4500 rpm, What is the Problem?

[redroadster]

Go Pro it!

[Curtis]

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.

Second driveshaft, same vibration. I'm beginning to suspect the clutch. I just can't imagine the pilot bearing having fallen out. They just don't come without a lot of effort and I certainly didn't find it anywhere.

[theunz]

Just grasping at straws here…..Ok, so when you press in the clutch it goes away right? Are you letting the engine rpm’s fall to idle when you do. We know that disengaging the clutch separates the engine’s rotation from the transmission, but when you are rolling all the gears in the transmission are still turning. If you put the transmission in neutral while rolling then I think only the main shaft should be turning. what if you got up to vibration speed and put the cutch checked for vibration, then put the car in neutral, checked for vibration, and finally killed the engine and checked for vibrations. Perhaps that would help to isolate the issue. Unfortunately I think you are going to find a transmission issue, perhaps a bad bearing.

[Curtis]

Did that stuff. Transmission is a borg warner that only had 200 miles on a rebuild.

I just took the exhaust loose at the front pipe because I had previously had trouble with it touching frame. It is no longer doing that since I took it to a muffler shop and had things fixed. It wasn't as loud as I thought it would be and no change in vibration. The engine and transmission will probably come out this weekend. I have a known good 4 speed. Also have all new clutch at hand.

[theunz]

I would trust a transmission with 20,000 miles more than one with only 200 miles! What a pain to have to pull the engine so soon, but it does look like your best course of action. Better to just get on with it rather than put if off. As I’m sure you know restoring these cars is often two steps forward and one step back. Good luck and I hope it’s something easy and inexpensive. Thank God it’s worth the aggravation to be able to enjoy such a fun vehicle.

[JT68]

Whooooa there hoss, I think you might be getting off base. I can't even imagine something with the clutch causing this. The clutch plate has an offset dowel, so you can't install that wrong.

You said the flywheel was balanced. What else could be wrong with the clutch and still function?

If it were the clutch assembly, flywheel or engine, the vibration would be there in neutral if the engine is rev'ed

As I mentioned, it wasn't going to be the header or the exhaust, Yes, the exhaust can rattle, but not cause a driveline vibration.

I think you said with the engine rev'd there is no vibration right? That pretty much rules out the FW&Clutch assembly.

What you are describing really sounds like it is happening behind the transmission. The rear of the 5-speed has a bearing, not a bushing, so that isn't it.

The reason it happens under load is the mass is deflecting outboard under load and when you push in the clutch, there isn't much load and things center up.

It could be the diff, but not too likely. (if someone dropped it on the flange, that would do this)

Do you have the original cross member you could bolt in? If the trans is off axis, that would do exactly what you are describing.

Before you pull the engine, why don't you send me a photo of the way the driveshaft is assembled before you pull the engine-just to double, double check.

[Datrock]

The somewhat hidden bolts that attach the transmissions rear mount to the tail housing loosened up and caused a mystery vibration I had in my 68spl, it was on a 5speed. One day it appeared out of no where and felt it mostly in the shifter. I chased the vibration for awhile and gave up since it wasn't real bad but it was noticed by me and wasn't there when I swapped over to the 5 speed. Then upon an engine removal I discovered the loosened bolts. I have heard that Urethane mounts can vibrate more than the stock rubber ones. Are you using one? If so, swap it out with a rubber one and see if things change.

[Curtis]

I spent well over an hour changing from the GM rubber transmission mount to the OEM Datsun/Nissan one. However, I think this is one of the repro ones, don't remember now.

Change of mount made no difference. And for some reason the car has decided to run even worse. Was fine earlier in the day. I think this car is just pissed off at me for restoring it and changing to the stroker. Before that it never gave me any problem. Didn't have much power from the tired old 1600 but it always went.

What I did find was I put it in neutral today and revved the engine and it does vibrate in neutral. Guess I didn't rev it enough before.

[Gregs672000]

So sorry to read of the continued challenges. Very nice of JT to offer his eyes. An alternative before pulling it would be a run in the rollers so you could walk about the car and find the culprit. Unfortunately that's some dyno time, probably $100 more to the cost...

[redroadster]

The input gear and cluster gears were a matched set back in the day .needed to be smooth, As I remember our trans tech telling
But na since?

[Curtis]

Put the stethoscope on it today. Really noisy at the tail shaft and almost no vibration at the bell housing. So we feel it is one of two things, missing pilot bearing or the main shaft. I can't imagine the pilot bearing since I was careful not to stand it on end. It didn't come out on the 4 speed when I pulled it and was not in the clutch. If it came out it ghosted on me since I have cleaned in the garage 2 or 3 or more times since it went back in. But I did not look at it before assembly, a goof on my part. The alignment tool did not wiggle around when put in.

I was wrong earlier, it has 2000 miles on a rebuild.

[garth]

HI Curtis,

I feel your pain and frustration! Your description of the vibration issue and your efforts to remedy seem strangely familiar. Roadster reassembly "deja vu"!

Early in the rebuild of my car I realized my engine had a few non original parts including a 240Z flywheel and clutch. For some good or bad reason I decided to reassemble with a proper U20 flywheel and new aftermarket clutch c/w new pilot and throw out bearings.
On startup the drivetrain had a moderate vibration that diminished with the clutch disengaged. Pulled the engine and separated the transmission. Quickly discovered the flywheel had a second pilot bearing jammed into the flywheel center, ahead of the bearing on the transmission shaft. My bad! I did not examine the flywheel carefully enough before reassembly and missed it. Apparently the pilot hole is bored almost deep enough to accommodate a second bearing but not quite. I suppose there might have been only .010" or 020" interference but enough to cause the vibration. Removed the offending bearing and the vibration disappeared. I was fortunate the final startup of my car was at Ross's shop as he and his mechanics were quick to diagnose and remedy the problem. Just one of several reassembly mistakes I made.

Good luck resolving your problem!

[JT68]

Yes, two pilot bushings would mess things up, probably would have destroyed the input gear or the nose of the main shaft long term.

Leaving out the pilot bushing would certainly be bad too. Yikes?

Curtis, there isn’t much that could go wrong with the tail end of the 5-speed, unless it got dropped on the rear flange. You can put a dial indicator on the tail flange and the diff flange. It would be next to impossible to bend that rear main shaft.

As mentioned, I have seen one diff that caused a driveline vibration like you describe, I swapped everything and it never resolved until I swapped the pumpkin. Probably had a bent flange.

Since your vibration is present in neutral, that sounds more like flywheel balance/pilot problem now.
Have the company that balanced it spin up the FW and clutch plate as a unit, really fast. Machine shops are human, so they can miss on balancing once in a while.

You do have the thicker trans spacer plate, yes? (Or two 1600 plates) I’m not sure if that would create this problem, but possibly. Ross will have one if you need it most likely. Very sorry for the troubles, been there done that, very annoying.

[Curtis]

As mentioned before the clutch unit was balanced and marked with alignment punch marks. Worked without any problem with the 4 speed.
The engine is coming out the weekend.

[JT68]

Ok, sounds good then on the clutch/FW. I missed the note that you had used it as-is with the 4-speed.