Today, I was putting on some miles to be sure the engine is broken in fully on the Z I recently "finished" restoring. I have a vibration that seems to become noticeable around 70 mph.

I have only owned two 240Zs, but I have experienced some driveline vibration with each of them. I was hoping not to have the issue with this one, but it is present. And it is bugging me.

First, a simple question: Is it perhaps, normal... for a 240Z to have a driveline vibration? I mean, maybe with me driving modern cars, I just have lost touch with how these old cars really were?

How do I describe it? Well, for one, the rear view mirror vibrates and blurs the image I see in the mirror a bit. That doesn't seem right. But, it isn't just the mirror. If I touch the center console, or the padded area of the transmission tunnel, I can feel the "hum" that is happening. And, I can feel it coming through the seat as well.

The driveshaft has new OEM u-joints and was shortened and balanced by Carolina Driveline in SC. The rear axles have new, OEM u-joints and when they were installed, measurements verified they had the right amount of axial play. The rear differential has all new bearings and was assembled properly. The differential location is stock - it has not been shifted back as was done by the factory for the 1972 and later cars.

I remember that the new engine mounts were thicker than the old ones by a bit. That may have raised the engine a touch. I also recall there being some slop in the transmission mount, which allows for a bit of side to side movement of the transmission. I think I will look at the propeller shaft angularity... to see if that looks off.

I am interested to hear how much vibration... or how vibration free... is your Z?

Edited Sunday at 05:40 PM1 day by inline6

1 hour ago, inline6 said:

The differential location is stock - it has not been shifted back as was done by the factory for the 1972 and later cars.

Not clear what year 240Z you're driving but Nissan moved the diff back because of vibration. I can't find a reference but it's been well-discussed. The shorter "pre-modification" propeller shaft was/is popular for people doing the 71C transmission swap because the length was perfect.

Anyway, maybe you're just experiencing the reason Nissan made a change. I think that it was actually mid-71 but not sure.

If I were looking for vibration:

Wheels

Driveshaft

Halfshafts - I would have these balanced

Stub axle runout

I also agree with Zed about the reason for the diff shift. That would be my first thing to do.

Your vibration description is identical to one I had in my early 71, except mine came on at 80 mph +. I described it as having a 500 lb. bumble bee in the car. The vibration was too fast to be half-shaft u-joints. I tried new u-joints, but they didn't improve the vibration. After carefully cleaning the shaft and upon closer inspection, I found a bit of scuffed paint and the slightest hint of a dent. The dent was only visible in bright sunlight and at the right angle. Off to the local drive-shaft company it went. They retubed it and installed new Spicer u-joints. The only brand of u-joint they would guarantee to not screw up the balance at the time, I reinstalled tyhe shaft and never had any more trouble with it for the next twenty years..

Thanks for that info, Mark. So, it seems like I should focus my efforts on the driveshaft.

While I had the driveshaft shortened and balanced by a reputable driveshaft shop, I am thinking I will need to have it checked. There are actually several driveshaft shops near me, I found out today.

I also am unsure if the alignment of the transmission to the differential is off. I need to check left to right of each as well as vertical angles of the rear of the transmission and the front of the differential. Raising the engine a small amount from stock (via the new motor mounts) may be a factor. I am going to buy a digital inclinometer to help with figuring these angles out.

13 hours ago, inline6 said:

Thanks for that info, Mark. So, it seems like I should focus my efforts on the driveshaft.

While I had the driveshaft shortened and balanced by a reputable driveshaft shop, I am thinking I will need to have it checked. There are actually several driveshaft shops near me, I found out today.

I also am unsure if the alignment of the transmission to the differential is off. I need to check left to right of each as well as vertical angles of the rear of the transmission and the front of the differential. Raising the engine a small amount from stock (via the new motor mounts) may be a factor. I am going to buy a digital inclinometer to help with figuring these angles out.

For best life and to minimize vibration, drivelines should operate at a slight angle, and not be perfectly inline. The small angle is to ensure that all of the needle bearings will see load and rotate. When I design drivelines for industrial applications I use about 2 degrees of parallel misalignment.

That said the likelihood of an automotive driveline being perfectly aligned is probably zero.

Edited 17 hours ago17 hr by CanTechZ

I had the same thought about needing some angle being necessary to work the needle bearings.

Side note about the "AI Overview". It is basically a boiled down compilation of everything available on the internet. Including all of the garbage and nonsense. The tech marketers want us to start believing what the AI algorithms produce. But, really, it should all be ignored and only verified professional sources should be considered. At this point in time, "AI" is good for entertainment purposes only.

If you really study the statement below you'll see that it actually says very little, and some of it makes little sense. Like "allow the shaft to change angle". Empty words, really.

No offense intended. It's just another of those things to be worried about. The word intelligence does not guarantee intelligence.

4 minutes ago, Zed Head said:

I had the same thought about needing some angle being necessary to work the needle bearings.

Side note about the "AI Overview". It is basically a boiled down compilation of everything available on the internet. Including all of the garbage and nonsense. The tech marketers want us to start believing what the AI algorithms produce. But, really, it should all be ignored and only verified professional sources should be considered. At this point in time, "AI" is good for entertainment purposes only.

If you really study the statement below you'll see that it actually says very little, and some of it makes little sense. Like "allow the shaft to change angle". Empty words, really.

No offense intended. It's just another of those things to be worried about. The word intelligence does not guarantee intelligence.

Hey, no offence taken. You are totally right about AI, you have to read the results carefully and still take what is presented with a grain of salt.