2000 XC70 rear differential pops when backing and turning

[idagon]

The car is great otherwise, drives quiet going forward, when turning going forward, and backing up straight.

But, when I backup and turn in either direction, it occasionally pops from the rear diff. It doesnt do it all the time.

Reminds me of an old posi that the clutches are sticky but only does it in reverse and turning.

Anyone have any ideas on the popping?

[idagon]

anybody?

[KlubMarcus]

anybody?

Do you rotate your tires regularly? Problems with AWD systems are usually caused by mismatched tires/wear.

You can also try changing the rear differential fluid and see if it goes away.

[JRL]

It could be anything
Check the large bushing on the bracket that holds the VC in place

[idagon]

Bushings are great and tires are new. It only does it in reverse while turning. going forward and turning is fine. I realize these viscous units lock in 4x4 when going in reverse though. I will replace fluid.

[lookforjoe]

Bushings are great and tires are new. It only does it in reverse while turning. going forward and turning is fine. I realize these viscous units lock in 4x4 when going in reverse though. I will replace fluid.

The freewheel mechanism is what engages the VC in reverse - so you may have a failing unit - since the VC & freewheel mechanism are combined in the unit. The rear diff has a posi, but unlikely to be that. Can't hurt to change the rear diff oil, but you have to suck it out the fill plug, there is no drain. The VC is a sealed unit, no way to service that.

Pics of all the components in this SS thread

[cattlecar]

Thanks for the cutaway VC photos!
The freewheel is what allows the rears to overrun the fronts so wheels won't be linked under hard braking above 50 km/h or 31 mph. In reverse, the rotation will be in the release direction for the freewheel. The centrifugal ball clutch is the mechanism for reverse power flow. The ball clutch is under the word "freewheel" in the first photo.
The ball clutch is probably not engaging fully and is popping out when the wheels attempt to go different speeds and your old dried up viscous gel has effectively locked the viscous coupling segment. In the great cutaway photos those stacks of discs should be surrounded by a gel that should be fluid. You can see in the second photo what looks like dirt in the area around the wavy discs. Wavy disc tabs are what you see, they would be engaged into splines in the part of the case that is removed. The other alternating wavy discs are in the dirt looking stuff and are hidden. The dirt is the silicone that has crapped out. A properly functioning VC will have a heavily damped movement if you have rear driveshaft out and you use a socket and breaker bar to turn the nut on the flange for VC with rear wheels locked by park brake. (a 100% functional AWD park brake on Gen 1's is rare now) With a dried up VC the torque applied usually will slip incrementally from the wavy discs passing by each other. If the ball clutch is jumping on yours in reverse then applying torque to flange nut CCW may recreate the big jerk you feel as the ball clutch slips. You may not be able to apply enough torque to get that ball clutch fail before you unscrew the nut or the VC yields if it still functions.

From AWD training manual for 97 Canadian AWD release and 98 70 series AWD release,
"When reversing, the freewheel unit is driven the 'wrong direction' by the incoming shaft. The freewheel releases and cannot transfer any power. Power can instead, in some cases, be transferred via the centrifugally controlled lockup." The "in some cases" would be referring to speeds in reverse below 31 mph. There are support illustrations showing the freewheel release CCW. Rears overspeeding the fronts will have the output going CW faster than the incoming clockwise direction motion of input so the freewheel releases.

[andre123]

Two months ago i heard the same thing with my xc v70... some mechanic guy told me that my drivetrain needed rebalancing... or a new CV joint... my solution?
Remove the drive train, run the car as a front wheel drive... cheaper, quieter. Save your $2K in mechanic nonesense, buy a new batch of good rubber and presto, a solid car again.
Keep it simple!