RED MX5

There are few things more frustrating than trying to nail down a problem by swapping out parts in the hope that we'll stumble across a fix. Maybe Billman or one of the other guys will have some insight to share.

Assuming that changing the half shafts and all four CV joints didn't eleminate the problem it's probably safe to assume that it's not related to the shafts or joints. You are running the same drop I am, and I know at last a half dozen others who are running a 1" drop without any vibration problems, so it's also unlikely to be related to the lowering. It *might* be one of the CV joints in the driveshaft.

Can you relate the frequency of the vibration to wheel rotation, revs, or road speed? If we had some more information maybe somebody here could help figure out what's really wrong, before you go and spend more money replacing parts that don't really need to be replaced.

Sorry for asking so many questions, but at this juncture I don't have any answers, and can't even venture a good guess. More information about the symptoms might not help, but you never know. Somebody here may have already been down the rocky road you're traveling.

GraveS2000

I just bought some stance coilovers for my S. I purchased some T1R spacers as well. I figured someone recommended them for something. Even if they aren't necissarily needed they can't hurt. So I spent the extra few bucks. I guess better safe than sorry. Though this doesn't really answer any questions.

saaboteur

Wheel bearing issue, perhaps?

I had some crazy vibration in the spring. Turned out to be a toasted wheel bearing, it was allowing the whole outer CV joint to move around. But the problem quickly went from noticeable to bad to really bad.

matthouston23

I like to describe it as a general looseness in the rearend that occurs around 40 and 70. It feels like it's coming from the rear wheel directly under the seat. It reverberates up the seat and into my entire upper body shaking my jaw most the time.

I know the source of a vibration may not always be where it's felt, but those are my symptoms.

RED MX5

[QUOTE=matthouston23,Oct 24 2007, 10:28 PM]
I like to describe it as a general looseness in the rearend that occurs around 40 and 70.

matthouston23

That's precisely what it feels like. Unfortunately, I've put the stock wheels/tires back on and it doesn't change the behavior at all. So all wheel/tire issues are out.

RED MX5

[QUOTE=matthouston23,Oct 25 2007, 03:55 PM]That's precisely what it feels like.

matthouston23

It's completely independent of road surface or gear or rpm. It's 100% related to the speed of the car. Starts shimmying at around 40, then quiets down until about 70.

It's funny, I can tell the speed of the car based upon the vibration as much as the speedo. As soon as I start to feel the looseness, I look down and it's at 40 - 43 EVERY time.

The propshaft has been inspected with the car up on the rack running and was found to be in perfect shape with no evidence of vibration.

Both half shafts were replaced last week, so all CV joint issues are out.

The shop that lifted the car and ran it on the rack said it may be originating from the differential, but replacing that is out of question due to the prohibitive cost. On top of that, they admitted it wasn't much more than a guess.

And, I swear it's coming from the rear wheel area somewhere based upon my experience driving the car.

McHeizer

very strange indeed!

when the shop had the car running on the rack, did they bring it up to the speed range where you experience the vibrations?

The only thing I can think of is the prop shaft.
Then again it should be at several speed ranges i.e. at certain prop shaft rpm. Depending on the gear you are in you should have different speed ranges with the vibs.

Possibly the diff, but inlikely in my eyes.

Hope you'll find a solution!
Anyone around in your area with an S & experience?


EDIT:
did you check if all your bolts on the rear subframe are tight?

RED MX5

Well Matt, I'm stumped too, but I do know what I'd do if I were in your shoes. I'd contact XViper and Billman250 and discuss the problem with them. Since you probably don't have XViper's e-mail address (and I can't hand it out) you can't contact him, but you could PM Billman250, and he just might be able to help you sort this out. I'm sorry I can't be more helpful, but as McHeizer said, this is a pretty strange problem, and I really haven't got a clue.

I'm grasping at straws with this one, but are you sure that it's not a front tire or wheel that's causing the vibration? This sounds so much like a tire out of balance or a bent rim I think I'd check the front even though it feels like the vibration is coming from the back.

Good luck, and please be sure to let us know what this turns out to be, once you nail it down.