Here you go. I drew everything out in my design software. Three positions from a dead on side view like yours. The three frame points are constrained to points in space, all the joints are spherical for maximum movement. Without proper dimensions supplied by the OP we are all just guessing about the true geometry of the situation. But this in no way is increasing the load on the spring. The spring can only hold the weight of the car up and cannot be construed as a suspension control in this instance. I have set up plenty of triangulated type suspensions with the spring mounted behind the axle very similar to this. As I said before I would like to see the lower connecting links mounted down lower off the axle similar to the pictures of the roadster I posted. This would give the car better floor clearance, exhaust clearance and a better anti-squat line. Will this example work? Sure, just maybe not as well as it could.
I'd like to see how that bone mount makes the rear suspension behave if the OP could set the e-brake on and try rocking the car back and forth. My guess is that it will behave very strange. That being just a guess based on nothing more than common sense....and I could be wrong
It wouldn't react much differently than a 78-84ish G-body. They actually have similar characteristics.
has anyone thought why not just but a small tunnel (like you would a driveshaft) in the floor board to accommodate the longer top link
Your work is very nice but I really think you have a taken relatively simple task and made it way too complex. I am doing the same thing on a '40 pickup (removing the torque tube) and will be using the Hot Rod Works set-up. It is simple and proven. Although their kit is designed for use on a 35-40, the same type of set up could be done in your application. You obviously have the skills and talent to pull it off. http://hotrodworks.com/shopdisplayproducts.asp@id=12&cat=Ch***is.html
Wow! Hot and heavy in here! I've got no way to check loads or anything on this setup...but I do know I wouldn't have built it like it is. Theres some obviously iffy thinking going on...(and maybe its ME! Hahaha) The lower arms for example... WHY run the round tube up into the radius rod (RR) and then leave a bit sticking out to reach the bushing tube??? Just cut the RR to the right length, fishmouth it and weld on the tube with no additional tubing running into the RR. Lighter, cleaner looking and no stress point like exists now. Just from a looks standpoint the RR attachment point is too high on the housing. Might even compromise the exhaust routing! IDK... I also feel its less stable than the same configuration several inches lower. (GULP!) I'd like a bit of additional separation between the upper and lower. JUST my opinion though...no need for dramatics over it!!! I really don't think I've ever seen a 3 or 4 link that had the lower arms mounted that high on a stock OEM rear axle...but like I said that could be just for floor clearance over stability. I don't understand WHY the builder chose this arm configuration over a 4 link though... SEEMS like it would have been way easier to just run two upper arms to the frame instead of fabricating the tubular bridge. (which WILL absorb quite a bit of punishment, being pulled on in the middle, as the car drives over road obstacles and rough surfaces for the next 10 or 20 years!) I don't feel this setup is nearly as durable as a parallel 4 link or the original Torque tube. There must be a 4 link "kit" available for this car...so where does IT place the arms on the frame and rear axle I wonder? Personally I would have gone with a stout tubular torque arm in this ch***is IF the car simply has NO room for a 4 link and the bushed RR's absolutely MUST locate to the housing inline with the housing tube. I would also consider focused "truck arms" or P&J style ladder bars. Flintstone...bulletproof. A 3 bar would have been well down on my list...but thats what makes life interesting! Variety!!!! LOL
question,,would it have not been easier to just take the radius rods out to the side and mount them on the frame ( like they are ) but leaving them mounted on teh axle they way the should be ,,,and then if need be another rod fro top of pumpkin forward to the X and mount it there ( again thats if it was needed ) ?? kinda like this http://www.jalopyjournal.com/forum/showthread.php?t=263584&highlight=point+radius+rods and I know someone made a fancier version of that as well but can't find it
"His" Radius Rods aren't as long, don't attach to the housing the same way (though workable) and aren't nearly as strong. The 36 style you have pictured are about the strongest of all RR's...the last version, like he's using, are about the weakest...and that Merc will be heavier than most Rods as well. That front RR/frame conection makes me a bit nervous...but it sure is slick!!! I'd LOVE to be convinced that its really strong because it sure is simple to do!!!!
Wow... I step away from the computer for a few days and come back to all this. I have to say there was definitely some helpful people here that brought up some good points, but then again there were some real ***holes also, I guess you have to take the good with the bad. The lower links can easily be moved to below the axle, everything is just tacked right now. And I am going to move the lower links. All the brackets are made out 1/8" plate and will be boxed. Now a couple questions, I considered ladder bars, however, explain to me how ladder bars being mounted permanent on the rear end and pivoting only on the front will not cause the pinion angle to change? As the rear end moves up and down the rear end will move in an arc, also causing stress on the spring, and changing pinion angle. Same thing would happen if I left the wishbones mounted permanent to backing plate and just added a torque arm. I think with moving the lower links below the center line this will work fine, yes it may have some pinion angle change, but with the amount of suspension travel this car has I dont think it will be a big issue, as for strength, this car is being powered by a mild flatty, and more than likely an axle will break well before the suspension will.
Ladder bars, focused to the trans output so you can have some body roll, will indeed change the pinion angle a bit...but the length of the bars combined with the small relative suspension travel make it a non issue. Same for the arc. Actually it would have exactly the same amount of "arc" acting on the spring as the original torque tube! Think about it.... Your late Radius arms are shorter and also weaker than the type commonly used to work with a torque support arm...especially considering the weight of the completed car. That resulting setup would...likely...cause some jacking effect as you accelerate from a stop as well due to its shortness. With those changes your going to make it should be much closer to perfect...but I still hope you intend to brace that bridge you constructed for the upper arm.
Yes it would have the same arc as with torque tube, however the torque tube only has a U-joint at the front, and being fixed to the rear end the pinion angle would not cause any vibrations as it moves. In all honestly I still don't understand why the customer wants open drive. he says its because torque tubes are old technology and open drive is much better, however he is still running an "old" banjo rear end along with an "old" ****** and an "old" flathead engine. I'll fix this set up a bit, rethink the upper link and post pics to keep you guys updated. Thanks to all for the constructive criticism.
EP.... Your correct. The only thing wrong with his picture is that the upper bar attachment point did not rotate with the housing. Thats IT. Everything else is correct, including the CCW rotation of the housing/pinion. This is due to the fact that the bars/links (if extended - side view) would converge behind the axle and the uppers/lowers are of vastly different lengths. Take a closer look at the guys drawings. 1) The lower bar is close to parellel (to the ground). As the lower bar attachment point on the axle raises up and moves through its arc its position in space moves gradually moves closer the front of the car. 2) The upper bar, on the other hand, is pointing down (on the axle end of the link) and as the upper bar attachment point on the axle raises up and travels through its arc its position in space rapidly moves away from the front of the car. 3) The movement of these points in this manner causes a counter clockwise rotation of the axle housing. As the axle housing rotates it may cause binding at the shackles given sufficient suspension travel...... leaf springs are very good at resisting side to side/twisting motion (the reason most factory leaf spring set-ups to not have any laterial locating devices). Spherical bearings mounted in the spring eyes and or perches that allow for some rotation during use would eliminate most spring related binding issues. As it stands (and mostly due to the fact that most HR suspensions have little travel), this guy's set-up would more or less function, however, I do not feel that having an instant center out at infinity is a good thing. The currrent set-up is going to squat like crazy. The throttle will come on, the axle will rotate CCW, the spring perches will drop even further which will drop the back of the car, some of the weight will transfer down/back and cause even more CCW rotation in the axle but because the geometry favors this counter clockwise rotation under both acceleration and suspension drop, there will be little or no counter action to push the body up/the wheels down to the ground and the car will be more than a handful under spirited acceleration because the tires will be continuously unloaded. Braking will be a whole new experience as the rear of the car jacks to the moon. Its tacked together and easy to fix at this point, there's no reason not to take a second look at the car and adjust as necessary. -Bigchief.
Bigchief, did you not see the solid model I drew and posted in #62? I am moving that axle vertically over 8 inches, well beyond what is considered normal for street driven vehicles. Yes there is some anti-clockwise rotation on compression. The pinion curve is backward to what is desirable in most cases, I thought I addressed that. I think you may be exaggerating the actual amount of squat and weight transfer here. The geometry here isn't significantly different than that used on the G-body GMs. Worse, yes but not to the level you seem to imply. Hence the reason for the anti-hop/anti-squat bars that moved the uppper control arms up some 3 to 4 inches. If you were to give this suspension adequate traction and enough horsepower, then some of the charicteristics you are attributing would show up. Algon was arguing this suspension system was putting more load on the spring just by design and not a function of weight transfer suggesting that the spring was taking on more suspension duty than just holding the back of the car. As you pointed out the axle is rotating under acceleration (anti-clockwise torque), yes it does. But don't fool yourself, even with a torque tube or practically any other suspension means there is some rotation of the axle or offset the spring must endure. The instant center of the suspension is not at the center of the spring but well behind it for most of the axles travel. And the closer to full compression the suspension gets the farther back the instant center goes moving the rotation point farther away from the spring. This one does not seem to be an unusually extreme case that is cause for concern. If the instant center was near the contact point of the spring then you guys would most definitely have a cause for concern. In any event though the Ford leaf spring and spring perch is hearty. The spring itself is very progressive and able to handle changes in load quite well.
EP, on my PC there is no pic and no red x. On that day, I figured you would add it, but it still does not show here.
Nope. Your drawing doesn't show up in the post (at least using my browser). Two things are going on here...pinion rotation and squatting. This suspension (as drawn/in actual images) has the pinion rotation or 'pinion curve' in the "normal" direction...the pinion wants to raise up...hence the use of pinion snubbers in many off-topic leaf spring equipped muscle cars to turn axle rotation into lift (anti-squat) and help plant the tires. When accelerating, the tires rotate clockwise and the rear axle is going to try and rotate the opposite direction (counter clockwise - this part is normal). With a link type suspension (as opposed to a parellel leaf) the relative lengths of the bars and pick-up point positions within thier arcs should help keep the pinion "curve" close to static (ideally) through normal suspension travel. The other issue is squat. In a correctly designed suspension the axle torque rotation and subsequent action on the arms/bars will keep the rear of the car level and/or lift the rear of the car under acceleration (known as anti-squat). The layout of the bars in this suspension do exactly the opposite. We really don't how bad everything is without actual measurements and seeing this in person but having any squat there at all is a no-no for me if I can design my way out of it....especially if everything is only tack welded at this point. G-body GMs are cl***ic examples of what we're talking about and why there is a large industry built around changing the rear bars and bar locations on those pigs. The OEM G-body rear suspension works OK to get grandma to the grocery store but isn't worth a **** when laying down some power. The geometry in the other posters drawings and in the OP's picture makes the G-body geometry look like a dream. What good is it if the thing just sits and spins the tires? ....or unloads them while merging into traffic on an expressway in the rain? By design it is trying to twist the perches/shakles off the spring eyes like a 10 year old biting the end off stale Twizzler. Now that was an exaggeration. With the bars placed at the postions and lengths shown in both the drawings and images there will be axle housing rotation due mostly to the short length of the upper bar/torque arm and the relative positions of the bar pick-up points in thier respective arcs (as shown). How much is too much? Dunno without some good measurements and probably a trial-error mock-up in the garage. Yes, the springs will take pretty much anything this flatty powered car will dish out....its the bars, brackets and hardware that'll give out over time. Minimizing axle rotation by initial design is always better than figuring it out after the fact...especially if a bunch of folks here are raising a red flag and offering up some constructive criticism. Never said that the IC is at the center of the spring....its behind the spring. I mispoke about it being at infinity (its not, its just always going to be in back of the axle based on these images/drawings instead of in front of the axle). The farther behind the axle the IC is located the more squat there is and the less the tires are loaded under acceleration, period. Thats a fact. Read any suspension book you want and/or try it out yourself too. There's nothing good that comes out of that scenario. As engine power is applied to the axle and as weight is transfered to the rear the IC moment arm will be leveraging to PULL the tires off the ground as opposed to loading the tires as they normally would. We're still beating a dead horse here. The kid's gonna recheck his work and take a closer look at what is going on as the suspension moves throughout its travel....that was my intention when contributing to this post in the first place. Mission accomplished. -Bigchief.
I know for a fact this is what will happen. If the lower arms where lower than center the axle would be trying to compress them during acceleration (sp)but this way the axle is going to pivot at that point and at the top arm where its bolted to the housing bracket. This will twist the spring mounts. Go ahead and try it.. the pinion will go straight UP.
Except that it can't. My previous response was to Bigchief. I fully understand what you guys are trying to convey but honestly that situation will not happen. The linkage while not ideal by any stretch as I stated earlier, would work and is not inherently dangerous. You guys are trying to make it out that I am defending this as if it is perfect and you couldn't be farther from the truth.
Yes, it shows up now. Thanks! Look at your images.....the axle moves straight up and down but the pick-up points on the front/ch***is end of your links are moving for/aft in relation to the axle/front of the car. If you 'pin' those pick-up points down (like they'd be in a ch***is) and then move the axle through its range of motion you'll notice that the housing rotates quite nicely as previously depicted in the other drawings. -Bigchief.
Well.....if your images worked the first time we could have avoided alot of this babbling!! Thanks again for fixing them.
I see the pick-up points ARE pinned/located in your screen shots....the images shifted around on the page is all. It'll be interesting to see how the kid makes out.
I hope you guys don't think your info is a waste of time; I had no idea a squat would actually lift the tires....I would have thought the tires would bite better...but now I get it
u- joint gone as soon as you get on it. and if doesn't distort that much that thing will squat like a dog ****tin, if you want to blow the tires off the car fine you'll do it, you want the suspension to lift the car, you have to change the bottom axle mounts period. make them longer where the mounting point on the axle is under itand give it alittle length, the longer the mounts the more leverege the mount has to locate the axle. the spring on the back is going to make this worse, I think it will work if you change the bottom mounts, but your call
The arms are pinned as you saw. This is a 3d solid model and I can move it about on it's arms. Unfortunately I can't put loads on it in this program. I have another that can but its been so long since I used it last I would need a refresher course. I have plotted out similar suspensions with similar spring dynamics before. Granted these are all with a ton less anti-squat but the spring attachment is similar. On these suspensions the instant center stays in front but under full droop it shortens up considerably and the pinion drops down.
I don't think this was a waste of time at all. There are nuances about this type of set up we could really dig into that haven't even been touched on but at this point I will consider them minutia and not really relevant to the discussion. If you decide to venture off on to the www.pirate4x4.com site, they have a pretty good explanation of why they like high positive anti-squat and how to measure it. There's tons of concepts that we as hot rodders don't really deal with in constructing our cars but occasionally we bump into them.
why do u need a computer program to figure this out? its pretty simple. i can make this using a few pieces of cardboard.. just like this: http://www.youtube.com/watch?v=YoAu-gPPktQ it should be ok if you change the bottom mounts. plain and simple.
I use a computer program because I have it and I know how to use it. I also have the added benefit of being able to move things around in 3D space so I can see other aspects of the design.
The Jalopy Journal
