1998 V70XC Viscous Coupling age questions

Post by **Ludermilch** » 18 Apr 2014, 11:14

Hi all,
Here are some facts and information. 1998 V70XC, 177,000 miles, tire tread difference is 2/32 , VC is now binding.

I have read that the VC will allow a 3/32 difference between front and rear tires without issue. I have also read that the VC has a limited lifespan.

I have had this XC for one month and until last week it was driving great, took me a few days to realize that the VC was what was causing the noises from the drive train and not the CV Joints or Universals. I pulled the driveshaft and no more binding noises.

More info. When I went to pick up the XC, not knowing how the AWD worked, put the car on a tow dolly and pulled it about 100 yards before realizing that it was engaged in AWD. I pulled the drive shaft out before continuing towing.

My questions are:
Does the VC allow 3/32 or less difference in tread?
Did my towing the engaged AWD destroy the VC?
Is the VC's age, including the above information, just kill the unit and cause the viscus fluid to fail?

BTW, I have already shopped for a replacement VC and see used ones are around $200+ . Are these used parts worth it?

Thanks,
Alex

Post by **rmmagow** » 18 Apr 2014, 11:32

First, I'm no expert. As far as I know, towing like that is prohibited, the car needs to be flatbed even if no driveshaft is in there. This might be a crock, but..... Tires are supposed to match or smaller diameter on the rear as long as overall they are pretty close. I don't know if the VC has a fixed life span. Although mine is disconnected, there's a test to see if the VC is OK and mine seems to pass the test. I'm at 215K, gave a glancing thought to replacing the propshaft but in the last 3 winters I had no issues with running only in FWD so I may leave it as is. The angle gear is more prone to problems I think.

instarx · Post by **instarx** » 20 Apr 2014, 02:10

Your towing did engage the AWD, the VC is designed to do that. That was very bad as I am sure you know now. The towing put a lot of stress on the VC since you forced the vanes to rotate in the thickened fluid when they are not designed to. Based only on the fact that the VC was fine when you bought the car and bad soon after you towed it, I'd lean toward the towing being the cause and not age.

I know nothing about an expected life of a VC other than I don't remember ever reading the phrase "Ah, you have xxx,xxx miles - your viscous coupling will be going bad soon". One does hear that said about other parts of the car. There are often questions here about VCs failing, but they are usually associated with "I just bought a car with mismatched tires", or "I replaced two tires", or "I towed it".

Post by **abscate** » 20 Apr 2014, 05:12

When I first read "Vicious coupling age" I thought I was on a different website....

Carry on

Post by **Ludermilch** » 20 Apr 2014, 10:20

I certainly appreciate the replies. Definitely the humor. As I suspected, I have ruined the VC before I really got to put it to use. On to more repairs.

Alex