Traction or lack of

[Puffster]

So I have a D5 AWD XC70 and I'm running M+S all season tyres - so far so good. Drove into wet grassy field and went to turn around. It was slightly downhill facing but not masses - say 1ft drop in 12ft or so. Put the car in reverse to go back up the hill and masses of front wheelspin & mud everywhere (plus a bit of sideways slippage).

Anyway, I know that wet grass and even the best tyres aren't always going to get along well but as the car is AWD and whatever the Haldex system and I know that its FWD until the electronics work out lack of traction and engage the rear wheels but

it didn't happen. Masses of front spin/slide but there was no rear wheel drive that I could see. The rears were almost on a level (though grass & wet) surface and I'm sure that had I had RWD as well then I would likely been able to reverse it out ok.

So why did the RWD not engage when the front had no grip?

(In the end I had to lay a path of stones under the front wheels in order to provide something to grip on - tedious but it worked)

[Tannaton]

I think first step is to get it plugged in and any codes read. I was always of the view that any electrical problem with the AWD would throw a message on the dash but I've seen a couple of posts recently where that hasn't been the case.

And/Or check the AWD properly, get all four corners off the ground on a 2 post ramp or 4 axle stands and run it - you should get all wheels spinning. Or find a level grassy field and boot it with full lock on - the car should oversteer (put the tail out).

[boggymarsh]

Trying to drive on wet grass on an incline is akin to driving on sheet ice with racing slicks and probably the worse surface to be finding grip on. No matter what gizmos your car is fitted with the laws of physics will more often than not win!
In situations like this it is probably wise to deactivate the DSTC system. Had you done this?

[Tannaton]

That's a good point actually - driving on mud or sand is one of the few situations where you will get more traction with a small, controlled amount of spin so flicking off DSTC is worth a go - even on 2WD cars.

[green van man]

I'm thinking your all wheel drive is not working. As to why that is afraid I have no idea.
I would be looking at the mechanical things first, haldex coupling and rear diff, if they appear sound you are into what controls them and that's ecu's and potentially a lot of money.

This is why I much prefer mechanical perminent 4 wheel drive, while you pay a price for the extra drag you know it's there when needed, even if it's only more sure footed cornering. I have made an audi driver look silly when driving the land rover, left him for dead around the bends, of course he flew past me on the straight, but I had made my point.

Would be interested to know what has caused your problems, every days a school day.

Paul.

[100K+]

Originally Posted by green van man

I'm thinking your all wheel drive is not working. As to why that is afraid I have no idea.
I would be looking at the mechanical things first, haldex coupling and rear diff, if they appear sound you are into what controls them and that's ecu's and potentially a lot of money.



Would be interested to know what has caused your problems, every days a school day.

Paul.

Plus One on what Paul says, save I'd suggest the collar sleeves in the bevel gear 1st being stripped. ( don't usually throw DTC codes) Does the long front/rear prop shaft rotate by hand when in gear.... if so collar/sleeves or Bevel gear is you issue. ( but the bevel issues usually growl/rumble/clatter)
Not so convinced about rear diff issues- mine have been reliable when all else has failed (collars/bevel/DEM controller etc LOL)
DEM controller might be at issue, there is a pressure valve that is prone to failure, and there are some issues of water ingress/damage on the actual DEM controller too.

1st thing is to check if there are any DTC codes - then you have a fighting chance of resolution - If you don't its a lottery of whats causing the issue, although checking the prop is an easy 5min check.

Cheers
Bob

[apersson850]

As far as I understand, this is with a 2011 XC70, mentioned in your signature?
Which then implies it's Haldex generation IV, which is the most reliable version.
Have you ever had the oil replaced in the unit?

Normally, your car is AWD each time you start, at least if you start with your steering wheel centered. The car releases the AWD right after starting, to see if you get any wheel spin. Thus you are more likely to get going from the beginning, and then can adjust AWD traction as needed, when the car is moving.

Did you apply the Hill Descent control? Although I've never been able to find any confirmation about exactly how Volvo does this, I do have confirmation from Haldex about that they allow an input to the clutch, saying that such an "off road" function has been enabled. The clutch controller can then be parametrized to increase locking force if HDC is active, since it's likely the driver intends to venture onto difficult surfaces, if he uses the HDC function.
It's reasonable to believe that Volvo does the same.

I have towed another car uphill, on wet grass, with summer tires, where people with front wheel drive couldn't get going in spite of as many as could fit across the boot were pushing on that car. With a working AWD system, when going straight forward and the surface is reasonably flat, so you don't get diagonal spin, the Haldex AWD system if very efficient.

I've towed a trailer up a hill where a rear wheel drive E-class Mercedes couldn't drive with the car alone, to give another example of what kind of performance you should expect.
I've towed a 1700 kg trailer uphill, on wet grass, with winter tires, where the engine (D5 230 hp) had to reach almost 2000 r/min, before the car got enough torque to get going at all. At that time, occasional rattle from the hydraylic valves for the traction control (across the car, sideways, not the rear wheel drive - that's silent) was heard. So this was just on the limit of available traction. But 2000 r/min input to the torque converter of the gera box, and first gear used, that's quite a lot. On a flat and firm surface, the car moves already at 700 r/min, even with the trailer on the hitch.

You're sure there was no spinning of the rear wheels? No marks in the grass, nobody outside the car seeing them rotate? If the surface is uneven, so that most of the load is on one front wheel and the rear wheel on the other side, then the drive isn't too efficient. In such cases, you can get diagonal spin, where one front wheel and the opposite rear wheel rotates, but without much result.

[Puffster]

With mechanic (non-Volvo but very competent) and he's confirmed that its currently only FWD. He says there's no drive to the rear at all (propshaft not turning), so we're going to look into why that might be.

Also replacing a CV joint on front driverside but don't think that's related.

[Puffster]

Originally Posted by apersson850

I have towed another car uphill, on wet grass, with summer tires, where people with front wheel drive couldn't get going in spite of as many as could fit across the boot were pushing on that car. With a working AWD system, when going straight forward and the surface is reasonably flat, so you don't get diagonal spin, the Haldex AWD system if very efficient.

I've towed a trailer up a hill where a rear wheel drive E-class Mercedes couldn't drive with the car alone, to give another example of what kind of performance you should expect.
I've towed a 1700 kg trailer uphill, on wet grass, with winter tires, where the engine (D5 230 hp) had to reach almost 2000 r/min, before the car got enough torque to get going at all. At that time, occasional rattle from the hydraylic valves for the traction control (across the car, sideways, not the rear wheel drive - that's silent) was heard. So this was just on the limit of available traction. But 2000 r/min input to the torque converter of the gera box, and first gear used, that's quite a lot. On a flat and firm surface, the car moves already at 700 r/min, even with the trailer on the hitch.

Yes, my P2 163bhp was excellent, towed my bro-in-law's Passat up a steep hill in 6" of snow when he got stuck one time. Kinda why I bought this one & last year in the Feb snow it had no problem climbing the hills where I live, though I realise now it may not have had AWD