CV drive shaft conversion

[alan.barker]

i think i'll stay with the CVDS from Aussie
Alan

[h20hamelan]

& worth every p

[Foxie]

Spyder conversion is one CV at the outer end and one Doughnut at the inner end.

Just checked with Spyder. 1 CV/1 Donut driveshafts still available.

https://www.spydercars.co.uk/lotus-elan-2-final-drive/

I couldn't find the double CVJ drive shafts on the Spyder website, so I email Andy. He replied that they don't do this type anymore.

Maybe the rubber donuts they use now have been upgraded. At £109 there are now almost two and a half times the price of the CVJ.

[rgh0]

The Cv and donut solution of Spyder aways seemed like a half pregnant response to me The originalCortina drive train had no rubber couplings and just had the clutch disk springs to absorb shocks and I dont see that a very similar drive train in a lighter car needs rubber for shock protection

Stick to donuts if you're after originality or go to Cvs if you want simplicity of maintenance and reliability.

cheers
Rohan

[2cams70]

Guys I’m not convinced by the arguments you are presenting. Please show me some numbers and calculations that the original diff mountings to the chassis for the Elan are up to the task of coping with the additional stresses imposed by CV’s. Is anyone up to the challenge? It was done for the offset piston pin effect on TDC argument now can it be done for this one?

[661]

I think he is talking about the one donut solution that Spyder sells Mr Fox, but could be wrong. I have that setup on one of my cars and find it great, not much different from the feel of 2 donuts.

Leslie

I actually had this set-up before I went 100% CVs. The surge was much reduced, but the remaining donuts were still starting to crack.

Exactly this , in my experience and why I changed to full CV

[rgh0]

Guys I’m not convinced by the arguments you are presenting. Please show me some numbers and calculations that the original diff mountings to the chassis for the Elan are up to the task of coping with the additional stresses imposed by CV’s. Is anyone up to the challenge? It was done for the offset piston pin effect on TDC argument now can it be done for this one?

Yes I could do it but its not necessary as i have extended real life experimental data

40+ years of extreme drop the clutch race starts in my Elan with Cvs has failed to do any damage to the diff housing top mounts or torque rod ears or the chassis mounts. This is despite sticky competition tyres and 170+ hp engines with very high torque at the 4500 rpm starting revs. Enthusiastic road driving in my Plus 2 with Cvs over the same time has failed to damage the diff or chassis also.

I can compare that to 3 donut system failures when doing less agressive starts, two in the Elan with one broken donut bolt and one failed donut and one in the Plus 2 with a failed donut many years ago before changing to Cvs in both cars. The two failed Donut events did signficant chassis damage. The Plus 2 had the Lotus pin and socket arrangement on the drive shafts which is supposed to protect against chassis damage if the donut fails but it was useless and just sheared of the pin. Both donut failures occured despie close inspection and regular Donut changes when any cracking was detected ( I got to the point I could change both donuts on one side in about 10 minutes) Also back then the donuts were much better quality than they are now.

cheers
Rohan

[2cams70]

Show me the numbers! - I'm not talking about the doughnuts and whether they fail or not. I'm talking about the diff housing. By calculation what is the reduction in life due to fatigue of the aluminum diff housing by using CV's instead instead of doughnuts? Are any of you engineers up for the challenge!

[Foxie]

Show me the numbers! - I'm not talking about the doughnuts and whether they fail or not. I'm talking about the diff housing. By calculation what is the reduction in life due to fatigue of the aluminum diff housing by using CV's instead instead of doughnuts? Are any of you engineers up for the challenge!

Ok.

Here's some numbers based my CVJ history:

Service (so far ) : 30 years
No.of diff failures: 0
Life reduction due to fatigue: 0

[rgh0]

Show me the numbers! - I'm not talking about the doughnuts and whether they fail or not. I'm talking about the diff housing. By calculation what is the reduction in life due to fatigue of the aluminum diff housing by using CV's instead instead of doughnuts? Are any of you engineers up for the challenge!

I said zero diff housing or chassis failures in 40 plus years of hard use in both road and race Elans, that is good experimental data. It would need a detailed Finite Element Analysis to determine stress level changes with donuts versus Cvs but experience says this is not needed.

I listed Donut failures to highlight that the risk of donut failure and damage is orders of magnitude greater than the risk of damage to the diff or chassis by fitting Cvs.

I have seen chasis damage where the torque rods are anchored and also where the top arms of the diff mount in Plus 2 but this has actually been in donut equiped cars and generally relates to loose bolts or failed rubber mounts.

cheers
Rohan

[2cams70]

Engineering numbers - you might have just been lucky!

Guys - Please don't infer that I'm saying there's a problem with CV joints. I am however interested if the effect of them on durability. I know it would be able to be determined mathematically by FEA or otherwise but I'm not smart enough to do it..

[rgh0]

Yes maybe I am lucky with Cvs and unlucky with donuts. But 80 car years of personal use is not a bad dataset. I have also looked at many other Elans over that time and know of no failures that can be attributed to Cvs and many failures that can be attributed to donuts so its not just me who is lucky with Cvs and unlucky with donuts

cheers
Rohan

[h20hamelan]

I only see failures in front drive c/v, due to turning of front wheels. I suspect TTR etc uprated diff output shafts fix problems inside, & their uprated out-board shafts help too?

While its likely true, the Elan was designed for 100 not 200hp.

[Andy8421]

Engineering numbers - you might have just been lucky!

Guys - Please don't infer that I'm saying there's a problem with CV joints. I am however interested if the effect of them on durability. I know it would be able to be determined mathematically by FEA or otherwise but I'm not smart enough to do it..

I'm an ex engineer (electronic), but looking at the problem logically, peak torque in the driveshafts (and corresponding moments on the diff case) will be set by the adhesion of the tyres, irrespective of the drive shaft joints. I could see that there may be a case for considering the rotational inertia of the wheels and tyres, as these will need to be accelerated as well, but I am very suspicious of the shock load 'cushioning' argument about the Rotoflex in limiting peak loads on the diff casing.

As for finite element analysis, its a complex system to model, and the diff casing is a complex shape. I would rather rely on real world testing (Rohan's extensive data set) than a FEA approximation.

[alan.barker]

6

I know someone who had MM CV fail but to be honest he is always fiddling and dabling on his +2. As they say a little knowledge is sometimes dangerous. I was following his +2 when the CV Cap screws came undone at a low speed. 5 Cap screws fell out and n°6 Cap screw get bent. I'm sure the Cap screws had NOT been torque loaded.
Alan
Ps. I think the fact that the Adapters are in Alloy the Cap Heads should be Loctited using also Loctite Activator.