rotoflex Drive shaft shortened to replace Rotoflex?

[TIMSGT6 X 5]

I have been considering a replacement for my very sketchy  Rotoflex discs. Having just shortened a drive shaft to accommodate an overdrive I was struck by the fact the flanges are shared between the axles and propshaft.

Taking this further, rather than going the Steve Smith route with  Datsun 240Z axles shortened and flanges adapted, why not shorten a driveshaft to about 15", cut off the rotoflex fingers from the stub axle and weld a flange on it. There is plenty of travel on the spline, more than is required, the incline angles aren't that bad to begin with even at full suspension travel.

Any drawbacks I'm not seeing?

I've added a pic of the Datsun axle for posterity, it still needs to be shortened.

Cheers Tim

Edited April 27, 2018 by TIMSGT6 X 5
additional info added

[GT6Steve]

Hi Tim,  My Datsun conversion wasn't to eliminate the roto's per se but rather the very weak assembly within the upright.  They can't take the abuse of racing.Your propshaft conversion will likely foul the frame as well.  That said, Cutting off the roto arms and installing a flange seems perfectly doable however.

 

[TIMSGT6 X 5]

14 minutes ago, GT6Steve said:

Hi Tim,  My Datsun conversion wasn't to eliminate the roto's per se but rather the very weak assembly within the upright.  They can't take the abuse of racing.Your propshaft conversion will likely foul the frame as well.  That said, Cutting off the roto arms and installing a flange seems perfectly doable however.

 

Hi Steve , good to hear from you. 

I too, don't really have an issue with the Rotoflex, other than the unreliability of the replacements offered today.

For myself I am content with the stub and hub assembly, would be nice to have a larger inboard bearing as you used though. 

My thoughts are the sliding spline from a GT6  driveshaft is actually quite small in diameter,13/8" compared to the Datsun. 

I don't want to hack up the frame for clearance, so maybe I'll thin down the mount bushing on the diff to tilt the front Of it up a bit while I have access to everything. I can model the movement to see if I can give it a bit more clearance. The intention is to have the spline end mounted from the diff side rather than towards the hub. 

Cheers Tim 

 

[Nick Jones]

Think also about the TR series of IRS (4A through to 6) and Stag.  All of which use larger UJs and are probably too long.  They use the sliding spline (considerably bigger) which doesn't always slide that readily under torque leading to an interesting "twitch".  The Datsun solution with it's ball splines is very superior!

Simplest solution along the lines you've suggested might be this one

Not best practice to use a UJ and CV on the same shaft but seems to work.

Nick

[TIMSGT6 X 5]

On 2018-04-28 at 5:43 AM, Nick Jones said:

They use the sliding spline (considerably bigger) which doesn't always slide that readily under torque leading to an interesting "twitch".  The Datsun solution with it's ball splines is very superior!

Yes, I would agree with that, I am thinking of using the later Spit propshaft with the cylindrical opposed bearings. Combined with a shorter Spit damper mounted on the frame it would in theory limit the extension range and prevent fouling on the chassis. I don't know if in practice that is a good idea. 

I will mock them both up to see where everything falls. 

Ive made up this device to preload the spring and give me some reference to movements and position.

[TIMSGT6 X 5]

I decided to work with the Datsun sliding axle but with a slightly different modification. 

I've  shortened the stub axle and machined a serrated spline on the former rotoflex end, added an original  yoke from the opposite end of the axle.

This yoke attaches directly to the slider portion of the Datsun axle , the Datsun yoke was removed and a centering bore machined in the butt end. The rest of the Datsun axle, unmodified,  is to be bolted to the existing diff  flange via an adapter. That slider portion has nearly 2" of travel .

Picking up the spline without an involute gear cutter, just a carbide endmill. 

 

 Successful marriage to the newly splined stub axle.

Mock up and measurements prior to welding an adapter to the slider tube end, 

Edited May 6, 2018 by TIMSGT6 X 5
Photo notations

[Nick Jones]

Really nice work - Solution looks factory!

Nick

[GT6MK3]

What bearing are you planning to use?

[TIMSGT6 X 5]

22 minutes ago, GT6MK3 said:

What bearing are you planning to use?

I am not planning on altering the hubs or bearings , though it is worth considering. 

[Gt6s]