World of Vibrations

[yodavstheworld]

Hey guys, need a little direction. I have a vibration that has popped up recently and I could use some help on where to start looking.

its in my 89 325i 2.5l m20 5 speed.

The vibration is rpm dependent and speed/moving independent so I think I can rule out anything from the transmission back. It starts around 2.5k rpm, peaks at 3k rpm, and stays until about 3.5k rpm. Everything before and after that is smooth sailing. It does get slightly worse under load. It does it in every configuration of clutch engaged/disengaged in neutral or in gear.

I can feel the vibration in my seat, in the foot pedals (especially clutch) and in my shifter but not in the steering wheel.

As a side note and possible cause to this and I just don't know it, I am due for a valve adjustment, I know a couple of the exhaust valves are off time/missing. I will probably replace spark plugs at the same time (god knows when those were last changed.)

Any idea what else I should look for/at?

[htown318is]

id visually check your mounts if one sheared. if its moved, then its gonna vibrate. then check your crank pulley with the jesus bolt.

then again, I didnt know my mount sheared until I replaced them, one just fell apart and wasnt even 1 piece anymore.

valves would have to be so bad that the car runs like ass for it to vibrate like that.

[dudem3]

I would check the guibo, sounds similar to the vibrations we get in ours when the guibo is going bad. If it is the guibo, it will keep getting worse over time as the rubber cracks get bigger.

[dudem3]

Of course, it wouldn't be the guibo if you have the clutch in and you're sitting still and revving to 2.5k rpm and it's vibrating.

[yodavstheworld]

Checked all the mounts. No visual sign of failure on motor or trans mounts. But i'm not going to rule those out just yet. I'll replace those soon.

Crank pulley Jesus bolt is A-OK and snug up. did a visual on surrounding bolts/ belts pulleys and everything feels tight/is tightened down.

Valve adjustment helped with ticking and gave me a little more power (might have been the fresh spark plugs I put in too, the old ones might as well have been sand. Sketchy.)

guibo and center support bearing both look great and as you said it would only cause vibration if the clutch was engaged. This is completely independent of movement/speed. Is a worn flywheel capable of this?

[htown318is]

might sound dumb, but a hole in the exhaust somewhere under the car could make it feel that way too.

as you said, an unbalanced flywheel/pressure plate combo can do this as well, but i dont know how that can suddenly become unbalanced out of nowhere.

[yodavstheworld]

I Haven't thoroughly inspected the exhaust. Gonna swing by my mechanic when I get off work today and see when I can get it up on a rack. Ill give it a good look see when I can.

From everything I've read, I'm 95% positive it's a resonant/harmonic vibration which points me to something in the engine being out of balance. Unless I'm completely deaf, I'm pretty sure there is no knocking in the engine (I love little turbo diesel engines as a side note but she doesn't sound like that) so maybe I need to go back over the crank/crank pulley/everything that spins in any way and look for something out of place.

I also don't know how the flywheel/pressure plate could have become unbalanced. Its really just a gut feeling that I have. Also might be that I feel the full vibration in the clutch pedal more than anywhere else. The clutch was acting up recently, dumping to the floor and not coming back up for a couple days...then back to normal for no reason. No clue about that one yet. I suspected one of the cylinders but couldn't find a leak anywhere.

[yodavstheworld]

Found it. Driver's side engine mount top bolt sheared/seperated. Everything checked out visually until I got it on the rack and jacked up the engine.

Would've saved me a lot of headache if I just did that 3 weeks ago