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Re: Chain noise from rebuilt transmission only in neutral: normal?
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Posted by Cmyles [Email] (#1126) [Profile/Gallery] (more from Cmyles) on Mon, 23 Jun 2025 13:42:25 Share Post by Email
In Reply to: Re: Chain noise from rebuilt transmission only in neutral: normal?, Goblin [Profile/Gallery] , Mon, 23 Jun 2025 10:18:42
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If a noise can be absolutely assured of coming from the chaincase then it's most likely to be either the hydraulic tensioner has failed to pump up and the chains are slapping around, the stamped steel collector cup is bent and rubbing on the chains, the upper chainwheel bearing has issues (snap ring not installed properly) or the 32 mm nut in the lower chainwheel is loose (should be torqued to 78+-7.8 ft/lbs with red loctite). I have seen a few chains with tight links too but that's not real common. Severely worn or damaged teeth on the chainwheels are pretty rare in my experience. If a #6 upper and #7 lower chainwheel are accidentally installed you'll probably have more slack than the tensioner can handle too.

Installing the hydraulic tensioner upside down (easily done) will prevent oil from filling it and it won't work at all. I just disassembled a unit in which someone had installed both tensioner shoes rotated 90 degrees from where they should be (vertical instead of horizontal!). It had to be making tons of noise.

I've seen that collector cup bent over enough that it was rubbing on the chains and generating metal swarf. There's nothing that will bend it once installed so it must have been installed bent.

The upper chainwheel bearing must be carefully installed in the chainwheel (race first then cup) and properly held by it's snap ring. That snap ring has an orientation as it's beveled on one side. That side must be outward or the ring is not fully in its groove. The small snap ring that holds the upper chainwheel on the aluminum case snout has to be well seated too or the chainwheel could wander with bad results.

The big nut in the lower chainwheel holds the chainwheel onto the input shaft but it also holds the entire input shaft and bearing assembly together so if it's loose you may have bearing noise for a while before the unit explodes.

The rear bulkhead of the chaincase contains the large ball bearing that supports the main shaft (aka pinion shaft) and a needle bearing that supports the cluster gear. Worn out or damaged bearings make noise. It's shocking how much thick goo and metal filings will accumulate in some of these bearings and other places after many years. I've seen pinion shafts so packed with goo that I could barely push a stick of filler rod through them.

On top of that there are the 1986-'88 units (e.g. GM55602) that have a small ball bearing supporting the tip of the input shaft. I've seen those installed wrong and causing problems.

I can't type any more. My fingers are out of breath.
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