Rotoflex couplings

[Mazzini]

Two of my Elans came with Ray's driveshafts, I've run them for many years without any sort of problem.

[dougal9887]

I used the Kelvedon shafts on my Plus 2.
They seemed well made and, in my opinion, transform the car.

Kelvedon drive shaft.

Only done a couple of thousand miles so can't vouch for longevity. No problems so far.
Dougal.

[Orsom Weels]

I don't think there have been any problems with the MM/Kelvedon CV's on +2's, it's the Elans where the problems occur due to the acute angles the very short driveshafts have to acheive. Reduced travel shock absorbers are recommended by Kelvedon with their CV's on Elans, but not on +2's, they also claim the UJ's are ok on Elans with the std shock's, hence our thinking of going that way. (it's a S3 Elan we're putting together & has new std shock's already fitted) Has anyone any experience of the UJ conversions that are available ? Preferably UK sourced.

Thanks again for all the input so far

Tim

[Grizzly]

The OP was talking about an S3 2 seater, you can't really compare products meant for a +2 due to the more aggressive Droop angle of the smaller car.

[pereirac]

I thought there was an issue with UJs locking if the wheels dropped too much which was why suppliers went over to CV joints as these were more forgiving?

Carl

[Sea Ranch]

Not sure about the Universal Joint itself, but . . .

I believe the UJ issue is that these driveshafts require a sliding spine to accommodate the geometry's requirement for changing shaft length. The sliding spline can bind and not slide, thereby hampering the suspension movement.

There's the beauty of the cv joint: aside from being smooth, it slides and accommodates this change in length. Designed specifically for a non-swing axle driveshaft application like "modern" front wheel drive cars.

I'll shut up now and let those who know take over . . .

Randy

[William2]

I fitted a set of Tony Thompson's sliding spline type driveshafts to an Elan I had a few years ago. They worked very well with no issues. You do have to restrict the suspension movement though by using different shocks or stainless steel cable attached to the lower wishbone.
I thought it was a well known fact that rubber doughnuts today are of a dubious quality.

[Andy8421]

Not sure about the Universal Joint itself, but . . .

I believe the UJ issue is that these driveshafts require a sliding spine to accommodate the geometry's requirement for changing shaft length. The sliding spline can bind and not slide, thereby hampering the suspension movement.

There's the beauty of the cv joint: aside from being smooth, it slides and accommodates this change in length. Designed specifically for a non-swing axle driveshaft application like "modern" front wheel drive cars.

I'll shut up now and let those who know take over . . .

Randy

Spline's Achilles heel is that they lock if you apply sufficient torque to the spline - which in the case of the Elan locks the rear suspension and can feeds large lateral loads in to the diff and wheel bearings if you hit a bump as the shaft won't plunge under load. Accelerating out of a bend will cause the rear suspension to lock, and then release at a gearchange point. In period, Chapman used ball splines on his competition cars as these didn't suffer the same problems.
CVs aren't allowed in historic racing, only TTR UJs / splines - and to be honest I haven't noticed the spline lockup problem when racing, but the rear suspension is lowered and rock hard, so there is very little rear suspension travel in the first place.
I use Sue Miller CVs on my road Elan, which for the reasons mentioned in this thread I think are a far better solution than rotoflex or UJs and splines.

[Sea Ranch]

Thank you, Andy. A more clear explanation, and some personal experiences, too.



Randy

[7skypilot]

Don't give up on donuts! I can see your's just fell apart, but hopefully that was just a bad batch.

I have the Spyder 'half and half' system on an S4 - inner Rotoflex and outer CV - which has been on the car for around ten years. I check the rotoflex at least twice a year and they are in good order. The Elan is driven, on occasion, reasonably hard on track days and on the Sun Run, 1500 miles of a gentle but competitive event in the French Alps, held in November.

The car is always jacked up on a block securely supporting the rear wishbone so the suspension is never left on full droop unless I really need to work on the it (or to check the Rotoflex when they are fully stretched at full droop). I'm sure that most of the damage to donuts occurs when the suspension is on full droop. When the car is left for a while for 'work in progress' I support the rear uprights on axle stands so the donuts are never out of line. I favour some rubber in the drive chain to allow some cushioning, largely to protect the rather weak gearbox and donuts perform that function admirably.

The wooden block rear wishbone support is illustrated, hopefully, here:
http://images.lotuselan.net/lel/6386/0/Block.jpg
Yet another idea I've used from this superb forum.

I've recently bought a couple of new Rotoflex's from Miles Wilkins - he orders a batch 'now and again' and I understand they are the 'real deal'. I'll keep them for when they're needed.

I'll retain this 'half and half' system for as long as it is working fine. If I was to replace it I'd certainly be tempted towards Colin's system.

[Orsom Weels]

Don't give up on donuts! I can see your's just fell apart, but hopefully that was just a bad batch.

I've recently bought a couple of new Rotoflex's from Miles Wilkins - he orders a batch 'now and again' and I understand they are the 'real deal'. I'll keep them for when they're needed.
.

The couplings from Sue were meant to be the 'real deal', as you refer to them, supposedly manufactured by Dunlop. When she decided to no longer supply her CV conversions, she looked in to what was available, no doubt talking to the likes of Miles, Kelsport, et al. She was very confident that they would be fine & was as shocked as us when she saw how they had fallen appart. As previously stated, they had not been on the car very long & had not been left with the suspension on full droop. The bonding between the rubber & metal plates had simply let go. Last I spoke to her a couple of weeks ago, she was in the process of returning them to her supplier & trying to get some answers.
Like you, I like the idea of some cushioning in the drive, however the gearbox & diff were both used on much heavier Fords, some with similar BHP figures to the Elan, & they are not known for their weaknesses. I don't think the loss of the cushioning is too detrimental, indeed, there are a lot of CV/UJ converted cars about now, & I haven't heard of any gearbox or diff failiures directly linked to said conversions.
Currently available do-nuts are just not an option untill there is some hard eveidence that another set won't just fall appart. I dread to think what might have happened if the car had actually been driven on them. It's CV's or UJ's for now, & given the costs involved, we're erring away from importing, so it'll be a UK based product.

Cheers, Tim

[vstibbard]

Check out the ones made by Chequered Flag racing in the US, they are listed in the businesses and vendors section

V