Quattro on a two wheel brake tester ??

[Tiger-G]

Hi,

I took my 2015 A4 Allroad for it's first MOT today, and the tester was going to put it on a two wheel rolling road brake tester. As I thought about cogs and drive shafts exploding, I told him that wasn't going to happen, as it's four wheel drive. He asked if it was permanent four wheel drive, to which I shrugged my shoulders, but thought in my head "no" ??

In the past he had checked my 2009 A3 TDi Quattro out on the road with a decelerometer, so thought he would be doing this with my A4.

Soooo.......to get to the point......could he have tested my Allroad on a two wheel brake tester ??

Cheers,
Graeme.

 

[daleyarrow]

My A4 Quattro gets tested on the 2 wheel system for the last 3 years since I bought it...never died yet. Pretty confident that it’s 2 wheel drive until slippage is detected on the front wheels, when it engages the rear wheel drive to compensate. I think the % of slippage differs from car to car, but quattro’s are never permanent 4 wheel drive...though I’m open to correction!


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[RyanJonS4]

A4 Quattros are full time 4 wheel drive, A1+A3 based quattros are haldex so are front wheel drive until 4 wheel drive is needed.

Your car uses an open centre diff so the front wheels can turn independently of the rears and the rears independent of the front.

I do remember reading that our cars should never be towed on a towing dolly where 2 wheels are lifted off the ground. I would think that due to the low speed the machine spins at for a short time it doesn’t do any damage.

 

[daleyarrow]

I stand corrected! I should spend less time listening to friends with RS3’s and more time believing what the forums say! A quick google confirms it, A4’s with the longitudinal engine has the Torsen system which is permanent 4 wheel drive with a 60/40 or 40/60 split depending on age.

I digress...as originally said mines never died yet in the last 3 years!


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[rum4mo]

You would think that the current standard of MOT equipment in these stations would could cover all cars that are likely to turn up, or be very aware of their limitations and turn away "unsuitable" customers.

So far, for my VW Group full time four wheel drive cars, I've only ever used my main dealer, VW for my B5 Passat 4Motion and Audi for my B8 S4.

My Cav GSI 2000 16V 4X4 disconnected the drive to the rear axle when the brakes were applied, so maybe VX garage due something about that during MOT time, it seemed to have survived okay though.

Edit:- I will say it has been a consideration when I've had any of these cars handed in MOT though.

 

[gary_a4_quattro]

The MOT station I use won't / wouldn't test either my previous B7 Quattro , my current B8 Quattro, nor my Charade Detomaso (FWD only ) but has limited slip diff on front axle. They use the decelerometer on road.

I guess all guidance regarding use of roller type brake testers is open to interpretation.

 

[youngsyp]

Your car uses an open centre diff so the front wheels can turn independently of the rears and the rears independent of the front.

Interesting. So the Allroad doesn't have a Torsen centre diff like the rest of the Av Quattros?

I do remember reading that our cars should never be towed on a towing dolly where 2 wheels are lifted off the ground.

That's true. Any car with permanent 4WD shouldn't have the front or rear wheels used independent of each end as damage to the centre diff (and transfer box if equipped) can occur. I'm not willing to risk whether it would or would not cause damage, no matter how long the axles are used independently of each other.
I've had only 4WD cars since 2001 and none of them have been put on the rollers at MOT time. Every time the tester just took them for a drive around the block to check the brakes. Far from a good test without a decelerometer but, that's their decision.

Paul

 

[Tiger-G]

Thanks for the info, should have trusted his superior knowledge

 

[RyanJonS4]

Interesting. So the Allroad doesn't have a Torsen centre diff like the rest of the Av Quattros?

That's true. Any car with permanent 4WD shouldn't have the front or rear wheels used independent of each end as damage to the centre diff (and transfer box if equipped) can occur. I'm not willing to risk whether it would or would not cause damage, no matter how long the axles are used independently of each other.
I've had only 4WD cars since 2001 and none of them have been put on the rollers at MOT time. Every time the tester just took them for a drive around the block to check the brakes. Far from a good test without a decelerometer but, that's their decision.

Paul

Yeah I think I’m wrong, it will have a torsen diff same as the rest.

I do think though that on a 2 wheel testing machine, as the machine is turning the cars wheels and the car is in neutral everything will be spinning freely and it’s not going to cause any damage to anything. The only way it could possibly damage anything is if our cars had a locked centre diff which we dont.

 

[PenttisHSR]

Modern Brake Testers have a 4 X 4 setting.
In this setting the N/S Rollers and O/S Rollers turn in opposite directions meaning that there is no drive to the centre diff.

In any case, Brake Rollers turn at about 1 mph and unless you have welded-up diffs or locked diffs there will be enough "give" in the system to cope.
That's why it's called "Limited-Slip".
You would be unable to drive the vehicle around a roundabout on dry tarmac if this was not the case.
That's why you can feel and hear noise when turning on full lock.

The slow speed of the Brake Rollers is also why ABS (Brakes) does not cut in.
ABS does not work below 4 mph.
Think about it, you would never be able to actually stop if it did!
Sometimes the ABS warning light can be activated due to one pair of wheels not rotating (i.e. the ones not in the rollers).
This should reset after going for a drive on the road.
OR do the brake test with the IGN/Engine off.

Some MOT Stations do not want to take the risk of damaging a vehicle and so take the car out on the road and use the decelerometer ("Tapley" Meter).
This just measures total braking effort.

 

[Tiger-G]

Modern Brake Testers have a 4 X 4 setting.
In this setting the N/S Rollers and O/S Rollers turn in opposite directions meaning that there is no drive to the centre diff.

In any case, Brake Rollers turn at about 1 mph and unless you have welded-up diffs or locked diffs there will be enough "give" in the system to cope.
That's why it's called "Limited-Slip".
You would be unable to drive the vehicle around a roundabout on dry tarmac if this was not the case.
That's why you can feel and hear noise when turning on full lock.

The slow speed of the Brake Rollers is also why ABS (Brakes) does not cut in.
ABS does not work below 4 mph.
Think about it, you would never be able to actually stop if it did!
Sometimes the ABS warning light can be activated due to one pair of wheels not rotating (i.e. the ones not in the rollers).
This should reset after going for a drive on the road.
OR do the brake test with the IGN/Engine off.

Some MOT Stations do not want to take the risk of damaging a vehicle and so take the car out on the road and use the decelerometer ("Tapley" Meter).
This just measures total braking effort.

Good info there, will know for next time

 

[youngsyp]

I do think though that on a 2 wheel testing machine, as the machine is turning the cars wheels and the car is in neutral everything will be spinning freely and it’s not going to cause any damage to anything.

I don't think that's true. The gearbox just acts as an interface between the engine and the drivetrain, whether it's in gear or not won't influence whether the front wheels are connected to the rear wheels, via the centre diff and prop shaft. Just whether they have torque applying to them from the engine.

The only way it could possibly damage anything is if our cars had a locked centre diff which we dont.

Our cars do have a centre diff that can lock though, it's just not permanently locked and allows a degree of slip too.

Paul

 

[Tiger-G]

Quick update:

It was MOT time again for my 2015 Allroad, and I decided to risk it on the two wheel brake tester. The guy doing the MOT showed me how when he was checking the front wheels and bearings he could have both wheels off the ground and spin them freely, which means in theory it should be ok on the brake tester.

Although I winced as he did the test, everything seems ok. There weren't any cogs and bits of gearbox falling off the car as I drove it away

p.s - I phoned Teesside Audi at 9am to ask them for their professional opinion on whether it would be safe to do. It's now 3pm, the MOT has been done, and I still haven't heard back from them. Well done again Teesside Audi, you continue to prove yourselves as f e c k i n' useless !!

 

[HOGG]

It's just lazy. My mot guy grabs a G meter and goes down the road.
Your mot OBVIOUSLY thinks that's to much like hard work

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[rum4mo]

My local MOT test station is within a Subaru main dealership, so if I ever move away from my Audi dealer for MOTs, I should be okay.

 

[Tiger-G]

It's just lazy. My mot guy grabs a G meter and goes down the road.
Your mot OBVIOUSLY thinks that's to much like hard work

Hmmmm........not sure I'd agree with that ??

I'd rather have my individual brakes tested on a roller so I know they are all working ok, than use a G meter that just tells you the brakes in general are stopping the car