Severe vibration from rear end
 

Hey guys, figured this would technically be in the s-chassis section, here's a little background,

I've got a Z31 that I've swapped an S13 multi-link into. I've got a severe vibration coming from the rear suspension from 45-65mph. It feels nearly identical to driving on the rumble strip. Here are a list of modifications in the drive train:

-Stance solid subframe bushings (press-in).
-Completely new balanced driveshaft, including u-joints
-welded diff
-ichiba rear 5-lug hubs
-ichiba 50mm extended studs
-d2 coil-overs
-50mm wheel adapters
-progress adjustable sway bar w/solid links
-no name RUCAS
-new rotors/pads

The vibration was not present pre-swap, so it's got to be something in the rear end. I feel it through my seat, not my steering wheel. At 60 mph, it feels like a massage chair, and my teeth feel like they're going to rattle out of my head. When assembling the rear components, I put thread-locker on all hardware before torquing down.

I've never driven in a car with solid mounts and welded diff etc., but the diff is making all kinds of noise. It clunks if I shift aggressively, and whines a lot. Also of note, when cruising at vibration speeds, if I accelerate hard, the vibration completely disappears. Then when I let off the throttle, it's right back in massage mode. The vibration tapers off after about 65mph. Another thing; when I was installing my drive shaft, there was about .625" of "free movement". I was told this is normal, but I just thought I would mention it.

My guess is the diff is the culprit, but I'm interested in hearing your experiences and solutions. Thanks alot!

Gotta ask a stupid question. Do you still have the other diff? Seems like a quick swap would answer this pretty quickly, but I may have misread something.

I do have the other diff still, but its from the original Z31 frame, and will not fit the S13 frame. I am picking up another s13 diff on my way home tonight, and I will give it a go.

Has anyone ever had a drive shaft out of balance? I mean, The shaft I got was supposedly balanced beforehand, and looks like it was (has weights welded in spots) but I am curious as to if this carries the same symptoms as I am experiencing.

Have a chick ride in the back seat.

Pre-sex orgasm. profit.

LOL.


If you can, check driveshaft/subframe SAFELY. If you have access to a 4 point lift. So you can check what's going on under the car while the wheels are in motion.

2 seater :-/

I don't have access to a 4-point lift, so I don't think I'll give that a try lol. I can just foresee disaster in my shop once that thing starts to vibrate, and the wheels will be spinning at 60mph haha. The vibration is bad enough, that I could easily see it vibrating off jackstands :eek:

Ah. Like I said, I missed that the other diff was a z31.

Swapped diffs last night. No change. Drive shaft is going to get RE-balanced today.

bad bearings in the hubs or did you get a alignment?

If the drive shaft is found to be within spec, I will look into the bearings. Although, just moving them around manually, they don't seem bad. Wouldn't they produce a "growling" even at low speeds if they were failing?

As far as alignment, I got the rear as close to spec as I possibly could using my typical methods (angle iron, string tape, etc.). It didn't track on the highway or anything, and feels solid. Plus the vibration is rapid, not like an out-of-round tire or loose bushing etc.

Thanks for the tips.

why would you put s13 rear end parts on a z31? i might be missing something since here since i know nothing about the z31 but i would think that is your issue

For MANY reasons, but this should be enough:

multilink > trailing arm

And no, this is not my issue. The s13 links and frame retain the same basic geometry (allowing the user to benefit from aftermarket support), so any issue that arises, will be with a component not the geometry as a whole.

so you changed the rear end from a trailing arm setup to multilink and you think it holds the same geometry?

btw this is not a s chassis question since it has to do with a z31 and not a s13/s14/s15. using parts not designed for your ride(s13) does not make it a s chassis question.

Yes.

Cool, thanks.

Anyway, got the drive shaft back from the shop, it was "off by a mile". Now to get this in and go for a shakedown run! :coold: