This problem is driving me crazy [E46 manual transmission knocking]

[sephirothcr]

There is a hard knocking sound when accelerating my manual 2002 325i at low RPMs, the problem has been there since I bought the car almost a year ago and I've already replaced the guibo and the transmission [mechanic's suggestion]. The problem persisted, he also checked the differential bushings, transmission mounts and clutch beforehand and said everything looked "OK".

To describe the problem properly; I hear a loud bang/knock/metal-on-metal sound when engaging or releasing the clutch, the sound it makes comes from somewhere around transmission [front] area, specifically when shifting. The bang is also present when accelerating/decelerating at low RPMs [below 1000] without pressing the clutch pedal.

I've read the whole internet and I can't see to find anything remotely similar to this problem. Any input is appreciated.


Thanks,
Kevin.

[Thaniel]

Sounds are difficult to diagnose without being There. What sounds loud to me might not be noticeable to you, and vice versa.

my first thought was clutch problems. Specifically the throw out bearing, clutch fork and pivot pin. But its wild guessing.

[VladV]

To me it sounds as differential subframe problem, might be that your floor pan is teared, but without a proper diagnose it's hard to say.

[snipez4664]

when my rear subframe tore, it sounded like there was a golf ball rolling around in the rear seat or in the trunk during similar times thats you are describing. Its sounds like it is something that occurs during a load transfer. it is likely either a torn subframe, worn motor/trans mounts, loose exhaust/worn mounts, drive shaft center support bearing, or a bad drive shaft u-joint.

[sephirothcr]

Thank you all for your input, I really appreciate it.
That said, the mounting bushings and subframe look great, the car itself is rust free, and even though you can hear a cluck coming from the rear, it's not really that loud or as loud as described when there is a rotting subframe/bushing problem..

The noise I described is definitely coming from the front of the car..

[jfussell]

Since I'm just guessing, I'd have a good look at that drive shaft center support. Not how I'd describe the sound, but that can get pretty subjective. Good luck.

[sephirothcr]

Ok, here are a couple of facts that I forgot to mention on my initial post:

1. If I start switching gears with the clutch pedal pressed [obviously], and then leave it on neutral, when I release the clutch pedal I can hear the "bang", and that's while the car is stationary. It's not as loud as when I'm driving, but it's there..

2. When driving below 10kph, on first gear, if I engage/disengage the clutch continuously and abruptly, you can feel the transmission moving a little and the bang sound is there, just incremented 10x..

[Adrianbruh]

I have the same problen when I am in 1st and 2nd gear. I hear a loud banging noise at 3.5k rpm comming from under the center console.

[mcafekd]

sephirothcr: Your issue sounds exactly like what I'm dealing with. I had found a thread a while back that had a solution but I didn't bookmark it!

Did you ever come up with a solution? Hope all is well..

[Honolulu]

What I'd do... and it may not be considered safe... is to jack up the car and support it VERY well. Start the car and replicate the sound, verify where it's coming from. Then get under the car and have your trusted partner (not someone who's named in your will) start the car and try to replicate the sound. You should then be able to hear and see (from movement) just where it's coming from.

If the trans has been replaced on the advice of your mechanic and at great expense, and it didn't solve the problem, time for another mechanic. They should never suggest major expense repairs that don't work. Still they are human...

It's possible that the clutch release bearing is binding (not sliding back and forth as it should) but you should feel a pronounced jerk when shifting, not just a noise. And since the trans was replaced, all should be good in there... was the clutch replaced, or re-used?

As the noise occurs without shifting, check your motor mounts, which your mechanic should have done, but check them anyway. Can do this from above or below, jack the engine and look from above for relative motion, or inspect the mounts from below as you jack the engine.