johnc Posted June 28, 2010 Share Posted June 28, 2010 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. This is the 7th broken AZC rear LCA that I've seen of that style. I've repaired 3. It doesn't take a lot of power to break those, just a lot of lateral load and some curb hopping. Quote Link to comment Share on other sites More sharing options...
mark Posted June 28, 2010 Author Share Posted June 28, 2010 I believe JT has this figured out. It's engineering geeky stuff to quote John. I'll let him explain. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 28, 2010 Share Posted June 28, 2010 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. Maybe Coffey will retell the story and/or break this issue out into another thread. Driving north out of Baker on the way to Pahrump (Spring Mountain Motorsports Park) I was behind a fellow competitor with a BMW M3 tied down to his trailer by the wheels. There are whoop-de-doos on that road and an oscillation developed as Jon mentioned. The sprung weight just started moving hard through its entire rage of travel front and rear for about 5 cycles. At the track the driver found both rear shocks were blown with oil everywhere and the right front shock had punched through the monoball on the Ground Control camber plate. Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 28, 2010 Share Posted June 28, 2010 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. On a 240 be very careful hooking into the rear suspension. When I started making some toe-link control arms I found a number of these had been bent from being hooked to and cranked down. The 280 arms are much stronger but after seeing this I built toe hooks like Jon mentioned to be able to quickly tie the car down. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 28, 2010 Share Posted June 28, 2010 Got pics of that Cary? I'd like to see if my plans match what you've actually implemented. Quote Link to comment Share on other sites More sharing options...
DrSideways Posted June 28, 2010 Share Posted June 28, 2010 This is the 7th broken AZC rear LCA that I've seen of that style. I've repaired 3. It doesn't take a lot of power to break those, just a lot of lateral load and some curb hopping. Do you have a better mouse trap? Would normalizing the welds help? I don't think Dave or his welder does this. I asked one time. Alan Quote Link to comment Share on other sites More sharing options...
johnc Posted June 28, 2010 Share Posted June 28, 2010 Do you have a better mouse trap? Would normalizing the welds help? I don't think Dave or his welder does this. I asked one time. Alan I do not have a better moustrap and generally question the need for these aftermarket rear LCAs for 90% of the folks who install them. For those that do need (want) them, I recommend the arms from Modern Motorsports. There is no need to normalize welds on tubing under .125" in wall thickness. That's an old practice that is not called out by anyone, anywhere in a current welding spec. Even the NHRA (the last bastion of normalizing in CroMo) has backed off that requirement. What's most critical (assuming proper design and material selection) is proper fit up before welding (no gaps larger then the filler wire used) and proper welding with as little heat input as necessary to achieve proper penetration and bead size. A improperly welded joint on thin wall tubing cannot be saved by normalizing. It just makes things worse. Conversely, a properly welded joint on thin wall tubing does not need any post weld heat control beyond normal air cooling at room temperature. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 28, 2010 Share Posted June 28, 2010 I'm still seeing studs inserted into the arms and welded as a potential fix here. I believe the hole is just about perfect for a 3/4" stud. The majority of the threaded portion of the arm would be cut off (assuming the threads aren't ridiculously deep into the arm) and if you're using stock bushings you might just need a bushing between the stud and the poly bushing sleeve, or better yet follow in Terry's footsteps and make it a full monoball setup as I linked to before. As far as a better mousetrap, I believe I have one, although you'd have to build your own. It eliminates a lot of the potential for side loading the strut, and I think should be stronger. I haven't actually used mine yet, but I am pretty happy with what I have and think it's superior to everything else that I've seen to date, in design if not manufacturing. I can't claim to keep up with John or Monzter in terms of fab skills. Here is a long discussion that led to my arm design, or you can just skip to the end and work backwards, there a pictures on the last page. http://forums.hybridz.org/index.php?/topic/62776-yet-another-rear-control-arm-design/page__pid__848922__st__120#entry848922 Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 29, 2010 Share Posted June 29, 2010 Got pics of that Cary? I'd like to see if my plans match what you've actually implemented. They are the same arms that were in one of the construction threads from a couple of years back. I have the toe-link at the rear but they are very similar to your. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 29, 2010 Share Posted June 29, 2010 They are the same arms that were in one of the construction threads from a couple of years back. I have the toe-link at the rear but they are very similar to your. I was looking for pics of your tow hooks that you use to tie the car down. Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 29, 2010 Share Posted June 29, 2010 I was looking for pics of your tow hooks that you use to tie the car down. Sorry, I totally blew that one. They also work really well when pulling the car out of a certain pond at the end of certain track ... but I don't need to say anymore about that. Cary "three times is too many" Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 29, 2010 Share Posted June 29, 2010 Hmm. I was thinking I'd have to reinforce it more like Coffey's tow hook on the ROD. I was even thinking of angling the eyelet so that it got pulled on radially so it wouldn't bend. I guess a hook like that doesn't bend when you tighten down the straps? What is the thickness? Mine are 3/16". Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted June 29, 2010 Administrators Share Posted June 29, 2010 ....They also work really well when pulling the car out of a certain pond at the end of certain track ... but I don't need to say anymore about that. Cary "three times is too many" This popped up from a search for 240-Z lake skipping. Hmmm... Sorry for the OT.. Quote Link to comment Share on other sites More sharing options...
260DET Posted June 30, 2010 Share Posted June 30, 2010 I'm still seeing studs inserted into the arms and welded as a potential fix here................................... Makes sense to me. An alternative thing is to look at how deep the stock end bolt goes into the threaded part of the tube, to fully support the tube it should be long enough to go well past the place where the tube typically breaks. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted June 30, 2010 Administrators Share Posted June 30, 2010 Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 30, 2010 Share Posted June 30, 2010 Hmm. I was thinking I'd have to reinforce it more like Coffey's tow hook on the ROD. I was even thinking of angling the eyelet so that it got pulled on radially so it wouldn't bend. I guess a hook like that doesn't bend when you tighten down the straps? What is the thickness? Mine are 3/16". 3/16 like yours. These got made in a hurry and I had intended to add a gusset but ran out of time. They do flex some but seem to work okay. My tie downs aren't at a super steep angle so maybe that helps. Quote Link to comment Share on other sites More sharing options...
tube80z Posted June 30, 2010 Share Posted June 30, 2010 This popped up from a search for 240-Z lake skipping. Hmmm... Sorry for the OT.. The pond is a lot bigger than you have here. Basically all the green after the straight is water. Too bad you can't see the big burn mark and tree I knocked over from a few years back. We're now entering the corner at the end of the straight in the low 90s. The last recovery should be on youtube judging from all the cell phone video I saw being taken. Quote Link to comment Share on other sites More sharing options...
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