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6 Speed Parts Interchange

Old 10-01-2017, 09:54 PM
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Default 6 Speed Parts Interchange

The last few weeks have been a learning experience for what parts can and can't be interchanged between the different model 6 speeds.

Background: Last year I picked up a disassembled 6 speed that had a bent main shaft and a box of parts from another 6 speed that were supposed to make one good transmission. Upon closer inspection, there was no good main shaft between the two. Some hamfisted press monkey had broken the edges off the teeth of the #3 gear which is machined into the shaft (bending one shaft and breaking teeth on the other). So pulled the plug and just put all the parts on a shelf thinking I might need them later.

Earlier this year I picked up a MSM 6 speed with a "grinding" 3rd gear for cheap. What we found during tear down is that the 3-4 selector ring had moved far enough that the detent ***** and springs were now gone or damaged.

3-4 Selector ring on counter shaft stack:

Damage to center ring, syncros, and gear tooth leading edges:

So over to the box of spare parts. I found a counter shaft with a nearly new looking set of syncros and gears. I also noticed that the standard NB (I think these parts is from an early NB1) have extra "nubs" on the outer edges of the teeth to keep the selector ring from going too far and exposing the detent *****.

Standard NB counter shaft (NB1?):

So we replaced some bearings, syncros, springs, and a damaged 1th gear on the main shaft (likely from a detent ball being loose and sandwiching between the gear and housing). As soon as we put the center housing in place we noticed that the gear mesh was not right. It was tough to rotate the main shaft. You could feel every tooth and it sounded like a rock in a crusher. We even tried installing everything hoping it would improve the alignment and it didn't change anything.

So we torn it back down, tried another standard NB counter shaft. Same issue. Swapped the MSM counter shaft in, smooth as butter. After removing the MSM counter shaft, we did our best to measure them. The best we could find is that the tooth cut profiles are different (no good pictures). Many of the gears have different part numbers between the standard and turbo gears. The assumption was that the gear cuts were the same and they could be interchanged. Definitely not true between the NB1 and MSM gears. The MSM tooth profile looks a little thicker at the base when compared to the standard NB.

Does anyone have any pictures of the a standard NB2 counter shaft? I am curious if the standard NB2 gears have the "nubs" that limit the selector ring travel or if the lack of them is a MSM only trait.

I'm trying to locate a better MSM counter shaft and or at least the 3rd and 4th gears. If you have something, let me know.

Last edited by Midtenn; 10-01-2017 at 10:11 PM.
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Old 10-02-2017, 09:16 PM
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I have a disassembled 6 speed that is supposedly from an msm.
I'm happy to take any pics or measurements you need.
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