Cluster Gear Wear
An inherent problem with Muncie transmissions is excessive wear on the thrust washer and scoring of the surface of the cluster gear on the first gear side. Many times I have had to have the cluster gear surface machined. When the machining is excessive, I also put a hardened shim behind this.
Factory specs are .025 maximum end play. I like to set them to .015.
Here’s a picture of the scoring caused by this problem. The surface should be perfectly smooth, and here you can see the scoring. The thrust washer was obviously chewed up, so anyone would immediately replace it. Don’t mistake tidy scoring as appropriate wear. This is caused by debris working its way between the thrust washer and the cluster gear, eating up both pieces.
If you don’t cut and machine the cluster gear, it’s like doing a brake job with new pads but not cutting the rotors. The job just doesn’t last.