Drive shaft vibration is back.

[leapdragon]

So I recently replaced a replacement drive shaft with a Colorado Driveshaft replacement. All was well for a couple of days, but now the drive shaft vibration is returning. I don't see any problems with the rubber in the carrier bearing on this one.

I know that in older series Volvos sometimes people solved driveshaft vibration by shimming the carrier bearing higher or lower to alter drive shaft angles.

I'm wondering if anyone has ever tried this on an XC70 and had success. It wouldn't be hard to install four washers under the carrier bearing bracket (to lower it), or two washers just above the bracket and below the bearing (to raise it).

Is it madness to try? I am loathe to send this back and try to install yet another one.

[Blacklab467]

Is this you're second one from CD? I got a low mileage one out of the wreckers off a car that had an accident and regreased the CV's and spray lubed the Carrier bearing as best I could and then had a local driveline shop balance it if you're looking for an OEM alternative. Maybe take it out and drive the car to be sure thats whats causing the vibration. I don't think shimming would improve anything unless your car has been lifted or lowered.

[vtl]

Is it torqued properly? I usually get under the car in a day or two after driveshaft work and make sure the bolts at flanges are still torqued good. Sometimes they may want to back off, even you think you torqued them to the spec.

Also consider that you may also have another source of vibration.

[leapdragon]

I'm judging the source of the vibration as the shaft (or something about its mounting) by the fact that every time I drive it without the shaft on (most recently for a week and a half while waiting for this one, including a good number of highway miles), the car was utterly silent and smooth, and that push/pull/jiggle/rotate on the flanges at either end without the shaft on feels solid and smooth as well.

Talking about torque... How likely is this to be the problem if slightly off? I mention it because to get tools on these allen-head bolts, I have to use 1/4" extension and 1/4" u-join and then step up to a 3/8" at the ratchet end, and frankly it doesn't feel like the torque wrench can get much accuracy with such thin pieces and a u-joint flexing, since the torque spec is quite high for tools of this size. I wouldn't be surprised if they're off by a good amount just from flex.

What tools does everyone use to get these things tightened/torqued down? I hit Amazon looking for good solutions, but I couldn't find tools that I thought would be better—combination of very low clearance both radially around the allen socket (i.e. it needs to be very small socket diameter to fit straight) and very low clearance stretching back from the allen socket (i.e. it needs also to be very low profile to fit between the head and the point where the shaft flares out and becomes much thicker).

The 1/4" low-profile allen head + 1/4" u-joint + 1/4" extension is the only thing I've found so far that will fit, but then I have to use a 3/8" torque wrench to get to 35nm+90 (front) and 50nm (rear) because I don't have (and can't seem to find) a 1/4" torque wrench that reaches that high. (And even if I did, it would still have a lot of elasticity in the path due to the 1/4" u-joint and extension, being used with the u-joint at a 45 degree angle or so).

I'm going to get out there and rotate the shaft 180 and retorque everything, but I'd love to find tools to do it properly if anyone has a good suggestion about specific tools to use.

[vtl]

Yes, I rotate the shaft 1-2 times to torque the bolts. I just put the transmission into N by clicking the PNP switch directly for the turn and then put it back in P for safety (the car is on 4 ramps).

Also my wagon has a 16 mm body lift, so I have extra 16 mm between everything mounted to subframe and body, which is very handy.

Try to pull DEM fuse and see if vibrations went away. If they did, the next thing I'd be looking at is how your rear subframe bushings doing, especially those one related to toe-in. It is possible the flex a lot under AWD load and loose the angle setting, which cases wheel to deviate from straight line, loose traction and slip back, many times a second. I had it, too. Fixed with new bushings in front LCAs and rear toe rods. Need to do the rest of them, I even bought a box of bushings a few years ago

[leapdragon]

So I pulled out the fuse to run without the rear and that made things maybe 5-10% better, which isn't much.

I got under the car on ramps and remembered when looking at the carrier bearing mount that it has maybe 4-5mm of adjustability in any direction, so I loosened it and slid it as far forward as it would go (probably a 4mm change). This had the result of what I would call "preloading" the rubber in the carrier bearing, i.e. of the concentric rubber rings in the carrier bearing, the inner one is protruding out the rear somewhat (in some tension).

Tightened up and drove it and that made the vibration maybe 60% better. But of course I'm adjusted to an extreme in one direction.

I hate to just trial-and-error play with it because it's all aluminum down there and pretty thin—repeated loosening/tightening doesn't feel like the greatest idea.

Anyone have any advice on the right "adjustment" for the carrier bearing? Should the rubber be "preloaded" in one direction or another? (i.e. protruding out the back a bit, protruding out the front a bit) Or should I be targeting as little load as possible (rubber "relaxed" if that makes any sense?)

Common sense tells me that also the goal is to get it as close to straight with the shaft (not at an angle in either direction) as possible, but it's hard to eyeball that, esp. with the carrier bearing above two aluminum plates where you have to get to the side to get a peek at it.

I suspect I need to get that into the "right" position to really see whether it could be the cause of the vibration—but I don't know what the best way to do that is. Any tips?

[vtl]

I haven't had to do anything with the carrier bearing. The shaft is also angled a bit as both of my subframes sit 16 mm lower.

Do you have another set of tires?

[leapdragon]

The vibration is only there under acceleration—if I let off the gas and coast, we're 100% smooth at this point. I think I could live with it as it is now, but having already had one carrier bearing fail in a year, I would not like to misadjust another, esp. if it's also allowing some undesired vibration/harmonics.

It seems clear that given the amount of adjustment that's possible, the forces through the carrier bearing can be adjusted in a variety of ways, directing the stresses on the rubber bushing in a variety of ways. Unfortunately, I don't know what the "right" adjustment is. Though I guess in the absence of other ideas, I may just twiddle it a couple more times and then go with "pick the orientation that's least annoying in the cabin."

[vtl]

The vibration is only there under acceleration—if I let off the gas and coast, we're 100% smooth at this point.

That's either CV axles or badly worn suspension bushings.

[leapdragon]

CV axles are new and a just a week ago driving w/o the drive shaft in place, car was silent under acceleration. Front control arms are relatively new and front struts/springs are also relatively new (<1y on both) and look to be in good shape.

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?