[The Ghost]

Setup - FBO E92, 6MT, NT05R DRs, and wavetrac LSD

Did a good 10 runs or so at the 1/4 track, one of which had a hard pop during launch. I got ittermittant wheel hop on a run, but nothing bad. On the last run, I could hear a loud hum at the top of third and into fourth gear.

When dirving home I noticed at low rpms there is a vibration and an audible hum throughout the RPM band.

I've mounted the center bearing upside down on the frame on my old car (e92) and it feels like that vibration, just not as bad (but just as audible). I put the car on jack stands and can't visually see anything wrong with the rear axles, diff, or diff output.

Any ideas on how to diagnose this and what could be wrong?

Thanks

[The Ghost]

Update -

I took it for a drive and noticed that the vibration was rpm, not speed dependent and I could feel it at 1500 rpms when in neutral.

If I hold the rpms (1.5-4k rpms) in neutral then press the clutch, the car vibrates and the engine note gets loud (sounds like it is resonating through the drivetrain).

This leads me to believe it is in the rotating assembly. I had my DMFW resurfaced (about 8k miles on it since new) and running a Spec 2+, with about 3k miles on it.

Thoughts on best next steps?

[MrRager]

may be a bad wheel bearing

[The Ghost]

Originally Posted by MrRager

may be a bad wheel bearing

Thanks. But since it happened all at once and happens when not moving, I believe it is in the rotating assembly, likely in clutch/FW area.

I'll probably tear it apart (again..) soon. For those who've had DMFW failures, what were your symptoms?

[The Ghost]

Checked codes and it throws a P2C2E. When I clear it, it returns right away. Does anyone know what that code means (I don't see it in my lookup)?

The code description reads - "lambda probe before catalyst 2, sheer test."

I assume that relates to a rear O2?

[JamesM3M5]

Maybe you broke a motor mount and the O2 wire is damaged, two troubles in one failure maybe. The vibration or noise could be from physical motor movement. Just a guess.

[Dave W.]

Originally Posted by JamesM3M5

Maybe you broke a motor mount and the O2 wire is damaged, two troubles in one failure maybe. The vibration or noise could be from physical motor movement. Just a guess.

That's a good thought. If it is the motor mount, it would be the drivers side since the engine pulls up on the drivers side MM when it's under power. I've seen a few broken MM and it's always the threaded stud that breaks off from the top of the rubber mount. HTH

[The Ghost]

Originally Posted by Dave W.

That's a good thought. If it is the motor mount, it would be the drivers side since the engine pulls up on the drivers side MM when it's under power. I've seen a few broken MM and it's always the threaded stud that breaks off from the top of the rubber mount. HTH

Thanks guys, I'll try to see if I can rule this in/out. I wonder how I go about seeing if #6 below is broken.

[Dave W.]

Thanks for posting the pic. The piece that breaks is the chunk of aluminum (aka aluminium for the euro peeps) at the bottom of the threaded stud, (top part of #4). It's a bit of work to check the MM. You'll need to support the engine while lowering the subframe, unbolt #8 so the MM can hang freely, then grab the MM and see if it's solid or not.

While your in there, check everything else. Wheelhop is nasty and can break many parts. The vibration you describe also sounds like an imbalance in the rotating assembly, possibly a loose or worn crank pulley, clutch or flywheel. Maybe one of the springs in the DMFW broke?

[The Ghost]

Yeah, I'm under the car now and both mounts appear solid, all bolts in place, and when I raise the engine slightly using a crowbar near the mount it moves back/forth with resistance. This isn't as good as your test above, however.

It vibrates at 2krpms in neutral and is amplified (soundand vibration) when the clutch is depressed. I wouldn't think the mount would cause this, especially under zero load like this in a stationary car. What symptoms did the broken mount exhibit for you?

Crank pulley has no play; verified operation and tightness of bolt.

My gut says the DMFW is broken somehow, although it only has 10k miles on it (it was resurfaced though).

[The Ghost]

Just to follow-up for those who find this later, I put my car way up on four points to begin removing the transmission when I noticed the bolt that secures the front driver's side of the diff sheared, leaving the diff cocked. This def could be the cause, although I would not think it'd affect the vibrations in neutral outside of perhaps harmonics being transferred to a loosely-hanging diff.

Replaced the bolt and the problem appears to be fixed. The loud rumble while driving is gone, as is the strong vibrations when driving. In neutral I can feel small vibrations at ~2k, but it may be me being hyper sensitive.

[The Ghost]

Bolt

[joec500]

what diff mounts are you running?

[The Ghost]

Originally Posted by joec500

what diff mounts are you running?

Stock diff mounts, stock sport suspension.

[joec500]

Originally Posted by The Ghost

Stock diff mounts, stock sport suspension.

Ahhh ok...the stock diff mounts can be deformed with your hands if you ever pull them out. Another reason to go with solid diff mounts or at the very least go with some super hardened replacement bolt.