I ran some searches, but I need to find out if I should beef up the area my rear rods are mounted to. I am running a for 8.8 with a Trac Loc, coils, vertical shocks, and a panhard. The radius rods are mounted on the outside of the frame rails with a single hole drilled through the rail and the heim just bolted to it. I'm asuming the panhard bar will absorb some of the twist, but should I change the design of the frame mount? IE, gusset it with some 1/4" plate? here is a picture for reference. You might have to zoom in as this is the only picture I have at the moment.
That is not going to work for long. A front "I" beam can have split bones/or hairpins out at the rails, because the I beam can twist as one wheel goes up or down. The rear axle assembly is tube and can't twist, so as one rear wheel goes up or down, you are going to tear up the hairpins or break welds. If the rear arms are beefy enough, the rear axle tubes will crack in two pieces...there are pics of that on hamb. Someone else chime in here...
X 2. The front of your radius rods should be mounted as close together as possible to reduce bind and CATASTROPHIC failure.
If you are planning to put very much horsepower in it, you might consider a 4 link, go triangulated to eliminate the panhard bar altogether. If it is all going to be up underneath anyway, it will be a more dependable, and less breakable solution.
Hate to be a party pooper, but those hairpins ain't lasting long trying to be ladder bars no matter how you mount 'em. Take a new direction and think stouter, stronger, and more geometrically correct. Glad you asked cause some body could seriously killed with the current set up.
I typed in a reply and then deleted it, I'm with the Tri-Angulated 4 bar set up on this one. Or if you don't like that look check out the So Cal Speed Shop rear radius rod set-up, real nice stuff!!!
Thanks for the replies. This was not my design, and this is my first build. After reading a bunch of stuff about hairpins, I started to question the way the PO designed the rear. It has been a few years since my steering and suspension class in college, but I saw this design as well, poor. I am running a stock 302 with an AOD, so it will be under 300HP. I guess now It's back to the drawing board. I will have visitation with the car this Friday. I'll try and remember to take pictures so I can show more of whats there to build off. Thanks again.
Seeing as you live on another continent I think it is a pretty slim chance... But be that as it may, I don't want to be the one getting killed either which is why I brought this design up.
i think he might have been responding tongue in cheek to the way that statement was phrased by the guy who wrote it. i'll give a thumbs up to the pete and jake's set up. a couple friends are building cars with them now, and they are super stout.
Lots of mis-information in this thread. . . hair pins can flex, wishbones can't. Those are rear, hair pin, radius rods (from Speedway). That little "Z". . . or "S" shaped gusset (depending on which way you look at it) is made to keep the rods from bending under torque, but still allows the rear ends of the hair pin to flex some. You can use them on the rear, but I'd mount the front ends closer together on the frame (mount them to the inside of "X" member itself).
Correct they are the ones from speedway: http://www.speedwaymotors.com/Classic-32-Inch-Rear-Radius-Rods,3363.html It might be tricky to mount them on the inside, as I will be limited for room with Fuel tank and bed. What are the downsides to mounting on the outer frame rails? Also, I will update with more pictures ASAP to give you a better idea of whats going on here. [/IMG]
The downside to attaching them to the outside of the frame rail is that it restricts movement when one side of the axle is raised (going around a turn, over a bump, etc. . ) This could cause the mount on the frame, or on the axle to break. There is some flex built into the design of those radius rods. . . but mounting them closer (in a tri-angle) will allow the axle to move more freely, and lessening the chance of the mounts breaking. I'd personally mount them to the inside of the "X" member by making mount (out of tubing with a threaded insert) that goes through the "X" member (where the radius rod attaches) to the frame. This way, all of the stress isn't on the "X" member. Ok. . . so I nerdded it up and made a "crude" drawing. Grey = Frame and "X" member. Black = Rear axle. Blue = Radius rods. and Red = Radius rod mounts (mounted to the frame rails, and through the x member). Hope this makes some kind of sense. . .
Another idea that may help on mounting them inboard would be to replace the existing axle bracket that centers them on the axle with one that mounts them lower on the axle. Maybe similar to the P&J bracket in the picture.
This issue comes up on the HAMB astoundingly often and has been properly explained many, many times. To get a better idea of what is at work here, try this: Put you hands in front of you, about chest level, about 6 to 8 inches apart...open a space between your thumb and index finger 2 1/2 to 3 inches....and keep the fingers horizontal.......now with your hands/fingers so positioned, turn one hand clockwise and the other counterclockwise and notice what happens to the imaginary "radius rods, bones, splitwishbones. etc.".....and particularly notice how they would have to rotate on the axis of the axle, whichever hand you designate the "axle". They would just try to break off the mount if they are rigidly attached, as in usually the case in these discussions.You COULD use the hairpins, and have them function okay IF you made them part of a 3 or 4 link rear suspension AND therefore had them attached to a bracket on the rear axle with ONE bolt that allowed the hairpin to move (pivot) in relation to the axle housing. The 3rd or 4th link would control the axle housing position during all phases of operation except lateral. A triangulated 4 bar would control lateral, or just use the Panhard bar you have now and 3 or 4 bar without triangulation will be sufficient. Edit: For the OP....another way to see this in action...put your chassis on 4 jack stands, put two more under the rear axle.....no springs so only the suspension components are involved...now take a floor jack to one side of the rear axle at the drum area and raise that side....watch what happens....you will see the hair pins try to twist and soon be raising the chassis from the jack stands on that side before they have moved much vertically. The rear axle range of movement, one wheel up, one down, will be very limited. Ray
Sorry, but that is incorrect too. The closer to the center of the axle/chassis the control arms are mounted, as pictured, the less the forces are for a given amount of chassis roll, but the forces are still there and unwanted and will either resist suspension movement and/or want to break something. You can deny it, doubt the accuracy of these statements, but it is just a fact of physics/geometry that wishing won't make go away. If you put the forward ends very close together you further minimize the forces at the axle end, but the control arms need to be able to 'twist' along their length to actually make a difference in the outcome. For that reason, square, rectangular or round tube (single tube style) are not suitable. GM truck arms were "I" beam shaped and would twist along their length, were mounted very close together at their forward ends and, lastly, used compliant rubber bushings for more absorbtion of movement. Ray
You guys got me worried now, My 29 model a coupe which weighs 2300 pounds has the speedway set up like that on it. I have put over a 1,000 easy miles on it with no problems so far. I looked in the speedway catalog and they sell frames with that set up on them.But my suspension has only about a 2 inchs of travel. Is thats whats saving me? or is it just a matter of time before I have trouble?
Amount of travel, if both wheels travel in the same direction, does not matter. But, each time one wheel goes up or down while the other wheel stays put, or goes the opposite way...then you have stress. Like on a bump on one side, or just a normal roll in cornering. as Clint said "are you feelin lucky?" How far "spead apart" are your front mounts?
The front hiems are right under the frame probably 2 inchs in farther then the rear where they mount on the axle housing.
I did exactly what Ray is suggesting on my track roadster that had a similar setup - the hairpins weren't even on rubber bushes where they mounted to the axle which may have taken up some of the movement in articulation. Scary thing is this car drove like this for about 12 years before I bought it. My new setup retains the look of the hairpin but only mounts as the upper link. Lower arms are triangulated inboard. They are pretty short but the axle moves though a 4" range of motion with no problems. Geometry could probably be better but this isn't a racecar and packaging was a consideration. One other thing: I would be beefing that up with a bung of some sort that is welded to both sides of the frame rail.
tfeverfred: I am running the lowers triangulated instead of the uppers which seems to be more conventional. Herb Adams book and other research I did seemed to show no issues running them either way. Length of the lowers was a slight concern in terms of pinion angle change and well as anti-dive/squat etc. With the fairly limited travel and type of use intended I don't see a problem
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