How Noisy Is Your Transmission At Idle?

[bmwman91]

Just out of curiosity, how noisy is your transmission when you sit at idle with your foot off of the clutch? Both of my Getrag 240's have been fairly noisy in terms of rattling noises and some amount of low-humming as the input shaft spins freely. On both, the input shaft has a fair amount of play when the tranny is out, and I just assume that it is rattling around a bit when the engine is spinning it freely under no load. As soon as I push the clutch in, disengaging the clutch disc & input shaft, the noise disappears. It has been this way for as long as I can remember on both cars.

Since I put in an 11lb M20 flywheel from Metric Mechanic, the rattling is a bit louder, probably because the light flywheel does even less to damp the M42's non-overlapping power strokes!

How about you?

[Bimmerguy91]

Have you checked your transmission fluid level?

[bmwman91]

Just filled it with fresh RedLine MTL before engine installation. From some searches of the interwebs, it sounds like a noisy input shaft is common on a lot of BMWs, and Getrag transmissions in particular, especially if one has a light flywheel on a 4-banger. There is (what I consider to be) a fair amount of end play on the input shaft too, which is probably because the transmission has 150k miles on it.

I also lubed the input shaft splines and all contact points in the clutch assembly where metal-on-metal movement occurs with Molykote BR-2 grease (recommended in the service manual), which I have never done in the past. Who knows, maybe that makes it even easier for things to rattle around.

[future rs]

The stock transmission in my 325i has a bit of audible noise (in cabin) when the clutch is out. When depressed it is almost silent.

[4DR_Lou]

mine whines/hums in neutral and underload, foot off the clutch.
the sound didn't get any louder after i had my flywheel shaved.
i'm wondering if using MT-90 would work better since it's thicker.

[bmwman91]

Yeah, the idea of using thicker oil crossed my mind. Some guys on Volvo forums were discussing that as a solution for their similar noise issues, and everyone who tried it said that shifting when the tranny was cold was yucky. I think it helped with the noise though. Also, make sure that you use GL-4 rated fluid (assuming that your owner's manual calls for it) as other types of fluid may cause or allow corrosion.

This weekend I will jump underneath and make sure that there is actually fluid in there. I know I put some in a month ago when I installed the engine the first time (it broke a valve spring shortly thereafter and had to come out again lol), but it has been a hell of a month and I can barely remember what day it is right now (wedding planning, weekly business travel, this damn car). Maybe I put the fluid into a different tranny or something....uuuugh. I am 99% sure that I remember being under the car and swapping a magnetic drain plug in, and then adding fluid via hose from the engine bay.

[nando]

getrag rattle. not a big deal, caused by lighter flywheels and old bearings. it will go *forever* like that. as long as the fluid level is good, just leave it alone and deal with your wedding and life.

thicker fluid is unlikely to make much difference. my G260 has about 300k on it and has had the rattle as long as it's been in my car (~75k). shifts smoothly and has no issues otherwise. I've run redline MT-90 as well.

[bmwman91]

Awesome info, thank you nando.

[LowR3V'in]

UUC uses this.

http://www.uucmotorwerks.com/html_techtip/techtips/tranny_rattle.htm

I just use MTL but the rattle is O.K.

[randomtask37]

i have the same 'problem'. I noticed it today, but apparently its normal and i need to get used to it. at least i know not to worry about it.

[93supercoupe]

mine has 250k, noisy as hell.

But it shifts mint and takes a beating every day.

[bmwman91]

I flushed the tranny with Red Line MT-90 this morning and it has reduced the rattle, as well as some of the noise during acceleration and deceleration. The Red Line MTL that was in there only had maybe 200 miles on it, but the tranny itself had sat for about 7 years in the back yard before I put it in, and it came out really dirty. I guess putting new fluid in last month was good for getting all the old gunk out, and everything is good now that it has been flushed again.

I have read that MT-90 can cause hard shifting in cold climates, but since I am in CA where there is no weather it should be fine.

Make sure to get the GL-4 version of the fluid, NOT the MT-90NS / GL-5 stuff. Apparently GL-5 fluids will eat yellow metals, like the brass that our synchros are made out of!