Questions for the mechanically minded

greenMachine · Postby **greenMachine** » Thu Feb 19, 2009 10:19 am

Wivvix wrote:Well today was an interesting day.

... It can't be the driveshaft, and it's highly unlikely to be the half-shafts as they spin at very low rpm.

Same RPM as your wheels, which you thought were the problem. However, I agree with the conclusion that a straight driveshaft would not be the problem - have you checked the straightness of your driveshafts? Or perhaps slop in the UJs? The more I think about this, the more likely it sounds.

I'm thinking it's probably a wheel bearing, hub, or something else which is affected down the line from having wheels mounted to the hub face.

Could be, if its not the driveshaft. Bite the bullet, get a couple of new (secondhand) uprights complete with hubs. It will be cheaper than replacing bits one by one.

An explosion diagram or something would really help in trying to visualise all the components from the wheel back to the half shafts

Any thoughts?

Good luck, seems like you are on the cusp of resolving the problem.

My apologies, I should have mentioned the narrow nuts. :oops:

Wivvix · Postby **Wivvix** » Sat Feb 28, 2009 4:27 am

Hello everyone. Just a minor update.

Took the car to wheels world today so that the rear wheels/tyres could be sent off to tyrepower in osborne park for road force variation testing. This is not what I knew it to be called, I believed it was road-force balancing, but whatever. Maybe this is just semantics? :?:

Anyway, apparently they managed to get one rear tyre down to 3.5kg and the other to 5kg.

Now going by what the fellas in the USA reckon, 8lb is desireable, 10lb is acceptable. 5kg is reasonably close to 10lb (11lb).
Does anyone have any comments to make on this?

Mr Morlock · Postby **Mr Morlock** » Sat Feb 28, 2009 12:48 pm

I am thinking this is beyond my technical ability however most problems come down to fairly obvious things and we all drive cars with mechanical anomalies without encountering such concerns. I do not think something out of spec by a few thou will be the problem. Is it possible it is something not even to do with the tailshaft or half shafts- can something not be tight- are the seats bolted down tight, a isolating bush be damaged, ( gearbox to chassis) the spare wheel shaking ie something you are not looking for? Could a clutch out of balance do it? Must be driving you mad but someone will get it.

PUR157 · Postby **PUR157** » Sat Feb 28, 2009 1:12 pm

I don't have anything technically useful to add... but just wanted to say good on you for sticking through this, as said above it must be driving you bat sh!7 crazy...
A lesser man would have lost the plot by now...

Hope you get it all sorted soon!

Wivvix · Postby **Wivvix** » Thu Apr 02, 2009 6:08 pm

Thanks everyone for your contributions.

Today I decided to bite the bullet and give Mazda a stab at finding the cause of vibration in my NA8, as a last resort.
Sure enough I just got off the phone talking to service and according to their "foreman", it's just how my car is.
Apparently certain mx5's do it, some don't.

What a relief! :roll:

I have come to the conclusion that any money spent is now money down the drain.
It's not something I want to live with, and I believe I have exhausted most expertise available in diagnosing the possible cause.

I will, therefore, give up. By give up, I mean sell this car. Enough is enough.
Wish me luck!

Wivvix · Postby **Wivvix** » Fri Apr 17, 2009 12:25 am

I actually decided to stick with this a little further.

I replaced the RHR flange which goes into the hub. The old flange had 10thou runout. This has made a reasonable difference. The rear end now feels much tighter, but that could also be because my mechanic also tightened up all the bolts in the rear end...

The vibration is still there though, so i'm going to exhaust diff as the cause because its free to do so, but failing that I will be selling it.

** I took the mx5 for another drive today, and BOY did that work the other day make a difference! The rear end is so much tighter and firmer now, it's really quite strange. My mechanic did note that the bolts on the diff mounts came undone very easily; this may have been contributing. He also noticed on his drives that the vibration seems to get worse when you back off on the acceleration, particularly in the harmonic frequency bands (50-60kph, 100-120kph).

To a point this furthers my resolve to look at diff mounts and the differential.
Fortunately diff mounts and engine mounts are cheap (engine mounts even more so in parts cost and labor!), and diff problem diagnosis is free.

That's all for now.

Wivvix · Postby **Wivvix** » Thu Jun 17, 2010 9:15 pm

Just an update to this now dead thread.

I have just got home from installing the FM butterfly brace. A drive around local streets and a drive up the freeway, although somewhat impeded by traffic at points, reveals that the shimmy has basically been eradicated from this car.

The car feels like one solid unit now, and the difference in cornering, turn in, and ride quality is pretty much astounding. It's really not all that astounding when you see what the floor pan of the mx-5 is made of, and more so how thin it is! :shock:

I see my mx5 getting a LOT more use, now that it is rock-solid enjoyable.

broady · Postby **broady** » Thu Jun 17, 2010 9:36 pm

Hadn't seen this thread before now, but I'm so glad for you that this is resolved.

Happy motoring!

Mr Morlock · Postby **Mr Morlock** » Fri Jun 18, 2010 6:59 pm

well that is very interesting- it seems that there must have been flex in the car and the fix hopefully successful has been a simple one albeit a long winded and annoying saga.

fattima · Postby **fattima** » Sat Jun 19, 2010 9:35 am

That's great news.
The butterfly brace is a wonderful bit of gear isn't it!

Thanks for updating. I find it annoying when people don't update if something did or did not fix their problem.