Just got my new Mazda 5 Gt, manual and noticed that around 105 km/h the second row seats start vibrating like crazy. I took the car back to the dealer and got them to re-balance the tires. The vibration is still there. The funny thing is that you cannot feel it in the steering wheel, but you can see the second row seats vibrating (side to side direction).

Found a TSB about "BODY VIBRATION AT CRUISE SPEED" for 2006-2007 models. TSB #03-001/07.

TSB DESCRIPTION

Some vehicles may experience a body vibration when driving approximately 55mph. This symptom is due to the
characteristics of the No. 3 & No. 4 engine mounts.
Modified No. 3 & No. 4 engine mounts have been established for service only. Customers having this concern

should have their vehicle repaired using the following repair procedure.

--------------

REPAIR PROCEDURE

IMPORTANT NOTE:

• This repair should only be performed if all tires and rims are confirmed to be in balance and all suspension
components are in proper working condition.
• Notify customers that use of the modified mounts will reduce vibration at cruising speed but may
increase vibration at idle.

NOTE:

Because idle vibration may increase, it is highly recommended to continue using mass production

mounts for all other service concerns.

What can I say, I hope I do not have this issue, because I don't want the engine to be hoisted out and remounted in a brand new car.

Any suggestions? Have you noticed this behaviour?

 

This is VERY interesting to me, as I experience a slight vibration at around 80-90 km/h (which is not far off 55mph)

I will have to print this off and bring it to the dealership with me to ask them...

 

Yup, this one has been around since the 2004 model year for the 3 series.
It never seems to completely go away.

 

So frustrating... I complained and the dealer told me it was the tires and how they are imperfect.. hmm... sounds like they probably knew the problem but just don't want to deal with it (assuming it is the same problem)

 

I had #3 (RS upper/drive belt side) mount replaced about a year or so ago. It was nice for a while, and while the mount is not bad again... yet, that minor little vibe @ 55mph had returned only about 2 months after the mount was replaced.

 

Many Mazda owners who mod their cars replace the motor mounts with aftermarket ones that are much firmer. The factory mounts are soft to reduce driveline harshness, but that may lead to premature failure and possible vibration.

 

Its a weak spot on these cars for sure. I had an AWR 77D rear in mine for nearly 2 yrs but couldn't take the vibration, especially with the A/C on. It drove me nuts and was a relief when I finally went back to the OE rear mount.
My last warranty trip to the dealer, I knew the RS mount had failed needed to be replaced. That's when I switched back to the OE rear and haven't gone back since.
No "kick" on startup and the dash and steering wheel are well controlled even w/the A/C on.
If I could only find a happy medium....?

 

While the Mazda5 may be an exception to the rule, I've never yet seen a car/engine combination that required the removal of the engine so that an engine mount can be replaced, and that even goes for models that have had the engine shoe-horned into the body such as the late 1960s V12 E-Type XKE Jaguars and 440 Magnum Plymouth Baracudas. Said another way, the replacement of an engine mount is pretty much a "no-brainer" when it comes to vehicle repair.