Lotus Elan

Other than money, any reason NOT to convert to CVs?

PostPost by: a price » Mon Apr 29, 2019 10:19 am

I bought the expensive Australian CV conversion from Elan Trick Bits. Very high quality and they are fit and forget (not forgetting the greasing) . Best mod I have made to my car
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PostPost by: tjb0274 » Mon Apr 29, 2019 11:57 am

rgh0 wrote:
You may want to ask Col at Elan Trikbits where the design for the Lotus marques CV conversion actually came from.

cheers
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Interesting - didn't know that, Rohan. They quote different weights, which suggests some differences somewhere.
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PostPost by: rgh0 » Mon Apr 29, 2019 12:53 pm

tjb0274 wrote:
rgh0 wrote:
You may want to ask Col at Elan Trikbits where the design for the Lotus marques CV conversion actually came from.

cheers
Rohan


Interesting - didn't know that, Rohan. They quote different weights, which suggests some differences somewhere.


i find this quote at the end of the Lotus Marques page on Cv's somewhat ironic given the history of Cv development application to Elans in Australia by various people over the last 40 years

"Those who cannot innovate can only imitate!"
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PostPost by: ericbushby » Mon Apr 29, 2019 4:57 pm

Hi Stuart,
Kelvedon recommended that I shorten my Koni's by 25mm.
They also supply Sue Miller
Cheers
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PostPost by: 74Twincam » Mon Apr 29, 2019 6:31 pm

Tdskip- where are you coming up with $200 for donuts???
Cripes Man, do share your source-
There are four root flex joints to replace at the same time, so my math is $800, vs. the $1100
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PostPost by: RichardHawkins » Mon Apr 29, 2019 8:42 pm

I carried out my own CV conversion. The car is a long term (retirement) restoration, that has taken much longer than expected and is not back on the road.

I bought CV joints designed for a VW Passat, measured the deflection that the joints would accommodate, and made the adapters needed. I bought the drive shafts from a company called Dave Mac prop shafts of Coventry. I made an error in my measurements of acceptable deflection. I did not rotate the joint whilst taking my measurements. On assembly I discovered that the joints were "lumpy" at full droop whilst rotating. I had to shorten the damper shafts by 14mm. Others have mentioned droop limiting of about 20 - 25mm so I may have further work to do.

Another thing I discovered is that the three bolt diff output shafts and the rear hub shafts were not correctly made, in that the bolt holes were not all at the same radius from the centre line. This error is probably not important with rotaflex joints. I made my adapters to correct this discrepancy.

I am of the opinion that if one can afford redesigned diff output shafts where the CV joint bolts to the diff output shaft without an adaptor, that this is a better option.

Hope this helps,

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PostPost by: tdskip » Mon Apr 29, 2019 10:34 pm

74Twincam wrote:Tdskip- where are you coming up with $200 for donuts???
Cripes Man, do share your source-
There are four root flex joints to replace at the same time, so my math is $800, vs. the $1100


Oops - newbie mistake apparently. I thought the donuts were about 100 bucks each and you only needed one aside. Time to open that workshop manual apparently!
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PostPost by: tdskip » Mon Apr 29, 2019 10:44 pm

Could someone outline, from experience, the pro and con of going with Lotus Marques vs Trikbits?
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PostPost by: snowyelan » Mon Apr 29, 2019 11:56 pm

I went with the conversion that uses the supplied diff output shafts. I had made a complete conversion myself about 10 years ago using golf cv’s. Functional, yes, but I couldn't come to terms with having welded 2 pieces of VW half shafts to make 1 with the required splines. I shopped around for custom shafts, wasn't happy with the cost.

My perspective on it is if I was going to change things it should be properly done. With that in mind we are stuck with the diff output splines on one side and the mounting pattern for the brake disc on the other. Beyond that the diff and brakes would need to change. Not within my budget and definitely not necessary. Using an adapter to mate to the inboard rotoflex pattern seemed an unnessary step between the parts that I wasn't willing to change.
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PostPost by: tjb0274 » Tue Apr 30, 2019 12:50 am

Grizzly wrote:The second was the lack of rotoflex's seemed to take some thing from the way the back end was sprung, the back end was quite allot softer with cv's / stock springs on and this is some thing i am looking to fix in the near future.


Interested in this observation - it's something that I was concerned about when I bought the CVs. The Lotus Marques page I linked earlier includes links to some basic experimental research that was done, concluding that any effect from the rotoflexes on overall suspension spring rate was marginal and probably not sufficient to be noticeable.

That was reassuring, but this isn't the first time I've seen reports from owners suggesting otherwise. My car has only had the CVs in my ownership, so I haven't had the opportunity to compare - it would be interesting to drive the rotoflex/CV back to back and see if there seemed to be a difference.
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PostPost by: SENC » Tue Apr 30, 2019 1:53 am

I haven't owned/driven the Lotus Marques version, so cannot compare for you, but I can say I have been very impressed with the cvds from elantrikbits in fit, finish, and use. I selected them because of user testimonials, here and elsewhere, and because the owner/builder (Col Croucher) is an elan enthusiast himself and seemed accessible should the need arise. The latter has proven true in spades, starting with great communication pre-delivery while the cvds was being made (he doesn't always keep inventory laying around) through a couple questions I had later. I also bought one of his baffled sumps second hand and sent him an email with a question and got a quick and helpful response. He is also regularly found on this forum and facebook helping other elan owners. All in all, the kind of vendor I like to support, and glad I did.

Installation was no problem, a straightforward replacement of the original intermediate driveshaft and donuts, and his design eliminates the need to take other steps to limit droop.

Good luck!
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PostPost by: Citromike » Tue Apr 30, 2019 3:53 am

My car has had CV joints since 1994. With no problems.

I see no reason why Rotoflex couplings should be retained.

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PostPost by: 69S4 » Tue Apr 30, 2019 6:21 am

ericbushby wrote:Hi Stuart,
Kelvedon recommended that I shorten my Koni's by 25mm.
They also supply Sue Miller
Cheers
Eric


An inch then. And at the bottom of the suspension travel. If you were in that part of the travel what happens? Do the CV's lock solid or just become 'notchy' or wear faster. Presumably we're talking about getting the rear end airborne or is it going to be an issue on 'spirited' cornering where one wheel is unloaded? I could imagine that one CV not rotating freely under such circumstances could introduce some odd handling characteristics but, in practice, how often are the rear wheels in that area of the suspension's travel?
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PostPost by: ericbushby » Tue Apr 30, 2019 7:46 am

Also when the car is jacked up.
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PostPost by: JonB » Tue Apr 30, 2019 8:02 am

But not on a +2 right?

I have a pair of shafts supplied last year by Sue Miller (she now resells the Kelvedon ones as noted previously) and they have been pretty great, except that the exposed steel on the CV joints themselves rusted quickly. I should have put some lacquer on them to prevent this. Have had no problems with binding yet.

Incidentally, wouldn't a binding CV joint make a bit of a noise if doing it under hard cornering? I have experienced this but I'm not sure what it is - may be tyres rubbing or the diff complaining? My car does seem to roll excessively into the bends and it's interesting to read this comment on antiroll properties of Rotoflexes. Problem is, I didn't drive it like this while it had the rotos fitted because the rest of the car felt so wobbly (bushes all knackered, but replaced now).
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