De Dion Fractures?

[ISmall]

Last Saturday I went for a spin (literally!) on a much frequented route between Westerham and Edenbridge. Many good bends and although it was a little slippery, not too bad. HOWEVER, as I entered the final DRY straight in 3rd at about 50mph, put my foot down and the back end broke away completely, so dramatically that I thought I'd had a blow out. Several opposite locks and heart fluctuations later, I ground to a halt with my fingers embedded in my MoMo. Having got out of the car, neither tyre was deflated, but it was obvious that the offside rear was at the front of the wheel arch and the nearside was at the back. Amazingly, no damage to the car apart from a small scuff on one alloy as I glanced off a kerb almost at a standstill. If something had been coming the other way, we would both have been exchanging insurance details in a hospital ward.

The car is now back in my garage thanks to AA relay, but the question remains- WHAT HAPPENED?? Red Line will inspect it tomorrow and the factory suggested that the symptoms suggest a De Dion tube fracture. Perhaps a bush is knackered? Has anyone else experienced this particular life-threatener in the past. If so, what were the conditions / outcome of the event. I've got a 1996 1.6K SS with 12000 miles on it. Without a hint of exaggeration, I could have met my maker if the problem had occurred 30 seconds earlier.

[Graham Sewell]

I thought that Caterham had solved this problem. IIRC this used to be quite common on early DeDions (late '80s) if they had been used on a track and taken over the curbs and rumble strips.

 

I'm glad everything is OK, in as much as no-one was injured.

 

Cheers,

 

Graham

 

P.S. Which roads around Edenbridge (not past the watermill by chance???)

[ISmall]

I'm not actually sure what the road number is, but I ended up calling the AA from the Royal Oak pub down the hill towards Edenbridge on the B2026 I think. The road in question runs from there to Westerham through lots of trees. Great road, but not so good when faced with a departure into the green stuff!

There's no record of accident damage on the car at any time and Red Line have known it since registration. I'll post their findings on the web once I know them myself.

[Simos]

Yeah, been there done that, got the de-dion tube sticker.

 

Booted mine out of a corner up a hill in second and then engaged in a period of "radical steering" before coming to a halt.

 

After getting out and seeing that I now had two inches of toe-in on each wheel... I called green flag !

 

About 20% of the circumference of the tube was still intact the rest had split wide open giving an interesting crabwise driving position (full lock to go straight when I pulled up).

 

Mine is a 91, I now have the heavier de-dion tube. Interestingly where it split looked to have been witnessed by the clips holding the fuel tank introducing a failure point which I had not noticed. They stick out far enough to hit the tube in full travel which isn't apparent when you build and not noticeable once the boot floor is in place, nice design Caterham. They're now filed off and bent up so they don't touch.

 

As a 96 you should have the heavier tube and from your description sounds like locating link failure as opposed to tube failure.

 

Now think about what Jacque was thinking when his rear suspension failed entering Eau Rouge at 180ish...

[R2D2]

It might be interesting to try to model the arrangement with a good Finite Element Analysis package and to try to estimate the fatigue loading.

 

I have a NASTRAN package if anyone has a detailed drawing of the tube.

[V7 SLR]

Chris,

 

I've actually got a spare De Dion in the garage if anyone wants to use it to create a model from.

 

Nig

[Pierre Gillet]

Actually seems that it happened to me also on my 1997 1.6K two years ago causing a brutal 90 degree left turn. It was immediately after a 90 degree corner taken in 2nd gear. I ended up in a muddy field.It was caused by the screw attaching the left radius arm to the chassis becoming loose and finally falling down. I understand that Caterham has modified the design by adding a nut in the cockpit, the screw going through the chassis tube rather than the chassis being threaded.

I was able to reach my home only 3 km distant as you describe it ...like a crab!

 

Pierre

[CHRIS CLARK]

My '93 car was re-chassised in '96 due to a past owners desire to go ploughing in Norfolk.

 

"Your mission Jim, if you decide to take it is to jack up the car this weekend and check it all out. This car could self destruct in 5 seconds"

[Richard Ince]

I understand that De Dion cracking is still a common fault on track cars. It is recommended to have the tubes crack tested at the end of the season.

I believe that a revised De Dion tube will be available in the New Year as the previous improvements have not been 100% successful.

 

[ISmall]

Dear All

Many thanks for your replies. It's reassuring (??!) that others have experienced this particular nightmare. All of the suggestions seem reasonable but I'll find out the real reason in the next 24 hours. Interesting that most of your circumstances were similar, putting the foot down coming out of a bend when I suppose the stress on the axle is at it's greatest. I suspect that the damage is on the left hand side, as I was leaving a right hander onto a straight. You can put my mind at ease even further if you can assure me that your cars were 100% after the repairs. I must say that this major failure has put a large dent in my confidence in the car. If this had happened on the Caterham by-pass on full volume, I'd be a gonner.

[EFA]

Ian,

 

1. You want to watch the Caterham bypass for unmarked Vaux Omega's and Volvo V70 T5's. All are fitted with video and I am sure that unless you can get off the bypass and hide up in Woldingham or somewhere(Keiths garage is apparently big enough..) Also a qick swing up timber lane and ito Redline got them off my tail a couple of months ago!!

 

Regarding the DiDion tubes, they crack where the triangulation for the lower centre bush mounts. There are 3 versions of the tube, and hey are a follows:

 

Dimensions are guestimate!!

 

1991 - 1993 Bilstein - narrow triangulation (say about 8") thin wall tube.

1993 - 1994 Bilstein - narrow triangulation (say about 8") thick wall tube.

 

In 1994 Caterham redesgned the tube so the triangulation was much wide (about 18") to spread the twisting moment along the main tube. I have not seen the wider version crack! (In fact the DiDion tubes now tend to bend rather than crack.) To fit this tube however, the back end diagnols in the chassis need to be moved (pre '94 chassis only)

 

You can identify the year of your chassis spec by reading off the dirves side upper seat belt bracket. It will say AM94 1835 for example where:

 

AM = Arch Motors

94 = 1994

1835 = Unique chassis number for that chassis type.

 

With 280 horse and 186ft/lbs going through my diff (which bends the std diff mountings) I have had no problems with the '94 on di dion tube.

 

Finally, its worth checking you don't have a cracked di dion ear. The ears do crack, especially the ones with more neg camber as they are thinner.

 

ALSO, IF YOU ADJUST THE CAMBER WITH WASHERS between the ears and the tubes, the fact that you do not have the loads evenly spread over two mated surfaces is a definate and regular cause of broken ears.

 

Regarding Pierres car, I would check to see if the original DI Dion tube on your car was a pre-94 spec. It would not be the first time something like this happened - my original Quaife gearbox supplied "new" in my 1993 CKD HPC kit contained a shaft which quaife discontinued in 1989!!

 

 

The Royal Oak is at Four Elms and makes a great pub.

 

Ian - Do you live near Edenbridge?? This is in the heart of the Norf Kent hack area - if you fancy a blast some time let me know! (I'm in Felbridge, just the other side of Lingfield.)

 

So bottom line is that the 94 on Di Dion tube is generally a safe bet.

 

AW

 

 

 

 

[ISmall]

Arnie,

 

Thanks for this full description. I'll look at the chassis year when I get home, but the fact that it was registered in July 96 should mean that it's a later model. I actually live in Purley Oaks and tend to head either down the A22 or through Westerham to other roads in Kent etc. I have a mate who lives in Lullenden (near Lingfield) and know the roads pretty well. Often in the Old Cage for a tactical livener on the odd Sunday.