Dave - Transmission Noise

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Posted by Matt Wilson [] on Tuesday, August 06, 2019 at 17:34:02 :

I looked at the photo you posted on the other site. The pitting you see looks just like spalling to me. Spalling is one of the most common failure modes of a bearing or race when it reaches the end of its life. That portion of the shaft is effectively a bearing race. This type of failure is caused by fatigue of the metal, which results from the rollers repeatedly making contact with the shaft as they roll over it again and again. This results in the surface "layers" flaking off (spalling). Yours has pretty extensive spalling and I would not be surprised if this is causing the noise.

If it were me, I would replace it. One of your posts on the other site mentions the inside of the input shaft also looking like this, although not as severe. I would be replacing that as well, and probably the bearing itself, even if it didn't look like it has any spalling issues.

If you will only be driving this truck a couple hundred miles per year, you might be ok to use everything as is for a while, but any more than that, and I would want better parts. As I said, these parts are at the end of their lives. Even if you do only drive a small amount per year, think about what may happen to those skinny little rollers running over those pits. The edges of the pits cause high stress points on the rollers, and will cause the rollers to spall after a while, and since those rollers are so skinny, any amount of spalling takes a lot of material off the roller, relative to its thickness, greatly weakening it. Also, when the rollers run over those pits, they are unsupported in the areas over the pits, which allows the rollers to bend and they're not meant to bend. The rollers are also brittle because they are a high-hardness material. All of this adds up to likely breakage of the rollers, the pieces of which will get cocked sideways and try to jam up this part of the transmission. I doubt they would actually be able to jam it, because there's too much torque running through there, but they could cause a substantial amount of damage as they get ground into smaller pieces and break some or all of the remaining rollers too. Eventually, all of this may jam or break something. I wouldn't want that in my gearbox.

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