lbhsbZ Posted February 5, 2007 Share Posted February 5, 2007 Explain to me how a Heim joint is any worse than a nut and bolt..???? especially considering that the damn strut bars ONLY WORK IN TENSION AND COMPRESSION??? splain me that one... I don't think there is much difference. A proper strut brace, IMHO, should be straight tubes welded to mounting flanges. The only bolts present should be those attaching it to the body, if that. Welding is prefered, but in the case of the front strut bar, that can cause engine servicing problems. Without the use of very expensive data logging and position sensors, its almost imposible to determine in what direction the strut towers will flex during track driving conditions. My gut tells me that they will flex in every possible direction depending on what wheel loads are introduced. The best way to eliminate the flex is to tie the strut towers into multiple locations. A bent brace will bend more as load is applied....a straight brace will be stiffer. Ideally, the struts should be tied together to eliminate the in/out flex, then tied to a structurally sound spot on the firewall to prevent back/forward flex, then triangulated to the cage to at the knee bar/A-pillar bar junction and the A-pillar bar/rocker junction to prevent up/down movement of the front end. I have a cheapo ebay strut bar, constructed of a bent piece of extruded oval stock aluminum and clevises, that I bought a long time ago for one of my VWs, and if I put one end of the ground and the other end against the wall, I can lean into it and produce a couple inches of deflection. My weight (I'm not too fat) doesn't come close to the forces present in cornering excercises. The bar that I made for the VW that I raced for the last two years was solid through this same excercise. It was a straight piece of 1.25 thinwall tubing with a 3 bolt flange welded to each end with gussets. My earlier statement regarding the worthlessness of heim joints in a strut brace were based off the amature tests done with the ebay strut bar vs my homemade strut bar. Quote Link to comment Share on other sites More sharing options...
SHADY280 Posted February 5, 2007 Share Posted February 5, 2007 i have the motorsport bar, its mount on some heavy plates, and got heims, man that thing works well. so for giggles, i bought a 7 dollar bar for my girls 03 mitsubishi gallant, it is mounted very cheaply, and the bar has no heims, but is adjustable. believe it or not, it actually helped. i was impress at such a cheaply made part. i cant even make one for 7 bucks! kinda goes to show anything will help, as long as its not pushed hard ina racing aplication Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 5, 2007 Share Posted February 5, 2007 Even my heavily modified front end structure MUST HAVE some removable components... the strut bars cannot be welded to the chassis.. This is simply not an option... So we can assume ALL FRONT strut bars will be BOLT ON... I did weld my rear strut bars in place... to save money and weight if nothing else... So what is the difference between a strut bar using Hiem joints and one using BOLTS???? They dont take bending and twisting loads anyway... How on earth does leaning on your bar at home represent anything that they will go through in use???? There are so many more points that ARE IMPORTANT in designing your strut bars... Heim joints affer a lot of other advantages... The structures the strut bars attach to could benefit from some modifications... For instance... 1. the tops of the towers have a thin layer of metal skinning a thick steel plate.. it is important to weld through the thin stuff in order to get a good connection to the heavy steel top tower plate.. 2. The firewall connection is totally unacceptable without modifications... The easiest way to avoid the weak/flexible center firewall is to go right through it and attach to the roll-cage dash-bar... but that eliminates factory windshield wipers... 3. eliminating twist in the towers is more easily accomplished using gussets and/or additional welded bars that run to the sides of the firewall and down to the frame rails... 4. The connection between the strut tower base and the frame rail is practically NONEXISTANT... there is only ONE layer of 24guage metal... hence the gussets I added to the frame rail tower interface... 5. the rear strut bars can and probably should be welded in place... but AGAIN the sheet metal skinning the top tower plate must be welded through to attach to the heavy tower top plate... there are actually several light guage strips of metal near the tops of the rear strut towers... these must be cut back to expose the heavy guage top plate for welding... 6. vertical bracing is not easily accomplished with removable strut tower bars... although I have seen some neat ideas for this... I would have to test them myself before I believed they work... I have seen dozens of S-30 z-cars using a triangle front brace attached to the center firewall... I have on several occasions asked about the ridgidity of this attachment point... everyone I have ever asked has said "It's fine... the firewall is stiff enough" I can say from direct observation that THE FIREWALL IS NOT STIFF ENOUGH TO BRACE AGAINST IT WITHOUT SERIOUS MODIFICATION... Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted February 5, 2007 Share Posted February 5, 2007 I'm saying that for the removable bars, make them bolt using at least 2 of the strut hat bolts on each side, Not a clevis or hiem joint. Weld a round plate to the brace, then bolt that 2 the strut tower. I think that would be a stiffer design than using a single attatchment point on each side. Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 5, 2007 Share Posted February 5, 2007 They only work in tension and compression.. the typical cheapo heim joints are rated to ~5000lbs... they don't give under tensile loads... The round plate is redundant weight... attach to the 2 bolts.. that is it... keep in mind that a lot of us dont have bolts anymore.. we have fabricated brackets that are welded to the tower top plate... the idea is to use several bars to triangulate the structure... all bars take tensile loads only.. no shear no twist... you won't get shear and twist strength from a long tube no matter how you attach it... Quote Link to comment Share on other sites More sharing options...
johnc Posted February 5, 2007 Share Posted February 5, 2007 Imagine the x-member and the strut towers as a incomplete rectangle. Now when you load one side (as in cornering) it will cause it to warp more into a trapazoid. Now a bar will complete the "rectangle." The "bling" bar will help the towers from changing inward and outward, but will cause it to change to a rombus in cornering. Now a "solid" will keep it more of a regtangle and keep it camber, toe-in and other suspension settings stable and more static as far as the frame is concerned in cornering. That would be correct if that's how the strut towers flex. But they don't move that way under load. The tops of the towers "twist" inward and towards the rear of the car under cornering loads. Adding a lateral STB reduces the inward movement and running STBs to the firewall reduces the rearward movement. The trapezoid analogy is correct if we are talking about 2D objects. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 5, 2007 Share Posted February 5, 2007 That would be correct if that's how the strut towers flex. But they don't move that way under load. The tops of the towers "twist" inward and towards the rear of the car under cornering loads. Adding a lateral STB reduces the inward movement and running STBs to the firewall reduces the rearward movement. The trapezoid analogy is correct if we are talking about 2D objects. We've been over this one before, but I think that the Z strut towers flex OUT under cornering loads and IN under suspension loads like going over bumps in the road. I had a link to a BMW site that showed how this worked, but I can't find it anymore. Anyway I read this a long time ago in a Porsche Club magazine. They had put tattle tale dial indicators on the strut towers and measured deflection before and after the strut tower bar install, and that's what they found. Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 5, 2007 Share Posted February 5, 2007 That would be correct if that's how the strut towers flex. But they don't move that way under load. The tops of the towers "twist" inward and towards the rear of the car under cornering loads. Adding a lateral STB reduces the inward movement and running STBs to the firewall reduces the rearward movement. The trapezoid analogy is correct if we are talking about 2D objects. and I would add that closing the top of the rectangle will not stop the structure from warping into a parallelogram... The triangle to the center firewall is an indirect approach.. but as John C. said... it is the most important approach in real life... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 5, 2007 Share Posted February 5, 2007 I just found a link to a site which has good info on bending stiffness of tubes, this is a good reference. Also his page on gussets is really good too. Not so sure I like his bender, but that's another story: http://www.thefont.pwp.blueyonder.co.uk/bikes/tube_size.htm Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted February 5, 2007 Share Posted February 5, 2007 I can say from direct observation that THE FIREWALL IS NOT STIFF ENOUGH TO BRACE AGAINST IT WITHOUT SERIOUS MODIFICATION... But from http://forums.hybridz.org/showthread.php?t=117151&highlight=finite+element Based on some finite element analysis done by Bill Savage there is no need to reinforce the firewall for a center STB mount. In side view the cowl section is a triangle with the firewall as the base. If your STB mount plate spans the base of the triangle (the top lip and the row of spot welds part way down the firewall) you have a very strong mount that spreads the load into the cowl section. I have some close-up pictures of the mounts in one of my galleries. http://album.hybridz.org/showgallery.php?cat=702 Seems like you guys have different opinions on the subject. Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 5, 2007 Share Posted February 5, 2007 We have 2 current builders(J.M. and I) who have ample evidence that this IS NOT STIFF ENOUGH... There are 2 gussets inside the upper torque box(cowl box) that tie all sides together... they are fairly far apart... I have seen numerous designs that span these 2 points on the engine bay side of the firewall... This is one step to attaining a strong mounting point.. BUT!!!! there is a caviat... The driver's side internal gusset does not continue to the inner cowl panel of the torque box.. It is cut off half way to allow room for the wiper arm inside the cowl... That also allows a great deal of movement on the driver's side even when you span the 2 intenal gussets... The driver's side gusset needs to be extended all the way through in order to provide stiffness... ANY ATTEMPT to put pressure on the center of the firewall without addressing these issues... 1. will cause the upper lip of the cowl box to flex.. It bends upwards in the middle... 2. improper reinforcement will simply cause the windshield mounting lip to flex(also part of the cowl box top) 3. failure to modify the driver's side internal gusset will cause the entire cowl box to flex on one side... especially at the lower windshield lip.... If any of you wish to dispute this fact then I can produce a video showing the amount of deflection, approximate pressure to delfect and the total amount of deflection on a dial guage... That is a fair amount of work.. But like I said.. You provide some personal experience and/or proof one way and I will provide proof my way... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 5, 2007 Share Posted February 5, 2007 But from http://forums.hybridz.org/showthread.php?t=117151&highlight=finite+element Seems like you guys have different opinions on the subject. You're right, I know that at least bjhines and I do differ with John on this subject. It's not completely unheard of for someone to differ with John, even if he is right 99.9999999999999999% of the time. My reasoning is that I can flex the firewall with my hand and I can flex the top of the cowl with my hand (visibly flexing), and as BJ said on another thread, my strut braces to the firewall didn't seem to tighten very well. On my old setup I actually cracked the seam sealer when I was tightening them down, so they moved A LOT. Now mine weren't centered the way John's and BJ's were and didn't straddle the 3 piece of the cowl's triangular structure the same way , but BJ's experience seems really similar to my own. He described the reinforcing that he did to the firewall to make it more sturdy in this thread here: http://forums.hybridz.org/showthread.php?t=118871. That is also a restatement of an earlier thread he posted when he originally came up with the firewall reinforcements here: http://forums.hybridz.org/showthread.php?t=109864. Also my 70 (build date 5/70) does not have that brace the BJ mentioned on the passenger side of the cowl. The driver side does have it, passenger side does not. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted February 5, 2007 Share Posted February 5, 2007 From the other thread a couple days ago I still think that welding a tube from here to the strut towers provides a very solid and well supported structure - EVEN AT THE FIREWALL. It's centered in front of the vertical support on the inside of the cowl (the one Jon only has on the drivers side by I have on both sides) and tied into the top horizontal plate creating a very stiff joint. Cameron Quote Link to comment Share on other sites More sharing options...
260DET Posted February 8, 2007 Share Posted February 8, 2007 Pic below shows one way to make an adjustable strut tower bar without using rod ends. If its not clear in the pic, two fine thread big studs (12mm?) were crimped and welded into each end of the oval tube. Each stud end then went into a hole in a bracket on top of the strut tower, with nuts either side of the bracket. Adjust to suit and lock up the nuts tight. In use the nuts never loosened, I thought they may due to movement. With the 280ZX project the strut tower brace is triangulated back to the firewall and bolts to the strut towers vertically and horizontally, using captive nuts welded inside the towers. There is no adjustment, it was all made to fit on the car prior to painting it, no pics yet. Quote Link to comment Share on other sites More sharing options...
buZy Posted February 8, 2007 Share Posted February 8, 2007 I totally agree about no difference between bolts and heim joints on the strut tower bar. The up and down movement as Jon described. Alum Rad X brace hmmm very cool. How about the PDK setup? Ok, I know it still won't stop the movement up and down. But for my car with no cage, never running a front tower brace, is it worth the extra bars to the firewall and sway bar mounts? (say yes cause I just recieved this whole kit last week! ) sorry if I hi-jacked the thread. Quote Link to comment Share on other sites More sharing options...
rdsk8ter Posted February 8, 2007 Share Posted February 8, 2007 I totally agree about no difference between bolts and heim joints on the strut tower bar. The up and down movement as Jon described. Alum Rad X brace hmmm very cool.How about the PDK setup? Ok, I know it still won't stop the movement up and down. But for my car with no cage, never running a front tower brace, is it worth the extra bars to the firewall and sway bar mounts? (say yes cause I just recieved this whole kit last week! ) sorry if I hi-jacked the thread. can i see some pics from the birds eye looks really good Quote Link to comment Share on other sites More sharing options...
buZy Posted February 8, 2007 Share Posted February 8, 2007 The pic is from the PDK website. This is not my car. Just an example of the tower bracing. Quote Link to comment Share on other sites More sharing options...
TimZ Posted February 9, 2007 Share Posted February 9, 2007 They only work in tension and compression.. the typical cheapo heim joints are rated to ~5000lbs... they don't give under tensile loads... the idea is to use several bars to triangulate the structure... all bars take tensile loads only.. no shear no twist... you won't get shear and twist strength from a long tube no matter how you attach it... I agree completely (sorry for the late post - I've been meaning to post on this for a couple of days now). Just to put a finer point on this - you don't want to put anything but tension/compression loads on the strut bar (or any long tube for that matter). Trying to control other motions will never be effective, and will eventually fatigue the mounting points. Because of this, the Heim Joint is actually the best solution, since it only allows tensile forces to be put into the bar, and it rotates for everything else. The bolt (clevis-style in double shear) is second best since it at least allows movement in one axis, and rigid mounting is by far the worst solution for a non-triangulated strut bar. The PDK bar above should be okay for fore/aft movement, since it does have properly loaded, triangulated bars to limit this, assuming the bulkhead is sufficiently stiff. If the towers actually do try to move up and down with respect to each other, it won't be able to do much about that. So, the lateral crossbar needs to be a bolt in so that it won't try to fight such movement - I can't tell from the pic if this is the case or not. Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted February 9, 2007 Share Posted February 9, 2007 ^^^ I agree as well. If you put lateral stress on a support not designed to take it it will flex. Only longitudinal stress should be allowed on this type of support. No... I'm not an engineer but this is the only thing that makes sense (to me). Quote Link to comment Share on other sites More sharing options...
260DET Posted February 10, 2007 Share Posted February 10, 2007 I agree completely (sorry for the late post - I've been meaning to post on this for a couple of days now). Just to put a finer point on this - you don't want to put anything but tension/compression loads on the strut bar (or any long tube for that matter). Trying to control other motions will never be effective, and will eventually fatigue the mounting points. .................... Torsion bars, anti roll bars are long bars/tubes. Quote Link to comment Share on other sites More sharing options...
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