2005 XC70 100k miles intermittent shaking in drivetrain(?)

[Stobbo]

Can anyone give me some pointers as to where the solution to my problem may lie -

My car occasionally starts shaking under my very normal commuter-style driving. The shake starts gently and then builds up so that the whole car is vibrating (apparently from the rear though I can't be certain and it certainly can be felt through the wheel though it is not like a wheel-wobble shake, rather the whole floorpan feels like it is shaking underneath the seats) and at 80ks an hour on the motorway it is very uncomfortable with the car feeling like it is going to shake itself to bits. Then the shake disappears; either gradually in the opposite way to how it starts or, if the engine is stopped (e.g. for refuelling or to phone my friendly neighbourhood mechanic to ask him about the problem) and then restarted, the shake is gone!

The source appears to be drivetrain because if you put the engine in neutral (it is an auto) so that the revs drop right down the shake is unaffected.

My mechanic said it might be a tyre - but they are all in very good condition and I don't understand how shaking caused by either tyre or wheel balance (his other suggestion) would come and go in the way it does.

My car-savvy brother-in-law said it wasn't likely to be tyre-related.

The shaking feels as though you are driving over a rough surface - e.g. over a surface like a continual rumble strip.

Any suggestions greatly appreciated.

[RockitShip]

Check wheel balance. Go from there

[Stobbo]

I can confirm that this problem is not a Wheel Balance issue - any other ideas anyone?

[RockitShip]

I can confirm that this problem is not a Wheel Balance issue - any other ideas anyone?

Drivetrain. Or suspension. Or both. Probably your axles.

[VolvoDaddy]

Drivetrain. Or suspension. Or both. Probably your axles.

By drive train, do you mean the driveshaft bearing ? This wouldn't disappear.

By suspension, do thou mean the row ends, sway bars or what ? Possible.

By shafts, do you mean wheel bearings ? Possible.

Anyhow, my 2005 with 80k miles has similar problem, but not as severe. Feels like a resonance between the force input I.e. road, and the body. I got a hammer and hit the tires and didn't find anything. Exhaust resonates slightly. So does sway bar links. Bearings and bushings seem OK, at least should be OK at 80 k miles.

Has new tires bridge stone 16 inch 65 series tires. I think its tire resonance since inflating , deflating tires make a difference. What tires do you have ? If I kick the top of the tire , the chassis will yaw about 4 cycles. Wife's xc90 only one cycle with 18 inch 55 series tires.

Any advice would help... I can't believe we are the only 2 people experiencing this.

Thanks in advance.

[sjonnie]

By drive train, do you mean the driveshaft bearing ? This wouldn't disappear.

Unless you have a harmonic vibration, that'll appear and disappear as the drive system goes in and out of harmony. Is the vibration worse or less under high torque? Increased torque typically causes more vibration in driveshafts.

[PierreC]

If I kick the top of the tire , the chassis will yaw about 4 cycles. Wife's xc90 only one cycle with 18 inch 55 series tires.

Worn shock absorbers can possibly lead to the intermittent shaking (un-dampened resonance) and the above quoted symptom also point to shock absorbers.

As far as the intermittent shaking is concerned, also check the REAR shock mounts. The front shock mounts get a lot of attention as they need occasional replacement, but the rear shock mounts tend to get neglected. [I had an intermittent shake on my 850 a few years ago, which was cured by replacing a failing / failed rear to shock mount.]

[RockitShip]

I'm taking a big guess but yes guessing it is driveline related as in anything that has a bearing connected to it. I first think of axles and you should also look at wheel bearing as well as propshaft. It is process if elimination you guys will need to go through entire drivetrain and suspension systems until you have at least narrowed it down.

[VolvoDaddy]

OK, so I figure out what was my problem.
1) Tires were at 35 psi versus 38 psi. Dropped down to 30, and improved ride. Now back at 38. Ride still OK.
2) On smooth roads, rides very smooth. On rough roads, still lots of "feel" of bumps through seat and steering wheel. NC has a lot of "micro-bumps" in the roads since they all sit on sand, and roads are contracted out to lowest bidder. Large bumps are not a problem.
3) I think the series/ID of the tire (65/16") and the tire brand / grade itself is responsible for some of the feel, and the resonance. But it will cost $1k to change to 55/17". FYI, the tires are new when I bought the car... made them put on a fresh set. They probably put on the cheapest tires they could get.
3a) I noticed that under side load, hard accel ( hard for a XC70) and braking the micro-bumps seem to go away. Could this indicate a suspension component?
4) Car just doesn't ride as good as my wife's XC90 (much heavier car) or my previous Saab convertible (low profile series tires, more sports car handling, but was able to soak up the micro-bumps somehow). I need to prove this out by test driving another XC70.

Other info:
5) looks at all bushings on suspension and they seem OK... no tears or such. Still need to look at lower engine mounts, but upper one is OK.
6) Noticed the following items resonate under the car (tapping with rubber hammer, looking for things that vibrate several cycles): muffler, right front sway bar link, car in yaw mode when pushing on top of tire, tires themselves.

7) Diagnosis and general vibration information.
7a) Harmonic means sinusoidal. Anything rotating can produce harmonic vibration, especially if its out of balance.
7b) Beating: when two sinusoids are close in frequency, say 5 and 6 Hz, the vibration will "add" every ~5.5 seconds, then will "subtract" or go away every ~5.5 seconds.
7c) Generally, out of balance shows up at a certain speed. Most common is tire. Driveshaft should act this way also.
7d) CV joints. You can feel them get rougher, and/or click when you turn hard in one direction. Which direction you turn tells you which side, but I can't remember if its the opposite side or not.
7e) Wheels bearings: People say that they can hear these (high pitched squeel) when they are going bad.

Question to the community:
1) I noticed that under side load, hard accel ( hard for a XC70) and braking the micro-bumps seem to go away. Could this indicate a suspension component?
2) Please edit/comment on diagnosis section above.
3) Does a vibration diagosis Sticky or FAQ exist?

[JRL]

It may be as simple as a bad tire
If you have a shifted/broken belt in one or more tires this can happen.
The belt stays in one place, everything feels fine. Then the belt SHIFTS and all hell breaks loose.

There is NOTHING inherently wrong with the stock tire 215/65/16 tire SIZE

I would have a TIRE SHOP look at your tires for this
If there is a shop there with a FORCE balancing machine, try to have them balanced this way.

if it's a bad belt it will never balance out correctly.

You could also have a bad wheel bearing or two