Occasional shifting clunk

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Jul 30, 2003
Anyone know what would cause a clunk occasionally during shifting? It's a stock 78 40. Does not always happen. Seems like the slower I move the shift lever, the less clunk there is. Sometimes it does not do it at all. The clunk also varies in loudness/intensity. The worst it was was one time going from 1st to reverse, really loud clunk and felt it in the floor. I noticed a very slight sort of whirring noise when I am in neutral with my foot all the way off of clutch. It shifts pretty smoothly although and doesn't grind or make really frightening sounds. I grabbed the front drive shaft and there was slight play when I spin it back and forth, but not much, might be normal. The uni-joints are tight and look good. Any ideas what to check?

Thanks a lot for reading and for any suggestions.
Crap Quality Gear Oil can make the Synchros clunk when you place it into gear. - I had this problem with Mobil 80W/90.

The worst it was was one time going from 1st to reverse,
That would be sought of normal, Becouse there is no Synchros on Reverse Gear, It could also be exasibated by crap Quality Gear Oil.
Until it starts poppin out of gear while driving or grinding during a normal shift, I wouldn't worry. Have you checked the level of the gear oil in the tranny?
Gear oil, output shaft bearing, output shaft stake nut, RR U joints, Motor mounts, tranny mounts Whirring noise is a bad sign that the clutch is riding on the TO bearing.
Last night I adjusted the release cylinder pushrod so that it was closer to the release fork. This made the shifting a lot better in general and has pretty much eliminated the symptoms, so far. Today I'll check the gear oil and if it's low, I'll replace it since I don't know what brand is in there now. Does anyone have favorite type/brand? I'm in the N.E. and get some very cold temps.

Thanks a lot for your time and suggestions

I've currently got Penrite Gear Box Oil Light 80w/85 that I was going to put in last Sunday, But I stripped the Head of the Filler Plug. :whoops:
In their currently is Valvoline HP 85W/140, That is making the Gearbox quiet and smooth. :) Except if I pull second from first too quick. ;)

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