Wheel Came Off

[pharriso]

You said “we” several times..

Was your passenger female? I’d love to know their reaction? Have they been back in the car ??

[vstibbard]

there appears to be little fretting on the taper, which points more to the nut having been overtightened in the past. that combined with wider rims and sticky rubber.... off it goes!

+1 for the TTR shafts and hubs, make sure you lap them in well.

Cheers

V

[MartinH]

The car was recovered by a mechanically sympathetic garage and will stay with them until we finish our holiday in another weeks time. It will then be returned to our house in Normandy where I can fix it. So no UK quarantine issues.

Its looking like some TTR billet shafts that will mate with the CV joints on the car. Thanks for the lapping tip.

I don't know what torque the spinners are fixed at, I have only ever done it by feel (as much as can be felt with a big hammer). I can't remember what torque the hub nut was fixed at but it would have been as per the workshop manual. I have seen some posts that suggest more than the reccomended torque should be used???? Up to 200lb/ft

The wheels are only 5J and the tyres are to original spec 155/13 but with the sticky compound on the XAS.

Yes a female passenger who was initially quite shocked (understandably), more from the noise of the hub scraping along the road than anything else. She recovered very quickly and focussed on being impatient with the recovery process, she is French so impatient is a massive understatement . It is amazing how stable the car was on 3 wheels.

[512BB]

I am interested to know what happened after the incident, to the car and to your holiday Martin.

We holiday in France once a year in one old Lotus or another, and fortunately have never had to call the emergency services. But I often wonder what would happen if we needed to, and if the car was not repairable in France, what would happen to our holiday, re transport.

I suppose I should find that out before such an event ever happens.........doh

Do tell what happened to you.

Leslie

[MartinH]

@ Leslie

I now live in France for most of the year only returning to the UK when business requires it. Like you we take trips across France on a regular basis for such events as the le Mans classic and the track days that Club Lotus France organise. Have also been to Italy to follow the Mille Miglia (a great trip). I have always had european breakdown cover via my UK insurance and have had to use it on 3 occaisions over the last 20 years.

Head gasket failure recovered to UK
In board drive shaft recovered to Normandy
This latest one recovered to Normandy.

This time we continued to our holiday destination via train and taxi all paid for or recoverable from the insurance company. They would also repatriate the car to the UK if I wanted and pay for our travel back to the UK if required. This time we are with family from my wifes side (all French) so will take a lift back to Normandy with them.

In the past we have had a hire car organised to continue the trip while the Lotus went in the other direction.
Despite the risk of driving a tuned 53 year old car around France sometimes in very hot weather we will continue to do it simply because it is so enjoyable and I still get a buzz out of taking it apart to fix the latest problem.
We used to have a 911 but sold it as we always took the Lotus for trips as the smile factor is greater.

I hope your run of good fortune with no breakdowns continues. (maybe you prepare your car better than me??)

Martin

[Elanman99]

Must have been loose on the taper for some time! the nut does not hold the wheel on.

I endorse that comment.

The nut and washer do have a secondary function of retaining the hub to the shaft (so stop the wheel falling off) but their main purpose is to hold the two halves of the taper locked together. With well mating tapered surfaces the hub and shaft are locked together effectively becoming one piece of metal. Bending and other forces from the wheel to the shaft should not impart any more tension on the thread than it had when it was assembled. The threaded portion of the shaft should not normally see any bending forces leading to fatigue.

It seems to me that there must be signs of fretting or other movement on the taper surfaces and the keyway groove and a picture or two would be useful.

Ian

[Donels]

I agree. Thinking about it, the wheel spinner torque should be reacted by the hub through the taper so should not play any part in the failure. Similarly the wheel torque should be through the taper, so the threads should only carry the tensile load from the nut.
That it failed on acceleration suggests movement in the hub. That should only occur if the nut torque was low. CheckIng the hub for signs of movement would show low torque, no movement would suggest a too high torque and eventual yielding.
Hope this makes sense!

[elangtv2000]

Very sorry you had that experience. I had an stock inner shaft fail on my S4 shortly after buying the car, but it simply stopped going down the road. Glad you didn't have much worse damage!

I installed TTR outer shafts on both my Elans years ago. They are excellently machined and finished, and appear to be much stronger than the original Lotus shafts. I installed CV axles at the same time. The TTR shafts do fit standard hubs (not just 26R).

[nmauduit]

I am assuming this is just metal fatigue brought on by a combination of age and some level of aggressive driving on the track days we do. The car has a 145 BHP 1700 twin cam, and I use Michelin XAS tyres which are very sticky when hot.

Tony Thompson has a suggestion sheet for modifying an elan to better cope with increased stress

https://www.tonythompsonracing.co.uk/wo ... your-elan/

no affiliation, but it does make sense to me to put in perspective the cost of some modifications for track days and sticky tires with potential damages that can result of a use a given car is no necessarily up to.

[Bigbaldybloke]

I suspect failure to lap the hub to the shaft on the failed one may well have been significant in why it failed, only the nut would have been holding the hub on, not the fit on the taper. If it had been well lapped in it would probably have failed at the inboard end of the taper. As pointed out by Rohan, this is more common and would leave the tapered part of the shaft still jammed into the hub. Good job you had a fire extinguisher to hand in the car and that it worked!

[alan.barker]

If you want to fit CVs and fit stronger output shafts on Diff then the CVs from the USA must be the best. More distance between CVs so less Angle deflextion.
Also TTR for Shafts at Chapman Strut.
Alan

[h20hamelan]

Another thought, though maybe I missed it.
Torque to yield.
No mater how careful some people are, when daft garages over-torque wheel nuts...wheels fall off because bolts break at mating surfaces of wheel.
So when one whacks spinner to unknown torque, most likely it stretches hub/bolt at same location. When you hit a pot hole...when you use the same hub/bolt for 50+ years. Important to follow the engineers report (did Lotus recognize replacement of hubs/bolts as a replacement item at __,____miles?)

I suspect this is something we all need to consider.

[Bigbaldybloke]

Confused on previous comment, however tight you torque the spinner it has no direct connection to the spindle, only the hub. The nut securing the hub to the spindle would normally only be tightened once when fitting the hub to the spindle, and the torque setting is in the manual.
Agree over tightening normal wheel nuts onto the studs can be a problem with untrained wheel fitters, but that is very different to Lotus knock on wheels.

[rgh0]

Overtime the hub tends to bell out on the shaft taper, loosing contact at each end. This is more significant with the original bolt on hubs which were not as rigid as the Knock On design. It also occurs more quickly with sticky tyres putting more side loads on the wheels.

If the hub starts rocking on the shaft then it will be putting oscillating loads on the hub nut and eventually lead to fatigue cracking of the shaft thread and the sort of failure experience. Usually though the loose shaft shears the key and spins in the hub first and you lose drive before you lose the wheel

cheers
Rohan

[74Twincam]

Very sad to hear of the incident, but bravo for continuing on with your holiday...!

I’m in the process of installing hubs to brand new TTR shafts, and am currently performing the lapping step mentioned here (the parts are excellent).

Any tips for the lapping procedure itself? How do I know when I’ve done it sufficiently? I’m using valve grinding compound and have worked them several times each, but is there a finish on the surface I should be looking to achieve, or apply toolmaker’s blue to check my progress? TTR instructions also mention to heat the hub prior to installation as well.

Given the above I just want to do this properly...

(Also, sounds like you have great insurance coverage!)