I have an 82 that has a vibration from 45 mph to 55 mph only in 4th gear. If I blow through 55 in 3rd it doesn't vibrate at all. My first instinct is that its the flywheel because when i rebuilt the truck that is one of the few things I skimped on and didn't replace. It had a high polish and some fine surface heat cracks but being already a couple Ks into it I opted to use it. The clutch and pressure plate were new and only have a few thousand miles on them. My theory is its chattering at those speeds because if I feather the clutch when accelerating at those speeds in 4th it goes away. I ordered a new fly wheel because if it isn't the problem it needed to be changed anyways.

Any thoughts? U-joints appear to be good but i need to thoroughly inspect them to 100% rule them out.

 

Your flywheel hits that same RPM range in every gear, probably not your issue. Please describe the "vibration" a little more, is it something you are feeling or hearing or both? 4th gear is a straight through 1:1 gear ratio (I think, someone back me up here), so you might have a transmission bearing issue, I have only experienced the opposite problem where I had a growling noise in every gear but 4th, it was a bearing problem on the counter shaft and in 4th there was no load on it. but it was an old truck and Toyotas are tough, so I monitored it to see if it got worse, 15 years later I sold the truck still slinging mud and pulling stumps.

 

I would describe it as a high frequency chattering. Shakes the dash and you feel it in your seat. Like I said I can barely feather the clutch and it goes away. It only does it in 4th gear so to me that rules out everything but the clutch or transmission. If it was in the drive line it would do it no matter what gear I'm in

 

Same with the clutch

 

So it's the transmission. Why would it stop when feathering the clutch?

 

probably because you are taking some of the load off of the tranny. I suspect you have enough play in an output or input shaft bearing to allow it to wobble when coupled directly to the other shaft, but when you are in any other gear the shafts tend to be forced away from the counter shaft and stay there. I'm not sure I can clarify that any better without trying to find pictures and mark them up (which I am not good at and don't have the time for right now).

 

That makes a lot of since since I'm in the 1to1 gear. What does it take to overhaul one of these Bruce Jenners?

 

I'm the wrong guy to answer this one, I have no experience working over transbreastites, I means transformers, I mean transmissions. You may need special tools, but I'm sure it's not too hard to tear it apart and have a look, check your fluid level and condition before you start though it might give you more information or convince you to replace the whole trans-sister.

 

@ kevin n wheeler:: You guys crack me up today.

 

Well I picked up a 5 speed this past weekend for $150 and got it swapped out. I took away most of the vibrations. Its still not silky smooth in 4th gear but it is a lot better. Now I need a gear reduction so I can use my new 5th gear. It will maintain 60-65 mph in 5th but that's about it. Not much acceleration.

 

Following up on this. It was the Pinion Nut. It was barley loose enough to allow a slight play in the joint. Put a crank on it and its silky smooth.