CV drive shaft conversion

[Breezehill]

Looking for thoughts on converting rear drive, removing doughnuts and changing tp CV drive shafts. Which are the best to go for and and mods that need to be done.

[JonB]

Do a search, the topic has been done to death.

But my vote is CV shafts from Sue Miller. I had a set on my Plus 2 and they were brilliant. Truly a purchase without regret.

[alanr]

I think it depends what you want of your car. if you wish it to drive and behave as Lotus originally intendend then I would say keep it on doughnuts. If on the other you crave the way a modern car behaves and drives then do a CV conversion. The Aussie, Elektricbits CV version, seems the best albeit the most expensive CV conversion from what I read.

Always bear in mind though that you are carrying out a modification. if you do go the CV route you will need to inform your Insurance company that your car is a 'modified' car. Failure to do so could have consequences!

Personally I will be keeping my +2 on doughnuts and I can't see what all the fuss is about. ! like my car as it is and I find it great to drive in this original driveline configuration. I carry out regular checks on the doughnuts and so far in my ownership (6years) I haven't and don't see anything that would persuade me to change my thinking.

Alan.

[englishmaninwales]

“…If on the other (sic) you crave the way a modern car behaves and drives then do a CV conversion…”

Given the vast majority of modern cars are either 4WD or front wheel drive, this is nonsense.

“Always bear in mind though that you are carrying out a modification. if you do go the CV route you will need to inform your Insurance company that your car is a 'modified' car…”

Agreed. No cost option, just add to the list of modifications for the insurance company.

“…I carry out regular checks on the doughnuts…”

If you don’t want to be jacking and crawling under the car up every two minutes to check the condition of the couplings, fit a CV conversion. I check the CV driveshafts twice a year - pre MOT (mid summer) and as part of winter service check.
All IMHO, of course!
Malcolm

[Lotus54]

I just installed Elantrikbits CV axles on my S3. No issues fitting, no modifications needed.
The donuts on the car were pretty rough- I chose the ‘minimal maintenance’ route and got the CVs. Plus I didn’t particularly like the ‘wind up’.

[UAB807F]

I fitted Sue Miller's kit in 2011 after 30+ years of doughnuts and no matter what the relative costs are, I wouldn't go back to doughnuts. It's a personal choice, the only issue I had with doughnuts was the constant maintenance and being sure that any replacements were good enough and not going to shred themselves in 6 months, but driving was fine. But with CVs you know you're not going to get a catastrophic failure and like all the other millions of cars using the same system, they are very reliable.

Mine's an S3 and the reccomendation is for shorter travel on the rear dampers which I've done during a suspension refresh from Kelvedon. To be honest I did drive the car with the OEM dampers for a while but I'm not going to be testing the limits of travel and was always careful when jacking up the rear end. I don't think the same problem applies if you've got a +2.

I also fitted a home made diff brace as on the later cars, don't know if it makes any difference but I did it anyway just in case the CVs were harsher than the rubber joints. .

[alanr]

I also fitted a home made diff brace as on the later cars, don't know if it makes any difference but I did it anyway just in case the CVs were harsher than the rubber joints. .

Yes and this is the problem. Fitting CV's eliminates any form of 'cushion' in the driveline making it harsher on the various components in our cars.
The diff setup on ours cars is quite fragile compared to other cars with the lightweight aluminium Lotus differential adaptor case just being suspended in mid-air by two rubber mountings and two tie bars to control fore and aft movement. Other cars that have CV's fitted as original equipment have a lot more secure and less fragile arrrangement.
My thinking is that fitting CV's to an Elan or +2 can't help but put additional strain and consquential future wear on these components particularly if driven aggressively.

If you do decide to fit CV's i would definitely check that you have the later heavier duty diff output shafts fitted in your car before fitting the CV's!

Alan

[englishmaninwales]

Alan
Whilst I’d agree with you regarding the potential for risk to the other transmission components from CV driveshafts, can you bring any evidence of transmission damage/accelerated wear/failure as a direct result of this modification (road going levels of torque and excluding competition or track day use)?
Malcolm

[berni29]

Hi

For me the only downside to the shafts is the additional weight added by the conversion. If you are a clutch dropping tyre smoking type of guy then I might be somewhat concerned about the diff and related components. But there again just price in the additional maintenance that goes along with that style of driving.

All the best

Berni

[Andy8421]

With all due respect to Alan's view, the choice of Rotoflex by Lotus was driven by cost. They weren't much good in period, and I am afraid they are probably worse now. Tony Rudd in his book 'It was fun' mentions that Rotoflex failures were the biggest cause of warranty claims during the Elan's production run.

26Rs had UJs and sliding splines from the factory, nobody I know (and I checked the entire grid a few years back) in historic racing uses Rotoflex. They don't fail safe, and can flail around doing significant damage or jam up and lock a rear wheel.

I am convinced that if plunging CVs had been available at reasonable cost at the time, the Elan would have had them fitted, along with inboard disc brakes (idea was ditched because of the wind-up of the Rotoflex).

If you like the feel of bouncing along on Rotoflex, then that's fine, but I really don't like them.

Picture shows frame damage caused by Rotoflex failure.

[elansprint71]

The "Rotoflex" couplings available today are nowhere near as tough or long-lasting as the ones available when the cars were new, so it just isn't possible to "drive as Lotus intended". They were not brilliant back then anyway; in conversation with Ron Hickman some years ago he said he wouldn't have anything but CV's these days and, as he designed the Elan, that's good enough for me.

I fitted Mick (Sue) Miller CVs years ago and found that the rubbish differential rubber mounts available these days didn't last very long, as the drive-line is subject to increased loads under accelleration/braking (all "rubber" components seem to be inferior now) I fitted Tony Thompson's racing diff mounts top and bottom and have had no issues since then.

[2cams70]

I’ll stick up for Allan! - of course if you hit something with a steel hammer the object you hit is going to be in a worse shape than if you had hit it with a rubber mallet. Do the standard Lotus components have enough in reserve to cope with the loads of being hit with a hammer instead of a rubber mallet? Who knows - but it certainly is a valid question to ask.

[alanr]

I think it would be useful for this thread to hear from Breezehill ( Sorry don't know your name) how long he has owned his car and driven it in it's present doughnut format?
Also how many miles does he drive in the car per year?
His he not happy with way the car drives presently?
This may then help towards answering the question why he personally feels that he wants to change to CV's at this time?

Alan.

[gus]

[quote="alanr"]I think it depends what you want of your car. if you wish it to drive and behave as Lotus originally intendend then I would say keep it on doughnuts. /quote]

So, as Lotus originally intended
On a Federal emissions car
Crack the throttle, mixture changes from traveling 3 feet through a tiny tube to straight through the intake.
Timing changes from full retard to standard advance
delay of almost a second

meanwhile, your brain senses the lack of motion and tells your foot to keep pressing
engine starts motivating, but wait, that motivation is winding up the donuts
finally the car rockets forward, everyone in surrounding cars shakes their heads and thinks "a88hole!"
You let off the throttle a little too harshly and the car bucks, rocking at the resonant frequency of the rubber donuts.
Took me a week to wire open the secondary throttle plate.
Yes, the majority of this is not the donuts fault, but 'as Lotus intended' always makes me laugh
They also intended that the wipers virtually stop at stop lights and the windows come to a grinding halt at idle, no, generators were cheap.
It really is necessary to filter out the engineering genius of Colin Chapman from the brutal cheap-ass of Colin Chapman

The halfshafts on the Elan are too short for U joints, and CVs were too expensive.

Not about design, its about money.

If the donuts gave you lots of warning of their eminent demise, or they did not wreak havoc when they failed I would say keep them. If new donuts were high quality and reliable, perhaps. IF they were not a screaming pain in the sack to deal with when doing other things on the rear suspension, again, perhaps.

But all of these things add up to...buh bye donuts.

[alanr]

gus,
Your car is obviously in need of some attention! My +2 doesn't do any of those things!

Alan.