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IDing M94 Bearing Type by Serial Number


tvpierce

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Evening Jeff

 

This from Antons' information--

 

"Towards the end of the M94 series, clean ball bearings were added to the input shaft starting with transmissions 10483DAF, 10776DAH, 12958DAK, 12650DAL, 12405DAG, 7864DAJ, 131DCF, and 101DCH. Clean bearings were used everywhere starting with transmissions [Dx]Q, R, S, T, U, V. Interchangeable with M97"

 

BUT-- if someone was into your trans in the past then all bets are off.

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Hi DR.

 

Thanks for the info.

 

I still have the plastics on my bike, so can't get to the number today.

 

Will check when I have a moment to dig into it.

 

Again, thanks.

 

 

 

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FWIW the type of input shaft bearing used is not related to the M94 gear skipping problem.

 

I realize that. But it's my understanding that compatibility with parts from a donor M97 is dependent on the type of input shaft bearing.

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I realize that. But it's my understanding that compatibility with parts from a donor M97 is dependent on the type of input shaft bearing.

I see. But unfortunately parts from a donor M97 isn't going to be an option, let me explain. The M94 gear skip problem is caused by worn shift forks. When worn the forks do no fully engage the shift dogs during a shift, leading the gearset to briefly unlock at some point after the shift and then catch at the next dog, causing the sensation of a skip or brief interruption of power. When the next dog catches it is usually with sufficient force to cause a full engagement which is why you usually experience the skip only once after selecting the offending gear(s). The reason the shift forks wear is that the M94 model has straight cut gear dog engagement surfaces (as opposed to undercut which ensures a more secure lockup) and this causes (depending on production tolerances) the gearset to bear against the shift fork, causing premature wear (the shift fork is made of pretty soft metal.) The M97 model uses undercut shift dogs which lock the gear securely and thus it doesn't create pressure on the shift fork(s). But it's a mixed bag because the M97 also went to caged roller (aka 'clean') bearings which are actually inferior (in this application) to the tapered bearings used in the M94 and this causes problems of its own in the M97. So neither model is necessarily superior, it's more a case of pick your poison.

 

Anyway, what I'm finally coming to is the unfortunate fact that the intermediate shaft of the M94 will not fit the M97 case, so you can't just swap the gearsets out of an M97 to an M94. You thus have 3 repair options:

 

1. Replace just the bad shift forks. This will be relatively inexpensive and the repair will probably last a while, but it will not be permanent.

 

2. Have the M94 gearsets undercut. A specialty shop can do this work, and I believe that Bruno's Machine and Repair (in Canada) does this work as a specialty, or at least they did in the past.

 

3. Find a good take-out M97. This will be a direct drop-in swap, although good take-out M97s can be scarce. You can take your time looking if you like though as your gear skip problem is more of an annoyance than anything that's going to strand you tomorrow.

 

 

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