Y33 Shimmy Rumble @ 50mph

[paranoidjack]

I think I've seen this on the board before, but I wanted to pass it by you and see if you agree with me before I get down and dirty with it.

My car is butter smooth at all speeds except 48-55mph. At 100 it is smooth as silk, same at 20. However when running about 50mph, I feel an inaudible rumbling (not too prevalent, but very noticeable in the steering wheel shaking) from what seems to be right under the center of the car.

140k miles.

Replaced shocks, bushings, transmission flush, diff flush. Motor feels A-OK when happening, no problem.

My hypothesis is transmission mount...sound about right? Do I need to dismantle the entire car to change that out? I remember seeing a g50 thread about the PITA to replace the transmission mount.

[Solini]

Yea I have that same issues and like you're thinking I changed the transmission mount and it didn't change a thing. I've learned to just live with it, as my mechanic at Infiniti says only other thing we haven't done yet was change the solenoids =/... I did notice it wasn't so bad after a flush and a transmission filter change

[qship96]

start with a 4 tire rotation and precision balance.

[elwesso]

trans mount is ULTRA easy, maybe 1 hour at the most with a beer break!

Theres many things to suspect. I would first consider a driveshaft issue or trans mount, after that maybe exhaust. G50s have a TSB on the exhaust causing a resonance. Does the noise change with RPM, for instance going said speed and downshifting to 3rd, does it change anything?

give that a try and report back.. Stiill not a bad idea to replace trans mount and exhaust hangers, and not terribly expensive either.

[bullittandy]

This is an interesting post b/c I have a similar issue with my 99. Minor vibration through the shifter is the other symptom that I have. I just had the tires mounted and high-speed balanced and get a fairly noticable shake from 55 mph to 60 or so that is bad when the car is first driven and is greatly reduced with some drive time.

I'm planning on replacing the transmission mount and exhaust hangers soon and will report back.

[qship96]

Andy, your issue sounds like tires are taking a set when parked and causing the shake when first driving, disappearing when tires become hot and thus more round.Very common problem especially in cold cimates, less so in hotter.

[paranoidjack]

start with a 4 tire rotation and precision balance.

Q-thanks for the advice, but I just had this done with a relatively new set of tires less than 5k ago, and the rumble was the same before and after.

Andy, my problem sounds 100% identical to yours. Let me know what happens if you do the mount/hangers first, and I will do the same. You nailed it on the head when you say cold Andy, when first started the rumbling can be VERY bad....goes away greatly once warmed up.

Wes, I'd like to rule out the driveshaft as this occurs in no other rpm in any other gear. If it was the driveshaft, I could keep it in first and theoretically recreate the rumble in any gear. Also, I should clarify-there is no "noise" that could change during different rpms's....it's really just a RUMBLE that can be felt and not heard.

[maxnix]

You chould check all exhaust hangers and verify the damper weight is on the passenger side back where it bends to the driver's side to go to the muffler.

Worn out hangers have no resiliency and tranfer all vibration to the chassis.

Cold tire set will affect all speeds and rpms until the tires warm.

[paranoidjack]

You chould check all exhaust hangers and verify the damper weight is on the passenger side back where it bends to the driver's side to go to the muffler.

Worn out hangers have no resiliency and tranfer all vibration to the chassis.

Cold tire set will affect all speeds and rpms until the tires warm.

Exactly, on the tire set, it is always 48-55 regardless of gear. Seems to lessen under throttle. I don't think that's it.

I will have a look at the hangers and transmission mount.