Lotus Elan and Lotus Elan Plus 2 Forums

Sorry to post yet another thread on this subject, I know it this has probably been done to death. My Rotoflex are due for replacement and I have the whole rear suspension off at present (for dampers, 1 new bearing carrier, new wishbone metalastic bushes).
Seems sensible to replace the driveshafts. I'm aware of these three current options:
Kelvedon (ex Sue Miller design) 2 CV with droop limiting dampers
Spyder combination CV/rotoflex
TTR 2 UJ sliding shaft

Not withstanding cost variation between the types, is there a consensus on the best? The car is an S3 coupe road use only.

I'll get my coat......
Thanks
Malcolm

imho
cv's and short Gaz shocks. Check top diff mounts if they are in good condition and diff tie bars

The alternative you haven't mentioned is Col Croucher's fully CV shafts. He machines the joints so they can cope with a larger angle of deflection and droop limiting is not required. They are expensive though, and have to be shipped from Australia. You can read about them here http://www.elantrikbits.com/ and here's a photo of mine.

Just thought I would add my bit...
I have the Miller cv shafts on my car (S3) and I have standard dampers i.e. I haven't limited the droop. I know I should do something about it, but I never have and it is fine. The only thing I have to do is be very careful when jacking up the car. I always make sure I jack up the suspension NOT the body. I use a piece of wood under the wishbone to spread the load and jack up this way. It does make it a bit awkward and is also a problem at MOT time but so far the tester has been able to jack under the wishbone / upright with the extended arms on his jack.
There is a really bumpy road that I regularly use going to work and if taken too fast the car almost becomes airborne so I have to remember to slow down here. One day it will probably catch me out and bugger the drive shafts but so far (x fingers) all has been OK and they really are the best solution IMO.

Thanks for replies.
The Oz supplier looks interesting and the CV shafts look nicely engineered, but cost variance with UK supplied is significant ( I know I did not put cost as an issue in OP! )
I am aiming to replace the dampers any how. Kelvedon use modified adjustable AVOs. Is there any disadvantage with the reduced stroke on the elan?
Malcolm

The reduced stroke dampers only limit the droop travel to about the same amount as the donuts originally limited droop anyhow. At least the Konis from TTR I fitted did that. This is the what's required to prevent the CVs going to the limit of their angular displacement.

So I don't see any problem fitting them

cheers
Rohan

I have always been curious about the concern of limiting the droop on CV joint axles. If you look at a front drive car of today, a full limit turn has the front wheels cranked, what appears to far further out of line of the axle than could happen, even with a long stroke rear shock absorber. I have full CV shafts on my Elan, and although I always raise the car via the rear wishbones, I have never really worried about the droop condition while driving. Maybe I am not using enough "full right foot".

Rob Walker
26-4889

The also the Rdent (http://rdent.com/index.html) setup that has replacement diff output shaft rather than bolting up to the originals.

My +2 has these fitted by previous owner but I am yet to get the car to a point i could drive it. So can't really comment on them. I know they are very pricey thou....

prezoom wrote:I have always been curious about the concern of limiting the droop on CV joint axles. If you look at a front drive car of today, a full limit turn has the front wheels cranked, what appears to far further out of line of the axle than could happen, even with a long stroke rear shock absorber. I have full CV shafts on my Elan, and although I always raise the car via the rear wishbones, I have never really worried about the droop condition while driving. Maybe I am not using enough "full right foot".

Rob Walker
26-4889

Rob

You are right, outboard FWD joints are designed to allow for significantly higher angular deflection than RWD drive shafts. After all, they can cope with full steering lock and full droop at the same time.

Unfortunately they seem to be always manufactured to be integral with the stub axle that holds the bearing and hub on, so they are not amenable to being adapted to Elans (unless one wanted to design a whole new rear hub, brake, and bearing arrangement. They would also be needed at the inboard (Diff) end. If it could be done, any adapter involved would make the shafts even shorter making the problem go full circle.

Ian

I will be in the minority but spyder half and half version gets my vote.
Cheers
Baggy

As an aside, I see a couple of posters referring to jacking the car up on the rear wishbone. I understood that this was unwise as it can result in a bent wishbone?

At full droop without limited stroke dampers would damage only occur if the driveshaft is rotated? I suppose getting the car airborne on an undulating road might cause damage? Is there any in service experience of this type of damage to CVs or is this whole issue theoretical?
Malcolm

Elanman99 wrote:
Rob

You are right, outboard FWD joints are designed to allow for significantly higher angular deflection than RWD drive shafts. After all, they can cope with full steering lock and full droop at the same time.

Unfortunately they seem to be always manufactured to be integral with the stub axle that holds the bearing and hub on, so they are not amenable to being adapted to Elans (unless one wanted to design a whole new rear hub, brake, and bearing arrangement. They would also be needed at the inboard (Diff) end. If it could be done, any adapter involved would make the shafts even shorter making the problem go full circle.

Ian

FWD outer CV joints generally have higher allowable angular displacement than CVs used on Elan replacement shafts, but the trade off is that they don't plunge. A typical FWD setup has an outer CV (the wheel end) that can stand high angular displacement but doesn't plunge, and an inner CV (the gearbox end) that only works over a narrow range of displacement but has significant plunge capability. This is fine as a FWD car outer joint has to cope with steering angles and suspension deflection, whereas the inner joint only has suspension deflection to cope with. In an Elan setup, both CVs need to stand high angular deflection, and there needs to be an allowance for plunge somewhere in the system.

TTR UJ's get my vote.
Just ensure your torque rod bushes are poly.

Terry

I have mentioned in another post how much I would like a set of these CV driveshafts for my Sprint only thing that concerns me is cost of having to replace rear inserts. I am currently in the finishing stages of a total rebuild and have fitted all new rear suspension which includes some expensive Koni adjustable inserts. Someone has said that these should be ok with CV shafts as they already have a limited stroke/droop. Does anyone know if this is correct.
Cheers
Ian

englishmaninwales wrote:Sorry to post yet another thread on this subject, I know it this has probably been done to death. My Rotoflex are due for replacement and I have the whole rear suspension off at present (for dampers, 1 new bearing carrier, new wishbone metalastic bushes).
Seems sensible to replace the driveshafts. I'm aware of these three current options:
Kelvedon (ex Sue Miller design) 2 CV with droop limiting dampers
Spyder combination CV/rotoflex
TTR 2 UJ sliding shaft

Not withstanding cost variation between the types, is there a consensus on the best? The car is an S3 coupe road use only.
Malcolm

For what its worth, my thoughts on driveshafts:

Rotoflex have little to recommend them. Cheap I guess in the day, but catastrophic failure modes and bounce in the driveline both unwelcome. I recall that the original intent was to have inboard brakes on the Elan but the Rotoflex weren't up to it.

UJs don't plunge so a sliding spline is used which has issues of its own. Splines lock under load, so when applying power, the rear suspension effectively locks up, feeding high lateral loads into the diff bearings. There is also the issue of the suspension unlocking at gearchange points, so potentially causing the car to jump if accelerating out of a bend. TTR UJ shafts are used in racing (I have them on my S3 - CVs are prohibited by the regs), but suspension travel on a racer is minimal, and I haven't noticed the 'jump' when coming out of a bend myself. It is interesting that low friction 'ball splines' were used in racing at the time to avoid this problem.

The UJ / Rotoflex hybrid has nothing to recommend it in my mind, but is the worst of all worlds. One of the reasons that CVs are used in FWD cars is that UJs introduce angular oscillation at high angles of displacement. Turn the input shaft of a UJ at a constant speed, and if the joint is at an angle, the output shaft goes slow-quick-slow-quick as the shaft rotates. That's why CVs are called CVs - the output is at a constant velocity whatever the angle. If you have 2 UJs at the same angle of deflection on a single shaft you can counteract this effect, one cancels the other out. The UJ/ Rotoflex does not, and therefore introduces this effect along with all the problems of having a Rotoflex.

Plunging CVs solve all the problems at the cost of limited angular displacement. As posted above, Rotoflex limit suspension travel anyway, so putting a droop limiting shock in doesn't really impact the amount of available droop.

There is an argument made that the cushioning effect of Rotoflex saves the driveline. My S3 has soft compound Yokohamas, an engine putting out 167BHP at the crank and TTR UJs. I have yet to have a transmission line problem.

My road going Sprint has Sue Miller CVs and droop limiting shocks. The Rotoflex went into the bin. Definitely the way to go IMO.