"Spring travel", as in Wheel Travel. is based on the spring rate. The length of the shackle doesn't influence the spring rate. I've seen factory set ups, and race cars, with shackles on front, others with shackles on back.So that is probably not super critical. Personal preference, I would put the shackles on back; but that is based more on appearance.
Normal automobile practice was to have the shackles on the front. There was a reason for this,it was to prevent the axle moving backwards on one side. If the axle moves back against the shackle it steers the car. The normal shackle would be just big enough to clear the spring eye. Such long shackles are going to allow the spring to behave in a manner that could be described as a "S" laying it's side . This will let the axle rotate in an axis. Small variations of 1-2 degrees are acceptable,you get that with the most modern suspension but,and i am only going on what i see in the photo, I can see the axle rotating enough to see the axle twist maybe 20 degrees (?) ,Moving from negative to psitive castor and viceversa. At low speeds (parking etrc it's no big deal,but we are discussing a high performance car here and theres really no allowance for any geometry change. It must be remembered that steering a car at speed only requires minute variations in the direction of the front wheels. By allowing movement in an axle you are allowing the axle to steer the car and I suppose you could say that i am suggesting that the design be revised to allow the axlew to move up and down but to shorten the length to which the shackle can move in a radius by adapting a shorter shackle. I cannot say if this will affect the ride and i would say that gudgys hasn't been able to determine if his springs will hard or soft (soft with rebound control is the accepted method) but I will say ,with qualification,that it will drive better .
With a conventional leaf spring suspension, the leafs get longer, eye to eye, as they are compressed. The shackles typically give less than 45 degrees travel in compression. before they bind. With an Underslung, the spring gets shorter, so the typical shackels will have perhaps as much 90 degrees of travel, if loaded sufficiently. Entirely different situation. Wrap up with leaf springs can be a problem on back, because of the amount of torque applied under acceleration. Any spring stiff enough to give a decent ride, is unlikely to wrap up under braking, because the torque generated is lower.
A lot of this has been based on my ideas, research, looking at other prewar setups, and some trial and error. This is not a common setup and there are no "1800underslung" help lines. You have to try and figure it for yourself and make it work. What i have is springrates on the front of 600kg per inch, rated for 1 1/2 inches of travel, which should be fine. Castor is to be set at 8-9 degress as there will be a small change in castor angle with suspension travel. Biggest headaches has been steering geometry and getting it all to look right. The fronts of the chassis are now made and fitted which improves the look and understanding of how it will all work. I will post some more pic's of it from home tonight.
45degrees, I disagree,it's more 5-8 degrees on practically any successful car design where the spring is loaded at road driving position. Under slung or over mounted,the spring doesn't know which side the axle is mounted on does it? It's just the chassis is under the axle instead of over it. Load applied is the same in either case. Image a circle,draw a line across the circle in a horozontal direction cutting it in half . then draw a line from the bottom of the circle to the top,cutting the circle into four parts. . You have bisected the circle into four segments. Now ,from the edge of one line travelling around the edge of the circle to the next line is 45 degress. Carry on in that direction to the next line and you have travelled 90 degrees. Do you see now that for any shackle on any spring to move 45 degrees in normal driving is both impracticle and improbable for a spring to work? and then to travel 90 degrees would mean the spring would in fact turn the shackle upside down. With his long shackels I can see gudgys potential problem,it's ordinary bumps in the road.Billions of them over the course of a cars life. All will have the potential to cause havoc . Theres more than enough information out there regarding spring design,cars have used springs from the First Benz's in the 1800's so there is nothing that needs to be discovered by trial and error. Stiff springs do not make for good handling or ride,it's myth perpetuated by ricers who insist of installing superhard springs because they think they have too. Not because they have to. Accepted enginnering wisdom says soft springs with adequte rebound control,in other words you use soft springs and control the bounce(rebound) by the design of your shock absorbers,nothing new there,they discovered that around 1900.
I think the photo of the rolling car front has confused the issue here a bit. The front of the spring is the retained end with the hangers at the rear of the leaf behind the radiator. The leaf springs will be pivoting at the front and i would be surpised if the hangers at the back rotated by more than 5-10 degrees. The bushes for the hangers have not been drilled & fitted to the chassis as yet, the temporary hangers just have the bottom bolt under the chassis so it "hangs" in the right place. The spring rate is not that high in fact i expect the ride to be soft, as jumping up & down on the chassis it feels quite soft, and much smoother in movement than my old T.
Interesting description, except for one very small detail. There are 360 degrees in a circle. http://commons.wikimedia.org/wiki/Filerotractor_katomierz.jpg Dividing a circle into four equal sized segments, gives you 90 degrees each. Simple geometry. Been that way for centuries. Try again.
Gudgyz: what are you planning for a steering box ? I like how you have the tie rod on back where it belongs.
from what i can tell you are going to have scrubline problems on the front. Im also building an underslung, and some more advice I can give is to mount the front axle in between the frame and the leaf spring. search for Inkorekt and his underslung for pictures.
I'm runnng cowl steer using a 1969 Holden HT box (mid size GM sedan made in Aus & NZ) mounted under dash, through side of cowl to a bellcrank up front which should simulate a front mounted box in cross steer. I was going to have rod direct from drop arm off the steering box to a slingshot style steering arm but it would have had HUGE bumpsteer. The arc that the steering rod pivoting at the cowl and the axle pivoting at the front of the chassis would have had the steering arm moving up to 1/2" at max travel. Bumps would have been real scarey!! Hence the change to a bell crank up front. Pivot will be directly behind the axle, inboard of the chassis. I have made a temporary "prototype" to prove it will work and will get a mate with a better workhop than mine to machine it all up.
i have been tossing around the idea of building an underslung for a while now i have seen a few done and its cool.
Thanks for the thought but this is going to need to be a custom item with the arms about 8" apart vertically. The lower one to the tierod will be about 1/2" above the chassis under the leaf srping pointing to the back of the car and the top arm will be about 2" above the beam axle pointing at the drivers side wheel.
I supported it at the ends as i figured that would be the stongest point of the tank, where the seams are. Thats also where i have placed the straps to lock it in. It is a tight fit, about 1/2" clearance to diff But plenty of room to fill up.
OK heres what i did on the front of the chassis once i had an idea how much the springs would drop with the weight of the car. I got some 5mm plate and cut it roughly to shape, made four the same for the sides of the chassis then bolted them all together and ground them all to the shape i wanted. I then cut some lengths of 50mm plate, same width as the rails and shaped these to box the underside of the side plates. After a whole lot of hours pissing off the neighbours i had two of these! I clamped a piece of offcut form the main rails inside so that if things shrunk during welding they should still fit over the chassis, good thing i did because the are a damn tight fit. here's the ends welded up, i had V'd where the welds were to go inside and out, welded the inside then the outside, came up strong as hell. They just a bit of tidying up on the outside!
A few more hours of grinding (and pssing off the neighbours) and they look something like this Then its time to cut off the front of the frame to make room for the new and fit the new frame horns Tacked back on and working out the steering, as i said earlier the temp hangers are just sitting under the chassis, proper tubes & bushes etc will be fitted through the chassis later.
I hope you dont have any problems with the steering linkage smashing into the leaf spring bottoms when you hit a bump. maybe im just looking at the pictures wrong.
Hopefully it will all be cool, there is a bit of clearance there, and not too much travel, so should be OK.
read it again and it is exactly what I .said. Read it carefully ...and do as i said. Draw a circle, divide,,,,,, ah forget you aint listening anyway ha ha ha .
You are right I was looking at your picture of the temp spring hangers. Perhaps a little artistic work with shaped shackles is in order? e.g have a look at mid fifties Chev sedan rear shackles,the curve shape of those would look great on your car . I was looning for my spring charts I got when serving my apprenticeship in NZ. It went into great detail over weight,length ,leaf thickness etc etc . But from what I do remember is that Those springs are short but the combined weight of car and engine /trans it really should ride smooth. My roadster has a tranverse leaf but i built it 15 years ago and i ran a hemi in it back then, but i have forgotten all the guff i worked out to get it right. It rode great though,which to me is more important than a sore back from trying to look cool... on a further note ,don't make the common mistake of just using bolts in the shackle. Real shackles have Pins,secured in one leg of the shackle and the opposite end is turned down to fit a smaller diameter hole through the other leg. Why, you ask? it's to prevent the shackle legs moving up and down opposite each other in a paralellogram motion. if you let the shackles do this it will steer the car in bumps. It happens on diffs when people either don't know or don't bother because it's too much work. On a front axle it's a lot worse. Like i've said previously ,the amount of deviation to steer a car at speed from a straight line is miniscule.
Okay, what am I missing here - you've gone from a front mounted shackle to no shackle at all? Or am I getting so old and close to depends that I can't see the obvious? Where is the shackle? Or did I miss an explanation of what is happening...
Interesting, i had not heard of this. I'm guessing you mean the pivot where the shackle bolt goes through the chassis and if so how much difference in hole size is required? would 9/16" on one side 1/2" on the other be enough or do you need more. I still have to drill the chassis for this, and get the tubes & bushes machined to suit so it would not be a big deal to make them different sizes (within reason).
did you mean a picture of the shackle? or a picture of the circle divided into 4 sections,either way it should not move to far . You can see a shackle move a long way when travelling slow over a large obstacle ,such as rock crawling but that doesn't really apply in this case.
Got it now. Not sure how the certifying engineers would go with welding the pins in though, they get a bit funny on some things like that but i will run it past the guy who has been inspecting the work to date. To register an new rod down here in NZ you need to get a certifying engineer to approve it all and the vehicle needs to pass through low volume certification before it can be registered for the road. Its also quite bizarre because if you import an unmodifed American car which you can register easier, our hotrod association also require to have it certified, as stock, before you can go on their runs. Madness!!
I really like the looks of what you are doing and the spirit behind it. The uniqueness of the car. Great pictures and illustration of your progress. I'd like to build something like it. Maybe not as radical but I like the basic look and concept. What you are doing is what makes hot rodding so great. Improvising and blazing your own path. No NOS or concourse 100 point snobbery here.
Big difference in things since I lived there!. Anything went as long it could a WOF. Welding the pins is the way manufacturers do it,.The last ones i made I used Bright cold rolled steel for the pins which worked well. If you press the pins home (.0025 clearance) and get someone to tig the outside end so it looks pretty the engineer should be happy. He would have to be happy with your efforts so far anyway. I was talking with a customer today from Auckland who was telling me that NZ won't allow cars older than 2002 and some cars won't pass NZ's crash standards...WTF?,it sounds like the crap we have to put up with here from pollys and beaurocrats who have never touched a engine or what ever in their lives.
The Jalopy Journal
