XC70 rear diff or AWD problem
 

Hi, guys. I am a newbie but been reading your forums and find them most useful.

I have a 2001 XC70 SE with 91,000 mile, petrol and automatic. Lovely car but I have had to replace lots of bits underneath. Recently I had a whistle/thrum when driving - especially at 40mph. Comes and goes a bit but does not depend on gear or accelerating/braking.

Replaced the front wheel bearing - and as they have all now been replaced I presume this is not the problem. The garage (McConnecys not mail dealer) tells me the rear diff has gone. Apparently they tell this by the noise and the feel as the two rear wheels are rotated by hand. The cost would be £2250 for diff and £250 labour.

Having read all the problems with AWD I am worried that it is something else, e.g. can it be the splines between the prop shalt and viscous coupler. The rear diff has a peculiar assembly on the front - looks like a bearing before it goes into the diff - could this be the problem.

Any advice. What can I check? Should I take it to main stealer before spending so much? Is it worth the risk of a second hand diff - what would this cost? What is the car worth anyway?

Appeciate any help guys. Cheers

sounds like some one is trying to lift your leg, £2500 is a lot of money for a little bit of noise and it may not be the problem, could be a u j joint, c v joint,

I have just had the same problem with mine. It sounded like a rear wheel bearing but turned out to be the rear diff. Replaced it with a good used one for £380

The first thing I'd say is that with that year car are you running the same make and model of tyre on all corners?
It's VITAL that the tyres are all the same and all the same wear level on pre 2003 cars.
If they aren't, it could be part of the problem and maybe warning you something is going to go bang very soon....

Thanks guys.

TG - Re tyres there is a different make on the back but just measured them and they are same size.

NVC - I like the sound of £380 more than £2500. What were your symptoms and how were you sure it was the diff?

I just had the two rear wheels up and when I spin them the prop-shaft turns easily- more easily than the other wheel in reverse even though the auto-box is in park. It also makes a squeak/rub from the front. Is this normal, is this just the viscous coupler, could this be uj on prop shaft which causes problem?

Any idea how I can confirm the problem - too dodgy for me to lift all wheels and run at speed.

The symptoms were just a drone from the rear (like wheel bearings) swapped bearings side to side which made no difference.

Removed propshaft (no difference)

With prop removed run car on 2 post ramp (no noise)

replaced diff unit and Hey presto !! quite again

Scott - I cant send PM - so reply below for you and others.

What I did was have the prop shaft taken off. That is easy with this type of drive. So I am down to 2 well drive.

The noise has gone away - problem is I don't know if the prop shaft is the problem or the rear diff is just quiet because it is has less strain on it.

There was no obvious problem with the shaft - all the joints feel tight. The prop shaft is in two sections - bent with a rubbery mount in the middle. I don't know if this is the problem. Is it possible for the shaft to go out of balance and oscillate in the mid mount.

In short - I don't know what to do now. I am open to suggestions guys.

I have a similar problem but from what your saying when you took the prop off the problem disapeared,set the prop on a couple of chairs or somthinr leaving the center mount free inside the rubber there is a bearing spin the mount by hand and see if its noisy could be the bearing at fault