C70 vibration during acceleration

[swampc70]

My 2007 C70 t5 (80k miles) has vibration you feel in the seat when accelerating. Vibration will end when the car gets up to speed or if you let off the accelerator. It doesn't matter if accelerating at 20 or 50 mph, you feel vibration. Service tech said it needed new CV axles, so replaced those and problem continued. Service tech then replaced new CV axles with another new set of different manufacturer, but problem continues. Only other thing service tech could think of would be that there is excess spline wear in hub where CV axle inserts in to hub, and I would have to replace front hubs. Note that I changed motor mounts and torque rod, before changing out CV axles, but that was no help either. Appreciate any guidance.

[matthew1]

Have the wheels been balanced?

[MadeInJapan]

I had the same symptoms...also replaced an axle, although not both. Vibrations were gone after I replaced the front lower control arms. I'd have to look it up but there are "sport" control arms for our model which are supposed to be beefier.... that's what I used and recommend, if you go that route.

[oragex]

I would walk away from that mechanic, he doesn't know his job.

The control arm bushings (the rear one for cracks, the front one for detached rubber) can indeed cause vibrations under acceleration on this car. I'm not sure though if that would cause the whole floor to vibrate. Just don't replace them at guess, be sure to inspect them as it shows very clear visually if they are worn or not. Be sure to replace only with Lemforder or Volvo.

I would also think about vibration coming from the engine. Does the acceleration pedal also vibrate?

[swampc70]

Thanks for the responses. I will check rear control arms. In my original post, I forgot to mention that the first thing I did was check tire balance and had them rotated to see if anything changed. No change. After balancing tires, when I took it to shop, the front lower control arms bushings were bad, so had those replaced before the CV axle work was done. No change in vibration with front lower control arm work. The thing that has confused me most about this issue is that it only occurs during acceleration when rotating components are under higher load, so you would think the vibration is initiated by the drive train, but how does vibration get transferred to frame where I feel it in car seat and dash, but not in steering wheel?

[MadeInJapan]

It could be the engine mount....the one on the passenger's side near the TB side of the engine is prone to going bad. When it does, goo will ooze out of it.