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  1. #1
    Veteran Member Four Rings BenMTL's Avatar
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    Dec 19 2012
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    106113
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    Europe

    Exclamation Differential Damage?

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    Hey guys, I've got a weird situation I am hoping someone here can confirm (the dealership can't even).

    So basically in the EU every year you have to do a stupid safety test. As part of that, a stopping power test is included where the front 2 wheels are spun and then brakes are applied (like on a 2 wheel dyno). Then the rear 2 wheels, same thing. So while the 2 front or rear wheels are spinning, the others are flat on the ground. This basically equates to towing our car on the rear 2 wheels for example (which I was told is a big no no for Audis).

    Every year I tell them the car is quattro and CANNOT be done like that and they listen and skip that part of the test, but this year they did said they can no longer skip it and ran it through that procedure. Won't this cause irreparable damage to my car now in terms of the rear differential? It wasn't for long, for like 10-15 seconds and at low speeds (10-15km/h) that the wheels were spinning sperately of each other but still....

    What kind of damage could have been caused and should I check anything?
    Race: 2006 A4 2.0 T / Quattro + 6 Speed / JHM Stage 2 93 w/HPFP / Custom 3" Turbo back exhaust / AWE Boost Gauge / JHM Short Shifter + Intercooler / White CF Trim / S4 Door Blades / DTM Conversion / RS4 RSB / HFC

    Daily: 2012 Audi A7 3.0 TDI / Twin Turbo / True Sline / Quattro + 8 Speed ZF / HUD + ACC + Sunroof / APR Stage 1 / Eurocode Alu Kreuz + Mounts / 034 RSB

  2. #2
    Senior Member Four Rings b7_Andy's Avatar
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    Jul 18 2015
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    343342
    Location
    Denver, CO

    It shouldnít have caused any damage being that it was for a really short period of time at pretty low speeds. When you drift in the snow you rear wheels can spin like 40 mph faster than your front wheels under hard load and itís designed to do that. When the rear wheels spin with the front ones locked, the driveshaft turns and the output shaft in the transmission turns which is connected to the center diff inside the trans. It spins the internal gearing in the center diff, while the center diff stays still and the shaft powering the front axles stays locked to the front half of the center diff. The same thing happens in reverse when the front wheels spin and the rear wheels are locked. The center diff is forced to stay still while everything inside it spins to allow the one shaft to move. This can happen when you drift and put a ton of power to the rear wheels. Over more than a few seconds though it builds up a ton of heat because thereís washers inside the center diff designed to create friction so that the diff has a front/rear bias and doesnít just spin freely sending the power anywhere. So when you load one shaft inside the diff itís spinning the gears in between these washers that start building up a ton of friction. Over time this creates a lot of heat. So if youíre towing a car on 2 wheels youíll 100% overheat your center diff and probably render it useless, if youíre really unlucky the heat will friction weld the gears together and youíll most likely destroy the output shafts in the transmission.

    Probably way more of an explanation than you wanted haha, but pretty much your car should be fine, that test is a really stupid idea though. I would really not want my car being tested like that, especially more than once.

  3. #3
    Veteran Member Four Rings BenMTL's Avatar
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    Dec 19 2012
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    106113
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    Europe

    Great info, ok great, happy to hear I should be OK

    Another thing....My A4 is manual. But my A7 is automatic and it has to go through the same test.

    I read some other manufacturers (BMW maybe even Benz?) for these EU tests make it so the rear diff can disengage or something so as to not cause damage? Including if it must be towed on 2 wheels. The way to disengage it is to put the shifter into Neutral. Does anyone have more info on this or know if Audi does this as well? On newer automatic models specifically.
    Race: 2006 A4 2.0 T / Quattro + 6 Speed / JHM Stage 2 93 w/HPFP / Custom 3" Turbo back exhaust / AWE Boost Gauge / JHM Short Shifter + Intercooler / White CF Trim / S4 Door Blades / DTM Conversion / RS4 RSB / HFC

    Daily: 2012 Audi A7 3.0 TDI / Twin Turbo / True Sline / Quattro + 8 Speed ZF / HUD + ACC + Sunroof / APR Stage 1 / Eurocode Alu Kreuz + Mounts / 034 RSB

  4. #4
    Senior Member Four Rings b7_Andy's Avatar
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    Jul 18 2015
    AZ Member #
    343342
    Location
    Denver, CO

    Automatic Audiís work pretty similar except that the center diff is outside the transmission. Theyíll definitely have the car in neutral while they test it, but itíll still be cringeworthy watching them do that to an A7



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