Time for our favourite game… ‘what’s this noise?’

[Spyder fan]

Your doomed I tell you - your doomed.....................

I can hear the chopper….. yep…. Doomed

[Timb]

I've not currently got a +2 but if I did and that was the only noise, I'd be very happy.
Speedo cable or head maybe.
Happy hunting.

[hysteric]

Your doomed I tell you - your doomed.....................

I can hear the chopper….. yep…. Doomed

Should end it all right now!

[Richard J]

Hi there,

I have the exactly the same noise as you (and Lee), and although I haven't found either the definitive answer and solution, I'm 95% sure I know what it is and have managed to reduce, but not eliminate it, in my car.

I'm sure it's gear lash/mesh rattle, which is that the gears that aren't in use rattling against each other, as a result of resonance from the drive train and/or the chassis. It doesn't mean impending gearbox destruction, but it is really annoying! I haven't the level of skill as Lee to whip my gearbox in and out in an afternoon, but I have managed to reduce the noise.

What worked for me was reducing the vibrations that the gears seem to rattle in harmony with.

Two things made the biggest impact. The first was the rear silencer/muffler mountings were not as tight as the should be, and the second was switching to solid driveshafts from rotoflexes.

Also using a recipe of higher viscosity of gearbox oil helped too. There's an interesting page here http://store.uucmotorwerks.com/articles ... rattle.htm as BMWs seem to suffer from a similar thing! You have to be careful with gearbox oil though, as modern additives in some can damage brass synchro rings. There are multiple threads on here about what you should and shouldn't use! I've currently got a blend of Redline synthetic oils in mine.

Hope that's at least a little helpful..

Richard

[Spyder fan]

If this were a Morgan forum I would suggest the noise is “Deathwatch Beetle”. Ash frames and all that…..

My wife gets annoyed at me for always wanting to find out what’s rattling or causing a noise in any car I’m driving, be it a modern or one of the Elans. I think it’s just down to the inherent engineer inside or an enhanced case of mechanical sympathy.

I’m not happy unless it’s working and sounding correct and then I get paranoid my senses are failing me when everything seems okay.

I sympathise that the noise really bugs!

[hysteric]

Sound advice on the mountings and gearbox oil mate.

I’ve managed to get the elan out for two big runs and I am of the opinion if it makes a noise the car is telling me to drive it harder…. So I did … and what fun we had.

Back to the topic the rattle is still there but either it’s less obvious or I’m getting used to it.

[Harvey]

Richard,

After all I have done to eliminate the chatter on overrun, including changing to CV joints and eliminating the speedo cable by fitting an electronic speedo driven by magnetic pickup triggered by the bolt heads on the CV joints, I have to agree with you that the noise comes from within the gearbox probably as you say, by the spinning of the gears themselves. I'd be interested to know what cocktail of Redline oils you found to soften the sound. I've been running Redline MTL per Rohan's recommendation. Would Redline MT 90 quiet the chatter? I'd be concerned the shifting wouldn't be as smooth and favor the chatter if that would be the tradeoff.

Lee

[hysteric]

To my ear it’s 100% drivetrain and either the gear rattle or resonance in the exhaust system caused by loose couplings or perhaps internal combustion in the exhaust ….

As with all things older car related at least it’s not doom for the car and will keep us entertained!

Vimal.

[Richard J]

Hi all,

Regarding the gearbox oil, I'm currently using a mix of Redline MTL and 75W140NS, which is based on what I'd read on the UUC website (link in my earlier post) and from Redline themselves.

I don't think the improvement is because it's Redline oil, or even synthetic, it's just that it brings the viscosity up so dampens the vibration.

What I have noticed is that I never get the noise from cold, it's only when the gearbox has warmed up a bit - and it takes longer than in winter than in summer. This all points towards the issue being gear lash rattle. My guess is that if I used 100% 75W140NS, or just good old mineral EP140, that it would dampen the rattle a bit more, but would slow down the gear changes and absorb a bit more power. As Lee said - it's about finding the right balance between shift quality and the annoying rattle!

I think the answer is trying to eliminate resonance in the drive train, particularly on the overrun when the gearbox is being turned by the wheels, driveshafts, diff and propshaft, rather than power from the engine. So I think wheel balance, rotoflexes/driveshaft joints, diff and mountings, propshaft and U/J can all contribute. Combine that with damping the rattle with thicker oil and then muffling what's left with soundproofing and you might get towards a 'cure'.

Alternatively just see it as part of the character of the car, and bear in mind that had you taken it to a dealer in the 60s or 70s they would probably have told you that "they all do that Sir"..

Richard

[JJDraper]

Have you tried soundproofing the transmission tunnel?

Jeremy

[rgh0]

The gear train rattle on overrun or when in neutral can come from the layshaft vibrating and wearing the case so that the layshaft drops a small amount increasing the gear clearance and backlash, hence the rattle. Can also be due to worn bushes on the gears or worn gears

Thicker oil can help dampen it as observed, at the expense of synchro speeds, but ultimately a gearbox rebuild and a replacement case maybe needed.

cheers
Rohan

[Richard J]

As always I think that's the definitive answer from Rohan!

That makes perfect sense and matches with everything I've been told and thought about my particular rattle, but never had quite enough detailed knowledge of the innerworkings of the gearbox to work out for myself.

I guess the key is making sure when that when a gearbox is rebuilt that as well as the gears and bushes on the shafts the builder checks the layshaft and holes in the casing it sits in, for wear.

Lee..do you know if yours was checked when it was apart?

Richard

[Harvey]

Richard,

When my gearbox was looked at by a couple professional mechanics they were looking for excessive endplay in the shafts. Neither specifically looked for any other cause of the chatter. I wonder if I were to resubmit the gearbox to one of them along with Rohan's thoughts whether they could identify the problem? The only flaw in my question is that I absolutely refuse to pull the engine once again until needed for some other reason. I've had the engine in and out so many times over the past few years I feel like the mythic figure, Prometheus?, who was destined to push a boulder up a hill only to have it roll back down again for the rest of his life.

Lee

[hamm61]

Sorry to be a pedant but i am certain that was sisyphus .
punished for cheating death twice ..... well very apt for Lotus Elans

[2cams70]

My experience with the three rail gearbox in normal use (that doesn't include use in a racing car) is that any wear in the gearbox casing apertures where the layshaft slides in is not significant enough to cause any issues. I've never seen one worn to the extent where the layshaft rattles around in the casing bores. If the clearance was such that the layshaft was rattling around in the casing bore it would become worse very rapidly - imagine a hammer bashing around inside the bore because that's the effect. Any gear miss alignment resulting from this would also be detectable through increased gear whine noise from the gearbox in the intermediate gears.

This really is one of those situations where it is very difficult to do a remote diagnosis. These gearboxes are generally very reliable. Most of the issues are caused by people not assembling them correctly.