C70: Juddering under acceleration

[StatusRed]

So just got my C70 back from the garage and looks like it has a new problem ;'(

It has a lot of judder when under load accelerating which seems to calm down when you're coasting, it feels like the car is bouncing back and forth, almost like misfiring but I don't think it's that.. There's no engine light and spark plugs were renewed for genuine ones less than 5,000 miles ago.

2.4i petrol engine, manual gearbox.

Any ideas?

[Cookeh]

Motor mounts would be my first go to. Either top torque mount, or the lower dogleg torque mount typically go first. Side ones can fail but dont tend to result in rocking.

[StatusRed]

Originally Posted by Cookeh

Motor mounts would be my first go to. Either top torque mount, or the lower dogleg torque mount typically go first. Side ones can fail but dont tend to result in rocking.

Do you think maybe the garage could have not connected something back up when doing the anti roll bar bushes then?

[Cookeh]

Anything in the back end would be more of a knocking or noticeable during cornering. If all is well when coasting then it's clearly tied to engine load, and hence not imo rear end.

[StatusRed]

Originally Posted by Cookeh

Anything in the back end would be more of a knocking or noticeable during cornering. If all is well when coasting then it's clearly tied to engine load, and hence not imo rear end.

I'm talking about the front anti roll bar, part of the work they did was fitting new poly bushes for the front anti roll bar, they said they'd need to remove the entire anti roll bar to do this.

[ITSv40]

I'm not sure if the anti roll bar bushes can be replaced without dropping the front subframe - I am assuming not as the bill would have been a lot more than what you paid. If so, there would be no need to touch the engine mounts to change the bushes. It must be the front bar bushes that were replaced as the rear bar doesn't have bushes.

I agree with Cookeh, most likely top engine mount or the dog bone tie rod under the engine/gearbox. easy to test: just give the engine a good rock back and forth and you will clearly see movement in the top mount. There are two bushes in the top mount - the main bush between the engine and arm and a smaller mount out of sight between the arm and scuttle. The black scuttle panel needs removing to see the mount. The dog bone tie rod can be seen once under the car - again easy to test with a prybar in the mount and rock the engine back and forth. There are three other mounts that might need replacing, but I would check the top mount and dog bone first.

[Cookeh]

Apologies. The jist of my reply still applies though. ARBs are a knocking noise and would be present at all times when going over undulations or bumps. To only occur under load it has to be linked to driveline.

[StatusRed]

Originally Posted by ITSv40

I'm not sure if the anti roll bar bushes can be replaced without dropping the front subframe - I am assuming not as the bill would have been a lot more than what you paid. If so, there would be no need to touch the engine mounts to change the bushes. It must be the front bar bushes that were replaced as the rear bar doesn't have bushes.

I agree with Cookeh, most likely top engine mount or the dog bone tie rod under the engine/gearbox. easy to test: just give the engine a good rock back and forth and you will clearly see movement in the top mount. There are two bushes in the top mount - the main bush between the engine and arm and a smaller mount out of sight between the arm and scuttle. The black scuttle panel needs removing to see the mount. The dog bone tie rod can be seen once under the car - again easy to test with a prybar in the mount and rock the engine back and forth. There are three other mounts that might need replacing, but I would check the top mount and dog bone first.

Originally Posted by Cookeh

Apologies. The jist of my reply still applies though. ARBs are a knocking noise and would be present at all times when going over undulations or bumps. To only occur under load it has to be linked to driveline.

Alright cheers guys, I might be able to quickly check top mounts tomorrow but underneath checks will probably have to wait til in the week or next weekend when I get an opportunity to jack the car up.. Really annoying as I thought things were finally sorted on the car now...

[ITSv40]

Edit to say: Both bushes on the top engine mount can be seen without any dismantling. The large one on top of the engine will be very obvious if collapsed, the smaller one between the arm and scuttle not quite so, but still clear to see. If this needs replacing - and I would recommend both if they are worn - the black scuttle panel needs removing to get to the mount bolts.

[StatusRed]

Originally Posted by ITSv40

Edit to say: Both bushes on the top engine mount can be seen without any dismantling. The large one on top of the engine will be very obvious if collapsed, the smaller one between the arm and scuttle not quite so, but still clear to see. If this needs replacing - and I would recommend both if they are worn - the black scuttle panel needs removing to get to the mount bolts.

Is this something that would have suddenly happened though? I mean, it is a very noticeable problem and severely impacts the experience of driving the car. I'd of already investigated it had I noticed it before.