Gearbox Teardown

It’s time to open the gearbox.

One thing that I noticed when tearing down the major parts, is that the area between the motor and the gearbox had a bit more gunk in it than I would have hoped for. Not all of it appears to be from the clutch, so I suspect there was a slow leak somewhere. Likely, the input shaft seal from the location of the gunk.

Bingo.

After a lot of cleaning, we can see that one of the previous owners has had the seals replaced, or done it themselves. Clearly, they used a standard seal puller to remove the old seal at that time and were not careful with it at all. There’s a deep score in the bore that looks to traverse about two-thirds of the sealing surface. You can also see an unfilled bur near the rim from the scored aluminum. You can also see aa dent in the rim on the opposite side (between 3 and 4 o’clock in the photo) where the puller was likely rested for leverage. This all makes sense with the gunk situation.

I suppose that if that bur had been filed, the seal may have held better. Instead, it looks like the bur would damage any seal put in and cause a leak. This area was all a mess from gear oil slipping out. Thankfully, the gear oil appeared fairly free from debris and metal, so it was likely kept topped up or at least the leak was very slow. The bigger issue will be what to do about the bore. I’ll ponder that in the coming weeks.

Moving on, the shafts all seem to be in good order. I tore down each shaft and inspected all the gears, mating surfaces and wear patterns. Nothing in any of that jumps out as troubling. The bearings are all in pretty good shape and have normal movement and what I expect is typical wear marks.

One thing that I do notice is that this unit has the infamous lack of a circlip on the output shaft. I’ll send it off to Max BMW to get the groove cut in before putting it all back together. I took a good look at the gear faces to see if I could find any damage from gears drifting without the circlip, but everything looks good. Fifth gear does appear a little more polished than the rest, but it is all even and there is no detectable wobble of the gears on the shafts. I am replacing fifth gear with a taller version anyway, so I am not going to worry about it.

Then there’s this guy. A simple sheetmetal oil baffle that is no longer available. At some point, it was cross-threaded and the sleeve where the screw attaches spins freely in the baffle. It was a minor pain to remove from the housing, and I am not sure it’s something that is repairable. I’ll have to hunt one down used if possible.

That’s all for today. All in all, a mixed bag. It could be worse, but that seal bore is going to be trouble.