Lotus Elan

Non Rotoflex Rear End?

PostPost by: tdafforn » Fri Nov 07, 2003 10:26 am

Hi All,
I am thinking of replacing the knackered rotoflexes with a full/partial cv rear end this winter from one of the usual suspects. Anyone have any experiences?
Easy to fit (have to be easier than the rotos)?
single (spyder) or double CV?
Does the gearbox/diff wear out more quickly?
Cheers
Tim
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PostPost by: Roy Gillett » Fri Nov 07, 2003 10:48 am

Hi Tim
I replaced my rotoflexes last year after a very scary donut failure (rear locked up, drive shaft dropped and locked against A frame which it bent!).

After some research I fitted the Mick Miller CV shafts. Perhaps not quite as strong as the Tony Thompson sliding spline ones, but there is no chance of spline lock up on full droop.

I have found them excellent. No wind up, they improve the gear change (again probably because the wind-up is gone) and having now done a Classic Rally with them on I am confident of their durability.

They are easy to fit (unless you have the "fail-safe" spikes on your diff output spiders - which have to be sawn and ground off. I had one on one side and not the other [not on the side that failed!!!!]. They seem very well engineered and I buy the physics that says that the cushioning of the drive from the rubber donuts is illusiory as all they do is store the energy which is then dumped through the transmission chain as they unwind.

My donnuts had only done 5000 miles when one failed which I thought was poor but others in the know thought was good for a +2 S130. On this measure the Mick Miller shafts will work out cheaper within 10000. And then there is the peace of mind! Once you have had a rotoflex fail, you don't want it to happen again, let me assure you.

Hope this helps.

Roy Gillett
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PostPost by: Ramsden » Fri Nov 07, 2003 12:14 pm

Tim

My recently acquired +2 130/5 had a solid UJ (Hookes Joint) conversion fitted by the previous owner. I'm not sure of the type. This system gives a very positive take up on accelleration but for the same reason requires careful handling. With unsubtle accelleration/clutchwork it is possible to induce considerable drive line shunt resulting in a nasty "clack" noise on take up.

From the accounts that I have heard, I agree with Roy that the original system gives less than satisfactory longevity, though a few lucky souls seem to be running around 30,000 mile rotoflexes. In addition the accelleration, windup sounds unpleasant, especially on the +2 with its longer drive shafts. However, fully solid systems such as mine do seem to promote premature wear in other components namely the diff, propshaft UJ (mine is worn after only 36,000 miles) and the radial clutch springs (which are left to absorb all the shock of any rough handling).

I understand that the previous owner of my car was more interested in racing than road work, so perhaps optimising performance at the expense of long term reliability was acceptable.

I shall be fitting the spyder (half rotoflex, half CV joint) system this weekend. It seems a good compromise beteween the new and old systems incorporating some flex to cushion what seems an otherwise fragile transmission. In addition, spyder have further developed lotus' rotoflex "failsafe" system that was fitted to later cars. Andy Withnall at Spyder considers that the original lotus failsafe system was not sufficiently robust to be of significant benefit, though it sounds like it may have helped Roy. The spyder "failsafe" system works on the same principle but is beefed up somewhat.

Whatever the pros and cons, I'll get back to you next week and let you know the results. I'll have a blast through the Cotswold B roads on the way back to London post fitting which should test the system adequately.

Regards

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PostPost by: markb » Fri Nov 07, 2003 12:58 pm

Tim
I have the Spyder set up on my +2 and i think it works ok, i bought the car with this system fitted. My previous cars have had the standard donut set up and i found this to be ok too. I've had no problems with any of these two set ups in terms of performance and safety in nearly 20 years of Lotus ownership. I guess that with the Spyder system i get less wind up, but with the sort of driving i do i don't think it makes much difference. I think you only notice significant differences on the race track.
I think the choices are:
For originality stick with the standard set up and ensure the donuts are fitted correctly, you buy them from an approved source, you change all the bolts and nylocs. Check them regularly.
For racing or if you have concerns about the donuts failing fit the TTR or Spyder system.

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PostPost by: dmreeceuk » Fri Nov 07, 2003 2:05 pm

I have considered converting my donuts.
The main reasons are
1 I cant be bothered to change them myself as it seems a bugger of a job!
2. The donuts are ?50 quid each plus labour (around ?360 for a change)
3. I worry they will fail.
I am not worried about wind up as the car drives great now.

My question is about the spider unit is .
Do you still need to change the donuts (all be it only 2 of them) as often and is it easy or difficult?

If you do then (and its still as difficult), the spider units dont really achieve what I want.

Is my reasoning correct.
;)
Dave

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PostPost by: Roy Gillett » Fri Nov 07, 2003 2:41 pm

Can't agree with MarkB. The Miller CV shafts I have fitted have a noticable effect on the drivability of my +2 that is obvious every time I drive it.

Also I am told by some with long acquaintance with the ELan, that the old rotoflexes we much more durable than the current design which 'tear' along the interfaces between the rubber and the vee shaped metal plates that form the bolt holes. Apparently the original design were not constructed like this.

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PostPost by: Ramsden » Fri Nov 07, 2003 2:42 pm

Dave,

I'm guessing here (as I don't fit mine until tomorrow) but I'd say that the spyder conversion probably isn't the answer to life the universe and everying as far as you are concerned.

The remaining rotoflexes will still need to be changed periodically. Though I understand that this is easier as the CV joint can be flexed with less effort than the rotoflex that would otherwise be at the opposite end of the shaft (famous last words).

The advantage in terms of reduced windup ought to be less on the baby elan than the +2 as the drive shafts on the baby elan are shorter reducing leverage on the joints.

Finally, I have head of people encountering difficulties with "binding" and extreme angulation of the drive shaft on baby elans (see chapman era forum). As UJs or CV joints tend to be wider than the rotoflex they replace, the solid shaft between the inboard and outboard joints must be shorter. The extremes of suspension travel require this shorter shaft to angulate more dramatically than the longer original thereby enhancing joint wear. This is less of a problem on the +2 as you start with a longer drive shaft in the first place. Whether the spyder system suffers this problem with the baby elan, I could not say.

A totally solid unit would solve the hassel factor on changing rotoflexes but this might be negatived by the added hassel of greater wear on the rest of the drive train and potential probles with drive shaft angulation.

Simon
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PostPost by: tdafforn » Fri Nov 07, 2003 3:18 pm

Thanks for the great info guys!
The Spyder system sounds like it could cover all bases altough having the rotoflexes on the inside seems to me to be putting them in the most inaccessable place.
Possible binding on full flex, surely that is really only a problem if you jump hump back bridges? I know it used to be a problem with some of the sliding spline racing systems.
Aren't most modern CV joints made for FWD cars and hence have to put up with much more extreme angles taking the steering of the hub into consideration?
BTW I contacted Mik Miller and they use Ford Sierra CVs so perhaps they would have been the way Colin might have gone? ;)
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Tim
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PostPost by: steveww » Fri Nov 07, 2003 5:07 pm

<!--QuoteBegin-Roy Gillett+Nov 7 2003, 02:41 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Roy Gillett @ Nov 7 2003, 02:41 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> Can't agree with MarkB. The Miller CV shafts I have fitted have a noticable effect on the drivability of my +2 that is obvious every time I drive it.

Roy Gillett [/quote]
You say the Mick Miller shaft effect the drivability - but in what way. Are they better or worse? What don't you like / do like about them?
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PostPost by: Roy Gillett » Fri Nov 07, 2003 5:50 pm

Hi Steve

Driveability is much better. Take off from rest is just like a modern car. You don't have to be careful about wind up and kangaroo starts. There isn't the 'surge' to contend with when you slow down (say for a roundabout) and then accelerate briskly and the gearchange is much improved (lighter and easier to engage). This last point I guess is down to a lack of wind-up in the transmission while disengaging and re-engaging gears. I haven't thought through the physics but the effect is striking.

I don't worry too much about the alleged extra strain on the transmission that eliminating rubber components is said to impart. Two things. First if energy is 'stored' in the wound up donuts then as they unwind they add that energy to the 'normal' power being delivered and so will load up the transmission components more not less. Second the ford gearbox is bulletproof and from a heavier and equally torquey car and though the diff. innards were designed for a 34BHP 105E Anglia, they see reliable service in a range of classic sports racers (Elans included) producing 160BHP plus.

I have done nearly 4000 miles including an energetic Classic Rally since I changed and so far so good. By the way on that same Rally a Triumph GT6 running close to us destroyed its rotoflexes very early on!

Mick Miller assured me that customers had seen 15000 miles on Elans runnning his shafts with no ill effects to the transmission and when he has stripped down prototype shafts after 5000 'spirited' miles he found no discernable wear. It is after all a very light car compared with the Ford metal that all the components came from! Thank you Mr Chapman!!

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PostPost by: types26/36 » Fri Nov 07, 2003 9:15 pm

<!--QuoteBegin-tdafforn+Nov 7 2003, 03:18 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tdafforn @ Nov 7 2003, 03:18 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin-->
Aren't most modern CV joints made for FWD cars and hence have to put up with much more extreme angles taking the steering of the hub into consideratio [/quote]
[/QUOTE][quote][/quote][QUOTE][QUOTE]
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PostPost by: types26/36 » Fri Nov 07, 2003 9:21 pm

Disregard last post
Brian.
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PostPost by: NickD » Sat Nov 08, 2003 12:27 am

My Elan S3 had solid Hookes joint splined shafts fitted when I bought the car. These joints had insufficient articulation to cope with the large drive shaft angles experienced with the suspension at full droop, so that the wheels could not be turned when in this condition. I wasn't too happy with this so I reinstated the original rotoflex setup. I soon wasn't too happy with these either, as the rotoflexes proved to be very short lived in my 145bhp car. I've never been too keen on rotoflexes since I had a fairly new one break on a +2S 130 that I had in the 80s. The loose shaft caught the handbrake linkage and broke the caliper off the rear upright - all of which cost rather more than a drivehaft conversion kit!

About 2 years ago, I noticed that Tony Thompson stocked a top-adjustable rear strut insert which limited suspension droop by about 2", with a corresponding reduction in drive shafts angles. These inserts have allowed me to refit the solid shafts without the Hookes joints binding. The result is a car which is much smoother to drive, and there is the added bonus that the shafts can be removed in about 10 minutes when changing discs etc.

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PostPost by: zman521 » Sun Nov 09, 2003 12:38 pm

I had hooks joints and was not happy as they bound up at full droop. I later installed CV joints from Dave Bean. This was the single best inprovement I made to the S3 Elan Coupe. No binding at full droop. Smooth clutch engagement. I would never go back to the rotoflex joints.
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PostPost by: Ramsden » Mon Nov 10, 2003 10:14 am

Well the weekend is over, the solid Hookes joint shafts are off and the Spyder drive shafts have been fitted.

The car has been given a minor flogging along some nice B roads, endured a long slog down the M4 followed by some bumper to bumper traffic crawling through London. So a pretty comprehensive test, road conditions wise. The verdict...

Very nice indeed.

B-roads - Nice smooth take up on accelleration from standstill. The previous set up was prone to giving a bit of a shunt as you took off. The additional flex in the drive line, provided by the single rotflex coupling on each side is discernable but actually feels better. Once you are up and running decellerating into corners and accellerating back the system feel good, retaining the positive feel of the solid setup whilst providing some cushion in the event of shoddy clutch work (who me?).
Gear change seems unaffected, by the change to single rotoflex system (see Roy's comments on the change from standard rotoflex to fully solid systems).

Motorway - No discernable difference, though after half an hour of the M4 I will admit that my senses had probably been numbed past being able to distinguish. Still, on letting the car go into overrun as traffic up ahead slows there was no twanging to be felt.

Urban crawl - This is where the flex in the new system is at its most discernable and where the solid system performed better. The typical on-off accelleration of this kind of driving does induce some windup in the system, interestingly most evident on engine braking decelleration. If traffic actually becomes stationary, rather than crawling, you still benefit from the cushioned take off, though the need to quickly let up on the throttle to slow for the next bottle neck soon reminds you of the presence of a rubber link in the transmission. This is no neck snapping, yo-yo like sensation but a mild surge is evident.

Overall: Well of course I like, them, I've just shelled out the wrong end of five hundred quid to buy them and spent a day in a cold concrete pit fitting them! Cyniscism aside I am genuinely pleased with the Spyder system.

In most driving conditions they are the equal of a solid system but provide that degree of cushioning to the rest of the transmission. Roy makes the point that the transmission components used by lotus are in the main pretty bullet proof, and I'm in no position to dispute this. However, I am "blessed" with the lotus 5 speed box which is anything but hardy. Finally, at a purely mental level I can't help thinking that the slight give discernable on hard accelleration or less subtle clutch work feels like it might insulate me from the need for costly diff/gearbox rebuild for a little longer.

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