Is It Just A Quattro Thing?
11-20-2010, 06:52 PM
#11
AudiWorld Super User
Also, be aware that the term "scrub" is referring to the tires scrubbing the pavement, not rubbing on any suspension components. It isn't noise as much as a feeling. It's the inside tire scrubbing the pavement because it is turning at the same speed of the outside tire, but covering a shorter distance.
You can really experience this in something like a Grand Cherokee with Command-Trac (Jeep's full-time 4-wheel drive). Mom's turn the wheels to lock, trying to pull into a parking space, and complain about the car "lurching" through the turn. It's really quite pronounced!
I think Audi really does an amazing job of smoothing out a tight turn while using a fully mechanical full-time, all wheel drive, drive train.
Anyway, for what it's worth...
You can really experience this in something like a Grand Cherokee with Command-Trac (Jeep's full-time 4-wheel drive). Mom's turn the wheels to lock, trying to pull into a parking space, and complain about the car "lurching" through the turn. It's really quite pronounced!
I think Audi really does an amazing job of smoothing out a tight turn while using a fully mechanical full-time, all wheel drive, drive train.
Anyway, for what it's worth...
11-20-2010, 10:16 PM
#12
AudiWorld Member
Thread Starter
Sorry fo the misunderstanding!
I take it all back!
I got the whole thing now and it's all good with my A8 in fact I'm more than sure it would pass Audi's Tough Inspection. I'm thinking after Tranny Flush I will take trip down to Alanta, GA since I've never driven it more than 45 miles away. Thanks everyone for easing one more worry. Laters,
That would seem a little Suspect for me Since I'm Running Spacers (20mm Rear/15mm Front) pushing my Tires away from any Suspension Parts. I would go on to say that most are probably not running spacers and are hearing/feeling the exact same thing. IDK, if you've experienced it, but check it out and let me know. Thanks & laters,
I experienced this (exactly) when backing out of a parking space in several inches of snow with my '87 5000CS quattro. I mistakenly locked both my rear and inter-axle (center) differentials. Back then the differentials were manually locked and unlocked using a dashboard rotary switch with cool display. With either differential locked, ABS was disabled. This was pre-Torsen and pre-electronic locking of the differentials.
12-01-2010, 04:06 PM
#13
AudiWorld Super User
Not quite the eurika moment I am afraid. Audi did not design the diffs to lock up as you start off.
The problem is not related to the front and rear diffs at all, these are both generally, completely open diffs (axcluding RS models) and do not offer any form of slip limiting.
This effect happens as a result of the torsen diff's tendency to send torque to the place which offers the most resistance - ie the rear wheels which are turning the shorter circle or more slowly. The torsen diff reacts to this in the same way that it would if the front wheels were on ice and the rear on tarmac. This extra torque being sent to the rear wheels, causes a shunt effect between the front and rear.
When the car is moving the whole system smoohs out because the realative speeds difference involved are a lot smaller.
It is not a pleasant feeling and can be quite alarming if you are new to a torsen 4wd system but the effect can be almost avoided by accelerating gently when in a tight turn, until the car is moving. Because of the torsen diffs reaction to torque, the greater the torque applied to it the greater the effect will be.
The problem is not related to the front and rear diffs at all, these are both generally, completely open diffs (axcluding RS models) and do not offer any form of slip limiting.
This effect happens as a result of the torsen diff's tendency to send torque to the place which offers the most resistance - ie the rear wheels which are turning the shorter circle or more slowly. The torsen diff reacts to this in the same way that it would if the front wheels were on ice and the rear on tarmac. This extra torque being sent to the rear wheels, causes a shunt effect between the front and rear.
When the car is moving the whole system smoohs out because the realative speeds difference involved are a lot smaller.
It is not a pleasant feeling and can be quite alarming if you are new to a torsen 4wd system but the effect can be almost avoided by accelerating gently when in a tight turn, until the car is moving. Because of the torsen diffs reaction to torque, the greater the torque applied to it the greater the effect will be.
12-01-2010, 06:25 PM
#15
AudiWorld Member
Thread Starter
Very Interesting Stuff!
I'm Feeling Quite EdumaCated Now and it looks like it Just A Quattro Thing! I can't remember this happening with my D2 so I'm wondering if the 6HP26A61 Tranny has something to do with the Difference that I noticed with the D3 over the D2? Thanks for knowledge and laters,
12-01-2010, 06:28 PM
#16
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I'm with Edd W. If it was EDL kicking in, your tires would be very worn, very quickly. I've felt the shudder making a left turn from a stop. The rate at which I accelerated at that intersection, tire scrub would have made noise. There was no tire noise.
12-01-2010, 06:42 PM
#17
AudiWorld Member
Thread Starter
You have to admit that it did sound logical at the time, so I would give a Big Bravo for the attempt to explain it which I'm sure could be an issue with other All Wheel Drives. As for the Tire Scrub, I've not seen any Unusual Tire Wear, so in essence I'm going to have to Jump Ship and give the A+ to EW and thank him for the Lesson. Thanks & laters,
12-02-2010, 12:22 AM
#18
AudiWorld Super User
What you have to do is try to think how the Torsen diff behaves when there is no traction all at one axle. It will force torque to the axle that still offers some resistance, or where there is grip available.
Well at low speed or in fact, from a stand-still, pulling away on a sharp turn will cause the same effect as running with 1" smaller diameter tyres on the front. The diff will sense the lower resistance/higher speed at the front and see it as slip, so it forces torque to the rear, this will push the car from the rear in a way that forces it to 'catch up' with the front in you like, that causes the judder through the car as the process continues.
I dare say you could create exactly the same process by fitting smaller diameter tyres on the front then simply pull away in a straight line.
I would think that if there was no play or backlash in the whole transmission at all, it would not happen, but it is inevitable there has to be some play to allow the whole thing to work and not bind up.
Well at low speed or in fact, from a stand-still, pulling away on a sharp turn will cause the same effect as running with 1" smaller diameter tyres on the front. The diff will sense the lower resistance/higher speed at the front and see it as slip, so it forces torque to the rear, this will push the car from the rear in a way that forces it to 'catch up' with the front in you like, that causes the judder through the car as the process continues.
I dare say you could create exactly the same process by fitting smaller diameter tyres on the front then simply pull away in a straight line.
I would think that if there was no play or backlash in the whole transmission at all, it would not happen, but it is inevitable there has to be some play to allow the whole thing to work and not bind up.
12-02-2010, 04:34 AM
#19
AudiWorld Member
Thread Starter
Ed!
What you have to do is try to think how the Torsen diff behaves when there is no traction all at one axle. It will force torque to the axle that still offers some resistance, or where there is grip available.
Well at low speed or in fact, from a stand-still, pulling away on a sharp turn will cause the same effect as running with 1" smaller diameter tyres on the front. The diff will sense the lower resistance/higher speed at the front and see it as slip, so it forces torque to the rear, this will push the car from the rear in a way that forces it to 'catch up' with the front in you like, that causes the judder through the car as the process continues.
I dare say you could create exactly the same process by fitting smaller diameter tyres on the front then simply pull away in a straight line.
I would think that if there was no play or backlash in the whole transmission at all, it would not happen, but it is inevitable there has to be some play to allow the whole thing to work and not bind up.
Well at low speed or in fact, from a stand-still, pulling away on a sharp turn will cause the same effect as running with 1" smaller diameter tyres on the front. The diff will sense the lower resistance/higher speed at the front and see it as slip, so it forces torque to the rear, this will push the car from the rear in a way that forces it to 'catch up' with the front in you like, that causes the judder through the car as the process continues.
I dare say you could create exactly the same process by fitting smaller diameter tyres on the front then simply pull away in a straight line.
I would think that if there was no play or backlash in the whole transmission at all, it would not happen, but it is inevitable there has to be some play to allow the whole thing to work and not bind up.
12-02-2010, 04:58 AM
#20
AudiWorld Super User
I know little about auto boxes but I do know that unless you have specific issues to address, new filters and fluid are good, a full flush is not good.