Roto flex couplings

[Lotus 50]

I've read about the cars surging due to the couplings, but I've never noticed it. My couplings were last replaced almost 20 years ago. Not a lot of miles since then, probably 15-20K.

Should I replace the couplings?

I know a lot of people switch to U joints, but I see the couplings as part of the design intent of the car.

[Fred Talmadge]

I think if you get under your car and look at them you will find them full of cracks and dry as a bone. If and when they break the half shaft will whip around and destroy the underneath of your car. YES! Please replace them.

[vxah]

Ahhh,if only you could hey! There seem to be none in existence at the moment? least not any proper ones that will last? I have been looking but none in stock is the answer i get all the time.... Been on order for the last year but no new ones manufactured as yet? Unless someone knows better? Please say yes,get them here!!!

[Galwaylotus]

I replaced mine a couple of years ago with ones sourced from Fibreglass Services (Mile Wilkins). When they go I'll probably go with U-joints.

As far as originality is concerned, Chapman used thye Rotoflex couplings as that waas what Formula cars were using at the time. There didn't seem to be anything much better available then - at least not for a reasonable price!

[Bill]

I have a spare new set of the good old ones on the shelf, maybe I should bag them in nitrogen gas for storage. I will keep the Rotoflex's on the type 26 but it will be C/V's on the 36.

Bill

[Andy8421]

Although only speculation, I do believe that if cheap CVs with the ability to plunge were available when the Elan was designed, Chapman wouldn't have given Rotoflex couplings a second glance. As far as I can see they have no redeeming features at all.
My old memory may be letting me down, but I recall Rotoflex were originally designed for the drive system on coal mine conveyor belt systems. Not exactly an aristocratic heritage.
Rotoflex were certainly used in open wheel racers of the period, but in that application they were easy to monitor and easily changed - hardly the case in an Elan.

[roblotus79]

I spoke with the folks at Spyder recently about their half CV-rotoflex setup. They sell the rotoflexes individually I believe and had them in stock 1 month ago.

[Baggy2]

FWIW I'm a fan of the one rotoflex / one uj solution and subscribe to the 'rubber provides some cushioning' argument. Some of the later rotoflex installations also has a fail safe 'peg and socket' arrangement to stop the flailing drive shaft horor. The rotoflex end of my drive shafts have such an arrangement.

Seasons greetings

Baggy

[vxah]

I have the Spyder drive shafts with one inner rotoflex coupling each side. They do indeed have a failsafe pin and pot on the inside. Before i fitted the drive shafts the car was a real pain to get a smooth gear change without the "surge" that Elan's suffer with,with the new shafts it was eliminated even when the rotoflex couplings were falling apart there was no surge! Spyder had no couplings when i called a few weeks ago?

I was steered away from complete solid shafts as i was told they can easily cause the inner drive shaft to fail due to the lack of shock reducing twist that a normal half shaft would provide on aggressive clutch operation,something that the two rubber couplings provide. I read a study recently about how the rubber couplings help with roll stiffness of the car as the forces needed to move them to an angle when the car corners acts as an antiroll bar... It went on to say that fitting cv joints would change the dynamics of the car? I thought newer tyre design and 40 or 50 years of motoring would probably change it more?

[rgh0]

Myths?

1. You need cushioning in the drive train provided by donuts i.e the inner diff drive shafts will fail if you put in cv's.

IMHO -- The older style original drive shafts will eventually fail with both CV's and donuts. The later drive shafts or new good quality replacements will not fail with either.

2. You need donuts are they provide roll stiffness at the rear.

IMHO -- the role stiffness contribution is minor and not noticeable by a normal driver in most situations. With modern tyres the Elan needs more role stiffness and retaining the donuts is not really a sensible way to do that even if they did make a major contribution which they don't.

3. The donuts are fine if you have the retaining pins and cups on the drive shaft

IMHO -- if the donut fails you will probably rip the pin off the shaft - been there done that.

cheers
Rohan

[saildrive2001]

Steve at S.J. Sportscars in the UK had them.

[roblotus79]

Rohan,

Thanks again for the synopsis. It was precisely that analysis that on the last thread when i was making my own decision that led me to go with the full CV conversion from RD enterprises that comes with new inner driveshafts. It is a more expensive solution but eliminates the possibility of any failures. It is what our local Lotus mechanic expert who races an Elan highly recommended as well. He has used this solution for years and has never seen any other failures along the drivetrain. For example nothing in the diff and nothing up the driveshaft to the clutch plate etc. So I see it as an expensive but once in my ownership type fix.

Cheers

Rob

[kstrutt11]

The pin and cup arrangement on the spyder shafts is far stronger than the standard failsafe set up, I am pretty confident it would stop the shaft flailing.

The cushioning will limit the peak torque in the complete driveline I have done quite a bit of work looking at peak driveline torques on rapid clutch release, even a small amount of compliance can have a significant effect, whether this is significant or not in terms of the durabiity of a particular driveline is another issue.

[rgh0]

The pin and cup arrangement on the spyder shafts is far stronger than the standard failsafe set up, I am pretty confident it would stop the shaft flailing.

The cushioning will limit the peak torque in the complete driveline I have done quite a bit of work looking at peak driveline torques on rapid clutch release, even a small amount of compliance can have a significant effect, whether this is significant or not in terms of the durabiity of a particular driveline is another issue.

I agree compliance limits peak torque shocks on the drive train. Even with the donuts removed the drive train has compliance with the rubber mounting of the engine and diff and the springs in the clutch plate. I have done probably more "drop the clutch" race starts with sticky tyres and a 180 hp engine at 4500 rpm over the last 30 years than most Elans with a cv setup and never had a failure so with good diff output shafts I believe the remaining cushioning is quite sufficient for the overall drive train not to be over stressed.

The biggest drive train problem I have seen apart from the early diff output shaft is the top diff mounts and torque rods pulling out or distorting the chassis especially on Plus 2's. Again this happens as much on cars with donuts as those without in my experience.

cheers
Rohan

[Sea Ranch]

The biggest drive train problem I have seen apart from the early diff output shaft is the top diff mounts and torque rods pulling out or distorting the chassis especially on Plus 2's. Again this happens as much on cars with donuts as those without in my experience.

Rohan, what is the best preventive, then, for the above? Which chassis mods/reinforcements?

Thanks so much,

Randy