I have a 4" drop tube-axle that I purchased about a year ago for a project. Now that I am (finally) building my car, I find that the batwings are to narrow. I guess this axle was for Speedway's 26" spring or something, but it isn't gonna work with my cen-pen airride crossmember. Car is a '30 chevy sport coupe. I'd prefer to stick with tube axle and hairpins. I've toyed with the idea of making it a spring-behind, but my perches would have to be about 2.75" behind the axle for that to work. My next logical design leap (oxy*****) was to grind off the old batwings, make new ones that relocate the perches behind the axle 2.75", and weld them onto the axle at the appropriate distance. Do I grind the batwings off and make new ones? Or move on and purchase a new axle? If I am to fabricate my own, is there a secret to them? I've searched the general discussion and tech forums without success. Most weld-on batwings I've seen are 3/8". I was thinking 1/2", and file down where the batwing clevis' go. Opinions? Thanks Andrew
How confidant are YOU about YOUR welding skills? Why increase the plate thickness to 1/2" if 3/8" has been doing quite well holding up cars for decades?
I'm very confident in my welding skills. What I am not as confident in is my mechanical design skills - is there a scientific method of locating the batwings on an axle (other than centering, obviously)? Is there a scientific method of determining the distance from the spring perches to the axle? I was going to use 1/2" plate for the batwings because I have some, and I don't have 3/8" laying around. Figured I could use what I've got, and save a few bucks. I have the dough to spend, but I have it because I'm not in the habit of needlessly throwing it away.
when i came to that road my idea was to get a 4x4 1/4'' box tube and cut a "c", drill top and bottom, weld in round tube for axle perches and then build from that...after that the design is upto you...havent done it yet but i had planned to make some hair pins and covering the outside to make them more like a trad wishbone... my project came with just a single round tube with a clevis welded to the the end and the tube going through a hole in the front axle...i may end up ditching this idea depending on time and costs...if i can buy something for cheaper than i can make it im going to.
i though "tube axle and hairpins" was a no no, tube axles need a 4-bar because they don't twist, hairpins are only used on an I-bean axle, I-beam axle do twist, am i correct?
Oh yeah, and that. You are correct. Tube axle + hairpin is a no-no. Tube axles don't flex, and will likely break a haripin or a 'bone, or the axle itself, or otherwise.
The Cenpen arms (replace the leaf spring) are 1/2 stainless with "eyes" machined in each end. Shortening would be tremendously labor intensive and probably a bad idea. I don't get it. I've seen a ****load of cars running this design, Speedway and others sell tube axle kits with hairpins attached. What am I not understanding?
thehotrodguy, do you have any pics of the current setup? and parts you're using? That would help out a lot with any advice.
The tube axle resists ch***is roll like a big sway bar. If you really lean on it, the tube axle/hairpin deal will try to hike the inside tire. If the 'pins are good quality, they shouldn't break. I looked at the cen-pen trad air setup but I couldn't tell if it uses the shackles on those arms??
yes, shackles. I am going out to the shop to take pics now of what I have. I guess I don't understand why the heim joints at the frame end of the hairpin don't allow for the articulation. The hairpins I have came with the axle when I bout it. I was planning to upgrade the 'pins to 36" ones (I have the 32") but perhaps I should rethink? Homemade 2"x4" box-tubing frame, mild 350 sbc w/ 700r4 is the plan. Running fenderless, just like a hotrod should
Stand back and imagine the ch***is trying to roll around the axle. One hairpin mount (on the frame) will go up and the other will drop. That means the hairpins will want to be at different angles. The axle has to twist to allow that to happen. Beam axles twist a lot easier than tubes.
Please bear with me, I am not in any way gifted with photoshop, nor did I try to do more than illustrate my point. First pic is the cenpen "springarm". I don't want to try to narrow or modify this, so on to the axle. Next is the axle and bracket as-is. The brackets are too narrow by approx 1.5", so I plan to move them outboard approx 7/8-1" each. While I am ditching the old and making the new, I'd like to make it a spring-behind setup, instead of spring-over. Then I'll show Speedway's weld-on batwings for tube axle. AT $12.95 each, these are likely the cheapest option. Cheapest and best are rarely the same, cost is not my concern here. I have included a quickie pic of the bracket that I think will work. The question I have is, does moving the axle forward create an appreciable increase in leverage, and make it unsafe? I don't know the measurement of the speedway axle to perch dimennsion, but I'm only adding about 3/4" to it. I believe this SHOULD be fine, just looking for intelligent insight from the HAMB - the greatest website in the world.
The shackles are a must, as the bags inflate and the springarms go up and down, the distance between the mounts changes. Just like a leaf spring.
Here are a couple of pics of some hair-pins i have made, one on a tube axle and one on an aftermarket ibeam. The tube batwings have a small gusset for lateral stress and are for spring behind. The ibeam has a piece of solid stock on top and bottom and the hair pins weld directly to them. The plate for the spring mount welds to them as well as the one" tubes to tie everything together. I have never heard of tube axles and hair pins being a no no, i have seen thousands of street and drag machines running them without problems. I would say 90 % of suspention travel is up and down and 10 % twisting as around a tight corner, or a driveway approach, where the twisting stress is at its worst. The hair pin kits sold by speedway and others are a fit all type kit. The adjustable clevises are for adjusting caster and length side to side to compensate for mismatched rear wishbone mounts and the like. The ones i have pictured are fabbed with 5 1/2 degree caster with the hair pins level with the ground, no need for the clevises and cleans up the mounting area.
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