Query: NCT rollers and AWD cars

Standard Toaster

Hi lads,

Just a quick one re the NCT. I've a Impreza and as you know they're AWD.
How do they test them on the rollers? Would it damage the diff if they tried?

(Same way if you ever get a tow truck the whole car has to go on the truck and not just the two wheels)

Cheers

Anan1

Don't let them put the car on the rollers, they have a decelerometer to test the brakes on AWD cars.

Standard Toaster

Grand thanks

sunshinediver

Anan1 wrote: »

Don't let them put the car on the rollers, they have a decelerometer to test the brakes on AWD cars.

Does this apply to RWD cars also?
cheers

Anan1

No, just AWD.

Ferris

What about RWD cars with LSD's?

Thinking it through myself I don't see an issue so long as both wheels remain at the same speed but i'm not sure.

Anan1

Ferris wrote: »

What about RWD cars with LSD's?

Thinking it through myself I don't see an issue so long as both wheels remain at the same speed but i'm not sure.

As you say, I can't see it being a problem.

Biro

Apparently it is a problem though, according to some people in a thread about this some time last year.

Anan1

Biro wrote: »

Apparently it is a problem though, according to some people in a thread about this some time last year.

What was the problem? Do the rollers rotate at different speeds?

puntosporting

If thats the case it would apply to FWD cars with diffs fitted also,must say ive never heard such an issue ?
Are the rollers seperate to each wheel?

gofaster_s13

LSD's should never be brake tested on a rolling road be it front, rear or four wheel drive.

Anan1

gofaster_s13 wrote: »

LSD's should never be brake tested on a rolling road be it front, rear or four wheel drive.

Why not? Can one roller slow much faster than the other, thereby putting pressure on the LSD?

peasant

Anan1 wrote: »

What was the problem? Do the rollers rotate at different speeds?

Im not entirely sure, but as I understand those rollers, they speed up together, but once they're de-coupled from the drive, they spin seperately (to measure the performance of the individual brakes)

So if you had a big imbalance on your brakes, your limited slip diff would go "pop" fairly quickly

gofaster_s13

Anan1 wrote: »

Why not,

For a variety of reasons the main one being the hand brake is tested one wheel at a time on the brake rollers, also if you have a problem with a brake imbalance one wheel could be turning significantly faster than the other.

Ferris

Jesus, just as well I asked :eek:. Thanks lads.

I just bought a 200sx and it will be going for an NCT shortly. Looks like its post-it on the steering wheel time.

How do they check the rear brakes then?

Beta Ray Bill

Ferris wrote: »

I just bought a 200sx

Quality Mo Mo!


I love them!

JimmyCrackCorn!

Ferris wrote: »

Jesus, just as well I asked :eek:. Thanks lads.

I just bought a 200sx and it will be going for an NCT shortly. Looks like its post-it on the steering wheel time.

How do they check the rear brakes then?

Shouldn't have an issue factory viscus diff wont complain.

gofaster_s13

JimmyCrackCorn! wrote: »

Shouldn't have an issue factory viscus diff wont complain.

Bad advice, your taking a serious risk to be taking, your putting the plates under a lot of pressure

ismynametoolong

There i no problem having a 2wd tested on a rolling road be it front or rear wheel drive even when fitted with an LSD it is the very same as rolling the car on a road in neutral.AWD's should not be tested on a single rolling road as the prop tries to drive back through the transfer or centre diff in the transmission and this can cause damage as both axles should rotate similtaniously, but generally when carried out it is done a low speed and not for very long and the possibility of damage is limited, i know a number of centres that have tested AWD,s on the rolling road with no problem but personally i would insist on the deacceleratomer placed on the passenger floor well , but this means they have to drive your car and they dont like to do this but if you tell them before they start the test there should be no problem

TomMc

OP, I stuck this notice on the dash of my car a few weeks ago and told the tester at the hatch as well - Job done. No problems.


*** PERMANENT ALL-WHEEL-DRIVE.

AVOID BRAKE TESTING THIS CAR ON ROLLERS.

AS PER HANDBOOK ROTATING FRONT OR REAR WHEELS ONLY MAY/WILL DAMAGE THE VISCOUS COUPLING.

PLEASE USE DECELEROMETRE ONLY (Tapley etc.) MANY THANKS.

---

As an aside, I could hear the girl in the test centre say OH MY GOD (several times) when the mechanic told her the car was been brake tested with a Tapley Metre. It was like the wacky races were about to take place in the centre itself. The tester must have did the test in the car park as the car was never brought out on the public road.

JimmyCrackCorn!

gofaster_s13 wrote: »

Bad advice, your taking a serious risk to be taking, your putting the plates under a lot of pressure

but the issue is your not putting the plates under any more pressure than under normal driving or even on a dyno.

This is different if there is a centre diff/transfer box in the case of 4wd which is a completely different ball game.

Brake performance
Right at the beginning of this section there seems to be an anomaly. There are four examples of vehicles which should not be tested on the roller brake test equipment. They are vehicles with:
• more than one driving axle permanently engaged
• limited slip differential
• belt drive transmission
• Brakes for which the servo operates only when the vehicle is moving[/SIZE][/FONT]

http://www.motester.co.uk/st15.html

Anan1

gofaster_s13 wrote: »

For a variety of reasons the main one being the hand brake is tested one wheel at a time on the brake rollers, also if you have a problem with a brake imbalance one wheel could be turning significantly faster than the other.

I was thinking about this again - if one wheel tried to turn faster than the other, wouldn't the LSD just stop it? I mean, isn't the LSD designed to cope with the maximum power output of the engine, ie booting it in 1st with one wheel on grippy tarmac and the other on ice? Or does the fact that the power is being channeled in the wrong direction make a difference?

gofaster_s13

Anan1 wrote: »

I was thinking about this again - if one wheel tried to turn faster than the other, wouldn't the LSD just stop it? I mean, isn't the LSD designed to cope with the maximum power output of the engine, ie booting it in 1st with one wheel on grippy tarmac and the other on ice? Or does the fact that the power is being channeled in the wrong direction make a difference?

Yes the LSD would try to stop but it would be trying to turn the wheels at the same speed against an applied brake and also against the brake rollers electric motors. The poster who compares a car being pushed in neutral to a rolling road is forgeting that the rollers are being driven by electric motors. I have tested hundreds of vehicles fitted with Lsd's on the rolling road (generally the customer will not tell you that it has an lsd fitted and you will only know when you jack the back axle) and I have only had one let go which was a Nissan viscous lsd

L-M

I was in getting a car Nct'd today and I noticed a sign on the wall. All it said was "Note to all 4x4 drivers, brakes will need to be tested", or something to that extent. No information, just a warning.