I have a 1998 V70 GLT/AWD A/T @ 141,000 miles.

I've experienced the following symptoms over the past week, which began suddenly, not gradually. I've done extensive research on this and other forums, but haven't really been able to narrow down the possible cause. My fear ($) is the viscous coupling going bad, but I hope to eliminate it through this discussion...

I hear a single loud thump in the rear of the car, as though something is hitting the undercarriage, when I back up slowly or move forward from a stop, mostly when turning, but occasionally going straight. Always at low speed, always a single thump unless I change directions (back then forward), where I get a single thump each direction. But it's not consistent -- sometimes it doesn't happen, and the loudness varies from very faint to very loud (where I feel the vibration).

Once I'm on the road driving, the car behaves beautifully at all speeds.

Because of this limited thumping, I've discounted the drive shaft and other continually moving parts, except for the viscous coupler and/or freewheel which engage at lower speeds.

But nobody has described observable symptoms of a broken viscous coupling or freewheel.

Some have suggested it could be as simple as a stuck parking brake or caliper, but wouldn't these continue to make noise when moving?

Could it simply be a loose bolt somewhere on the drivetrain, and the thump only happens when the drive shaft changes direction, exerting opposite force on the brackets and slipping once until direction is changed?

Many have described very expensive "trial and error" fixes performed by professional mechanics, both indy and dealer -- this is something I want to avoid. I want to take it in fully informed, with concrete suggestions.

Thanks in advance for your responses!

(sorry about misspelling "viscous" in thread title)

 

Just an update...it snowed like crazy today, so I performed a test. I found a parking lot that hadn't been plowed yet, and I took the car through left and right turns at slow speeds, forward and backward, and the clunk continued to occur. If it were the viscous or the flywheel, I would think a slippery surface would stop the clunking, due to the wheels' ability to slip. True? What exactly is "clunking" if it's the viscous clutch or flywheel?

I've also noticed that it does occasionally occur at higher speeds going forward, when I gun the engine. This leads me to believe it's the middle drive shaft support bearing -- either it has a loose bolt, or the rubber surround has deteriorated and/or fallen off, allowing the 2-piece drive shaft to whip up against the undercarriage when the load combined with speed and direction changes. To further lead me in this direction, I have begun to hear a faint metal-moving-against-metal sound in the middle of the car, which disappears when I step on the gas, and returns when I coast, indicating perhaps that the mid-bearing moves up when increasing speed, and rests down on rubber-less bracket when coasting.

I need to find a dry spot to look under the car to confirm -- does this sound plausible?

If it is the problem, what damage can be caused if I let it go for a while?

And if this is the problem, I've confirmed that the 98 V70 does permit replacing just the mid-bearing/bracket, without replacing the entire drive shaft -- $170 vs $1170!

 

The Torque Tube upper arm bushing, where the torque tube is bolted to the undercarriage, fails over time. Mine split/disappeared, enabling the clunks. Indy mechanic showed me the driveshaft/torque tube movement and clunking with the car on the rack while his assistant accelerated forward, reverse quickly. It rests on bolt head, then when torque increases, lifts up and bangs into the undercarriage. Rubber bushing prevents this banging. Cheap part, cheap labor.

Photo here...
http://carrepairphotos.shutterfly.com/pictures/9

 

Hi,
I have the same problem.
What is the part number that you replaced?
Please let me know
Thanks
Alex

 

I just called volvo dealer and they gave me this part number:
9143894
It's for torque tube bushing