[KMsea]

2014 XC70 T6 heading up a slippery hill in snowy Seattle. All seasons loose traction. My attempt to back down the hill ends up spinning me sideways and put the rear wheels in the ditch. Whrrrr! - stuck. Kind motorist in a Jeep offers two traction boards and we try them under different wheels. He tells me the front wheels are spinning but the rear wheels are not turning at all. The fronts are sunk too deep to bite the boards. Finally another kind motorist arrives with a shovel and digs out the snow and mud packed around all the wheels. The front wheels finally grip the boards and we pop free.

Thinking if the fronts were spinning the rear wheels should have at least made an attempt to turn?

 

[pbierre]

I agree the rear wheels should have at least turned.

You can set up a more controlled test on flat dry pavement. Take a couple of flattened cardboard boxes, wet them real good and let them freeze overnight. Then, park front wheels over these icy slip-pads, rears on dry pavement. You should be able to accelerate fwd, fronts slipping, and rears doing the work.

If the AWD is not working, you'll want to study the Haldex 5 service video. The pump could be shot, or clogged. The fluid should be refreshed.

You'll want to verify that the propeller shaft is turning when driving fwd. Reach under and put a chalk mark on the prop shaft. Lay cell phone camera on the driveway, camera shooting video upward, then drive center of car over the cam. This will show you if the prop shaft is turning (must be to get AWD action).

 

[zamram]

I put front wheels in the grass and the rear on the driveway to see if your AWD is working.
Always remember that the strongest braking wheels (front) with limited traction will lead. You would be better using the E brake backing down a slick hill.

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[pbierre]

This might be considered trivia, but KMsea's experience raises this question:

Is the Volvo-Haldex AWD designed to work the same when the car is in R backing up?

The answer can be seen at 6:30 in this video:

 

[pbierre]

I put front wheels in the grass and the rear on the driveway to see if your AWD is working.
Always remember that the strongest braking wheels (front) with limited traction will lead. You would be better using the E brake backing down a slick hill.

Sent from my SAMSUNG-SM-G891A using Tapatalk

These P3 Volvos have an electronic parking brake (EPB) which only offers ON-OFF -- unlike the older tendon-mechanical-lever PB where the driver can apply a variable amount of braking.

 

[KMsea]

Thanks @pbierre, it didn't get cold enough overnight for the frozen cardboard test but we did test on some good slush - a few brisk starts on a slight uphill while the missus took video. The rear wheels do spin so AWD is working but not sure how well. Will get it checked out at the next service for sure, didn't know Haldex could go bad like that. It has 86k miles. Maybe the rear wheels are torque limited? Or short of 4WD I was just stuck too deep for AWD to crawl out. Was also wondering if DSTC works in reverse, the way I spun ignominiously. Also, something more serious than the all seasons could have saved the day, though never had a problem in PNW winters until now.

 

[pbierre]

KM, I've heard differing opinions on how often the AWD should be serviced. The one that's worth ignoring is the Volvo Maintenance Manual, which doesn't specify any AWD service.

I did my wife's 2013 XC70 at 108,000 mi. The full AWD service consists of these 3 tasks:

• Angle gear (90 deg. gear from front transaxle --> propeller shaft) -- replace angle gear oil
• Haldex coupler - remove fluid pump, clean filter, new pump o-rings & bolts, fresh Volvo AOC fluid
• rear differential - (resolves difference in rear wheel speeds on corners) -- replace gear oil

86K wouldn't be too soon to have these done.

The rear wheels can deliver up to 50% of torque output from the tranny (when fronts are slipping). Did you see the video clip above? The Volvo AWD does a pretty good job in snow with snow tires. All season tires are going to be traction-limited.