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About a year ago, I had my awd car towed 12 miles with the front wheels on the lift, rear wheels on the ground while on neutral gear. The car's drive train is the front wheels.

I just learned awd should be towed with all wheels off the ground (as stated online and in the car manual. Otherwise, the viscous couplings will be damaged. However, it has been a year and I haven't felt any issue with the car.

So what can one expect in my situation? Is the awd still working? Do I need to change the fluid in the viscous coupling? Is transmission indirectly damaged, that I be required to replace it in the future?

So far the car is running fine for a year since being towed, but I am being troubled by this notion. I'm looking for a second opinion before I have the car checked. I will update this post with the checkup results within a month.

EDIT: I finally had my car serviced at a local mechanic shop and asked a veteran mechanic this question. According to him, you will notice the problem immediately, such as hard steering, noises, and not normal feeling of the car changing gears. So it seems like i should'nt have any issue. But I will still ask my dealership shop for another opinion when I do visit them. and will update further.

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    Welcome to the site. What is the year/make/model/engine/transmission type of the car?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 24, 2017 at 2:06
  • I agree, we probably need some model-specific details since there are many variations of AWD systems.
    – Ellesedil
    Commented Jan 26, 2017 at 20:04

2 Answers 2

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Read about how viscous coupling works

Your mechanic was probably partially correct. The coupling has nothing to do with gears and you may not feel partial degredation in functionality. But I can see why he would think that you would feel it right away. Because most people wouldn't go to repair shop unless they feel the problem. Therefore he mostly sees problems that you can feel :)

I found you a nice reading material which talks about viscous coupling failures and testing That should clear your mind hopefully :)

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    Excellent answer. In reading your second link, the main concern here is that the fluid has been overheated and is no longer effectively transferring torque between the wheels?
    – Spivonious
    Commented Jan 25, 2017 at 15:47
  • Actually, according to the article when liquid goes bad, it gets harder so it transfer torque constantly which may damage the whole system. I found another interesting article: bellengineering.co.uk/5.html You would feel it if liquid gets really stiff, because it would feel strange when making tight turns (since wheels have to turn at different speeds), also as the article mentions. It is very difficult to get more specific because you didn't tell your car model :) You should probably figure out how to test it for your car model by making a web search or telling us more :)
    – Evren Yurtesen
    Commented Jan 25, 2017 at 16:06
  • I'm not the OP :)
    – Spivonious
    Commented Jan 25, 2017 at 16:10
  • @Spivonious I blame not drinking enough coffee. :) In either case apparently the fluid goes bad in time by itself also and cause the VCU to get stiff and damage stuff. I guess if it was my car, I wouldn't worry until I feel something is going on while turning etc.
    – Evren Yurtesen
    Commented Jan 25, 2017 at 16:32
  • @EvrenYurtesen, i'm the op. The car i mentioned is the caddilac xts 15. According to kelly blue books, the xts uses haldex limited slip differentials. The manual recommends but does not require all 4 tires to be change at once even though the car is awd. Perhaps, the tolerance of this car is much more forgiving than other cars. My friend has a subaru wrx and he said according to his manual, his car requires changing of all tires if one is to be changed, that is, if the tire tread is too different from the new tire. Thanks for the links! hopefully it helps others as well.
    – NYCity
    Commented Feb 17, 2017 at 22:10
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Worrying won't fix anything. It won't hurt to change the viscous coupling fluid, but it may just be a "feel good" action. I think you should pick a more important thing to be anxious about. What's done is done.

It always helps to post he specific model of your car. Some may have peccadilloes that the "generic" car doesn't.

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