rumbling noise/vibration

[moyest]

Hi folks

I've posted questions on this a while back, see if you can spot the problem -

When I hit 50mph I get a rumbling sound in the cabin, and vibration from the rear. Once I hit about 65mph+ it disappears.

Suggestions so far are things like tailshaft, CV's/U-joints, outer bearings, etc...

UPDATE: I had my car on a "rolling road" DYNO last week, and when I hit 50-60mph the guy said my rear left wheel was tramping up and down a bit (kind of wobbling).

Makes sense. I guess if my rear left wheel is bumping along the road then it would feel a bit like an out-of-balance driveshaft or similar. Kind of feels like I have one square tyre!

It's not tyres though, because the first thing I did was balance and rotate the wheels.

SO WHAT WOULD CAUSE THAT? :stupid:

[2ManyZs]

Since you are quite sure it isn't the wheel/tire, then the next obvious things would be the stub axle, u-joints, worn out strut cartridge, worn bushings, or a combination of more than one of the above.

I'd start with the strut cartridge, then go to the stub axle, then the rest of the driveline and bushings. It is possible that it is something other than these, which might have been a result of hitting a curb and bending the control arm, or something of that nature...

[Zedrally]

You didn't mention the rim?

I'm not sure if it's the same thread, however I mentioned in one that I had a similar problem caused by the rim going off centre.

2 possible solutions where:

Buy new rims, which I did and the problem went or have them plug, welded up and new holes drilled.

Good luck

[moyest]

Thanks guys, but I rotated the wheels (rims) front to back, so even after I changed the wheels around the noise is still there.

And assuming the "strut catridge" is the thing that the suspension strut sits inside, that is OK too. I had the suspension done a month ago (and the noise started before that), but the suspension guy said all the bits looked really good.

What about C-clips, U-joints, and other letter-related items?

[moyest]

Oh, and I haven't hit any curbs or had any dramas at all. The noise just "developed" of its own free will.

Don't think I've even hit a pothole lately! :classic:

[2ManyZs]

I wasn't speaking of your driving, but you never know what a previous owner may have done...

I'd check the stub axle first, take the wheel off and see if there is any fore and aft play in the stub axle, or even up and down, which might show if you have a worn out bearing and/or a loose stub axle.

Secondly, check all the u-joints, not just the ones on the half shaft at that wheel, since the vibration could be transmitted through the entire driveline if the u-joint is really bad and you haven't replace the suspension bushings yet, which would only amplify the problem. Also, check all the mounting bolts on the flanges as well.

[Bambikiller240]

Originally posted by moyest

Thanks guys, but I rotated the wheels (rims) front to back, so even after I changed the wheels around the noise is still there.

And assuming the "strut catridge" is the thing that the suspension strut sits inside, that is OK too. I had the suspension done a month ago (and the noise started before that), but the suspension guy said all the bits looked really good.

What about C-clips, U-joints, and other letter-related items?

How sure are you that "the suspension guy" actually did replace the strut cartidge (which is INSIDE the strut), and did it right? Is he familiar with Independent suspension? Has he ridden in the car to experience the symptoms that you describe?

These are a few of my favorite questions.

[moyest]

Yep, the guy that did the suspension knows his stuff. He is a Z car specialist mechanic, and he sets up Z's for racing and rallying. He owns an absolutely mint 240Z. He does suspension work for lots of people.

I really have to get this problem sorted, because tomorrow I'm having triple Weber 45's fitted and I don't want to have to drive everywhere under 50mph if you get my drift...

[Bambikiller240]

Has he ridden in the car? Looked for the problem after the install? I know from being inside a car (driving) it's hard to find problems, just wondering if they have or could put it on a lift and run the car to see how the rotating assemblies look while moving. Hope you find the cause soon. Be sure to post the results so others can benefit from your experience.

[EScanlon]

I had this same problem on another car, and what it turned out to be was that one of the belts on the tire had broken. The only way I was able to fix the problem was to buy new tires.

2¢