blueovalz Posted December 12, 2005 Author Share Posted December 12, 2005 Yeah, I wished I knew more about the forces on the CA. For example, intuitively, on would think that fore and aft forces only are a majority of what these bearings/bushing experience (in regards to acceleration and braking only), but I'm re-thinking this in that I believe it is more a twisting force on the bushings. I now believe the strut and control arm would rotate around some common point whenever force is applied to the axle, and not pull straight forward or backward (in braking). Thus, I think nearly all the forces the bushings/bearings see are lateral to the bushing/bearing axis, and not longitudinal. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted December 12, 2005 Share Posted December 12, 2005 This was part of the problem we missed when doing testing on the tubular rear arms we built. The units that failed on Steve/ Ians race car and Mark Icard's Yellow car tore the tubular metal and not the weld. Both arms suffered the same failure on the same side arm. There is a tremendous amount of force from multiple directions being applied to the arm, and is one reason I now believe the factory arm was boxed the way it was for strength across the plane of the arm. Mike Quote Link to comment Share on other sites More sharing options...
blueovalz Posted December 12, 2005 Author Share Posted December 12, 2005 This is one reason why I am so adamant about trying to use the OEM arm verses redesigning the wheel so to speak. Quote Link to comment Share on other sites More sharing options...
tube80z Posted December 13, 2005 Share Posted December 13, 2005 I'm not sure this helps at all. I'm planning on doing some compliance testing. The idea is to simulate a load on the tires laterally and longitudinally by spreading and pulling on them and measuring the change camber, toe, etc. This would let you see if this design had any obvious issues. Cary Quote Link to comment Share on other sites More sharing options...
Mikelly Posted December 13, 2005 Share Posted December 13, 2005 I"m no engineer, so excuse my crude description of the machine we used to do stress analysis on the arms I built... This contraption was a table base with multiple mounts and pedistals that had hydraulics running to them, so you could move and place the mount against specific areas on a given item like the tubular arms we built. YOu could load them vertically, horizontally, logitudenally, diagonally across the plane of the item being tested. We actually tested the square and round tube designs as well as a front control arm/ TC setup on this table. None of these parts failed at the welds and the force required to sheer the tubing was an amazing amount of pressure (in the hundreds thousands range). The unit was on loan to a friend of mine who owned a machine shop. He did a lot of work for the marines at Quantico and that machine was US Gov't property and had been sourced by the USMC for testing on parts my friend was desinging for some tract vehicles. He offered it up to me for some stress analysis and ran it for me and did the analysis. Did I mention two arms failed over time on the cars? Oh, sorry... I did. (Just scrolled to my previous post!) Fatigue over the life of the part is the big unknown. That Machine I mention above didn't do cyclic load testing, which would have been nice... We could see the tubing flex, under severe loads we assumed the vehicle would never see, but couldn't cycle the part through those ranges repeatedly to see how it delt with that sheer stress load. Now I know... I personally think the rear control arm/strut assembly is the most stressed part on the driveline in a Datsun.... Spooky stuff! Mike Quote Link to comment Share on other sites More sharing options...
tube80z Posted December 13, 2005 Share Posted December 13, 2005 Interesting, any pics of the failures? Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 13, 2005 Share Posted December 13, 2005 Off of the failure analysis for a second. Are these inner bearing supports going to have to be cut and then machined like resizing a rod? Maybe spot welded back together for the machining process or something? Presumably if you just machined the part then cut it lengthwise there would be a gap the size of the saw blade between the two halves... Quote Link to comment Share on other sites More sharing options...
blueovalz Posted December 13, 2005 Author Share Posted December 13, 2005 As I see it this gap should not have any impact in strength on the "carrier". The gap will allow the bushing retainers to squeeze the two halves together, thus ensuring a clamping of the bearing, which to me is a good thing. Quote Link to comment Share on other sites More sharing options...
zlalomz Posted December 13, 2005 Share Posted December 13, 2005 This could be taking 3 steps back but how about keeping the rod ends in the back and welded clamping plates, like you used Terry,on a split, threaded connecting tube and used a QA1 double adjuster in the center. Quote Link to comment Share on other sites More sharing options...
johnc Posted December 13, 2005 Share Posted December 13, 2005 Typically rear LCAs under acceleration try to toe-in and many passive rear steer cars encourage this through bushing compliance. The revere happens under braking and the passive rear steer cars discourage this through either bushing design or control links. Add lateral loads to the LCA and you get a twist. The driver's side LCA under acceleration in a right turn will twist counter-clockwise (viewed from the driver's side of the car) and the passenger side LCA under acceleration in a left turn will twist clockwise (viewed from the passenger side of the car). The reverse (to a much lesser degree) occurs under trail braking. Quote Link to comment Share on other sites More sharing options...
Mike Mileski Posted December 13, 2005 Share Posted December 13, 2005 Here's a picture of what I did with a pair of Mike Kelly's rear arms. I welded in another cross support tube at the outer end and then used a pair of high strength rod ends with spacers to center it on the upright. I slightly knurled a 5/8" high strength bolt to make it fit a bit snugger in the spindle pin hole. The hole is only about .004" bigger so it didn't take much. The female portion of the rod end is 3/4-16 thread and the ball has a 5/8" hole. I could have used a set of double adjusters with male rod ends but Mike's LH/RH adjusters do the same thing. Mike Mileski Tucson, AZ Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 13, 2005 Share Posted December 13, 2005 This could be taking 3 steps back but how about keeping the rod ends in the back and welded clamping plates' date=' like you used Terry,on a split, threaded connecting tube and used a QA1 double adjuster in the center. [img']http://img.photobucket.com/albums/v201/zlalomz/srearToe_build_parts4.jpg[/img] This is an interesting idea. I kinda like the idea of using the toe adjuster that I already made, plus the monoball spacer, sleeve, carrier whatever you want to call it still needs to be machined for the front end of the control arm. But that might have been a good feature to incorporate into the poor man's toe adjuster. At the time I think the focus was on adjustable toe, not so much rod ends or monoballs. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted December 14, 2005 Author Share Posted December 14, 2005 Zlalomz: Fascinating idea, and very similar to one I considered when I fabricated the toe adjuster. My concern/issues were the shear forces placed on the neck and shaft of the rod end. With no sway bar used at all, there would be none in an up and down plane, but I was too unsure of what forces were involved in the fore and aft plane. Until I have a very thorough understanding of what forces work on the bushings, I will try to avoid any "extended" (such as rod ends) mounts for the control arms and remain with those that are fully enclosed, or close to it. I realize that the rear bushing mount is a little "wierd" in that it's a flat plate that could flex fore and aft, but be very rigid left to right (which is why I began wondering if the forces on the bushing were all lateral, and not logitudinal). What I wonder is if DATSUN designed the front mount to be so rigid in every plane, that it would provide the needed rigidity (through the CA tube that connects the front bushings with the rear bushings) in the fore/aft plane that the rear mounting system could not provide. Many interesting questions that I could never resolve. Ultimately, I tried to keep as much of the OEM design (a well proven design) intact knowing that it was overdesigned from the beginning and allow me to use the rubber bushings until I felt comfortable with another option. Perhaps the time has come for another option. I just love building things... Quote Link to comment Share on other sites More sharing options...
Mikelly Posted December 14, 2005 Share Posted December 14, 2005 I had pics, but I can't seem to locate them... Had several hard drives die in the last couple of months and have lost a lot of data... The failures where on the outboard side rear tube that held the bushing and sleeve that the spindlepin bolted through. The torquing against that mount point TORE the metal, not the weld. Initial picures from Steve's car showed what we thought to be weld failure, but once we got a better look at the failure, you could see the welded metal in place and the sleeve just split and let loose. Same thing happend on Mark Icard's car on the same side, and same point. That tells you that the loads are pulling the strut assembly in a front to rear motion, changing toe as John C. suggests and that motion repeated over time (two years hard driving with two drivers in Steve and Ian's case) and using RR slicks and very aggressive alignments in the rear probably contriubuted to the failure. On a street car, you probably wouldn't induce such loads, but I wouldn't want to risk it. Mike M. have you had a chance to give the new rear design a try? I'm probably going to use your design on my personal set of rear arms, in conjunction with some camber plates welded into the rear towers. Mike Quote Link to comment Share on other sites More sharing options...
Mike Mileski Posted December 14, 2005 Share Posted December 14, 2005 Mike Kelly wrote: "Mike M. have you had a chance to give the new rear design a try? I'm probably going to use your design on my personal set of rear arms, in conjunction with some camber plates welded into the rear towers." No, I haven't installed them yet. I'm still accumulating/building all of my suspension upgrades and I want to put everything on at the same time. Mike Mileski Tucson, AZ Quote Link to comment Share on other sites More sharing options...
zlalomz Posted December 14, 2005 Share Posted December 14, 2005 I wonder if you put the rod end in double shear somehow if that would be strong enough? Machine those spherical bearing retainers Terry and I will be your first customer. Here is a clean set up used by John Thomas in FP. He was the fastest Z on the second course once he sorted out some fuel delivery problems he encountered on the first day. Quote Link to comment Share on other sites More sharing options...
Mike Mileski Posted December 14, 2005 Share Posted December 14, 2005 Designing something to give you double shear on the outboard side would be pretty difficult. That is, unless you're designing your own custom upright that utilizes the stock outboard Z32 TT axle end, like Jamie T is doing. Hmmm... Mike Mileski Tucson, AZ Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 14, 2005 Share Posted December 14, 2005 Double shear on the outboard end doesn't seem necessary. None of the control arm manufacturers have that feature. Seeing zlalomz's pics makes me feel like we're on to something good here... Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted December 14, 2005 Share Posted December 14, 2005 Could someone please explain "double shear"? I'm no engineer, just a fabricator. What I've built seems like it will be plenty substantial for my needs, but what do you guys think? Also FWIW, I'm redesigning my hub/strut assembly to make it better than what I had before. I've learned alittle more since then thanks to all of ya'lls input and just reading threads like this one. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 14, 2005 Share Posted December 14, 2005 Double shear to my understanding means that the bolt or whatever is being used to capture the suspension goes through two surfaces. So the inner bearings on John Thomas's suspension are in double shear. If he had a single tab welded to the frame and the bolt went through the one tab then through the rod end and that was the only thing holding it on, it would be in single shear. I believe your inner pivot was in double shear because you had 2 tabs welded to your diff cradle. Your outer is in single shear because the spindle pin will still go though just the center part of the strut. There is no outside part of the strut for it to go through on the other side of the rod ends. Quote Link to comment Share on other sites More sharing options...
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