Yesterday, when slowing in a parking lot (5-10 MPH), and taking a slight right turn, I got a HUGE vibration in the rear end of the wagon. From the driver's seat, it seemed as if it came from the right side, but I can't swear to it.

This wasn't a "slight" vibration --- and it wasn't "out of round rotor"-type vibration (had an 850, I've had PLENTY of those !!!)..........it literally shook the entire rear portion of the car -- it was that loud. It was also a constant frequency -- that is, it didn't raise or lower in pitch depending on my speed. It remained the same (rather low) pitch the entire time it was going on. As I came to a gentle stop, it (quickly) got softer and stopped.

It definitely seemed to be associated with the braking, somehow. Braking effectiveness was not apparently affected. No pad squealing that I could hear.

What was odd was that when I braked from a FASTER speed, or braked HARDER, the vibration didn't happen, even making the same right hand turn. It only happened when I was already going very slow, and VERY GENTLY braked to a stop.

I started wondering if it was some sort of ABS sensor malfunction --- causing the ABS to activate on one rear brake. The reason I speculate this is that it almost seemed that another "force" rather than my braking force was activating the vibration.

I've never experienced this type of thing in 24 years of Volvos, so any suggestions anybody has would be most welcome.

Regarding home diagnostic techniques involving the ABS - and please forgive me if this is a reeaally dumb question - but is there a safety aspect to consider in deactivating the ABS to remove it from the equation? If not, is there an easy way to accomplish this, beyond pulling Fuse #3? I don't have the info sources for this machine yet that I've accumulated for my other Volvos, but it would be a useful nugget to file away against the inevitable(?) brake and suspension woes ahead.
Regards,
Garth.

Is this sound more like a major groaning sound or harmonic vibration than an up and down movement type of vibration? I have exactly the same symptom. A local shop told me to replace the rear pads and install the proper shims (along with the grease) to correct it. I have not done that yet. Does this sound familiar?

Hi, folks:

Didn't get a wheel or rotor off, but did take a "ride" last night with a friend who is a mechanic for an area fire department - 19 years experience. We got it to duplicate the sound only once, but he instantly concurred that whatever is setting up this vibration is not a function of road speed or engine speed. He feels that pretty much rules out suspension, or even drivetrain, since that will be causally related to the road speed.

His reason ? It's that the vibration has no apparent relation to the speed of the car or the speed of the engine. It's so clearly defined that it's almost as if a switch were thrown, turning on the vibration -- suggesting an electrical circuit is being closed when it shouldn't be. He's tending to think ABS, since there's not really anything else back there that could "set up" a big vibration. Also, the lack of change in pitch or intensity of the vibration -- it's either doing it or it's not.

Could something in the ABS be activating only one side ??? Or activating in an abnormal manner, setting up a vibration nothing like the vibration felt through the pedal during normal ABS operation ????

We have yet to pull a wheel or rotor, but we will certainly run that down.

In the meantime, maybe the one other guy in Volvoland who has ever experienced this will read this, and save me hours in the heat popping a wheel and rotor........

Thx !!!!

True, the ABS system works on the rear brakes, but I doubt that is the problem. Then you would "feel" it on your brake pedal.
Does it also make this vibration on left hand turns? If not, I would suspect the top shock mount is in need of replacing or some other piece of suspension is worn/bent/loose.

Klaus
--
I still miss my 164 and my 854T. Just driving a V70R :)

It's not anything in the suspension system. It's like it's being applied from an external source - that's the only way I know how to describe it. It's as if --- when the moment comes --- the vibration "kicks in" at full strength --- and then when I roll to a stop, it decreases almost instantly and stops. That's what made me think of the ABS -- what else would be applying pulsating pressure ??? And this is definitely pulsating....you can hear it and feel it.

Now, I DO feel just a tad of pulsating in the brake pedal --- but I've activated the ABS on ice, etc., plenty of times, and it's not as pronounced as that..........but you can feel just a bit of pulsing. But, it's also at a much FASTER rate than when the ABS is kicked in.

It's got the *hit beat out of me.......NEVER heard anything like this before.

Hi all.
I dont think the ABS works beneath 10 mph, so factor that into the diagnoses (if it did work; I dont suppose that we could come to halt).

I think that 'back end' wants a very carfull inspection on a ramp before you go much further.
Best regards.
Howard.
Isle of Skye.

Is this an AWD car? You didn't say.

If it is the ABS acting up, you need to look at the axle next to the hub on the inside of the rotor. The sensor looks at the teeth in the axle and your teeth may be plugged with dirt for some reason. Rust does build up in that area and a good cleaning never hurts. Just wear safety goggles.
You might be able to see it with just the wheel off, I hate removing the rear rotors.

Klaus
--
I still miss my 164 and my 854T. Just driving a V70R :)

Not AWD.

I'll pull her off tonight and see what I see. I'm going to start with the passenger side, and if there's anything, see if cleaning it makes any difference.

Thx !!!

Don't forget to checck the rear shock mounts for play. Once the wheeel is off the ground, try shaking it before you take it off the rotor.

Klaus
--
I still miss my 164 and my 854T. Just driving a V70R :)