Plus 2 UJ Shaft Conversion

[111Robin]

Very true, I think it's inevitable, may take some time though so I'll try the UJ setup while I save.

[Andy8421]

In principle, there is nothing wrong with a driveshaft with a hooke (universal) joint at either end and a sliding spline. You have one connecting your gearbox to your diff - as do most of the rear wheel drive cars on the road in some form or another.
The challenge on the Elan (less so on the Plus2 given the driveshaft length) is that as the rear suspension goes into bump (or droop) the driveshaft needs to change length to accommodate the suspension movement - that is what the spline is for. Unfortunately, splines lock up under load, so worst case, you are coming in to paddock hill bend at Brands, the suspension loads up at the bottom of the hill, you power on to balance the car, the spline locks (locking the rear suspension), you go to straighten up, change gear (dropping the torque on the driveshaft), the spline releases, the rear suspension jumps, the rear wheel breaks traction and you are in the gravel. All a bit far fetched, but in principle that is what happens. Chapman used 'ball splines' (which don't lock under load) in his formula cars to avoid this problem, and a few years ago a 26R owner posted pictures of his factory supplied driveshafts which also had ball splines. They are many times more expensive than simple sliding splines.
In historic racing, hooke joint / sliding spline joints are widely used on Elan rear driveshafts with no apparent ill effects (I have them myself), but the suspension travel of a competition car is much less than a road going car.
E-type Jags have a similar problem, but have chosen to use the driveshaft as one of the suspension links so it can be a fixed length.
Apparently, the Elan was originally planned to have inboard rear discs (like the E-type), which having just sent my rear calipers to be restored, would have significantly reduced the unsprung weight at the back, but the rotoflex couldn't cope. It would have been a much nicer arrangement if the Elan had used inboard discs, hooke joints and ball splines but I guess the cost was prohibitive.

E-Type rear suspension showing inboard discs and fixed length driveshaft as a suspension link:

[111Robin]

I won't be driving mine that enthusiastically so shouldn't have the issues experienced at full suspension travel. It all depends on whether or not the yokes can be correctly oriented, the master spline position will determine this. I'll report back after a more detailed review of them.

[111Robin]

Hi Robin

Are those driveshafts actually off your Plus 2? They look more like Triumph TR6 items to me.

Regards
Andy

Hi Andy,

Yes I have just removed them. According to a previous owner (in the 70's) he fitted modified Triumph shafts so you could be correct there although he said they were from a Triumph 2500.

[111Robin]

Well at least I can confirm that with the splines engaged (orientation governed by the master spline) the yokes are in alignment as required. I can also confirm that there are adapter plates bolted to the original 3 bolt output and outboard shafts to provide the 4 bolt interface.

[andyelan]

Hi Robin

Yes, the TR6 has a much narrower track than the Plus 2 so Triumph 2500 saloon does seem more likely.

If the shafts are a home made conversion however, I'd want to check the length is correct and that there's enough axial movement on the splines to go allow the Plus 2 suspension to go through it's full travel without them binding or pulling out.

The CV joint shafts available from Lotus parts suppliers have shafts specifically made of the correct length to suit the Elan and the Plus 2

Regards
Andy

[pharriso]

I can also confirm that there are adapter plates bolted to the original 3 bolt output and outboard shafts to provide the 4 bolt interface.

I need to send an e-mail to my wife to say that I was right....

[111Robin]

I can also confirm that there are adapter plates bolted to the original 3 bolt output and outboard shafts to provide the 4 bolt interface.

I need to send an e-mail to my wife to say that I was right....

doesn't happen often so definitely do it !!!!!

[111Robin]

Hi Robin

Yes, the TR6 has a much narrower track than the Plus 2 so Triumph 2500 saloon does seem more likely.

If the shafts are a home made conversion however, I'd want to check the length is correct and that there's enough axial movement on the splines to go allow the Plus 2 suspension to go through it's full travel without them binding or pulling out.

The CV joint shafts available from Lotus parts suppliers have shafts specifically made of the correct length to suit the Elan and the Plus 2

Regards
Andy

Thanks Andy,
The spline engagement length is approximately 3" so I think it's more than enough but I'll double check with the suspension fully extended to make sure the minimum engagement is sufficient.