hey guys. Last month I swapped out my TH350 for an M-20 in my '69. Everything turned out great and I'm enjoying it every day. At 60+ mph there is a vibration about 90% of the time. When the vibration is there, I can eliminate it by pressing the clutch in and letting it out again. This remedy works about 75% of the time. When it doesn't eliminate it, then I shift into neutral and back into 4th, and that usually fixes it. Pretty weird! If I do one of the above things and it goes away, it won't come back again no matter how far i drive, unless i downshift and then shift back to 4th. then again about 90% of the time it's back. The only thing i questioned during the tranny swap was the clutch fork/bearing assembly. the bearing would snap into the clutch fork, but it was off centered until the tranny slid in and sort of pulled the bearing out of the fork a bit to center it. is this correct? any other ideas???

no the throw out bearing should not touch the input shaft. i bet if you look in the inspection cover it is moving around.sounds like wrong fork or pivoit mount.

superpro69, i don't follow what you mean about the bearing shouldn't be touching the input shaft. i'm sure it's adjusted properly, it seema to be pulling back off the clutch fingers OK, and it fits over the input shaft normally. as far as the clutch fork, as i look in catalogs, it's the only one available for all the GM's. Anayone else know about how it's supposed to fit in the fork? Should it stay tight in the fork or should the input shaft pull it out a bit and center it?

The "fingers" of the fork should be centered on the bearing. If you slide the bearing all the way into the notch, it will be pulled back out a bit when you install the tranny. At least that's what always happened in my experience. Everything check out alright with the driveshaft/u-joints and tranny mounts?

yea, new u-joints, just had the driveshaft balanced, checked everything over. Could it be something in the rear end? i'm about to install a different rear end this weekend - maybe that will help. thanks

One more thought... Did the pilot bushing check out alright? Bearings on the input & output shafts of the tranny good? Good luck! Mine likes to grind if you horse it into 4th, but if you wait a second it shifts smooth as a baby's behind. Even after the tranny was rebuilt. Never have figured out what's up with it.

Have you checked your driveline angles?

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the tranny was rebuilt with all new bearings and the pilot bushing is new. i did play with the driveline angles also. i thought they were OK, but i still tried adjusting up and down a bit to see if it would help, but it didn't. i guess i'll keep digging.

Couple Questions ?? Is this vibration something you feel or hear?
Does the vibration change with throttle postion? ie Does it change when you let off, or get worse when you put more load or is it there when you are at a cruise speed only?
I am thinking that there has to be something inside the tranni that is causing you grieve, I would venture a "guess" that the mechanic that rebuilt your tranni lost one or two of the needle bearings that fit into the input shaft, where the main shaft lines up, as these units rotate together in 4th missing needles would be enough to cause a slight imbalance of the assembly, by hitting the clutch the torque is reversed, this would align the needles, and the vibration would stay gone untill you shift out of 4th, then the needles would pile up together, while in the other gears again causing an imbalance when you get to 4th.