Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Final drive belt jumping survey

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Normally 2,700 minimum but if coasting to a stop and then changing to pulling away (for example a traffic light changes as I approach) then I can get a clonk as I drop a gear and feed the power back in.

Playing in the rain today: same 2 bangs pulling away from some lights (followed by a little lateral movement as the rear slid a bit). Definitely sounded to be from the rear. Too wet to attach a camera under the rear!

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It's a pain to stay above 2700rpm when forced to stay in the 50 to 70 km/h range, you shift between 1st and 2nd gear producing noise like a teenage driver!

Thanks everybody for your input. Based on your notes and my own experience my theory and it is only theory, is that there are two distinct symptoms arising from the same fault. The fault being the lost motion or backlash in the coupling. The symptoms being:-

1/ at low revs when running light the constant change from drive to overrun causes the coupling to slap to and fro in its own backlash and -

2/ At high power transmission combined with minute loss of traction the coupling whips back to the overrun position causing the bang and immediately takes up the backlash again when the bang can be repeated several times till driver reaction or road surface change breaks the cycle.

The noise is probably generated by the sudden take up of slack in belt or, in my case chain, final drive, which is why so many seem to think it is the belt jumping over the sprocket teeth and also why the noise is less when the drive belt is run very tight.

Mention is made, above, of " soft return " which means the unit works in both directions and photos published here seem to confirm this. I am not sure if this makes my conclusions more or less likely but it seems to indicate that some attention has been given to eliminating any banging when the backlash is suddenly reversed.

My solution is to eliminate the backlash with moulded rubbers which completely fill the cavities in both inner and outer elements of the coupling and which, therefore, do not roll back and forth. This will be a much cheaper fix than the replacement of the coupling with another design altogether. It may be some months before I can devote time to this but as soon as I have conducted a good trial I shall publish my findings here and elsewhere - successful or otherwise!

P.S, I seem now to get no response from the factory or Centa when I mail them. Like so many, they probably think I am mad!

Well I dont think your mad.
However!!! The original compensator although flawed was designed to reduce torgue spikes entering the drivetrain. Presumably both high and low frequency.
My guess it was better at the high rather than the low.
The centa is more of a cush drive but the cam like cut outs I think are intended to provide ramp up/down damping. My guess is the centa is better at the low end.
Removing or reducing damping of torque spikes may have consequences for the gearbox! I wonder how mazda damped out torgue spikes from the small truck that this gearbox was sourced from?

I have a lot of empathy with this idea.

No doubt the Centra worked very well,...better / much quieter than the original .

However as said the power spikes travel down the transmission ...and my Bevel Box quickly became much much noisier and developed a loud Bang on change down. I do believe that the BB gear mesh was affected.

Seems a reasonable theory. But why don't all M3W owners experience it when their rear wheel loses traction? Perhaps we need to correlate bangs with tyre type?


Or are most drivers more sedate / driving bath chairs?

Most definitely not! And I don;t get the banging described above, for whatever reason.

I have long maintained the drivetrain design is subject to both forward and backward backlash , so your thoughts make complete sense to me Phil. Cant explain why it only happens to the select few , but that in itself seems to be a Morgan attribute.

Thanks for your support folks. I do wonder if there have been different hardness rubber rollers used but I guess I will never know.
Certainly I agree with the ramping up and down aspect of the coupling but I think that leaves a sloppy area in the middle especially now the original Centaflex unit seems to have been modified to operate in both directions.
I have been looking in to blocks of polyurethane which can be cut to shape on the bandsaw thus allowing lots of experimentation; it is a shame the engine has to come out every time one wants to change the coupling elements - I guess I'll just have to get good at it!