Drive shaft vibration is back.

[vtl]

I understand what you were saying about rear suspension bushings, but in that case shouldn't it get quiet if the rear end is disconnected by removing the fuse?

Haldex transfers about 5% of torque in any case. It can't be fully disengaged unless prop shaft (drive shaft) is removed. Though 5% is insignificant amount of torque.

How's your vibration compares to one with the old shaft?

[leapdragon]

The drive shaft history:

~10k miles ago original OEM shaft developed "chirping", replaced w/aftermarket shaft, all was well at first
~After 10k miles, hit a pothole in road, developed significant vibration both under acceleration and when coasting
~Checked tires, wheel bearings, replaced CV axles, not resolved
~Dropped aftermarket shaft out of car, center support bushing completely torn off of its frame
~After dropping aftermarket shaft (FWD only), car was silent both under accel and coasting for a couple of weeks (car is driven every day)
~Installed a fresh reman Colorado shaft about a week ago
~All good for the first few days, but late day before yesterday, started to get similar vibration as before only when accelerating
~No vibration when coasting at any speed (all the way up to 85 mph / 125-130 kph)
~Pulled rear end fuse, about 5-10% better under acceleration (not much improvement, but slight)
~Reinstalled rear end fuse, moved center support bearing from just behind center to forward as far as it will go (this morning), about 60% better (now probably livable, but unsure about longevity)

The reason I bothered to test the center support positioning is that for other cars I have owned, there were specific instructions about center support positioning and tension. Not so for this car that I can find in VIDA, BUT it's clearly meant to be adjusted, as there are heavy rings on the aluminum plate that have big holes in the center to make it so that the mount bracket can be bolted up with a decent amount of variance in position.

[vtl]

Call Colorado Drive Shaft, maybe they can advise?

[leapdragon]

Okay, it's been a few days since I could take a look at this, but today I have a free Saturday, so I got back underneath the car and took another look at things.

Where the carrier bracket meets the bottom of the car, there are four bolts holding it in, and those four bolts pass through not just large holes, but actually four steel washer-like things. I say washer-like because as I messed around with them, it was clear that they are actually a kind of sandwich, they pass through the bracket and have washer-like surface on both sides, and then the bolts pass through them.

Between these washer-like things and the bracket is rubber, which presumably is supposed to isolate them from the vibration that they get from the shaft. However, this car has >200k miles on it.

So as an experiment, I got out some thin rubber sheeting I happen to have around and cut four additional "washers" out of 2mm rubber that I placed *between* the bracket and the car frame (i.e. the bolts pass up through the bracket and bracket washers, and then through the additional rubber "washers" before threading into the car. I cut them large enough to ensure that the bracket washers and the car frame don't come into contact.

As I positioned the bracket, I also ensured that none of the bolts were touching the insides of the metal washers as they passed through the bracket, and torqued everything (with some Loctite since rubber will mess with torque) in that position to what seemed like reasonable torque (I may have to play with this over time).

The result: vibration is almost entirely gone, now just a slight patterned sound on acceleration that you can't hear unless you turn all the accessories entirely off (i.e. if 1-2 bars of interior fan are on, you can't hear it).

I consider this a win, and the theory of the fix that basically the stock isolating washers, which are actually fairly complex for what they are, have exhausted rubber and weren't properly isolating the center carrier bearing vibration from the car. This may have been exacerbated by the pothole and torn carrier bearing from earlier this year, not sure.

Anyway, job now is to watch these bolts every week for a while to make sure they're not losening up and that the new rubber is holding.

But, I think I've finally fixed it. And if you are having driveshaft vibration of the "annoying but probably not dangerous" variety with a new shaft that ought to be good, and your car is old, could be worth a try to place a thin layer of rubber in between the mounting bracket and the car, as the rubber-mounted washers built into the bracket may no longer be isolating very well.

[leapdragon]

Quick addendum, it looks like there is a replacement part available called a "floor plan AWD cross member", Volvo 31367497 (though the in the Volvo US Parts photo, it looks like an updated part vs. the one in my car). But at $150, I'll give it ago with my own rubber first.

[jonesg]

persistence paid off.

[XC70Rider]

Nice work.

I'll peak at the center bearing during next oil change.