cruiser647 Posted March 19, 2008 Report Share Posted March 19, 2008 [ QUOTE ] [ QUOTE ] I cant see any problem with rolling testing a quattro car [/ QUOTE ] ??? Since the centre diff on non-Haldex quattros is a Torsen, then rolling road testing on one set of rollers will "wind up" the centre diff ... Worth reading this http://en.wikipedia.org/wiki/Quattro_(all_wheel_drive_system) [/ QUOTE ] Your suggestion implies that their might be quite a few Quattros out and about with 'damage' or wound-up centre diffs caused by the MOT Centre. How would you fix that? Link to comment Share on other sites More sharing options...
Botang Posted March 19, 2008 Report Share Posted March 19, 2008 [ QUOTE ] [ QUOTE ] I cant see any problem with rolling testing a quattro car [/ QUOTE ] ??? Since the centre diff on non-Haldex quattros is a Torsen, then rolling road testing on one set of rollers will "wind up" the centre diff ... Worth reading this http://en.wikipedia.org/wiki/Quattro_(all_wheel_drive_system) [/ QUOTE ] Wouldnt the centre diff only wind up if both rear wheels were turning the same direction? Link to comment Share on other sites More sharing options...
PetrolDave Posted March 19, 2008 Report Share Posted March 19, 2008 [ QUOTE ] Wouldnt the centre diff only wind up if both rear wheels were turning the same direction? [/ QUOTE ] The centre diff will wind up if there is a significant difference in speed between the front and rear axles - so front axle turning and rear stationary (or vice versa) will cause centre diff wind up. Link to comment Share on other sites More sharing options...
PetrolDave Posted March 19, 2008 Report Share Posted March 19, 2008 [ QUOTE ] Your suggestion implies that their might be quite a few Quattros out and about with 'damage' or wound-up centre diffs caused by the MOT Centre. How would you fix that? [/ QUOTE ] As you have posted there is an allowed duration and speed within which the wind up is allowable. What I was doing was pointing out that careless use of a single axle rolling road CAN cause damage - if the speed and/or effective distance while on the rollers is too long, so the statement "I cant see any problem with rolling testing a quattro car" is not 100% accurate. Care must be exercised - and it's ALWAYS worth reminding the MOT test station of that. Link to comment Share on other sites More sharing options...
Tobes49 Posted March 19, 2008 Report Share Posted March 19, 2008 [ QUOTE ] [ QUOTE ] Wouldnt the centre diff only wind up if both rear wheels were turning the same direction? [/ QUOTE ] The centre diff will wind up if there is a significant difference in speed between the front and rear axles - so front axle turning and rear stationary (or vice versa) will cause centre diff wind up. [/ QUOTE ] As long a you have a open diff in the front or rear axle and rotate the wheel in opposite directions, No winding up of the centre diff will happen. If the rollers are rotated in the same the direction, winding up of the centre diff will happen but as most brake rollers (I would think all but can not be 100%) operate at speeds less than 10 MPH this means you would have to sit in the rollers for at least 30min . (As per towing instructions you would be allowed 2.5 Hours!) I know it the garage will take the hit if something goes wrong, So I would recommend garages decelerometer tests the car. But I cant see any problems with brake rolling testing a quattro car! Link to comment Share on other sites More sharing options...
PetrolDave Posted March 20, 2008 Report Share Posted March 20, 2008 [ QUOTE ] As long a you have a open diff in the front or rear axle and rotate the wheel in opposite directions, No winding up of the centre diff will happen. [/ QUOTE ] And how do you suggest that the MOT garage does that? They would need a set of brake rollers plus a movable (to cope with the different wheelbases of vehicles) set of rollers geared so that one side turns one way and the other side the opposite way... That would be a VERY expensive setup, which most MOT garages could not even think about paying for. Far better to insist they follow the advice given to the MOT garages and brake test YOUR quattro on the road. Link to comment Share on other sites More sharing options...
Tobes49 Posted March 20, 2008 Report Share Posted March 20, 2008 [ QUOTE ] [ QUOTE ] As long a you have a open diff in the front or rear axle and rotate the wheel in opposite directions, No winding up of the centre diff will happen. [/ QUOTE ] And how do you suggest that the MOT garage does that? They would need a set of brake rollers plus a movable (to cope with the different wheelbases of vehicles) set of rollers geared so that one side turns one way and the other side the opposite way... That would be a VERY expensive setup, which most MOT garages could not even think about paying for. Far better to insist they follow the advice given to the MOT garages and brake test YOUR quattro on the road. [/ QUOTE ] If you spin the wheels in different directions on one axle at a time no winding of the centre diff will happen (If you have a dual axle set-up like you talk about then you can roll all 4 wheels the same direction at the same time and carry out a roller test like driving). Most brake rollers come with opposite direction rollers as standard. Some major makes in brake rollers: Crypton Boston Link to comment Share on other sites More sharing options...
PetrolDave Posted March 20, 2008 Report Share Posted March 20, 2008 [ QUOTE ] [if you spin the wheels in different directions on one axle at a time no winding of the centre diff will happen (If you have a dual axle set-up like you talk about then you can roll all 4 wheels the same direction at the same time and carry out a roller test like driving). [/ QUOTE ] So you've just agreed with me without realising it! Any garage with dual axle rollers (i.e. a tiny minority) can do the brake test on a quattro safely - I think we all agree on that? BUT any garage with only single axle rollers (i.e the vast majority) is unable to brake test one axle while rotating the wheels on the other axle in opposite directions - because they only have single axle rollers!!! So they should do the brake test on a quattro on the road. Link to comment Share on other sites More sharing options...
cruiser647 Posted March 20, 2008 Report Share Posted March 20, 2008 [ QUOTE ] [ QUOTE ] [if you spin the wheels in different directions on one axle at a time no winding of the centre diff will happen (If you have a dual axle set-up like you talk about then you can roll all 4 wheels the same direction at the same time and carry out a roller test like driving). [/ QUOTE ] So you've just agreed with me without realising it! Any garage with dual axle rollers (i.e. a tiny minority) can do the brake test on a quattro safely - I think we all agree on that? BUT any garage with only single axle rollers (i.e the vast majority) is unable to brake test one axle while rotating the wheels on the other axle in opposite directions - because they only have single axle rollers!!! So they should do the brake test on a quattro on the road. [/ QUOTE ] It will come down to where you go. I get my MOT done by an VAG indy - who takes it to another MOT garage. He obviously knows what to do or my man wouldn't use them. Just be wary of where you get it done - I suppose. Link to comment Share on other sites More sharing options...
Tobes49 Posted March 21, 2008 Report Share Posted March 21, 2008 [ QUOTE ] So you've just agreed with me without realising it! Any garage with dual axle rollers (i.e. a tiny minority) can do the brake test on a quattro safely - I think we all agree on that? [/ QUOTE ] Agreed [ QUOTE ] BUT any garage with only single axle rollers (i.e the vast majority) is unable to brake test one axle while rotating the wheels on the other axle in opposite directions - because they only have single axle rollers!!! So they should do the brake test on a quattro on the road. [/ QUOTE ] If you rotate the wheels on the same axle (eg N/S/R spins forward and O/S/R spins backward) with the other axle (eg front axle) stationary no winding of the centre diff will happen) As long as they have front and rear open diffs. Image of a front or rear open diff If the driveshafts (Red and Yellow) are contra rotated the planet gear (green) just spins and crown wheel (purple) doesn't move. I know I'm not the the best at getting things from my head to paper Link to comment Share on other sites More sharing options...
MGquattro Posted March 22, 2008 Report Share Posted March 22, 2008 OK Just had my A4 B6 Quattro Mot'd yesterday, Here's what they did. One set of rollers used, only drove one wheel with their rollers at a time, and let the other wheel free to rotate in whatever direction it wanted to do. Then pulled the rear axle onto the rollers and repeated the operation. Car drove off afterwards so must be ok Mike Link to comment Share on other sites More sharing options...
Scotty Posted March 23, 2008 Report Share Posted March 23, 2008 I wouldn't be happy if I was you. When my wife took it in this year, she reminded them and they said they knew. If you were allowed to do it then they wouldn't have known not to. Link to comment Share on other sites More sharing options...
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