Wheel Came Off

[rgh0]

You can tell by the lapping paste itself and how evenly it spreads and gets ground as to how close you are getting. I then do a final check with engineers blue to verify the fit. Heating the hub should not really be needed and I have never done it on my Elan but I guess TTR may have found it helps with some race cars. Getting the hub off in the future may be more challenging than it already is if its been heat shrunk on. I do check the hub nut a couple of times in the first few hundred Km's and re-torque to the specified number and sometimes find the nut moves a little

cheers
Rohan

[74Twincam]

All good, thank you!
Cheers

[vstibbard]

I fitted the keyed TTR shafts, carefully lapped, radiused ends the keys and did not use heat when fitting them. Like Rohan, I re checked the hub nut torque over the first 500 kilometres.

V

[MartinH]

@NMAUDUIT

Thanks for sharing the TTR list of mods. Ironically I have almost every single one of these on the car except the uprated hubshafts.

The car was returned to my house this morning so I will start looking at the damage and share more photos this evening. A quick look at the underside shows the underside of the upright heavily ground away along with the underside of the brand new adjustable bottom wishbone.

Martin

[nmauduit]

@NMAUDUIT

Thanks for sharing the TTR list of mods. Ironically I have almost every single one of these on the car except the uprated hubshafts.

The car was returned to my house this morning so I will start looking at the damage and share more photos this evening. A quick look at the underside shows the underside of the upright heavily ground away along with the underside of the brand new adjustable bottom wishbone.

Martin

too bad... I hesitated when I did the restoration of my street S4 as it was low mileage and good mechanically, and eventually opted for the "upgraded" version in case I did use it for occasionnal track days, then I was glad I did, and nowadays track days are the best motivation to push me to fetch the car from where it is stored and use it. With sticky tires, It's hard not to get caught into it and it does pull quite a bit (almost 1G laterally from what my phone told me) while the street car is more than 100kg heavier than the GTS... even if I try to avoid the curbs as much as possible.

[MartinH]

Found some time to have a closer look at the damage and possible root cause of the hub shaft shearing.

Almost certainly down to a loose hub nut I think
1, The photo shows the nut to be well down the thread
2, Out of interest I checked the torque on the other side and it was below 50 lb/ft. I think the setting is 100lb/ft

The hub is heavily ground down and will need replacing.
The bottom wishbone is also scrap.

Both shafts have been off the car recently for a skim to the legs for mating up to new discs. The hub nuts and bearings are new.

Please share your thoughts

Thanks
Martin

[nmauduit]

as mentioned before, the rust on the shaft is a symptom of poor hub fit, eventually resulting in the nut being lose and in turn exerting a cyclical load on the threaded end of the shaft: as soon as the nut does not pull 100% axially, trouble is bound to happen, sooner rather than later.

If the Chapman strut holder is not leaking at the bottom of the shock, you should be able to keep it...

good luck for a smooth repair and back on the road !

[Barney]

The same happened to me back in the 80s, to everyones amazement the Lotus dealer in my intended destination (Goldblatt & Webb, Cardiff) had a bolt-on type hub for an Elan on the shelf.
Mine happened near Exeter on the A38 as it became the M5 and was probably travelling at 75-80 MPH.
The sensation of rear wheel steering was very disconcerting and caused a few moments. The wheel actually stayed more or less in place trapped by the wheel arch.
I felt very lucky there wasn't any more damage done.

Try as I might I was unable to persuade the AA operator that my wheel had fallen off due to a broken hub, so had to go through the process of an AA man turn up having been told by the operator that I probably just had a loose wheel!

[74Twincam]

In your third picture, of the end of the shaft where the nut sheared off, it seems like there’s rust along the edge as if there was a pre-existing crack at the threads... hard to tell because of the focus.

[vstibbard]

I agree there does look to be rust on part of area that sheared, the bottom of the strut looks fine, if it weeps oil, just get it welded up.

Cheers

V

[rgh0]

Its a classic fatigue crack, you can tell by the "beach" ripples on the crack surface before the last part failed in tension. The crack has been present and growing slowly for some time hence the rust.

The bottom of my rear strut looked the same as yours and I just brazed a new end plate on the cap as it had worn a hole when my hub shaft broke on the track at about 120kmh

cheers
Rohan

[Donels]

I agree with Rohan. It is a fatigue failure that seems to emanate from the thread root and then has progressed across approx 80% of the area and finally failed in overload. The thread should be in tension such that any bending stress is lower than the tensile stress, ie it won’t fail in bending. The failure indicates the tensile stress was lower than the bending stress, ie the nut was not tight enough, as you have stated.

If you count the beach marks it will tell you the number of cycles to failure, but probable getting a bit too techy here!

As the nut is also under tightened on the other side it is highly likely that the thread is also cracked. If not it will be fatigue damaged and have a reduced life, so simply tightening to the correct torque is not the answer. It should be replaced.

If the taper is not accurately seated then it can later 'bed in' reducing the torque loading and thread tension. Best to retorque the nut after 100 miles or so.

[MartinH]

Thanks to all for the feed back and guidance.

I am ordering TTR billet shafts, extra strength hubs, bottom wishbone, bearings and will either repair or replace the upright.
Will make sure the hubs are well lapped to the shafts.
Will make sure hub nuts are torqued correctly and then check frequently during the first few runs out.

Thanks
Martin

[USA64]

I'm learning things here that I hope I never need to know. How would it be possible to spot the crack before failure?

[Donels]

I think you’re unlikely to get cracks if the nuts are torqued up correctly, and wheels coming off is very rare. However, if you really want the check you need to get a None Destructive crack detection Test (NDT).

This is standard industry practice but you can probably buy the chemicals to do yourself. The process is to clean and dry the area, then apply a dye penetrant, then apply a developer. The penetrant enters the crack and then shows the crack when the developer is applied. No indication means no crack. I’m sure someone could do this for you.