I'm workin' on the trailing arms for the HooDoo Witch, and thought I'd run this through the mill to see what everyone's thoughts are. They're pretty much the same shape as most ladder bars, but cut from a 1/2"x9" plate and about 5' long. They'll be welded to the rearend (no bolts) and the spring (model-T rear) will be in front of the axle. Needless to say, they're heavier than tubing. I figure some of their weight is taken up by being hung in the front, but how will this added unsprung weight play on the handling, acceleration, wheel hop... etc? Like everything else, I already have them cut, and I'm gonna use them, regardless, but that doesn't mean I can't drill 'em or torch out some of the middle. I kinda like 'em solid, though. Whatcha think? JOE
Im hoping this is a drag car only..... I reckon the spring shackle welds will bust first. then again a flat plate would have more give in a twisting motion,which is what itll have to deal with constantly if driven in anything but a straight line on a flat road...i.e. a dragstrip. unsprung weight shouldnt be greatly different as a percentage,when you take into account axle,brakes,wheels and tyres. would look better with some holes,maybe triangles in an alternating pattern,giving a bridge lattice look...(does that make sense?)
The problem I see with that design is that it will tend to want to bind as the rear suspension travels. Look at the mods I made to your drawing. The arrow that goes straight up and down indicates how the tranverse spring is designed to travel. The curved arrow shows the arc that the rear axle will want to try and follow with the pivot point being your front eyelet on the bar. The Xs indicate areas that will be highly stressed as the suspension loads and unloads. (Although I forgot to put one on your pivot point too.) A four link system would allow the axle to move up and down and still be firmly held in correct alignment. Ladder bar set-ups will work, but they need to be made into a "full floating" design to avoid binding. (I tried a set-up similar to what you have pictured on a big 4x4 and it snapped the eyelets off of the home-made bars. I had to install a shackle that worked like a leaf spring at the eyelet to make it work better. Still wasn't exactly "right", but it didn't bind.) The U-bolts mounting your spring to the perch will be the weak link in your system, from my best guess. I replaced a bunch of broken u-bolts on an old bracket car of mine before I realized that my traction bars were binding and causing them to snap! Learn from my mistakes! You need to allow for the slight "back and forth" movement at your front pivot point somehow. If those bars are welded to your housing, the "give point" has to be at the front eyelet to avoid pushing and pulling the spring back and forth.
I assume you will never drive this car on the street. why waste your time building those arms when you could buy a cheap set from CE or SW race cars. Ladder bars on the street will break shit, no joke. The will turn your axle housing into a giant torsion bar and it is one stout sumbitch. Gasser bars from SW That was taken from the Summit site, 200 a pair is pretty cheap and it includes all the brackets and stuff. As far as the spring mounting goes, the spring will twist to the angle of change in the ladder bar. you aren't gonna be moving nearly as far as some of our rock crawling buddies.
By the way you could run the springs like you have them in the drawing. You don't have to run airbags. It's a cheap homemade setup that works well. Clark
I can certainly see the tortion issues I'd be creating by the solid mounting to the axle and bars. Still, this set-up (not taking into account the spring position) isn't any different than the early split bones, but, I'm for sure gonna look at mounting the axle differently... either heims or poly bushings. As far as "Why make 'em?"... Well, why not? It's what I do. I have my own fab shop, I had three 20' lengths of 1/2 x 9 flat and no use for it. 20 minutes with the torch, 5 minutes with the grinder (if you're good with the torch) and there they were. FREE! Spring bind... I really don't think it's too big of an issue, here, and I can't say I know the reason for all the broken bolts, but I figure, if the spring and perch are correctly positioned, the shackles should take up alot of what twist there is on the spring. As far as the spring in front design... When it first crossed my mind, I couldn't remember having seen it done. So, I started keeping an eye open for similar designs. I've seen it a few times, and mostly on track and lakes styleroadsters. There's one on pg. 47 of the Dec. Street Rodder. Oh, and do these jeans make my butt look big? JOE
What I see is a car that the rear will rise under acceleration.And having the spring ahead of the c/l of the axle is not a good choice, it definetly will bind under too much power.If youre HP level is low and you run a auto trans it will work.Sprung and unsprung has nothing to do with ANYTHING below the springs.Sprung and unsprung weight is what your springs are carrying - the body-motor-trans.--Feder
Take a metal ruler,12" long. Hold one end secure,and try to twist the other end with your fingers. Not too difficult.Right? This shows a leaf spring can twist with no problems. [ QUOTE ] Still, this set-up (not taking into account the spring position) isn't any different than the early split bones, [/ QUOTE ] That's why split bones got a bad reputation for ride quality.They create a bind in the suspension.The wider they are split,the worse the problem.
Feder, Where do you work out that sprung and unsprung weight is what your springs are carrying???? Unsprung weight is anything that moves up and down with the road, basically 'below' the springs, as in wheels, axle, brakes, ladder bars, tyres, and about half the spring weight. Sprung weight is the chassis, body, motor etc. Anything that is resting 'on' the springs. What this car basically has is very heavy ladder bars, no more, no less, which will bind and tear up the axle if one wheel goes over a bump. The spring and it's connection is no great issue as it has a certain amount of flex in it in all directions, and remember, them ladder bars are 5' long, so very little for and aft movement, unless the axle has 8" of travel or more! Highly unlikely. The spring being in front of the axle makes very little difference. This is my rear end, just a four bar, panhard rod and leaf spring. Simple, and the unsprung weight is half the four bar, the axle, wheels, tyres, half the panhard rod, and half the spring. You have the 'halves' because half is attached to the axle, half to the chassis. So the weight is effectively spilt. Lots of tech to suspension, but most of it is very basic stuff. Paul
UNK- I was thinkin' I'd have that same "ruler" flex in the arms themselves. However, I can see the stress that'll end up on the rear axle tubes. That's gonna be the weak spot, if I were to make the connection solid. Here's a pic of the rear suspension in my coupe. It was taken right after I re-built it in '84 and right before the fire. They're chrome-moly with urathane bushings. Note the lack of any verticals, just the fork and not tied together at the rear, either. I was 19 when I built it, and I welded 'em with wire and straight CO2. Corvair front coils went where the wood blocks are, and I've beat the living piss-bag out of this thing... so far, so good. These are more triangulated, than the ones on the HooDoo Witch, as I think they'll be more parallel Like I said, I will be putting a flexible union at the back of the bars on the HooDoo Witch. As far as them being big and bulky looking... I'll let you all wait till what's in my head is on the road. Then I'll know if all this craziness is gonna work. Besides, it'll be more advertising space when I hit the big-time. JOE
By the way, I do have a limited bit of knowledge about unsprung weight (and advertising space). I used to race 7/10 mile oval on the ice of Lake Superior. Guys would do anything for more traction, as we weren't allowed to stud the rear tires. Some went toward "unsprung weight". They'd wrap chains around the axles, etc. I never tried it, so I was just wondering... and I wanted to stir up a little tech talk, since I missed the boat when RYAN deleted my post during Tech Week, on "Fastener Direction" Here's my hotrod from a few years ago. '85 Monte Carlo SS. No rust and not a dent in it... till the first turn. Sort of my tribute to the guys that wasted all the great old iron before me. You wanna run on the ragged edge... race ice oval. JOE P.S. I still have the wing and I plan to put it on my Honda CRX. I'll post pics.
Morrisman - I stand corrected your right.I was still on my first cup of coffee. I was more thinking about preloading springs.--Feder
JYD, I believe farmers put salt water in their traktor tires sometimes for traction. But if you get up to any kind of speed an heavy assembly is not going to follow the bumps in the road like a light weight assembly would. So at higher speeds ( like more than 10 MPH )it is going to cost you traction.
Metalshapes, That's exactly it. The lower (lesser?) your unsprung weight, the faster your wheels can react to the changing terrain underneath. On a dead flat pinball surface track you wouldn't need suspension at all, but when the going gets rough you don't want your whole car going up and down just to keep your tyres on the ground. Paul
Joe, that system looks good, as the ladder bars nearly meet at the front, so that cuts down a lot of the binding that happens when they run parallel. You have panhard rod, so there's not a lot more you could do to improve that system. Do the same geometry with your 1/2" plate ones and you'll be looking good, and plenty of ad space! Or you could gas axe a few fashionable shaped holes in 'em to save weight? Paul
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