I've had my Infinity G35 coupe manual for a few months. When I purchased the vehicle I did notice the engine moved a little. I heard a little bit about some of the common issues motor mounts being one of them. I figured it just needed motor mounts. I've recently replaced the motor mounts and transmission mount with the Z 1 Motorsports mounts. The issue continues to happen. When I am at a stop and move forward the engine seems to be bouncing. It's the worst from a dead stop in first gear but I can still feel the motor moving in between gears if I don't work the clutch just right. I don't think the issue is motor or transmission mounts . When I have the hood up and I try to move the engine it seems to be pretty sturdy . Not really sure what's going on can anyone help.

 

I'm assuming replacing your motor and trans mounts made your engine stay in place, but it still feels as though you've still got slop going on/off power when you drive it. Is your shiftier still bouncing around?

Most likely culprit is the differential bushings. After that, maybe sub frame bushings or driveshaft center bearing? Jack it up and take a look at all the rubber bits underneath.

 

What happens when you are in 3rd gear going about 30mph and you quickly press and release the throttle a few times. If you feel a jarring "thud" through the vehicle then yes you have something shifting and check those items listed above.

However you specifically said you were having issues on a first gear launch, that's not typically where you feel mount problems, if you feel a "shudder" type of rapid vibration through the chassis that is likely the clutch.

 

I will deff jack it up and check it out after your responses i beleave it may be sub frame bushings not going to be a fun project but well worth it after complete. When im in 3rd gear going 30 and let on and off the throttle it fells like the engine is going to jump out the car very bouncy. Thank you for the responces very helpful.

 

I just replaced my engine mounts and I've got a bit of driveline lash too - nowhere near like it was but I can still make it happen if I try - which means it'll just get worse with time. The only things in the drive line I haven't replaced diff, the center bushing and sub frame bushings.

Blue, you might want to check out the Z1 subframe spacers, they're advertised to do the same thing as subframe bushing replacement but cost $150 and you don't have to drop the subframe.