V70 AWD Transmission: 2001 XC70 Driveline disaster! Need help!!!

[iceni1]

Hi


Background - In the spring the gearbox failed and was rebuilt by a transmission specialist. In the summer after doing approx. 3,000 miles with the repaired gearbox, the transfer box went quite dramatically on the motorway. A new Volvo transfer box was fitted by the transmission specialist, things were going fine on local trips (but I did think the car was smelling a bit hot) and then on the next long run on the motorway the transfer box failed again. Fortunately this time the unit was repairable as I was told only a bearing had gone. It was diagnosed that the reason this had happened was that the viscous coupling had locked up and this in turn was putting pressure on the transfer box, so a new viscous coupling was fitted.

After weeks and weeks off the road I got the car back supposedly 'fixed', having by now spent thousands trying to get the car going. But after driving the car approximately ten miles home from the garage I noticed it was still smelling hot and there was a new whine possibly from the rear diff. So the next week it went back to my Volvo Specialists to check out the cause of the smell and noise only to get a call telling me the transfer box and possibly the rear diff too had gone on a test drive on the motorway!

This car is my second Volvo with AWD, I had problems with the first one due to a tyre retailer putting one odd size tyre on when I bought a new set resulting in the whole transmission being replaced. Subsequently I have been extremely vigilant at checking the tyres and tread on the current XC70,so that can't be the reason for the transmission going this time.

Currently the car needs loads more work and everyone is scratching their heads as to the cause of the problem. The techs have tested the car on the ramp to check the new viscous coupling hasn't failed, there is movement in the rear wheels so we are guessing not. The current theory is that the problem could go back to the gearbox repair, maybe the wrong ratios have been set up ? Please, has anyone got any other ideas and or checks we could do to determine the root cause of the problem?

This thread was previously posted in the wrong section so apologies if you've already seen it!

Also I must be crazy, whilst this car is off the road I've just bought another Volvo this week , my sixth!

[TiredGeek]

I've been googling on and off for you to see if I can find any info on the final drive / diff ratios but it's proving VERY hard to find any trustworthy sites. About the only thing I have found that is half trustable is that it seems the petrol and diseasal cars (XC90) do have different gearing in the diffs.

Again I have no definative proof of this, but a dealer might be able to tell you if the rear diff from a petrol XC70 and diseasal XC70 are the same part number. If they are different, then you maybe have a miss-match between front and rear diffs

The more I think about this the more sure I am that it's your problem. I don't know how you'd go about testing it though as putting it up on blocks and rotating the wheels wouldn't take into account that the viscous coupling has to "see" slip before it locks up, so you'd get a variation in rotations straight away. On Land Rovers you could simply pop the diffs out and count the teeth, there were 3.5-1 and 4.7-1 versions, I presume petrol and derv engined XCs would need different diffs also, but they're a hell of a lot harder to get at.......
I'll keep googling as this is bugging me now