Lotus Elan

Halfshaft replacements

PostPost by: JonB » Sat Dec 02, 2017 5:26 pm

Yesterday I was talking to a certain well known Lotus parts and restoration specialist and I asked about CV joint conversions. I was rather surprised at the vehemence of the reply; long story short was "don't fit them - ever".

So what was the reasoning?

  • Destroys the character of the car (hmm, I think windup is character I prefer to do without)
  • Everything else has to take the additional loading / shock
  • Output shafts can be sheared in two
  • Clutch springs (the radial ones) get squished to hell and back and eventually fail. Could fall into the plates and prevent the clutch from working at all.
  • Diff mounts can be torn loose / diff upper arms can snap off
  • Car is harsher to drive (someone please quantify what this means?)

It all sounded a bit apocalyptic to me, so I asked about modern rubber as used to make donuts and he said that there had been problems but quality was improved nowadays. Not sure what to make of that. He's claimed to have got 90,000 miles from a set of donuts before needing replacement and what is really needed is for me to learn correct use of the clutch on a donut equipped car. It was pointed out that some modern cars still use flexible couplings in the propshaft for the reasons outlined above.

With my clutch as heavy as it is I'm not entirely sure "feathering the clutch" is right for me. But anyway..

The thing is, I have read all sorts of threads like the one I am attempting to start now. I do live in fear of the donuts letting go on the motorway but equally I don't want to over stress the halfshafts or drive train. I should have asked if the 90,000 mile claim is for original donuts or modern ones. Probably original.

My options are:

  • New donuts all round, about ?450
  • Sue Miller CV jointed shafts, about ?600
  • Spyder shafts, with one failsafe donut on each side, about ?800, because the doughnuts don't come with the shafts.

There's probably others (like the super expensive Aussie ones or a sliding spline design - neither of which appeal). I'm in no rush, but would like a critical analysis / discussion of the points raised by the supplier as listed above, as well as the thoughts and experiences of those who have taken the plunge - especially those of you who have done high mileages.

Thanks
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PostPost by: ericbushby » Sat Dec 02, 2017 6:29 pm

Jon,
My short experience with Sue miller type (Kelvedon) CV Shafts is that I am very pleased with them. I find the drive smoother, and it will now accelerate away from rest easier and smoother than was possible before.
I don't know about clutch control, but after 1 and 1/2 million miles over 60 years, I have driven most variations by now, and I found it difficult to get the response I wanted.
It now feels as I think it should. I find nothing that could be called harshness.
If you are concerned about the diff shafts, then stronger ones are available, and a brace is sometimes recommended to support the diff mounting lugs. I am considering that myself.
So that is 1 vote for CV conversion, albeit a recent one with little mileage so far.
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PostPost by: lotusS2guy » Sat Dec 02, 2017 6:57 pm

After breaking a differential output shaft about 35 years ago, I installed a sliding spline rear drive assembly. Nothing has broken back there since then, and I'd never go back to donuts knowing how the quality has deteriorated over the years.
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PostPost by: miked » Sat Dec 02, 2017 7:08 pm

Same as Herb. I run sliding spline UJ's. No problems on 4 different cars. My last do nuts did about 4k before they went soft. Fitted a diff brace as a Zetec up front.

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PostPost by: RichardHawkins » Sat Dec 02, 2017 7:15 pm

Jon,

Most of the transmission items I believe to be common with the Lotus Cortina, clutch gearbox and differential components. The Cortina has different half shafts. As the Cortina half shafts are longer, there is probably some small amount of flexibility. I am not aware of complaints from Corina drivers due to a lack of flexibility in the drive train. I suspect that Lotus chose rotaflex couplings due to availability and price. CV joints were not readily available at the time. Rotaflex couplings may reduce shock loads to the differential casing and its mountings

Many industrial drives use some form of flexible coupling incorporating some rubber elements, but this is mainly to accommodate poor alignment.

I think that if CV joints had been readily available, Lotus would have used them.

There has been much discussion on this site on the relative merits of independent rear suspension drive components, and without the advice of someone who designs such things it seems to be down to the individual to decide.

I chose CV Joints.

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PostPost by: JonB » Sat Dec 02, 2017 10:01 pm

Are there two types of Lotus original fit output shafts? One being stronger? And if so how would I tell?

(I'm doing the diff seals soon.)
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PostPost by: Paul Chapman » Sat Dec 02, 2017 10:12 pm

Hello Jon

I have only limited experience with universal joints & no sliding splines & no do nuts on my S3, they were fitted by the PO so say around ten years of service with around 18k mileage with no problems. Annual maintenance consists of a thorough clean / inspection and re-grease.

I also agree with & support the comments of Eric & Richard, flexible couplings are great for coping with misalignment issues & sliding splines will help with any minor directional changes that may occur. In a past life I covered many miles in a TR with IRS that had UJ's & sliding splines again with no issues or failures.
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PostPost by: jimj » Sat Dec 02, 2017 11:04 pm

A 73S already has the stronger output shafts and should have the so-called fail-safe donut arrangement. I`m guessing your "specialist" is the acerbic one who thinks everyone else is an idiot. Some of his uprated stuff is well respected but I`d rather deal with pleasant people.
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PostPost by: prezoom » Sat Dec 02, 2017 11:21 pm

I have CV's on both the S2 and the P2. Dave Bean's on the S2, elantrikbits on the P2. Have driven all three (3) combinations, donuts, ujoint, and CV, but not a combo like the TTR. I would only have CV. As far as clutch parts coming adrift, nonsense. They are basically the same parts as the Cortina. The Cortina weighs more that a P2, and can put one heck of a lot more strain on the drive line, yet they trundled around the world for years, under all sorts of conditions, with minimal failure. The only driveline failures I have ever had, was with my S7 and the Triumph 10 rear axle. Even changing the diff output gears to GT6, having special axles made, with a Detroit locker, it would still break the small splined section off the axle with around 140 horse power. In those days, we did standing starts. Sell CV axles once, donuts forever.
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PostPost by: Robbie693 » Sun Dec 03, 2017 1:45 am

JonB wrote:Are there two types of Lotus original fit output shafts? One being stronger? And if so how would I tell?

(I'm doing the diff seals soon.)


Early shafts were 'waisted' i.e. smaller in diameter than the splined portion. Later ones were increased in thickness so that the plain part of the shaft was the same as the splined portion. No way of telling for sure until they're removed but the later shafts usually have failsafe pins on them too. Usually...

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PostPost by: rgh0 » Sun Dec 03, 2017 2:14 am

The stronger later shafts were introduced around 1970 with the Sprint and +2S 130 but if your car has ever had a diff change there is no knowing without pulling the shafts out.

cheers
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PostPost by: el-saturn » Sun Dec 03, 2017 7:39 am

i'd say the donuts are part of the entire concept ( take a look at the single seaters! lots of donut solutions) and i was told in 1981 (when i started restoration) to keep the donuts as they provide for the loads being distributed in such a fashion that every delicate area doesn't get more tension, compression, buckling etc than it was designed for. the only true arguments to have CVs is racing OR trying to beat (ef) corvettes at intersections and i aint no boy anymore. so whether my chassis nor any other critical components have ever cracked or needed reinforcing etc. so i'll stick with my donuts, even though i had one disintegrate 30 years ago (my roll cage kept my butt in order!!) sandy PS: i do check my donuts once in a while and have spares!
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PostPost by: nigelrbfurness » Sun Dec 03, 2017 10:03 am

IMHO the original decision to fit rubber donuts was nothing to do with spreading loads or preventing shock to various other drive-train components but more to do with an easy and cost-effective solution for the problem of driveshaft flexibility in an independent rear setup. All the other parts generally functioned well on other cars with standard drive components. Donuts had already been used in Lotus race cars prior to adoption in the Elan so Lotus were already familiar with them when the time came for the Elan to go into production.

I have had the Spyder CV conversion which retains a single rubber coupling now for over 20 years in my car. I fitted TT diff output shafts too. I have had output shafts shear and diff casing "ears" break off several times on earlier cars with standard donuts. I have a Sprint diff brace fitted to my car now as a result. All in all, I have had no problems whatsoever after switching to the Spyder shafts and would honestly recommend them.

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PostPost by: JonB » Sun Dec 03, 2017 11:43 am

Great, it's looking good.

I've inspected the doughnuts and they have surface cracks, very small, plus some evidence of stretching round the bolt holes. I have some good used replacements, I will probably fit them for now. My diff has the strengthening plate fitted across the ears. (looks like a simple bit of angle iron... really, Colin? Was that the best you could come up with?).
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PostPost by: alan.barker » Sun Dec 03, 2017 11:53 am

When you fit the doughnuts compress them like this
rotoflex-circlip-001.jpg and

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