This is the third gearbox I’ve seen with expelled shift forkroll pins. I think when they get hot and vibrate the pins work themselves loose. I road course this gearbox and lean on it REALLY REALLY hard with no lift shifting and full on driving to the limit. I slowly started losing 3rd gear last week while making large left hand sweeping turns registering in the 1-lateral-G range. After about 120 consecutive laps third gear began to sneak some grinding. After about 140 laps I was consistently grinding and then suddenly I was blocked outof gear entirely and 3rd gear disappeared altogether. I opened up the gearbox and these were my observations.
Shift fork roll pin is expelled on one fork (it snapped inhalf when I tried to pull it): gahh: The roll pin worked itself out it allowed the shift fork to slide toward the end cover about 5mm. I observed the fork resting on 4th gear entirely. It was locked below the hub/slider keeper step and consequently didn’t have enough reach to grab third because of how far it slid down the shift fork rail. At first I thought I rounded all the teeth on third gear because I ground it at least 20 times at 7500 rpms and then I finally whizzed the gear and it hummed for a second or two and blocked me out. After further inspection the gear/hub slider teeth are in good shape and it appears I just need to replace the synchro. I also discovered I melted the oil splash pan at the mount. Also appears the adjacent shift fork roll pin is starting to work itself out also (it’s projecting about 3mm).
Surprisingly, I didn’t observe any metal flakes or chunks in the gearbox or in the fluid I drained. Just before I hit the road course I drained my Mitsubishi OEM Diamond Gear Lube and swapped in Royal Purple 75w-90 Full Synthetic Hypod Gear Oil. Can't say wether or not the full synthetic was a contributing factor. For the most part everything else in the gearbox is good to go. The synchromesh looks good on 3/4 but I’m going to swap in new synchros for my own sanity.
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