na6 driveline noise on throttle off

[CeJay]

Hi All

My wife recently bought an na6, and I've noticed on taking the throttle off from acceleration that there is a rattling / grinding noise coming somewhere from the car. It doesn't happen when you put the clutch in and let the throttle off. I've taken it to the local mx5 specialist and he seems to think it might be the heater hoses at the back of the engine.

I'm just wondering if it is more likely to be the tailshaft on its way out, or the differential?

Thanks

[greenltd]

This may sound weird, but are all your wheel nuts tight? Speaking from experience here, rumble on trailing throttle. .........

[CeJay]

It's something I'll check tonight, but this noise has happened on two different sets of wheels. Went from 17's to 14's when we first bought the car. But like I said I'll check. Very embarressing when your driving and the car is constantly doing it off throttle. Like I said it feels to me like it's coming from the tailshaft or the rear diff. But who knows im probably totally wrong.

[hks_kansei]

Like I said it feels to me like it's coming from the tailshaft or the rear diff. But who knows im probably totally wrong.

I would say though that you would be 100x closer than the supposed specialist (I still cant fathom how a rubber heater hose could cause a rattle....)


I would suspect either the diff (worn, perhaps the lash on the crown/pinion was set incorrectly?)
the tailshaft (the uni joins do wear over time, not sure if they are sealed or replaceable on the MX5)
Gearbox input bearing (these are pretty common to wear out as often people re-use them when replacing the clutch)

[aka_juffa]

I have owned a total of four NAs. With the exception of the current one, all have had this issue. In two cases it only started after the gearbox was removed/re-installed to replace the clutch. I have put it down to drive line lash. The noise disappeared after installing a differential (torsen) from an NB in my 3rd NA. Please excuse my lack of the right technical term, from what I understand after researching this, the NB diff has a thick rubber pad where the drive shaft mounts to it. This pad absorbs the lash and removes the associated noise.

I would also like to add that despite not attempting to resolve the issue in the other two NAs the noise got no worse and did not reduce the reliability of the diff or drive line in general......having said that the 'lash' noise was annoying.

J

[hks_kansei]

Please excuse my lack of the right technical term, from what I understand after researching this, the NB diff has a thick rubber pad where the drive shaft mounts to it. This pad absorbs the lash and removes the associated noise.

Sort of.

The rubber pad is on the NB diff, however is not to do with the lash, the pad is purely there for balancing while spinning (like a harmonic balancer)
The NB diff still has the standard metal flange mount on the diff, same as NA.

Whether the rubber thingo's balancing effect helps noise, I cant say.

[93_Clubman]

Very common source of rattling/zinging sound on the NA was the exhaust heat shields, in particular the one for the exhaust manifold (next to the heater pipes), as well as the rear bullet resonator one near the diff. However, this tended to be on acceleration around 2000-3000 RPM. In both cases securing metal tabs break causing the rattling/zinging.

[manga_blue]

x2. Tap all the exhaust heat shields from the engine right back to the tailshaft see if any rattle. If they can rattle then you can be sure they'll pick up any resonances anywhere in the car and amplify it for you.

[KevGoat]

I found some bits of gravel trapped above the one heat shield that had been causing one of my rattles. Didn't solve the annoying deceleration noise though. I even replaced my speedo cable as there's some suggestions on the forums that these cause rattles as they age, didn't change a thing. It eventually turned out to be the clutch fork rattling. Put a new boot on it and some grease around it and it stopped.