What the heck is that sound!

[CheyneX5]

I have an annoying sound/ problem with my 1990 NA6.

It started off as a loud clunking noise from the front of the car on right hand turns, this was fixed by replacing the front and rear wheel bearings on the left hand side. Left hand turns are very quiet and normal.

After replacing the bearings, this revealed a new sound, a grinding/rubbing/slight knocking sound coming from the rear of the car. It only happens on right hand turns, it gets louder as more load is applied.

I should also note that the car has adjustable Koni Shocks with King Springs and Rear Subframe bracing.

I have been to the MX5 factory numerous times, so far we have:

- Replaced rear left wheel bearing
- Inspected left half shaft from diff
- Inspected chassis and bracing
- Inspected all suspension components including replacing bolts etc
- Replaced one or two bushed from main suspension arm
- Removed everything loose from car including jack and spare wheel
- Inspected diff


My mechanic even hopped in the boot while i did right hand circles around the car park to get a better idea of where the sound was coming from!

Is anyone able to shed some light on this? It's driving me bonkers, it is making me very cautious to drive the car.

Thanks

Cheyne

[mxfive95]

It might be a long shot but have you looked at your exhaust? There might be a broken flange bolt and when you turn right it opens up?!?
It might also be the rear sway bar D bush bracket that attaches to the body... (I had a similar problem with an old 626) try the front one too.

See you at the garage

[CheyneX5]

Good call on the swaybar craig, will check it out.

We have thoroughly checked the exhaust.

[manga_blue]

I had flat spotted tyres that sounded exactly like shot wheel bearings.

[fattima]

Have a good inspect and see if you can see any witness mark where things are rubbing. Check that the roll bar as mentioned as well as the end links. You say they have inspected the drive shaft, do you know if the CV joint is OK, it was the first thing that sprung into my mind when you mentioned the problem.

[manga_blue]

It started off as a loud clunking noise from the front of the car on right hand turns, this was fixed by replacing the front and rear wheel bearings on the left hand side. Left hand turns are very quiet and normal.

After replacing the bearings, this revealed a new sound, a grinding/rubbing/slight knocking sound coming from the rear of the car.

This matches my experience with replacing bearings and finding the noise moved to the back. Did you rotate the wheels when you changed the bearings? i.e. did you move a bad wheel or tyre from the front to the back? If you move the wheels around now does the noise move with it?

[bruce]

Sounds like wheels/tyres. Could be a flat spot on the tyre, or a wonky rim. Are the nuts done up tightly?

[CheyneX5]

Thanks for all the pointers, one would think it would be the wheels, however, we did put on a set of nb8a wheels and still it had the same problem.

I am not sure if the cv joints have been checked...

[manga_blue]

Oh well, the wheels and tyres were worth a try. Would have saved me heaps if I spotted them earlier on mine.

You're really checked all the obvious things with suspension, Cheyne. Tyres hitting bodywork are too obvious.

You get centrifugal force when you turn corners. Heavy drivetrain and exhaust components can move and touch bodywork. The noise gets transmitted into the body. It sounds like stuffed bearings. It's hard to say where it came from. How are engine mounts and diff mounts? Can the exhaust or anything else move enough to bridge the isolation between drivetrain and body? I've seen one MX5 where a broken mount meant the engine moved enough to let the throttle brackets touch the bonnet.

[GS]

Im just throwing ideas out there, but what about a broken or cracked PPF?

[CheyneX5]

Oh well, the wheels and tyres were worth a try. Would have saved me heaps if I spotted them earlier on mine.

You're really checked all the obvious things with suspension, Cheyne. Tyres hitting bodywork are too obvious.

You get centrifugal force when you turn corners. Heavy drivetrain and exhaust components can move and touch bodywork. The noise gets transmitted into the body. It sounds like stuffed bearings. It's hard to say where it came from. How are engine mounts and diff mounts? Can the exhaust or anything else move enough to bridge the isolation between drivetrain and body? I've seen one MX5 where a broken mount meant the engine moved enough to let the throttle brackets touch the bonnet.

Thanks for being so thorough mate, I am beginning to feel more and more that it's something related to body noise, it's loud with the roof up, almost not there with the roof down and you can not hear a thing when outside the car. The car has a full aftermarket exhaust system which looks to have some age, we 'have' checked this, but not to the extent of the other parts of the car.

GS, excuse my ignorance, the PPF is the powerplant frame if I am correct, where can I find this on the car? I have no idea what It looks like.

Thanks again for the help

[GS]

Sorry, i should have expanded my comment slightly. The PPF on the MX5 is the ladder type structure that runs along the side of the driveshaft. It basically bolts onto the gearbox at one end and the diff at the other. There has been cases of the PPF cracking, sometimes around the diff area, but usually its been on higher powered cars.

Actually, if you want to search i think Hammer might have posted some pics of a broken PPF from his SP on the forum a few months ago.

Its unlikely to be the issue in your case, but i thought id mention it to cover all bases. Good luck!

[05ragtop]

Cheynex5--- when you shewed me those photos under your car--remember there was one of the diff that looked like it had a crack in the case. Check it out it may also be a bearing in the diff itself. Just a thought. Cheers Johno

[manga_blue]

... exhaust swinging across on turns and dragging on the half shaft?

[Wivvix]

1. Raise the rear up 1 perch. Go for a drive.
2. Remove non-standard sub-frame bracing on the rear. Go for a drive.
3. Check/replace exhaust hangers.
4. Inspect CV boots.