I bought my 2005 R50 in a broken state with a very bad clutch, so I have no experience with how it is supposed to sound or act when working properly. I noticed when I was doing my normal triage after buying it that the transmission had a faint rattling noise at idle that was audible from underneath the car, so I decided to tear down the transmission and rebuild it. The car only has 83,000 miles on it, and most of the transmission was in good condition. I did find two bad parts though: a differential bearing and the reverse idler gear bushing. The differential bearing was disturbingly bad as it had deeply pitted rollers and upon cutting the outer cage off, I found that only half the inner race had been machined! The other half had the texture of 80 grit sandpaper. German quality...LOL! Mini graciously offered to sell me a whole new transmission for 2x what I paid for the car, but no internal parts (I politely declined).

I did end up successfully rebuilding the transmission despite the lack of servicing information from BMW (they are REALLY insistent on selling new transmissions, aren't they?). I used a kit from E-Bay that included the bearings and seals for $110 shipped. I also poorly filmed some of the experience for YouTube and posted it to my channel. I later bought a new reverse idler gear for $125 (shipped) to replace the bad bushing. It was one of the easier transmissions I have ever done (with one hiccup thanks to the lack of servicing information...) and I thought it would be better than when I took it apart. I thought wrong. Upon starting the car again, I noticed a faint sound, like a bad throwout bearing mixed with a traditional power steering pump being run dry of fluid. The car had a brand new Valeo clutch, freshly machined flywheel and new torque to yield fasteners done to the proper torque, so it was not the throwout bearing. I used the screwdriver to the ear stethoscope trick with the car on ramps and determined that the noise was strongest under the debris magnet, right by the attachment point for the reverse idler gear (strangely the bolt for attaching the shaft had less noise).

This leads me to today. I figured that I may have installed the idler gear backwards, so I spent many, many hours disassembling the car again and removing the transmission. What I found was that everything was done properly the first time. I also found some metal in the gear oil. Not much, mind you, but the transmission only has about 3 miles on it (driving to the the entrance of my subdivision to put gas in it). When I spun the gears with the "top" case off, I could duplicate the noise. As the idler is only in there with one bolt, I removed it and found the noise went away. I tried the old gear and it was quieter. I also could see no areas of wear or contact consistent with any kind of issue. Compared to the 408,000 mile Nissan Transmission I just did, with it's original gears and just new bearings and blocking rings, this thing is much noisier at idle.

So, my question is, how loud should this transmission be at idle, in neutral, with the clutch pedal not depressed? Is a faint noise normal? Should I just run it and maybe let the new gear wear in and establish it's relationship with the other gears in the system? I can't hear it when driving, only while sitting still at idle. It also shifts smoothly but balks a little sometimes going into reverse. I just don't want to reinstall the transmission and...well... everything else in the front of the car only to have it fail on me.

Oh, one more question: Will the Getrag 6 speed bolt in place of the Getrag 5 speed without changing any other parts? I only ask because they are more common and I see them in the self serve yards from time to time for under $200. If this trans fails, it would be nice to have a reasonably priced alternative to another 5 speed.

 

Here is a link to a video of the noise I posted on YouTube. It's not the best, but it shows the inside of the trans, the new gear installed and run in neutral and reverse as well as the used one. There is a significant difference when in gear, which is in the last 2 minutes of the video. I also test it with no gear to show the difference.


There are other videos of this transmission on my channel as well, and they pretty much show what to do and what not to do with one of these transmissions. It's not hard to do, but it's not easy either. None of them are filmed all that well as my phone is my camera and it is old and dying. The money for a new phone went into trying to get the Mini going...

 

From what I have heard and read, the 6spd will bolt right in and work in place of the 5spd trans.....the issue that I have read has something to do with the shifter cables & bracket.....different years used different pieces

That's about all the help I can offer, I'm in search for another 6spd LSD trans for my '06 R52 JCW car.....mine has a 4th gear clash when shifting up or down.....the trans shop here said I would be $$ ahead by finding a good used unit instead of having the bad one in my car rebuilt

Bryan

 

I decided that I am going to put it back together as it was. Nothing seems to show signs of wear and I figure that the new idler gear just needs to break in as the old gear does not make as much noise. I would expect a little noise as reverse is straight cut and not helical, like the forward gears. I will, however, check the input and countershaft bearings in the bellhousing before bolting it together to see if perhaps they have an issue. I bought another complete rebuild kit before taking the car apart in case it had an issue (it was cheaper than the bearings by themselves), so replacing either is fairly straightforward with my blind hole bearing puller. I plan to change the gear oil after 500 to 1,000 miles to get rid of any shavings that breaking in the gear might generate. If the whole trans fails then I will consider replacing it with another Getrag 5 speed or a 6 speed. The car has to go together today as it is the last day of Memorial Day weekend, and no doubt one of my neighbors has already been calling code enforcement on me and I need everything to look OK when they inevitably drive by tomorrow to try and ruin my life.

 

I have done the swap to 6 spd. Need shifter starter and axles. All bolts right up. No tune needed.