Vibration at speed

[240ZMan]

I just finished putting a 5 speed transimission and 4.11 R180 into my 73 240. So far I really like the new ratios, but above 70-75 mph or so I start to feel a vibration that doesn't feel like a tire, but gets stronger as I go faster. It feels like it's vibrating the whole rear end of the car and it wasn't there before the transplant.

So here's where I need help from the group. I figure it's either the tranny or diffy that has a balance issue (since that's what I changed), OR maybe it is the driveshaft which is now turning faster.

Here's my reasoning: I have things right in my head, given my old diffy was a 3.36, for the same speed my driveshaft should now be turning about 22% (4.11/3.36 = 1.22) faster. So if I always had the driveshaft balance issue, I wouldn't have seen it until over 85-90 mph before. Given the roads around here I rarely go that fast.

So my questions are:

1) where would you start?

2) have any of you had a diffy or tranny that was out of balance? I have to say I've never heard of that before.

3) I assume it would be posssible to remove the driveshaft and take it in to a shop to have it balanced? Any of you done that, and what are the things to look for?

Thanks,

Daniel

PS. I'm hoping it's the driveshaft as that's the easiest to deal with:)

[e_racer1999]

mos def sounds like a driveshaft issue. check that AND the u-joints. if you have spicer(sp?) u-joints then just shoot some oil in there.... otherwise look at replacement

[Bambikiller240]

I think that I'd remove and reinstall the driveshaft first, but I'd rotate the flange on the diff 180 degrees before the reinstall. If that doesn't fix it, I might take the d/s to a shop to check it's balance. If the problem still persists, I'd suspect either the trans or diff has issues. You didn't say if these were rebuilt units or straight out of the junk yard/parts car/whatever. It's always a guessing game when installing parts that weren't from a car that you've driven before and really know the condition of.

Good Luck

[240ZMan]

I tried Carl's suggestion and rotated the drive shaft 180 degrees and the vibration is better, but still worse than before the swaps. I'd guess the drive shaft and diffy are having "issues" together. So does anyone know if it's possible to get the driveshaft balanced while in the car?

I read once that one way was to put 2 hose clamps around the drive shaft and start with the clamps opposite each other. From there you make small adjustments until the problem goes away. Seems like a lot of trial and error. Anyone tried this?

Jason, I'm guessing it's not a u-joint issue as this came about only after I did the swaps. I guess it could be a coincidence, but for now I'm guessing that's not the issue.

[e_racer1999]

^^i was assuming that the driveshaft was also swapped.... sorry.

did you replace the entire diff arse'y? do you also verify that nothing was bent? that's all i can think of.

[240ZMan]

Spent some time tonight under the rear of the car and I think all the U-joints are ok as they all feel tight with no play. However, where the passenger side half shaft connects to the RR hub there is a lot of play between the flange and the housing. From what I can see in the Haynes manual I'm guessing my inside wheel bearing is shot.

Does that diagnosis make sense?

The manual suggests you need a slide hammer to remove the axle shaft stub. Do you really need one? I assume I'll need to get a machine shop to press the old bearing off and put the new one on?

Any suggestions to make the job easier?

[Murph]

Getting someone with a big f-off press to remove the old bearings is a good idea. I tried it myself......now that was an exercise in futility!

Btw, I have a similar vibration problem....I'm also assuming it's the driveshaft. Whenever I get around getting the new motor and box in the zed, I'll be getting the driveshaft balanced. I hope that fixes it.

[240ZMan]

Well, it turns out I only wish it had been the wheel bearings. When I pulled the half shaft away from the hub the nut fell out! I guess the threaded end had sheared off the rest of the stub axle. Needless to say I got lucky in that at first I didn't notice the vibration until 70+ mph.

Looks like new ones are around $280. Any thoughts on a used one, assuming I can find one in good shape?

[e_racer1999]

ouch! good luck! i'm assuming that a decent JY one would be fine...

[Murph]

Wow! That'd take quite some abuse (or defect) to shear something that size. That's concerning.

[sblake01]

Wow! That'd take quite some abuse (or defect) to shear something that size. That's concerning.

Or it could just be normal wear on a 30+ year old rotating part.

[240ZMan]

I was wondering the same thing. But my father has had the car for the last almost 20 years and I KNOW he didn't abuse it. And I've gone over all his service records and there's nothing done to that side, although the other side was replaced in '92 and it did require a replacement stub axle (no mention of why).

I will say that I love hard cornering, and had 3 track days last year. But I wouldn't call that abuse, and one would think the car could take that occasional stress.

For now I'm treating it as a case of just being unlucky.