Rotoflex to swing spring conversion

[Dick Twitchen]

12 hours ago, clive said:

goodnessknows why Triumph used an "iffy" rubber donut

Lotus used them in the Elan and their GP cars, as did Alfa Romeo and the Hillman Imp had them.  All the rage at the time and fine with Metalastic Ltd manufactured items?

Dick

[Pete Lewis]

ive come across a couple of swing shafts failures  all from a crack eminated from reversed torsion ie  LH second hand shaft fitted to a RH side  so the torsional memory has been reversed 

ends up with nice smooth split almost looks like its been cut off .

most rotaflex couplings of original specification do last for many years , it the crap after market copies that give up early 

there are some nice poly/neoprene type ones used in marine drives , no idea if they would take the torque of driving wheels ,  not done any homework on them .

Pete

[Clive]

11 minutes ago, Dick Twitchen said:

Lotus used them in the Elan and their GP cars, as did Alfa Romeo and the Hillman Imp had them.  All the rage at the time and fine with Metalastic Ltd manufactured items?

Dick

Yes, I am aware of that. But the 2000 range used a sliding splines/double UJ setup, which is better, and others (1300fwd?) CV joint which is what Dave at CC used on his CV conversion. But using a rubber donut is an inferior solution to the problem.

I know that bubber donuts are used in many propshafts, I assume to soften take-up, which is a plausible theory with the triumphs to reduce diffs breaking/warranty claims.

As to reproducing decent new ones, it will be the usual problems. (a solution in CV shafts exists at a price, but mainly that many will see a cheap/nasty £30 donut and won't understand that £100-200 version is worth the extra. So a quality version will sell is such small numbers nobody will bother unless there is a large volume of demand elsewhere)

[Pete Lewis]

I agree the dougnut design is a tortuous use , far simpler on Imps etc  as a straight fit inboard not the  contorted  inside out fitting  inside the wishbones of triumphs idea, 

it does make you wonder why when CV were used in much of the BL range of the day , maybe futile independance like the stag engine 

icant see it was to protect the diff as whilst not the best they had they are not particularly  explosive in normal use 

its anther love it hate it thats lasted 50 years 

pete

[NonMember]

What we tend to forget these days, now that CV joints are universal and dirt cheap, is that in the 1960s they were still expensive. And unnecessary. You point to the other BL cars that used them - remember two things: Triumph and Austin were not the same company when the Mk2 GT6 was designed, and the cars that did use CV joints were FWD, where the joint needs to perform round a very wide angle. Even the Triumph 1300 only used CV on the outer - the inner was a Rotoflex.

As to the tortuous fitment, it allows the doughnut to be further outboard than would otherwise be the case.

[Colin Lindsay]

53 minutes ago, NonMember said:

What we tend to forget these days, now that CV joints are universal and dirt cheap, is that in the 1960s they were still expensive. And unnecessary. You point to the other BL cars that used them - remember two things: Triumph and Austin were not the same company when the Mk2 GT6 was designed, and the cars that did use CV joints were FWD, where the joint needs to perform round a very wide angle. Even the Triumph 1300 only used CV on the outer - the inner was a Rotoflex.

As to the tortuous fitment, it allows the doughnut to be further outboard than would otherwise be the case.

+1 to that; you must remember that at the time, they were fitted as a simple and innovative solution to large suspension movements and flex and if anything went wrong they could be replaced by the garages of the time, as much as a service item requiring regular replacement. I don't think Triumph expected them to last forty years, or for owners to have problems sourcing replacements.

 

[Steve P]

12 hours ago, Nick Jones said:

 

Built our Spit up as roto (with CV shafts) in considerable part due to the number stories of lost rear wheels....... Three wheels on my wagon and no brakes.....  no thanks!

Another angle to that is that all the OE shafts are at least 40 years old now, so fatigue has had time to do it's work.  So you might think that new ones are a wise investment - and on the face of it, you'd be right.  However, having heard a few stories and seen a few pictures of new shaft failures, or near failures in the last couple of years..... perhaps not.  Problems seem to be mainly with the way that the UJ yoke forging is attached to the shaft and being rather less secure than the OE ones - which very rarely fail at that point.

Nick

Myself and american Bill were exiting a roundabout just outside Bude in Cornwall,going uphill at about 30 when the rear started wobbling,the wheel came off with the brake drum still attached,car slid along the road on the twin box exhaust,managed to pull to the side ok,the wheel ended up in a ditch.

I looked at alternative swinger shafts,Sommers Bros in the US,i think Chris Sherrington used them on his T6,but they were nearly a grand a pair.

CV virtually fit and forget,about £700 all in.(diy fit)

Steve

[Cookie]

Handbrake guides are different, they are chassis mounted for swing spring and body mounted for Rotoflex. You'll need to cut the handbrake guides off a swing spring car and weld them on to your chassis plus maybe  cut the old guides off your bodytub as they might be in the way. I have heard of people neglecting to change this and the handbrake either binds or doesn't work depending which way around you are converting. 

[Steve P]

19 hours ago, Cookie said:

Handbrake guides are different, they are chassis mounted for swing spring and body mounted for Rotoflex. You'll need to cut the handbrake guides off a swing spring car and weld them on to your chassis plus maybe  cut the old guides off your bodytub as they might be in the way. I have heard of people neglecting to change this and the handbrake either binds or doesn't work depending which way around you are converting. 

You don`t need to cut off the guides,mine is a Mk 1,just needs careful setting up of the brake balance and handbrake,mine works fine.

Steve

[rlubikey]

On 23/07/2020 at 19:05, clive said:

I think"rotoflex" suspension refers more to the style rather than the actual components. At least these days. And yes, goodnessknows why Triumph used an "iffy" rubber donutrather than the CV which was used in other Triumph cars. Possibly cost? Or I did hear a whisper it helped diffs to survive.

Yes, I've been told that it helped the diffs survive too.

Cheers, Richard

[Mast 69]

Hi Guys

My first car was a 1600 Vitesse, front suspension was a good layout, back end was a shocker. 
Driving up a hill, l heard a loud clonk, when l reached the crest the brake pedal hit the carpet. I had to stall to stop. 
The bolt holding the hub carrier within the vertical link had sheared on both sides, the hub carrier twisted within the vertical link and the flexible brake hose wrapped itself around the drive shaft, instant loss of fluid. First mistake, brake lines should not be located in proximity of revolving shafts. Likewise the handbrake cable had wrapped itself around the driveshaft. Great no brakes. The bolt that had sheared takes all the acceleration/braking stresses. It’s supposed to turn within the steel bush, but lack of grease by Canley employees, water ingress due to poor sealing caused it to seize. Lots on the forum re leaf springs, but that 10mm bolt could be a life changer and for that reason would never buy a Triumph with that method of hub carrier support. Whilst carrying out the repairs, l inverted the third leaf on the spring to achieve negative camber, it made the suspension 100% better on a layout that was 200% bad. The Mk2 GT6 set up was far superior, better located, but lower wishbone far too heavy, unsprung weight and all that. A tip from Triumph dealers, when replacing the rotoflex coupling, remove the strap, place in hot water, then lever it over the yoke on the half shaft without removing it from the hub carrier and fingers crossed the rubber doesn’t tear.

Happy memories

[NonMember]

So you've come on here, for your first post, to misquote a boring bit of "pub wisdom" and exaggerate it based on erroneous claims supported by an incident of an extremely rare terminal failure. How sad.

If a critical component of the suspension on a Ferrari fails terminally due to rust and neglect, it will result in a dangerous situation. But you're attacking the engineers at Triumph for something that can't be blamed on them.

[johny]

That description of the action of the rear trunnion bolt isnt quite right. The bolt that goes across the upright is supposed to clamp the steel sleeve it fits in tight as the sleeve is slightly wider than the hub carrier. There shouldnt be any rotation of these parts so grease would just be for corrosion protection while its the top hat plastic bushes held in the hub carrier that turn on the outside of the sleeve. These being plastic dont need lubrication although again its not bad practice to put some grease on them.

Due to the location corrosion can be a problem with the bolts but usually as the bushes need replacing quite frequently this is found long before it becomes dangerous. The other possibility is that bolts of the wrong type get used and they dont have the strength to withstand the correct tightening torque....  

[68vitesse]

10mm bolt? what was that doing on your Triumph undersized by at least 10%, had correct sized bolt seized in hub but never had one break unlike a front vertical link.

To easy to blame "bad design" instead of bad maintenance, as an aside the Triumph 1500 FWD used the same rotaflex as Mk2 Vitesse and some GT6's.

Regards

Paul

[Pete Lewis]

2 hours ago, johny said:

That description of the action of the rear trunnion bolt isnt quite right.

spot on Jonny    agree fully with your answer   

Pete

 

[JohnD]

In addition to the above uses, Rotaflex doughnuts were used for many years in Formula Ford racecars.  Not so shabby, eh?

[Wagger]

Nearly all big engined BMW's used a six hole donut in the propshaft. It lasts for ages, as did the first ones on my 1500 FWD Triumph. It is the after market inferior stuff that causes problems, even on BMW's. Probably cannot find 'Original' parts now for the Triumphs, they would be very old rubber. Would you use an 'Unused' 1970's tyre?

As PeteL states, drive shafts should never be swapped side to side due to the formation of Helical Torsion in the grain structure after a few years. That steel is good in tension, but poor in shear strength. If swapped over, they experience shear and break.

It is impossible to know which side they came from if they are in a pile of bits. Experts may be able to use 'Heat Treatment' but that is a very specialised procedure.

[JohnD]

Wise words, Wagger!    And you may like to consider them about another rubber Triumph component, the crank damper pulley.

Triumph was unusual in building straight six engines for general market cars - the only other example was the MGC , and that wasn't a great success.   'Luxury' manufacturers produced sixes, because they are the best balanced engine you can have, so less "Noise Vibration and Harshness", and one of the first, Lanchester, in 1920 put a crank damper on his engines, because the long crankshaft brought resonances down into the useable rev range.   Without such a damper, the long crank is more prone to torsional vibration damage and failure.

Lanchester's was a complex, multiplate, oil filled design, but by Triumph's time, the viscous rubber damper had been invented.   Cheap and easy to build, no wonder they chose it, and almost all  moderns have them today.     But moderns use advanced 'elastomers', while the rubber in Triumph's crank dampers was not really different from tyre rubber.    Today, all the original dampers are at least fifty years old - would you use fifty year old tyres?   

In the heat and oily atmosphere of the engine bay, the rubber in these dampers has deteriorated, gone stiff, no longer viscous  and providing no damper t the crank, and in some cases the rubber has lost adhesion to the metal parts.      As they bear the crank timing marks this makes them a nonsense, and in a few cases they come apart entirely

If you ever wish to time your Triumph six cylinder, I suggest that you check the TDC positions by some other means before relying on the crank pulley marks!

OR, send me the pulley and I can test it on my instrumented engine rig, and report on its function .

JOhn

[Mark B]

I've changed the rotoflex couplings on my mk2 gt6 4 times in twenty years, but less than 20,000 miles covered in that time. What helps to kill them is not moving the car for long periods of time, their under tension and will start to tear from the metal deviders. I've only ever managed to find repro versions, and in my experience they just don't last. My first rotoflex Vitesse had metalastic versions that lasted for years. I think the technologies/ materials used back in the day have been lost in time. Next time I'll go CV.

I have used 50 year old NOS rubber in the form of track rod end boots, after the new repro ones disintigrate before I even had chance to roll the rebuilt rolling chassis out of the garage. I also bought NOS door check rubbers after the repro ones started to crumble away within 18 months.  The NOS rubber looks and feels like new. I would think twice about 50 year old safety critical parts. 

[Ian Foster]

3 hours ago, JohnD said:

Today, all the original dampers are at least fifty years old

John

I know you have done a lot of testing on this subject and posted previously.

Have you considered the practicality and cost of refurbishing dampers, or is the only option in the case of failure to find a better used one?

Luckily a have a 2L car where any slip does not affect the timing marks.

Ian

[Pete Lewis]

if you want a good quality rotsflex i suggest you talk  to Robush  always helpfull they make most of their components in the UK 

ROTOFLEX COUPLING - Robush Ltd

Pete

[Mark B]

Thanks Pete, I'll have a look.

[JohnD]

6 hours ago, Ian Foster said:

John

I know you have done a lot of testing on this subject and posted previously.

Have you considered the practicality and cost of refurbishing dampers, or is the only option in the case of failure to find a better used one?

Luckily a have a 2L car where any slip does not affect the timing marks.

Ian

Ian,

Triumph dealers, eg Rimmer's, sell rebuilt damper pulleys.  Not cheap!   There are workshops that offer to rebuild them for you, but as an engineer I don't want to be recommending any, else my testing service could be seen as biased.

Loss of function can occur long before slippage, or even detachment happens. I can test your damper, tell you if it's working, even before it loses the timing!

John

 

 

[johny]

Interesting, are there any detectable symptoms John - I mean before slippage occurs? 

[Wagger]

22 hours ago, JohnD said:

Wise words, Wagger!    And you may like to consider them about another rubber Triumph component, the crank damper pulley.

Triumph was unusual in building straight six engines for general market cars - the only other example was the MGC , and that wasn't a great success.   'Luxury' manufacturers produced sixes, because they are the best balanced engine you can have, so less "Noise Vibration and Harshness", and one of the first, Lanchester, in 1920 put a crank damper on his engines, because the long crankshaft brought resonances down into the useable rev range.   Without such a damper, the long crank is more prone to torsional vibration damage and failure.

Lanchester's was a complex, multiplate, oil filled design, but by Triumph's time, the viscous rubber damper had been invented.   Cheap and easy to build, no wonder they chose it, and almost all  moderns have them today.     But moderns use advanced 'elastomers', while the rubber in Triumph's crank dampers was not really different from tyre rubber.    Today, all the original dampers are at least fifty years old - would you use fifty year old tyres?   

In the heat and oily atmosphere of the engine bay, the rubber in these dampers has deteriorated, gone stiff, no longer viscous  and providing no damper t the crank, and in some cases the rubber has lost adhesion to the metal parts.      As they bear the crank timing marks this makes them a nonsense, and in a few cases they come apart entirely

If you ever wish to time your Triumph six cylinder, I suggest that you check the TDC positions by some other means before relying on the crank pulley marks!

OR, send me the pulley and I can test it on my instrumented engine rig, and report on its function .

JOhn

That was very interesting John. My 2.5 TC engine has a pulley similar to the typr shown. According to the strobe, it was running retarded by 20 degrees. I ignored the marks, checked TDC via plug holes, set the Dizzy, then by ear when running, I;ll take a picture sometime and send yo you so that you can tell me which pulley I have. I suspected that PO's fitted the pulley without a key.