How determine whether rattle is trans or t/o bearing

[Gene in NC]

How determine whether rattle is trans or t/o bearing. '89 525 5s has a rattle at idle w trans in neutral and clutch engaged. Is it t/o bearing or trans?

Found bolt missing from trans mount bracket to exhaust and assumed that was cause of rattle. Rattle still there.

[brodee]

How determine whether rattle is trans or t/o bearing. '89 525 5s has a rattle at idle w trans in neutral and clutch engaged. Is it t/o bearing or trans?

If I am correct the throwout bearing is only spinning when the clutch is dis-engaged (pedal down). That would mean it's not your TO bearing in this case.

Have you checked your cats? When they go bad they will cause a rattle that starts at idle and continually gets worse. It also would not be there when the car first starts but would show up as it gets warm. Comes from the same general area as the tranny so can be deceiving sometimes.

[JonE]

So, Gene, is it making the noise when in neutral and clutch pedal is pushed in? Like Bodee indicated, if pedal pushed in, and making the noise, I would vote for throw out bearing. Otherwise, I am not sure what it could be, sorry.

[Bill R.]

longtime owner i'm guessing you already know this. The dual mass flywheel on on the m20 will also rattle some, so it could be either one of those, the throwout bearing is typically a lighter noise than the flywheel or trans.. more tinny sounding if that makes any sense.





How determine whether rattle is trans or t/o bearing. '89 525 5s has a rattle at idle w trans in neutral and clutch engaged. Is it t/o bearing or trans?

Found bolt missing from trans mount bracket to exhaust and assumed that was cause of rattle. Rattle still there.

[Gene in NC]

Oh, Oh. Didn't know 525 had the dual mass mess. Did e30 325is have the dual mess? My son has one and it rattles under same conditions.

[Gene in NC]

Whoops, brain in neutral. I meant pilot bearing or trans. Now I have a third alternative of the dual mess flywheel. Good to know but not a welcomed addition to my BMW info.

Cats not in BMW really not different from my Sub w 5.7. Cat rattle from loose stuff inside generic or GM cat is loudest at idle and low rpm. As air flow and pressure build with rpm the sound goes away. Uncertain if overwhelmed by air flow, engine, or exhaust noise, but it goes away.

Incidentally, any muffler can replace your cat for a lot less $.