytt wrote: »

Never affected the car, though. Bear in mind - that's a situation that could happen in real life - reversing out of a snow bank........??

you should be reasonably ok once

- the car actually manages to climb out of the rollers
- and the rollers are driving the primary driven axle

Once the car doesn't move or the rollers are driving the wrong axle, thus winding the 4WD system the wrong way round something usually will go "twang"

Also the speed with which the rollers are accelerated plays a role. If the thing goes from nought to full speed within a few revolutions, something surely will have to give

rex-x

Now i'm not a 4wd expert but I do deal in scaled electric and nitro models with 4wd systems that operate with identical mechanics minus the electronic controls, and there is no way for anything of this nature to damage the 4wd system, once one wheel can spin while power is being applied it will be totally fine, you should be able to run full power through the centrer diff with no ill effects . . . . . . as said I am not an expert on the full size but i'd imagine it is exactly the same

Biro

rex-x wrote: »

Now i'm not a 4wd expert but I do deal in scaled electric and nitro models with 4wd systems that operate with identical mechanics minus the electronic controls, and there is no way for anything of this nature to damage the 4wd system, once one wheel can spin while power is being applied it will be totally fine, you should be able to run full power through the centrer diff with no ill effects . . . . . . as said I am not an expert on the full size but i'd imagine it is exactly the same

Depends a lot on the diff. The scaled versions aren't identical to the full size cause they're simplified versions. Also they don't have to deal with the same level of stress, even a scaled level.
Isn't there soemthing about a 2WD LSD not supposed to be tested on rollers too?

Anan1

There are very clear warnings in my Forester AWD's manual about the dangers of trying to tow the car with two wheels on the ground. I've also been advised to ensure that there is even wear on all four tyres, as differences in wheel rotation speeds can damage the system over time. Mind you, I still can't understand why the car didn't move.

mickdw

My understanding of the system in audi quattro (well TT at least) is that the front wheels are normally the driven wheels. If grip is lost at the front or additional grip etc is required, the back wheels are then engaged. So there is not a solid mechanical connnection 100% of the time.

Surely for the brake test, with the car is not in gear, the rollers spin the wheels and the rear wheels would not be engaged id assume. open to correction though

VanhireBoys

I had a GSi 4x4 Cavalier a few years ago. The 4x4 is an absolute night mare of a system on these with no centre diff. When I took it for NCT I removed fuse 19 so that the power steering engaged clutch for the 4x4 would not operate. This left it 2WD

I just didnt trust them "Failed Mechanics and Wannabe Mechanics" in the NCT centre. Theres no point in even explaining to them about the system, they are too arrogant and pig headed to listen. They know everything and look at you with "I am an NCT Inspector" head

Go and look for the manager - make an appointment with him if possible and then tell him what happened to your car. Tell him hes going to have to cough up if there is any damage done. Get a solicitor involved and dont lie down to them f**kwits...!

gn3dr

mickdw wrote: »

My understanding of the system in audi quattro (well TT at least) is that the front wheels are normally the driven wheels. If grip is lost at the front or additional grip etc is required, the back wheels are then engaged. So there is not a solid mechanical connnection 100% of the time.

Surely for the brake test, with the car is not in gear, the rollers spin the wheels and the rear wheels would not be engaged id assume. open to correction though

Yeah that's the system on the TT & S3 & other transverse mounted eningnes etc - it's different on the A6 though which has a longitudally mounted engine.

I'm thinking that the fact the car didn't push itself off the rollers means it probably has a viscous type centre diff - but I'm not sure. I did try it on gravel after the test to check drive was going to all wheels and it seems to be.

peasant

vanhire boys

bit harsh on the NCT there, aren't you?

Personally never had any issue with them and certainly wouldn't call them what you did

milltown

I'm trying to get my head around what the potential issue here is. The rollers are turning the wheels, yes? Is there no freewheeling ability built into the 4wd system, at least on the two wheels that are only part time driven (rears in this case I'm guessing)?

peasant

milltown wrote: »

I'm trying to get my head around what the potential issue here is. The rollers are turning the wheels, yes? Is there no freewheeling ability built into the 4wd system, at least on the two wheels that are only part time driven (rears in this case I'm guessing)?

That is the problem ...there may or may not be.

Depends on the actual system.

On a selectable 4x4 something mechanical, pneumatic or electric goes "clunk" and pushes a cog into place and you have mechanical drive straight through or not.

On permanent 4x4 systems there are so many different systems out there, that it is a science in itself to try and understand them all (I don't even pretend that I do)

Google viscous coupling, haldex clutch and torsen differential for starters and see can you explain it

VanhireBoys

peasant wrote: »

vanhire boys

bit harsh on the NCT there, aren't you?

Personally never had any issue with them and certainly wouldn't call them what you did

I am not going to start NCT Baiting/Bitching
and I do apologise if I offended any NCT inspectors but the fact is that I have brought up 7 cars and every time I seem to get the "Know it All" I have no problem them failing me for sommit but when they start the "better than you" craic. :mad:

The types I have met have neither mechanical skill or people skills but I must have met the wrong ones .. Just like the OP who must have met the wrong one as well

Johnny Utah

I have an NCT booked for next week, and I'm just wondering if there is anything I should look out for when they are testing my car- diesel RWD.

Would the RWD require the decelerometer as opposed to the standard brake test on the rolling road?






And if the OP is still here; how did you get on with your complaint?

NiSmO

This post has been deleted.

smokingman

Johnny Utah wrote: »

I have an NCT booked for next week, and I'm just wondering if there is anything I should look out for when they are testing my car- diesel RWD.

If you've a turbo diesel then watch to make sure they don't do the smoke test for petrol cars. The last two times I've had an NCT, they've put the hose on the exhaust and revved the bejaybus out of it.
None of my protestations were heard in time and while the turbo wasn't blown afterwards, I was just very lucky. This also happened my neighbours Land Rover Freelander but his turbo didn't fare as well and was leaking when he left the center. They had put the smoke test on the results sheet though like with mine so at least we had proof of what was done.

Anan1

Surely revving an engine shouldn't blow the turbo unless it was already faulty?

Johnny Utah

smokingman wrote: »

If you've a turbo diesel then watch to make sure they don't do the smoke test for petrol cars. The last two times I've had an NCT, they've put the hose on the exhaust and revved the bejaybus out of it.
None of my protestations were heard in time and while the turbo wasn't blown afterwards, I was just very lucky. This also happened my neighbours Land Rover Freelander but his turbo didn't fare as well and was leaking when he left the center. They had put the smoke test on the results sheet though like with mine so at least we had proof of what was done.

Yes, I have a Turbo Diesel. It's an E46 320d, which has a reputation for turbo failure, but thankfully I've never suffered any trouble on my own car.

What smoke test should I ask for? I thought that they had to attach a hose onto the car, whether it was petrol or diesel?