Another De Dion Tube failure

[Michael Murphy]

While reinstalling one of the rear dampers I discovered that my De Dion tube has cracked around the weld at the point where the lower mounting lug is welded to the tube. There is a history of these failures on blatchat.

The crack was obscured by the damper and was hard to see, and I probably would not have seen it at all had I not removed the damper.

I began running ACB10s in the middle of last season and had maybe five weekends on them. The stresses are significantly greater with those tires than on street rubber, so if you are running very sticky tires hard on the track, pay close attention to your suspension (and everything else for that matter). I checked for cracks several times last season... was not expecting this.

Ugh.

[magnusfeuer]

A good summary of the failures is given at blatchat:
http://blatchat.com/T.asp?id=94283

I will check my tube as I install my Avo damper kit this week.

/Magnus F.

[moosetestbestanden]

Ouch.

I've followed that particular thread pretty closely. Imo, you should contact CC and CCUSA r.e. remedies.

Edited to add: Post pics if possible.

[Elv15]

year?

Michael,

What year is your car? I was under the impression that Caterham had fixed this in the newer model years...

[Michael Murphy]

It's a 2000 year construction. The blatchat thread shows that there have been a number of evolutions of the de dion tube. Mine is not the latest version. I have seen photos of a more recent version of the tube which show an additional strengthening tab welded around the mounting lug. Looks like it would prevent a similar failure. So maybe Caterham have fixed the problem in more recent years.

[moosetestbestanden]

I began running ACB10s in the middle of last season and had maybe five weekends on them. The stresses are significantly greater with those tires than on street rubber

Depending on what street tires and what size I think. The CR500s in a 13 are pretty soft as well. What tires were you running before? Did you change from a 15 or anything else to a 13 at the same time? Failures of this nature are from fatigue and result from acumulative stresses. Mileage incurred prior to any change of rubber, particularly on rough roads typical in Ca., would certainly have had something to do w/ the occurance of failure. So is the fact that you're driving on the track at 10/10ths most all of the time as well (or so my spies tell me).

Next question: Did you change the DeDion ears when you switched to the ACB10s? While perhaps minimally a factor, the change in camber between a radial tire and the Xply ACB10s may have contributed to, uh, assist the mode of failure.

Please know that I'm not excusing the failure here. The design is clearly lame.

As I understand the problem, Tom is correct r.e. the design change. Make sure you get a new one for sure. And, imho, switch the ears too, if you haven't already.

[Rod]

Year or photo of improved tube

Does anyone know the year the tube was fixed, or does anyone have a photo of the improved tube?

I am worried now that I am running CR500 15 inch for daly use and I just go a set of 13 inch ACB10s.

[magnusfeuer]

Ok. I was fitting my new suspension kit from Freestyle motorsports and took a good look at my 2002 SV (#39) De Dion tube.

It seems like it has an uppgraded version 3 tube (according to the blatchat post referenced earlier in this discussion), with a reinforced damper mount boss while also retaining the second hole that runs through the tube itself (pointing it out as a version 3 tube).

I found no cracks or other problems on it when I inspected it.

See pics and compare them to the failed version 3 tube in the blatchat summary: http://uk.pg.photos.yahoo.com/ph/ima.../ph//my_photos

I strongly recommend everyone to visually inspect their tubes prior to Button Willows since this track apparently is faster than Willow Springs, with additional risks.
/Magnus F.

[Doug Liedblad]

Magnus

That's the same way mine was done. Standard track, built in Sept 2001

M. Murphy's doesn't have the tab.

I forwarded this info and a link to Ian, he is the person that started the blatchat thread and is still interested in collecting information on the various versions of the DeDion tube.

Apparently our tubes are between the older style, with most of the failures, and the newer heavier wall tubes now being fitted.

Doug

[magnusfeuer]

I spoke to [email protected] today, and he told me that the tube that Doug and I have are reinforced and manufactured with a different process. No problems have been reported with these.

I believe that the telltale sign is the little reinforcement plate that is welded to the underslung boss where the damper is mounted. As shown in Doug's and my pictures.

If you don't have it, take a close look at your De-Dion tube. That means *you* Brad.

A new tube (of the new design) is $709, which may seem like a lot, but is probably cheaper than a suspension failure on the track.


/Magnus F.

[slomove]

A new tube (of the new design) is $709, which may seem like a lot, but is probably cheaper than a suspension failure on the track.
/Magnus F.

If it is not broken yet, why not take it to a skilled TIG welder and have it reinforced. I have had similar jobs done for $30.
That little plate or similar is easy enough to make. Looking at Michaels crack....I mean the crack of his tube, specifically the DeDion tube, I don't need to be a mechanical wizard to see that this failure is designed in.

Gert

[magnusfeuer]

According to Caterham USA, reinforcing the mount will not help since it is the tube itself that is too weak. You will only push the break point to where the reinforcements stop.

Please note that this mostly seems to happen to cars running slicks and/or extensive track times.

/Magnus F.

[Clark]

DeDion - A LowFlying Interview

Like everyone else, I'll take a good look at my DeDion tube this coming weekend. I've got quite a few track weekends on our Seven, but always have run street tires - Hoping for the best (45,000 miles and accumulating!). Despite the Caterham reputation for DeDion tube cracks, it would be interesting to learn more about the history of Michael's car and the incidents (off-track/road excursions, pot-holes, etc.) it has seen. Many Sevens take considerable punishment, including the use of slicks, without this failure. In a LowFlying interview several years ago, Jez Coates was asked about this issue. In reply, he stated that the failure had only been observed in race cars (aren't they all?), and that every owner should check things over carefully prior to any track event; especially hubs and the DeDion tube. Kind of a Mom & Apple Pie statement, but very true.

Warmest regards,

[slomove]

I may be talking bollocks here because I suppose somebody with a thin tube already tried it.....but I assume the tube thickness is not the worst problem. Of course the reinforcing bracket should be done in an intelligent way as to spread the load. For fun I did a quick FEA of the original situation vs. a tapered bracket (I do not have the proper dimensions but to show the principle). The latter reduces maximum stresses in the joints to the tube by a factor of 5-10, which would surely be sufficient. Just beefing up the tube to fix a marginal design is a poor solution.

Gert

[Rod]

2002 de Dion tube inspection

I inspected my 2002 standard track De Dion tube.

It seems like I also have a version “3.5†tube. According to the blatchat post referenced earlier in this discussion I have a hybrid of a 3 and a 4, with a reinforced damper mount boss while also retaining the original hole that runs through the tube itself.

I also found no cracks or other problems on it when I inspected it.