My vehicle has started to vibrate very noticeably at specific speeds (2018 Volvo XC90 AWD) . The vibration seems to come from the transmission and the whole vehicle will shudder. It will vibrate at around 18-20 mph , stops vibrating and then vibrates again at 38-41 mph - so it feels like it happens on gear changes (automatic transmission) . The vibrations will stop at any speeds other than these two ranges. And it does not vibrate when I tap the accelerator when on idle. The local service center has its earliest appointment to diagnose this issue only a month from now, so I was looking to get some insights from this forum on what might be happening. Thank you!

 

the fact that the vibration changes with road speed suggests its something in the wheels, hubs/rotors or axles. Take a look at the axles. Any sign of grease leaking from the CV joint boots? Try a few more tests like putting the shifter into a select gear then drive from 15 to 45 mph - does the vibration seem the same as when the transmission is allowed to shift? Does the vibration chane if you lightly apply the brakes? Any change if you lightly apply power or lift the throttle at speed (ie to force the axle to torque one way then the other)? Does the vibration change if you are going 40 in a left hand sweeping turn vs a right hand sweeping turn (this will load up left vs right side wheel bearings). Next is to recruit a helper to test the motor mounts. Open the hood and with the engine running, "power brake" keeping the car stationary (car in gear, brake pedal firmly on, then apply power. ) Don't do this in a garage and stand to the side in case the driver accidentally lets the car lurch. Does the engine lift up or roll when power is applied and let off? (signs of a bad motor mount/torque rod or possibly a transmission mount).

This kind of diagnosis can be done by any competent mechanic so call around - you don't need to wait a month for your dealer or local mechanic to determine if you have a safety issue or are at risk of doing additional damage. Best to invest an hour of shop time to get a pro inspection.

 

Excellent suggestions ! It is an automatic transmission vehicle, so some of this advice won't apply but lots of other things that can be checked. It does not change on steering one way or the other, so its all very much based on exact speeds. I will follow your advice on getting a diagnosis from an independent mechanic

 

I had assumed your car is an automatic (ie power braking test) so you can try any of these during a road test. +1 on having an indy tech look at the car. Things like worn bushings or wheel bearing can be hard to diagnose without a lift or some tools - but these tests are helpful when explaining to the shop what's going on.