My 1995 XJR has a low resonating "rumble" that only starts when the car approaches 37mph peaks at 40mph and quiets down around 43mph. It's annoying because this is the typical speed for around-town driving. I eliminated tires and wheel balancing as a root cause and am now focusing on exhaust system mounts/bushing.

A Brit car expert/mechanic friend told me that cars tend to have a unique frequency at the chassis shows resonating vibration (that has to be addressed during design/testing) and for the X300 40mph may very well create this frequency...and therefore exhaust vibration made audible by bad exhaust bushings.

Funnily enough he told me MGBs' resonate at 60mph, a common highway cruising speed.

I am going to explore this further with my XJR, but thought I would share some info that was new to me!

 

check driveshaft hanger bearing...

 

Does it increase in intensity when you apply the throttle pedal, and decreases when you back off the gas? If so, +1 on the hanger bearing. I replaced it on both my Dodge Ram Cummins and my XJR (what haven't I replaced in the undercarriage.....) with same symptoms.

 

Took the XJR to my friend's shop (shameless plug: Sports Car Warehouse) and replaced the drive shaft carrier bearing and expansion joint. Problem solved.

Next for replacement transmission mount and missing exhaust mount.

Carrier bearing before replacement


Bad transmission mount


My car among some older British relatives!

 

95XJRBlack,

Thanks for the follow-up post and the great photos!

Cheers,

Don