Bret

I'm hoping to be an s2000 owner soon, but until then I'm driving my '93 240SX SE. Since most here seem pretty knowledgeable about how things work in a car I am hoping that you can help me solve a problem that I have.

I get a low vibration throughout the car at various time when going through the gears. It consistently occurs at about 60mph in 5th gear. I took it to the local Nissan dealership. The tech said that he thinks it is the drive shaft. Not believing that the drive shaft has gone bad, I took it to a place that works on and makes only drive shafts. The owner took it off the car and tested the balance, inspected the U joints, and inspected the center support bearing. He said that there is nothing wrong with it.

Last night I put the rear of the car up on jack stands and ran the car through the gears without the rear tires touching the ground. Everything was smooth until I got to about 50mph and then the vibration starts. The vibration would get worse until about 60mph. After that increasing the speed wouldn't make the vibration worse, but it didn't get any better either. When I took the car out of gear, the vibration still happened until the speed went below 50mph. I had a neighbor run the car through the gears while I observed the drive shaft and differential. I couldn't see anything vibrating. I then opened the trunk while he was still at about 60mph and removed the carpet. I could then hear (as opposed to feel) a noise that seemed to be from below the spare tire.

I don't think that it's the tires because I have previously rotated the tires from front to back without any change. If I jacked up the car again without the wheels on it and get or don't get the vibration, what does it tell me? What should I do next to figure out what the problem is?

Thanks in advance,

- Bret

S2kRob

First thing I'd try is take the rear wheels and tires off the car and run it through the gears on the jackstands again. See if the vibration is there or not.

If it is, it could be your axles, or maybe your wheel bearings are bad. Check your brake rotors while you're at it.

Good luck!

The Reverend

Yeah, either you've got a bad bearing somewhere in your drivetrain or something is bent/out of balance. But what exactly is the problem is pretty hard to diagnose, especially over the 'net. Like Rob said, try it without the wheels so you can rule out the wheel balance. If you have access to a dial gauge, set it up against the driveshaft and turn it around (you might want to use the axles to turn the driveshaft so you don't get an erroneous reading from your hand shaking anything. Anyway, the runout (difference between the highest point and lowest point as it rotates) should not be more than 5, maybe 10 thousandths of an inch. After your check your driveshaft, check your axles. And while you're at it, check the runout on your rear brakes to make sure they're not what's wobbling around. If both axles, brakes, and the driveshaft are straight, you've either got a bad bearing somewhere or you have something bent inside your rear end or inside your transmission.

HTH - good luck tracking it down, this sort of thing is never easy to accurately diagnose.

cmnsnse

How about 60mph in 4th gear? if it's still there, are your tires worn/old?

S2kRob

Good idea, but the driveshaft, rear diff and axles will all be still rotating at the same speed . . .

cmnsnse

yeah but at least you'll rule out your tranny/engine, which is my point - I have a nissan 5 speed that shimmy's in 3rd ONLY at about 45 mph, not present in other gears.

BTW - My autoshop teacher used to say if your butt shakes its the drive line, and if your stearing wheel shakes its your alignment.

stbrnd

I responded to this thread ( I think) in another topic.

I have a small vibration in my 91 240 that starts at about 45-55. As I stated it works itself out at any higher speed.

I have an automatic transmission, so if this is the same vibration that may suggest a rear end problem.

I never really thought much about it, just thought it was the wheels out of balance or something. Doesnt do it all the time.


Hope you find out what it is. PM me if you do.

Bret

I put my 240SX up on jack stands last night and took off the rear wheels. The vibration is not as noticable without the wheels mounted, but it is still there. I think that perhaps the wheels and tires are amplifying the vibration. When I run the speed up and take the car out of gear, the vibration is still there until the speed gets below about 50mph. Therefore, I don't think it has anything to do with the transmission.

The good thing about putting the rear up on stands is that you can run the car in first gear without it stalling out. When doing this I can easily see the runout of both axle half shafts. The left side looks like it is running out about 1/16" and the right side is running out about 3/32". I would logically think that you should not be able to see any runout, but I don't want to assume anything. There is also a leak comming from the drivers side "side flange". So, my questions now are: 1) Is the runout that I am seeing in the axle half shafts normal? If not, what caused it to get this way? (the car has never been wrecked) 2) Could the leak at the side flange have caused damage to some internals which is causing the vibration?

There is one other thing that I found is interesting. When the tank is empty, the vibration is most noticable. I went for a drive after I was done and the car was vibrating pretty bad at 60mph. I filled up the tank and the amount of vibration went down a good bit. Any more insight would be greatly appreciated.

S2kRob

Can't help you with the runout tolerances, but the full gas tank just added weight to the rear axle, damping the vibrations more.

The Reverend

Well, I can't speak for certain as the the acceptable tolerances on a 240, but 3/32" sounds like more than should be there. I'd say you need new axles, but don't blame me if that doesn't fix the whole problem.

BTW, what was the runout on the driveshaft?