Elan - CV or Sliding Spline/U-Joint Half Shafts?

PostPost by: "m2500tvr" » Mon Jun 06, 2005 12:59 am

I'm trying to sort this out. I don't have enormous issues with fresh
Rotoflex couplings, but I'm mothballing my original Elan (a 67 S3
dhc) driveshafts to replace them with something showing less
elasticity.

I had requested of the shop doing work on my car to fit CV-jointed
shafts. I would prefer the to sliding splines. The shop purchased
and fitted splined/u-jointed drive shafts. They're nifty things,
really. Nicely made, very beefy (like too beefy/overkill), with
some low-friction coating on the sliding splines. I think they also
fit the 240Z Datsun/Nissan.

They claimed that CV axles wouldn't accomodate the suspension travel
of the Elan.

I'd just like to confirm whether this is the case. It seems to me
that the travel of the many softly sprung/long travel suspensioned
road cars using CV axles today has to be greater that what the rear
suspension of an Elan will see. I've also seen CV conversions done
to Elans.

I'd appreciate your thoughts and/or experience on this.

- SJ
"m2500tvr"
 

PostPost by: elanplus2 » Mon Jun 06, 2005 1:15 am

Hi,

The steering angles achieved in most modern front wheel drive CV systems
way exceed the travel angles in an ?lan rear suspension. Therefore, IMO
your workshops fears re CV systems are somewhat misguided.

Ray Edwards


-----Original Message-----
From: ***@***.***lto:***@***.***
Behalf Of m2500tvr
Sent: Monday, 6 June 2005 1:00 p.m.
To: ***@***.***
Subject: [LotusElan.net] Elan - CV or Sliding Spline/U-Joint Half
Shafts?

I'm trying to sort this out. I don't have enormous issues with fresh
Rotoflex couplings, but I'm mothballing my original Elan (a 67 S3
dhc) driveshafts to replace them with something showing less
elasticity.

I had requested of the shop doing work on my car to fit CV-jointed
shafts. I would prefer the to sliding splines. The shop purchased
and fitted splined/u-jointed drive shafts. They're nifty things,
really. Nicely made, very beefy (like too beefy/overkill), with
some low-friction coating on the sliding splines. I think they also
fit the 240Z Datsun/Nissan.

They claimed that CV axles wouldn't accomodate the suspension travel
of the Elan.

I'd just like to confirm whether this is the case. It seems to me
that the travel of the many softly sprung/long travel suspensioned
road cars using CV axles today has to be greater that what the rear
suspension of an Elan will see. I've also seen CV conversions done
to Elans.

I'd appreciate your thoughts and/or experience on this.

- SJ













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PostPost by: "m2500tvr" » Mon Jun 06, 2005 3:15 am

Hi, Ray:

Thanks for your reply. I'm going to fit CVs then. Is there a handy
CV axle recipe around?

- SJ

--- In ***@***.***, "Ray Edwards" <ray.edwards@u...>
wrote:









"m2500tvr"
 

PostPost by: Frank Howard » Mon Jun 06, 2005 3:30 am

SJ,

My understanding is that it is the U-joint set up that can lock up at full
droop, not the CV set up. Part of the problem is that the Elan is so narrow, so
the joints require more angle because the shafts are so short.

Frank Howard
'71 S4 SE
Minnesota
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PostPost by: saarhus » Mon Jun 06, 2005 4:02 am

A small clarification on the U-joint. The splines will only lock up when a certain level of torque is exceeded, preventing their movement in and out. This can occur at any point in the U-joints travel, or angular displacement.

Stan

My understanding is that it is the U-joint set up that can lock up at full
droop,
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PostPost by: elanplus2 » Mon Jun 06, 2005 4:38 am

Hi,

eSe a previous email I sent last week re CV systems. The Elan factory I
Melbourne make one.

I have developed my own system with the help of Ken Woodburn in Auckland
NZ. It uses adapter plates, Audi Quattro CV's, and shortened Audi 80
half shafts. The Quattro CV's made this a very expensive project. I am
in the process now of developing a cheaper version with another type of
CV.

Ray Edwards

Hi, Ray:

Thanks for your reply. I'm going to fit CVs then. Is there a handy
CV axle recipe around?

- SJ
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PostPost by: john.p.clegg » Mon Jun 06, 2005 5:45 am

Stan
I don't think that was the point,the u/j's themselves will only "twist" a certain amount (i've got them on my plus 2) and they are near the limit-especially if you fit them with the grease nipple in the wrong place

John


Stan Aarhus <***@***.***> wrote:
A small clarification on the U-joint. The splines will only lock up when a certain level of torque is exceeded, preventing their movement in and out. This can occur at any point in the U-joints travel, or angular displacement.

Stan

My understanding is that it is the U-joint set up that can lock up at full
droop,
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PostPost by: denicholls2 » Mon Jun 06, 2005 1:36 pm

There are three issues that some are confusing here:

1. Concern about binding on the splines, due as already mentioned to
the application of sufficient torque to "lock" the spline from
sliding. Much conjecture about this, but I don't recall anyone here
reporting it being an actual problem.

2. Exceeding the droop capability of the U-joint, at whick point it
will lock. Jumping your Elan into this condition could, as gravity
is applied, result in damage, catastrophic failure, and off-roading
your Elan.

3. Exceeding the ability of a CV-joint to stretch to cover
suspension droop. Possible, but highly unlikely in a well-designed
conversion. Also unlikely to be catastrophic to anything other than
the joint itself as joints usually disassemble when travel is
exceeded, though locking is possible here as well.

That your shop was concerned about droop issues is good, that they
don't understand the physics involved (and the greater risk
associated with U-joints vs. CV joints) is not good. If they fitted
the splined shafts without a method of preventing droop lockup, they
failed. Otherwise, you'll probably be perfectly happy with them.

Doug Nicholls, 54/1822 (No droop issues in a Europa)
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PostPost by: steveww » Mon Jun 06, 2005 1:44 pm

To ensure that the UJ do not lock up under full droop just fit droop
limited shocks. I am going this route with TTR drive shafts and matching
dampers.

An other thing to keep an eye on is spring rate. The rubber donuts
provide an amount spring that will be lost when CV/UJ are fitted.
Ideally you should fit a slightly stiffer spring.

denicholls2 wrote:

--

Regards,

Steve Waterworth
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PostPost by: mikecauser » Mon Jun 06, 2005 2:12 pm

On Mon, 06 Jun 2005 14:41:48 +0100 Steve Waterworth <***@***.***> wrote:


Good try, but no coconut. Assume the driveshaft is horizontal at rest,
now when the wheel goes up the doughnut will be trying to push it down,
ie increased spring rate, but when the wheel is in droop the doughnut
will be trying to push it up, ie reduced spring rate. If you thought
that this characteristic is essential to the Elan's handling you could
duplicate it with a couple of torsion bars -- like two anti-roll bars
but anchored to the chassis not to the other side's suspension.


Mike
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PostPost by: steveww » Mon Jun 06, 2005 2:37 pm

Hmmm... good point. Would be interesting to know what the "rate" of the
donut is compared to that of the spring.

Mike Causer wrote:

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Regards,

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PostPost by: lotuselan2 » Tue Jun 07, 2005 1:52 am

Easiest way to offset the uneven "dampening" of the donut is one click up on
an adjustable damper.



Ken

'69 Lotus Elan +2 with BDR

_____

From: ***@***.***lto:***@***.*** Behalf
Of Steve Waterworth
Sent: Monday, June 06, 2005 10:37 AM
To: ***@***.***
Subject: Re: [LotusElan.net] Elan - CV or Sliding Spline/U-Joint Half
Shafts?



Hmmm... good point. Would be interesting to know what the "rate" of the
donut is compared to that of the spring.

Mike Causer wrote:


--

Regards,

Steve Waterworth
***@***.***

Einstein: "The faster you drive, the slower you age..."








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PostPost by: rgh0 » Tue Jun 07, 2005 11:45 am

Replacing donuts with Cv's in an elan will normally give you a problem
with the CV's partialy locking up at full droop. The angle that they
adopt in an elan due to the narrow track and long droop travel exceeds
the angles they are normally designed for even in front drive
applications on golfs and audis. Uni joints have the same problem but
more so. Some of the integral CV's and drive shafts used on many
(especially japanese) front drive cars can accomodate more angle but
the bolt on Lobro style CV's used in all Elan conversions I have seen
from Volkwagen/Audi and BMW ( and some other mainly European cars)
accomodate less angle.

Assuming you get the length of the intermediate shaft right so it is
binding on angle and not on axial travel how much of a problem you have
depends on:

1. Thickness of the adapter plates you use

2. Which CV joint you use

3. The amount of droop you shocks allow

4. The detail design of the metal section of the rubber boot over the
CV.

Getting all of this right is not a trivial problem. Most of the
commercial suppliers of the conversion kits dont understand all these
variations.

I use droop limiting cables on my elan as easier than modifying the
shocks. The last couple of inches of droop travel are not meaningful.
Normally the donuts prevent it anyway and the spring loads at this
point so low that the wheel is not doing anything in handling terms
either.

Rohan
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