4500 rpm, What is the Problem?

[JT68]

The vibration sure sounds like a driveline issue(not engine related). It would not be header related-that moves with the engine, some and exhaust systems rattle, but would not cause what you are describing.

Compare the way you have the 2000 driveshaft u-joints aligned with a 1600 drive shaft. It sounds like they are out of phase, but could be other things.

Also, what year frame is this? 66-67? 67.5?

[Curtis]

The changes in the driveline are 5 speed transmission, driveshaft and rebuilt pumpkin. The engine components and clutch were all balanced and marked so the clutch went back in per the stamped marks.

I just went down and checked the driveshaft again. The marks are aligned and it is in phase with U joints perfectly matched. How much can a tube be out of balance? I see the balancing of the shaft as mostly related to the yokes they have many irregularities. I'm thinking I should pull it off and have it checked again. My damn Summer driving is going down the hole and it's not like we get a long season here. I just want to fit some drives in between my chores.

[Curtis]

I wonder if they check the run-out of the tube. This is of course a used driveshaft I bought.

[23yrRebuild]

FWIW, ...IMHO... to anyone who is thinking of, or in the process of doing, a lower end rebuild of their engine.... I considered the extra expense ( and I'm talking less than $100 overall expense for engine, clutch and driveshaft) of the "balancing" services of these components to be an EXTREMELY positive cost / value, perspective.

[JT68]

I’m guessing a 66 frame. Did you drop the crossmember down? If not, the rear of the trans is too high.

You are right, the driveshaft tube is probably not the issue.

[Curtis]

67 frame, same thing. I built a custom mount that puts the 5 speed at the correct height. The old recommended way is to just drop the 4 speed mount to the lower holes. Had to get hold of the 5 speed mount to get measurements, then time on autocad.

[JT68]

You are positive the u-joints are right? Can you take a photo of the entire shaft assembly?

Is a bad u-joint a possibility?

Assuming the custom crossmember is correct, the driveshaft or u-joints are still the most likely culprit. Do you have
or could you borrow another 2L driveshaft to swap in?

Another option is take the shaft (complete assembly) to a driveline shop and have them spin it up.

If the shaft is ruled out-at this point it isn’t-perhaps the diff flange is bent. (Rare, but I’ve seen it at least once).

[Curtis]

Driveshaft was taken to Drivelines NW, a very good shop. They currently have a 4 speed shaft and I'm thinking of pulling the 5 speed and having them check it again. I have two other shafts in unknown condition.

[Curtis]

Swapped in the extra driveshaft for my dinner time. No change, same vibration that goes away with the clutch in. I'm considering disconnecting the exhaust and running just the header and hope I don't get a ticket. be one more thing to eliminate.

Got a PM asking if I am using a urethane mount which I am not.

[theunz]

Any noise from the throw out bearing?

[Curtis]

Not that I can tell. I have someone coming to help me this week.

[redroadster]

Is the tail shaft bushing snug on the d shaft
It will start orbiting if not

[Curtis]

Trust me, it is all bolted down.

[spl310]

Is the tail shaft bushing snug on the d shaft
It will start orbiting if not

I had the tailshaft bushing fail on a non-Datsun years ago. It made a horrific vibration! It didn't stop when you clutched though.

[theunz]

While not exactly a safe or fun test, you could remove the drive shaft and have someone tow you. If no vibration then it’s the drive shaft.