Lotus Elan

Rotoflex "surge" - a definition?

PostPost by: Steve S2 » Wed May 29, 2013 1:29 am

How would you describe the surge associated with Rotoflex couplings to a layman?
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PostPost by: john.p.clegg » Wed May 29, 2013 8:05 am

...ever tried bungee jumping??

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PostPost by: trw99 » Wed May 29, 2013 8:56 am

"A characteristic which bothered us at times is the springiness in the transmission" - Autocar 1964

"A mixed blessing are the rubber 'doughnuts' ... which take a lot of shock out of the drive ... they are also responsible for slight surging at constant low speeds in any gear and for some reversing judder ... they cause the slight tendency to hang in gear, normally only noticed during fast changes under load" Motor 1964

"Unfortunately the transmission is spoiled by the rubber 'doughnuts' ... they are a little too elastic and in traffic the Elan kicks and bucks in an alarming fashion ... there is also some wind-up in the transmission when making fast starts; the car pauses momentarily while the doughnuts wind up and then catapults itself away rather jerkily" Motor Sport 1965

"... the rubber-band effect of the rubber donuts used ... accelerate or stop at a rapid rate, and you can feel these joints compress and unload, transmitting a very discernible lurch ... you have to learn to [u]drive[/u] it" Sports Car Graphic 1966

" ... it causes a disconcerting pitching oscillation every time the throttle is opened or closed - it's unpleasantly reminiscent of being rocked in a baby carriage" Car & Driver 1966

" ... and the early doughnuts gave some drivers trouble (oddly enough, not always the fastest drivers)" Motor Sport 1966

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PostPost by: john.p.clegg » Wed May 29, 2013 11:37 am

...and just a slight deviation of thread,if one has replaced the doughnuts with a more solid alternative U/J's,CV's would there be any need/benefit in fitting a single doughnut in the drivetrain (propshaft?)

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PostPost by: Bud English » Wed May 29, 2013 9:27 pm

Those all look like pretty early quotes. Are the later "sprint spec" donuts any less prone to wind up? All my driving has been on the donuts with the metal interleaves. I really haven't found them to be noticeably troublesome. ...but then it has been awhile.
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PostPost by: billwill » Thu May 30, 2013 2:39 am

In my first month or so in 1968 with the original doughnuts, I often found I did kangaroo hops down the road when starting from zero.
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PostPost by: Stuart+2 » Thu May 30, 2013 3:35 am

I replaced my doughnuts with a CV kit 6 years ago. The improvement in driveability was very noticeable. However, last year my inner driveshaft failed. I doubt that the CVs are wholly responsible, but it is true that doughnuts are good at dealing with torsional shock loads.

I still recommend the CV conversion, but I'd be upgrading my driveshafts at the same time for good measure.

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PostPost by: Steve S2 » Thu May 30, 2013 7:38 am

Sue Miller has stopped offering the CV-joint conversion, correct?
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PostPost by: c42 » Thu May 30, 2013 12:31 pm

Still supplied for the plus 2 I believe.

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PostPost by: sutol45 » Thu May 30, 2013 12:56 pm

Steve S2 wrote:Sue Miller has stopped offering the CV-joint conversion, correct?


ONLY because Elan owners retain the original 'long' shock absorber! Elan owners (not Plus 2) MUST use a reduced length Koni! And then there's NO problem, honest...

Check out the 'FULL' droop on my car with Mick Millar CV driveshafts (@ 10k miles), a 5-speed gearbox and a 4.44 dif.
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PostPost by: Steve S2 » Thu May 30, 2013 2:57 pm

c42 wrote:Still supplied for the plus 2 I believe.

Regards
John


Interesting. The topic has been done to death, but I can't find a comparison between the products of the main vendors of rotoflex replacement solutions:

Sue Miller (CV joint solution)
Spyder (CV joint outer + rotoflex inner)
Tony Thompson Racing (...not sure of their solution but am sure they do one)

Can anyone offer an opinion, with pros and cons for each?
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PostPost by: sutol45 » Thu May 30, 2013 3:18 pm

Tried 'em all, even made my own, but the CV joints are best - and that's why modern cars use 'em!

My Old Driveshafts.jpg and

And an experienced opinion (41-years of Lotus motoring while maintaining my own and other peoples cars): the original twin doughnuts can 'wind-up' easily for the less experienced Elan driver making the car 'kangaroo' down the road; the single inboard doughnut with sliding-spline and outboard Hooke joint less so. The twin Hooke joint with sliding-spline arrangement is harsh for the road and should be kept for the track only. But the CV jointed shafts provide that little bit of flexibility that cushion the drive-train without the 'kangaroo' effect. I like 'em! You'll like 'em.

Just remember on an Elan (not Plus 2) to adjust the length of the shock absorber!
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PostPost by: AHM » Thu May 30, 2013 4:48 pm

The doughnuts are a clever feature designed in to the drivetrain, they are supposed to surge and induce the kangaroo effect.... How else would you start in gear and get the clutch plate to release?


sutol45 wrote: But the CV jointed shafts provide that little bit of flexibility that cushion the drive-train without the 'kangaroo' effect.

They are by definition constant velocity. No cusioning, and no flexibility.
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PostPost by: sutol45 » Thu May 30, 2013 5:25 pm

AHM wrote:The doughnuts are a clever feature designed in to the drivetrain, they are supposed to surge and induce the kangaroo effect.... How else would you start in gear and get the clutch plate to release?


sutol45 wrote: But the CV jointed shafts provide that little bit of flexibility that cushion the drive-train without the 'kangaroo' effect.

They are by definition constant velocity. No cusioning, and no flexibility.



You really are missing the point! I mean, a Ford Cortina in the period did not have 'doughnuts' but you were still able to "release the clutch plate", hello?

The Metalastic doughnut as applied to the Elan was a cheap way to accommodate the change in driveline angles, and Chapman copied it from the Hillman Imp!

The first Elans actually used Hillman Imp doughnuts - until they broke-up. Lotus then had to use the next doughnut in the Metalastic range that would accommodate a higher torque. You really do need to do the research.

Lotus was champions at adapting the high-volume components used by other local UK manufacturers into his own cars in order to reduce costs! Where do you want me to start? Door handles, boot hinges, steering columns, brakes...

Chapman would have argued vehemently the attributes of a doughnut costing ?1 over that of a CV joint (had it existed in the 60s) costing ?2 just to get a car out of the factory door!

Chapman's interest was F1, F1, and F1. Road cars paid for that and nothing else.

You really need to understand the logic and/or have been in that environment to appreciate the ideology applied...

Every Lotus is a fabulous car, but the primary elements designed and manufactured by them, that make their cars as wonderful as they are, are supported by the components mass produced by others: Ford, Rover, Triumph, etc.

And the Metalastic doughnut is one of them. It was the easy, cost effective option. So it broke-up? Sell 'em another set (cost ?4) and ?25 and they'll be happy.

And we were! I was!
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PostPost by: Spyder fan » Thu May 30, 2013 5:53 pm

sutol45 wrote:Tried 'em all, even made my own, but the CV joints are best - and that's why modern cars use 'em!

My Old Driveshafts.jpg

And an experienced opinion (41-years of Lotus motoring while maintaining my own and other peoples cars): the original twin doughnuts can 'wind-up' easily for the less experienced Elan driver making the car 'kangaroo' down the road; the single inboard doughnut with sliding-spline and outboard Hooke joint less so. The twin Hooke joint with sliding-spline arrangement is harsh for the road and should be kept for the track only. But the CV jointed shafts provide that little bit of flexibility that cushion the drive-train without the 'kangaroo' effect. I like 'em! You'll like 'em.

Just remember on an Elan (not Plus 2) to adjust the length of the shock absorber!


Spyders system for the standard Elan diff uses one CV and one doughnut, Mr Thompson say's " It's a terrible system", but I think that Spyder have it correct especially if you don't want to go to the expense of uprating the diff output shafts to take the un-cushioned stress if there is no elasticity in the driveline.

From memory, a double doughnut system required a sensitive left foot to almost slip the clutch on take off before releasing fully once underway, launch control had to be learnt so as not to look stupid with all the hopping about that came with a heavy clutch release, different take off speeds required a sense of timing.
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