Even the good stuff breaks

[mark]

I was at CMP this past weekend with THSSC and Triangle Z. Great bunch of guys. A very fun event. The car was doing OK considering the hot greasy track. I was on track at speed and heard a pop and then a big puff of smoke from the right rear. The smoke was cause by the rear tire hitting the fiberglass flair. Great, more body work.

 

I do inspect the car on a lift and I inspect the control arm welds with light and magnification. I don't think I would have caught this even with disassenbly and inspection.

 

The rear inboard attachment point broken

 

http://forums.hybridz.org/uploads/1276690252/med_gallery_787_732_2565090.jpg

 

http://forums.hybridz.org/uploads/1276690252/med_gallery_787_732_1654562.jpg

 

And this is what will replace the rear control arms.

 

http://forums.hybridz.org/uploads/1276690252/med_gallery_787_732_589558.jpg

[jgkurz]

Scary stuff. I would like adj rear arms but the debate on HBZ have always made me weary. Arizona Z also has the billet aluminum control arms with heim joints that might be worth a look.

 

Who makes the new arms in your bottom picture?

[Montezuma]

This is a rare problem with that part? I have brand new set sitting in the garage waiting to go a project. I have never seen a broken one before.

[JMortensen]

viperredls1z broke one of those arms, and then if I recall he fixed it and broke it again. The similarities between Dave's car and Mark's are that they both have big power and big wheels and tires. I don't think I've heard of a "more normal" Z breaking one of the AZC arms.

 

Mark, it seems like the problem is the stress risers created by threading a relatively thin walled tube and then putting a bending moment on it with a pivot point essentially right at the threaded area. On my arms I used a .120 wall tube and then inserted a threaded tube end into the thicker wall tube, so that might be an idea for you. You might also look into what Terry did with his arms, as I seem to recall that he had studs sticking out of the tube and nuts on the end. If you do it like he did you can get heims jointed inner pivots as well. Might be able to mod what you have there.

 

http://www.fototime....B95FCD9B5}&nt=a

Edited June 26, 2010 by JMortensen

[jt1]

Is that the same one you broke the stub axle on?

 

jt

[mark]

Stub axel was broken on the other side.

[mark]

Anybody notice the rust inside the tube? Is it possible this was a contributing factor?

[mark]

The new arms are arizona z arms as well.

[JMortensen]

Re: rust, there was a bit of discussion in that other thread, which I've located for you: http://forums.hybridz.org/index.php?showtopic=57264

[DrSideways]

On formula cars with significantly less weight but same materials, the control arms and other suspension components are magnafluxed at least once a year. With more weight and a curb or two...

 

In the "Prepare To Win" by Carroll Smith he would only use Krylon spray pain on them for easier strip down and checking between each race weekend.

 

Alan

[jt1]

After some thought....and a couple of 95 deg Sat afternoon beers....I have concluded:

 

Mark's car has too much horsepower!!!!!

 

Actually, I'm wondering if an external weld on an internally threaded tube is a good idea.

 

Mark, can you post a good close up of the ends of the broken tube?

 

jt

[JMortensen]

Actually, I'm wondering if an external weld on an internally threaded tube is a good idea.

Very interesting point. I don't think it's that exactly though; just look at all of the arms that are made with threaded tube ends, and failure at the weld isn't something that I've seen a lot of.. I could see it being a combo of thin wall with thread cutting and then maybe the welding on the outside and the resultant heat affected zone. I wonder if those arms are heat treated, and if not if having them heat treated would prevent another failure. Here are some links on fabrication and heat treating. The second link points out that standard DOM does not need heat treating after welding, and shows a HAZ failure which occurred 4-6 mm from the weld.

 

http://www.netwelding.com/Heat_Treated_4130.htm

http://www.formulastudent.de/public-relations/fsg-news/news-details/article/pats-column-space-frame-chassis/

[mark]

Jon, THanks for the info and links. Alan, I appreciate the insight. JT, here is the pic you asked for.

 

Thanks guys.

 

http://forums.hybridz.org/uploads/1276690252/med_gallery_787_732_2534735.jpg

[jt1]

Not what I expected to see. My preconceived notion was that it started at the threads, but that one started from the OD and worked it's way in. Got to think that one over a while.

 

jt

[DrSideways]

Jon, THanks for the info and links. Alan, I appreciate the insight. JT, here is the pic you asked for.

 

Thanks guys.

 

http://forums.hybridz.org/uploads/1276690252/med_gallery_787_732_2534735.jpg

 

Glad to throw some light on the deal. It is so easy to overlook stuff that is "working" when there is generally a list of stuff that isn't.

 

Although it is more work, a duty cycle type of operation can help overcome this type of issue. A lot of formula guys also use an hour meter to help. The one thing that doesn't count is trailer time. I have seen cars have all kinds of loose stuff after long tow trips.

 

If this was easy everyone would do it. Just think of the mess that would be:)

 

Alan

[mark]

 

 

If this was easy everyone would do it. Just think of the mess that would be:)

 

Alan

 

 

So true!

[Mayolives]

Glad to throw some light on the deal. It is so easy to overlook stuff that is "working" when there is generally a list of stuff that isn't.

 

QUOTE: I have seen cars have all kinds of loose stuff after long tow trips.

 

Alan,

Christ, Now I will need to worry about what is wearing out on the Red Bird, while I'm hauling it down to road.

[DrSideways]

Alan,

Christ, Now I will need to worry about what is wearing out on the Red Bird, while I'm hauling it down to road.

 

 

Afraid so. It isn't as bad when you are going 2-3 hours. Some roads are better than other too.

 

Two days @ 10 hours each and I would want to leave time to nut and bolt things. No different than running my car on a Friday & Saturday. Sunday morning is spent flushing the brake fluid and tightening things up.

 

I also ran my shocks back to soft and tied the car down using wheel bonnets.

 

John C. may have something to say about tie downs and shock wear/damage. Then we would be getting off track a bit, but good to cover none the less.

 

 

Alan

[260DET]

Towing tie downs are a bit of a hot topic around my way at the moment, the weight of opinion seems to favour body tie down rather than wheel. The theory is that body tie downs restrain the car from bouncing around much on its suspension.

[JMortensen]

I think that's the general consensus Richard. I recall Coffey telling the story of a BMW that was on a trailer with the wheels tied down and went through a road like Pearblossom Hwy or something (short rolling hills as far as the eye can see) and when they got to the destination the strut had punched through the tower. I think the idea is that the trailer oscillates and the car oscillates, and if those two oscillations line up perfectly you get a pretty sharp impact on the chassis.

 

We're getting into thread jack territory, but I got some tow hooks from www.zccjdm.com and my plan is to modify and strengthen them and then to tie the car down on the trailer directly to the tow hooks. Added benefit is that you don't have to climb around under the car to hook to suspension. Suspension is probably stronger than a tow hook but still leaves the chassis less restricted.

 

Maybe Coffey will retell the story and/or break this issue out into another thread.