The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by Devin, Feb 4, 2008.
Hairpins should allow a little more comesnsation to binding by flexing more than a ladder bar, no?
Triangles have 3 corners, not 4.
Ladder bars, Radius rods, whatever they are whatever you want to call them need to be mounted to a single point in the front. Anything else puts a twisting force(moment force) on the rear end housing. For a very long time a lot of cars have gotten away with mounting the bars close together up front, as seen by a number of pictures of the better designed suspension systems posted here. They can get away with this because the arms are long, the distance moved by the rear end is small and by having a bit of flex in the structure.
Mounting the bars to the framerails is a shit design, and shows a lack of understanding of the structure of the system. Everytime you hit a bump, even the small ones, you are forcing deformation in the structure. Build it as beefy as you want... its still gonna break. David
Four-Thirteen said it right and best!
So you're saying EVERYONE that has used radius rods or hairpins is going to experience breakage? That sounds a bit extreme to me...
It makes no difference if you use ladder bars, hairpins, or wishbones - the geometry is the same.
If you want to understand the geometry, try this ...
1. Take a strip of cardboard
2. Fold it into a U-section. The centre piece represents your rear axle and the two legs are your ladder bars, hairpins or whatever.
Put it flat on the desk and with one hand hold points A & B down on the desk.
Then try to lift point C up. You can see that the whole "axle" wants to lift up.
Now put another finger on point D and try to lift point C up. It isn't easy and if you force it, you can see the cardboard deform.
This is what happens when you are driving down the road and you hit a pot-hole with one wheel. In the real world, it is your brackets, welds and rear axle that have to flex to allow that one side of the axle to move. Sooner or later somethings gonna give.
To see the benefits of a triangulated rear suspension, move points A and B together until they touch and then try to lift point C up. See how much easier it is ??
No. And not all drunk drivers get DUI's...etc, etc.
My straight ladder bars lasted for 16 years, but they did finally fail. I didn't know any better when I was 18 years old. I saw drag cars set up that way, so that's how I set it up.
I know better now and wouldn't set up a street car that way...
Your mileage may vary.
So if not every setup like that breaks, how can one build that setup to allow for the safest setup possible?
You still want to use the arms mounted to the outside of the frame and you want to know how to make it safe?
Read the *30 response again and do a search of the other thread I mentioned.
You know...this gets on my nerves because the facts are: EVERYTHING wears...EVERYTHING has stress applied to it...and sooner or later: EVERYTHING wears out and breaks.
The further toward the center up front, the better, but, unless, as stated, they are an absolute triangle, there is going to be flexing stress.
With a crossmember ( NO frame mounts...), double shear mounts, Grade 8 bolts, misalignment bushings, and long hairpins, and good welds, you will rack up a whole lot of trouble free miles.
You should always be looking at how your car is wearing, and aging, anyway...just because you have a four link, or triangulated bars doesn't mean things are NOT wearing or stressing other parts...A suspension stresses the frame, tires hooking stress the suspension, the motor stresses the driveline... They are ALWAYS wearing.
Springs break, tires wear, bearings fall apart...
I would definately not mount them just to the frame rails, however...
so what im hearing is im fucked , i have mine on the sides of my frame rails , if i new i would not have done it , so i guess ill be plaining on changig it next winter and just drive the car around easy for the summer , and after all this ,i still dont know the best why to set up the rear if you could have anything or any set up what would it be ?
I hear you guys loud and clear. I've abandoned my plans to mount to the frame and have already ordered a set of triangulated bars. This is my first rod, I don't plan on dying in it and taking anyone else out at the same time. I was pretty much just curious about all of the pictures of cars as well as kits being sold which mount the bars to the frame. Thanks for the solid explanations everyone.
Well apparently I won't get any answers here from any of the thousands of people who've safely mounted hairpins...I guess I'm better off buying everything from a kit like everyone else...thanks for nothing...
Love your attitude. Please buy whatever you want. A lot of people have tried to help you. You'r welcome!
Well, besides the "it'll never work" crowd, there's been no advice from the folks who have the type of setup we were asking about, and it's obvious it isn't deadly since it's used everywhere, hell, speedway sells chassis kits with clevis and heim mounted hairpins that mount to the frame...apparently they're murderers...
the reason hair pins last is because of the thin tubing used and the lack of braces between the 2 tubes. they will flex and bend before it puts the stress into the rear end housing.
the shorter the bars are the more stress that gets transfered to your welded on brackets and rear end housing.
a car can look like it has wish bones mounted to the frame but they may also just be the lower links of a tri 4 link
i admit not the best but i have them on 2 of my cars and to no breaks or cracks of anything.they do run right along side the frame to a coil over set up and the other to a buggy spring style no pro blems as of yet and i drive them all the time.
Everything binds, hence bushings on leaf springs...I've decided to use 4 bar style bushings on all 6 mounting points of my ladder bars...or modify '36 ford front wishbones...
I have been running 36 bones on the back of my Model A Pickup, bolted to the Big Pontiac rearend straight forward to the frame rail....Drag raced the hell out of it,drive it on the street, but am always looking over the entire truck, I have a check list......I constantly put it up on jack stands and get the creeper out and a bright light...I do this because I punish the thing......If I was worried about body roll and if my cruisin chair would fit in the trunk, I would be building a streetrod....If I want the rearend to do its job at the strip and I was building a hotrod/dragcar I am in favor of a ladder bar setup........I totally understand what the rear suspension is doing and understand the pros and cons of it all.........You can get them all to work and they all can fail........I did make a custom triangulated set up for DeathsDoorStep due to my room constraints and am anxious to see how it will react to a prepped track...I was just looking over a Bucket T rolling chassis that had the ladder bar set up pointed inward at the front.........and guess what ...cracked at the rear of the housing on both sides at the attachment points.........bottom line is be careful period, check your stuff out especially if you think your built so called correct.............Littleman I would like to add, I started to pull my engine tonight, I will be bolting in a new more powerful engine and have plans on beefing up what I have as far as the 36 bones or making my own bars........for what I do with my truck it is possible that it will be the new weak link and will need to be addressed along with a roll bar of sorts.....a real roll bar not a bolt in.....
Dave, do you happen to recall the mounting hardware used on those ladder bars? Notice any bad welds? Are your '36 bones front or rear bones originally?
The bolts were grade 5, I would have to check the dia. again........shitty welds all over this rig...it was a real eye opener for this guy after he dropped it off for me to look at, him and his wife paid 15g's for this thing, its truely amazing that so much scarry stuff is on the street........The more I look at cars the more I see alot of it is builder error/lack of welding prep and technique...alot of under built stuff as well.........My bones are rears originally with the old spring mount cut off.........I know my setup on this hotrod is not perfect, but has worked well for me up to now...but with the introduction of atleast another easy 100hp thrown into the mix...I am rethinking my own setup for an upgraded setup of the same...Littleman...their is all kinds of great ideas on this site, pick one that works for you....
I meant if the ladder bars had bushings, heim joints, tie rods or clevis'? I often worry about the quality of my welding, which is why I'm constantly putting practice pieces in my press and trying to break them...only bent pieces so far...paranoia makes for better builders...
The ladder bars had a heim up front and clevis out back, I am describing the ones I found cracked on the guys bucket T.......the ladder bars are homemade, with the scariest weld holding them together up front where the two tubes merge together......Littleman
I have no problems with my parallel hairpin set up.
But there are a lot of other things to consider, not just them, that contribute to the whole thing working, and, I am also always crawling all over my car.
Now that somebody whom everyone respects said it, maybe all the grumbling will subside a bit...or maybe not.
I DO, however have an S+W crossmember, for them to attach to inside the frame rails. I know a friend with his pins mounted inside the frame w/ no crossmember, just tabs, and he has thus far had no problems, but again, you have to consider the whole setup, the way it is driven, etc...
I personally feel better with the crossmember, and the heim ends being in double shear, but I am also prone to taking this thing to the track as much as possible.
There are people who spend their entire careers and a lot of their personal lives studying the principals by which mechanism and structures like this work.
I suppose there are two, real effective ways you can go about designing a system. The first would be to copy an existing model you know is effective. The second would be to understand the forces involved, design mechanics, material sciences, and design metrics (the measure of how well the design does its job). Failing that, you could seek consultation from someone who does understand the mechanics of the system, and listen to what they have to say.
I haven't seen many if any hot rods that weren't modeled by method one, copying other designs. It’s been hammered out pretty well what works and what doesn't, things like drop axles, spring rates, tube shocks, and actually everything else on the car. Designing a car 100% from nothing would be time consuming and pointless, namely because we already have many effective designs. The problem arises when a bad design works its way into the system. I'm somewhat hesitant to call it a design, because that would imply that someone actually understood the workings of it before implementing it. Copying a good design completely and accurately is pretty safe; almost copying a good design can be dangerous.
As a builder, it’s your job to make the decision as to exactly what happens on the build. The people who know the systems you are building typically are rarely wrong in their understanding of the system, and they will generally know exactly how wrong they are. They are called engineers, they can guide you. Engineering rarely if ever fails, it’s the poor decisions as to how to use it that fail.
Engineering rarely, if ever fails?
Did you just say "Typically/rarely" and "Generally/exactly" ??
Your one 'O them engineers, aren't you?
And there are many times that engineers say something won't work and it does...living a life in theory and design does no good if it's not also put into practice...we're not re-inventing the wheel here, just putting to use an apparently wrong principle that somehow works for some people...
and fails for even more.
will it work indefinately? yes.
is it a good idea? no.
make your decision and quit arguing.
if it works then you can tell everybody to blow it out their caboose, if it breaks they'll say 'i told you so'
its been that way since the dawn of time.
I've been pondering the ladderbar question for some time myself, and have decided that if used, they should be as long as possible, 36" minimum (I have heard of 5-foot ladderbars!), have urethane bushings at all six points, mounted with grade 8 bolts and nylock nuts, in double shear at all six points.
Whether to run them parallel or triangulated is a separate question.
So let me get this. I'm taking my purpose built altered off the track and putting it on the street after YEARS of hard thrashing. It has ladder bars mounted to the frame rails, and has no indication of cracks or broken welds yet.
Now, since I'm going to be on the street is the issue body roll that doesn't occur on the drag strip? If so, would I be better off cutting the middle bars out to make them into regular hairpins? thanks, Mike
Sounds like a nice load of those ChiCom fasteners we've been buried in for years! I don't think I'd blame the ladder bar system until I'd elimnated the bad fasteners as the culprit here
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