V70 AWD Transmission: 2 new transfer boxes in 2 weeks.!

[ronald ray gun]

Hi, I just joined today so please forgive any mistakes I make.

I love my X reg XC70. I've only had it for just over a year and I've spent a few quid on it. My friend is a mechanic and in the last 6 months:- full service and replace timing belt, 4 new tyres, new front brakes and discs, replace suspension lower arm (whatever that is) and new front bearings. All in around £1,500 but that's fine - I need a reliable car as I travel all around South-East UK.

For the last few months I had been noticing a sort of whining noise above 50 mph. A friend and my mechanic both agreed that it sounded like wheel bearings, so new ones fitted to front wheels. The old bearings were definitely knackered (I saw them). The whining noise improved a lot but was still there in the background.

End of November - disaster. On the M25 and suddenly huge vibrations and horrible clunking noises meant I had to get recovered by the AA. Recovered to my mechanics place - who told me he thought it was the rear diff. He couldn't do this (re-build it) so he put me on to someone in a local garage who could arrange this rebuild via a 3rd party. I actually know this other local guy as well so I felt quite comfortable. A few days later he called me and told me he had removed the rear diff and this was NOT the problem. He said the problem was the transfer box. He said that as the rear diff was out he would check it over and fit new seals before re-fitting it. He sent the transfer box to the 3rd party for re-build but then I got the message that the transfer box was so badly damaged that a £500 re-build was not possible and the only option was a brand new transfer box from Volvo (£900 for this part alone).

OK I thought - decision time. If I scrap the car then I just have to buy something else and I won't know what state it will be in. However... I've spent a lot of money on this so far so let's do it. Better the devil you know.

We did it. 2 weeks later and £1,700 lighter I got my Volvo back. The first drive I did with the new transfer box was around 90 miles to Ipswich. The first 40 odd miles I was thinking how lovely and quiet it was now. Then - gradually I became aware of a very slight whining noise. Nothing really bad and Ipswich and back went fine. The noise was enough for me to go back to the local garage guy and get him to sit in the car with me on a little drive. He agreed it was a bit noisy and could hear exactly what I meant. He booked it in to investigate. The next day (New Years Eve) I was off to see my sister in Henley. M25 and the noise was getting worse. Also I could see smoke in the rear view mirror. I pulled over and was intending to limp home on the side roads but the noise I was hearing - even at low speed - prompted me to get AA recovery again. Having looked under the bonnet I could see the smoke was caused by oil dripping onto the first part of the exaust pipe (or baffle..?) directly behind the middle of the engine.

Now - after another week driving my Mother-in-Law's Micra (nightmare), I have been told that this new transfer box is knackered.

The local garage guy could not explain how this could have happened but I do have confidence in him. At his expense he will be fitting another new Volvo transfer box on Monday and said I could have the car back Monday or Tuesday - with nothing at all for me to pay. He said he will have a few months of arguing with Volvo but that would be his problem. He explained to me all about the viscose coupling and how it works and he's completely happy that this is not the cause of this problem. The car has always driven and cornered perfectly smoothly. He also said he had done some research and told me that I would be amazed at how often these Volvo transfer boxes fail.

I should be getting my car back in a couple of days but I'm scared. Does anyone have any advice for me or my local garage guy.

Thanks in advance

John

[david philips]

like any mechanical thing transfer boxes fail , maybe a bit more often than some mechanical bits , but the first one original lasted what about 11 years.

if the first replacement was faulty then you just had a bit of bad luck and this next one you get should be covered with some warranty . your 4 wheel drive should be as reliable as any and better than most on the road.

i think theres a lot of failed 4 wheel drives on the road the owners just dont know they have failed, so if you do decide to sell (not recommended) then someone would get a really good one.

hope everything works out and that's the last big expense you get.

[fungus]

Off topic, but my mate did his research into buying a Land Rover Discovery. Apparantly it's a good idea to check if the drive shaft to the rear axle is present. They are removed to get rid of a noise or two!

HTH

[ronald ray gun]

Thanks David, The local garage guy said it was just bad luck so I'm keeping my fingers crossed this time. John

[TiredGeek]

You have the same amount of tread on the tyres all round haven't you?
Even a small difference front to rear could cause just this sort of problem, so if you haven't been rotating the tyres front to rear or have had new ones fitted to just one end it could easily be the cause of both failures....

Good luck

[ronald ray gun]

Thanks, Brand new front around 4 months ago - Michelin I think - Eagle something or other. Brand new rears around 2 months ago - Yokohama. I'll tell the mechanic this and I'll get him to check the tread depth. Would a very slight difference in tread depth really destroy the transfer box in around 200 miles..? Thanks

[mattyfezf]

Regarding tread depth, I too have an awd, and so is a concern, but if I recall, the official line us they must be kept within 2-3mm of each other.

Not sure how practical or safe for the drive chain that is, but that to me says keep an eye out, watch pressures like a hawk and use matching tyres, and rotate front to rear at service time or bi annually depending on mileage/wear rate.

Stories about the awd system do scare me though, feels ike I'm sitting on a ticking bomb!

[TiredGeek]

Right, viscous AWD 101

Early cars with the viscous coupling are very sensitive to differences.
This is how your AWD works: your viscous coupling has a fluid inside which when both ends are rotating at the same speed remains viscous, however, when there is a difference in the speeds of the input and output shafts, which means the shafts from front to rear of the car, the fluid starts to, lets say harden. Once the fluid has hardened then the two shafts are essentially locked together and rotate at the same speeds. Thus transferring power from the front wheels to the rear as now they are all locked together. (it's not quite as cut 'n dried as that, the fluid "drags" even if it's not fully locked and transfers some power to the rear if there is a very small speed differential)
So, you're in snow, the front wheels start to spin, the viscous coupling "locks up" and you get power to your rear wheels and you drive off. Perfect.

Now imagine a small difference in diameter of the tyres, even 3mm. Drive at 50mph and each end of the car the tyres are rotating at a different speed.....
So your viscous coupling starts to "think" the front wheels are slipping and starts to lock up as described above, and is designed to do. Once it has then there is mechanical wind-up in the prop shaft between the front and rear.

If you're on mud or snow then there will be a slight slippage at the tyres and the force is dissipated, but you are on tarmac so this can't happen.
The next weakest point will break to relieve the strain, which unfortunately, and expensively, is either the angle gear or if you're lucky the splined coupling between angle gear and gearbox.

If you think this isn't a known problem, just google for Range Rover mysterious crashes from the '80's. I'm sure it will bring up many hits. They changed the transfer 'box design to a viscous coupling and then found the vehicles were having crashes on motorways where they would spin for no apparent reason. Turned out to be related to tyre pressures / tyre diameters etc locking up the viscous coupling and causing mechanical wind up in the transmission. They'd made the 'box so strong though that eventually the wheels would slip to unload the stresses and spin the whole car round....

In 2003 (AFAIK) Volvo dropped the viscous and went with a Haldex unit, which works in a totally different way and is computer controlled, so doesn't suffer AS MUCH. Later than 2005 the Haldex was refined and they are much less sensitive to a small difference in tyre sizes, but if you're smart you still play safe and rotate your tyres and change as a set!
I swap mine front to rear every 6k or so, just to be sure

Your problem could very well be tyres. Different brands of the same size do actually vary in size: one makers 215x65x16 won't be exactly the same as another makers, fitting one brand to the front and another to the rear could well be the cause.
If I were you I'd jack the car up, take off a front and rear and put them side by side to compare them. Also bear in mind that if one has a softer tyre wall / different pressure then it will compress more and be a different "rolling radius".


Sorry for the long post, hope it helps

[ronald ray gun]

Thanks for that. What you say makes perfect sense - along with your explanation of how the viscose coupling works. I will check the wheels and tyres. What you say could explain everything. Around 4 months ago brand new front tyres (Goodyear Eagle). Then around 2 months ago 2 brand new rear tyres (yokohama). This ties in exactly with your suggestion.

Thanks again

John

[ronald ray gun]

OK Chaps, I just found out something really interesting - that also ties-in perfectly with the explanation of how viscose coupling works (thanks TiredGeek).

I just got my car back with another brand-new Volvo transfer box fitted. The first thing I just did was to measure the tyres. I measured the RADIUS of the FRONT wheels (from the ground to the centre of the wheel) and they're both more or less bang-on 12 inches. Then I did exactly the same measurements on the REAR wheels - both more or less bang-on 12.7 inches. SO... here is a BIG difference between front and rear tyre sizes - The fronts are about 1.4 inches diameter smaller than the rears.

All 4 are the exact same size (215/65 R16 98H). The fronts were fitted around 4 months ago and have covered maybe 1k miles. The rears were fitted around 2 months ago and have covered maybe only around 250 miles (I've been without the car for 4 out of the last 8 weeks).

HERE's THE THING:- The front 2 are Goodyear Eagle and the rear 2 are Yokohama.

Originally there were all 4 Goodyear Eagles fitted. I drove these all to pretty low tread and then put 2 new Goodyear Eagles on the front (September 2011). This was around the time I would have began to notice a whine at over 50 mph - which I (and my mechanic friend) put down to front wheel bearings - but which I now realise could have been the transmission struggling with different size tyres front to rear.

At the beginning of November my mechanic friend fitted 2 new front wheel bearings AND a new pair of Yokohama's on the rear. Then the noises seemed to have changed - and they also seemed to be noticeable at lower speed.

A couple of hundred miles later and on the M25 at 6.30 am on a Sunday morning. No traffic so I put my foot down. 5 miles later... BANG - Transfer box wrecked.

New transfer box fitted and I got the car back just before Christmas. Around 200 miles later New Years Eve and again on the M25 - loads of smoke and horrible noises - Transfer box wrecked AGAIN...!

Because the Yoko's on the rear have only done a few hundred miles I've decided to replace the Goodyear's on the front with identical Yoko's. These should arrive today and will be fitted immediately. Then I'll measure all 4 again and pay particular attention to tyre pressures.

I'm off to Norwich on saturday so please wish me luck.

Having now got a rudimentary understanding of how my viscose coupling works, I certainly won't be doing any mix-n-match with the tyres again.

Thanks for your help and advice

John