Looking for opinions on setting up rear suspension for traditional Gas Class drag car with ladder bars. I'm looking for the bite, as well as the look...
i just installed a set on a customers 55 chevy gasser, we kept the stock leaves in it and the ladder bars ran up to the middle of the door. we ran them at about a 2 degree decline from front to rear, mainly for aesthetics. sorry no pics didnt get a chance to snap any before he picked it up.
I just want to know how to get the best bite & stability. Short wheelbase fullbodied Gas Class car I'm planning to build. Seems all the info I can find has coilover setups and I'd rather go with the leafs for the period style.
The Thunderbolt style bars work and certainly look old fashioned. Easy to make from 1/8th steel and 2 x 3" tubing. On my 64 Fairlane which is sort of a natural application I made 'em 32" long and they pivot about 10" from the ground with 30" tall tires. The car will do big wheelies on 9" tires.
If you do parallel leaves then you need sliders/rotators on the axle housing to prevent the ladder bars from fighting the springs. If it's transverse leaf or coils you need a panhard or watts or other means to control side/side movement. Longer bars equals better traction. They tear up the front bushing or eye with a lot of street use, plan for replacement when they're built. good luck
Look depends on what traditional period you are shooting for. Just like ride height and paint scheme etc. As far as bite a good starting place is for your instant center to be about 4" above the ground and just slightly beyound the center point of the wheel base. Then tweek it from there.
If you want to run parallel leaf springs why not look at the Mopar rear suspension used in the early 70's? It's engineered to work without ladderbars. Or you could go with some kind of slapper bar like Lakewoods and not worry about having the ladderbars bind up the springs or viceversa. It worked well enough for Jenkins in the late 60's. As far as ladder bars go, in the early to mid 70's it was in the rulebook that ladder bars couldn't be any longer than half the length of the wheelbase. I don't know if the rule still applies or not, wouldn't hurt to check. Larry T
Are you sure? A bar that is real long picks up the front of the car and lets the rear drop. If the rear of the car is dropping, it's the same as the tires trying to pick up off the track and unloading. Also a bar that loads more of the weight of the car (imagine a jack positioned to pick up the whole car) loads the ladder bars harder than a long ladder bar that just trys to pick up the front of the car. As usual I could be wrong, but that's the way I always figured it. Larry T
I was thinking of using 4 heim joints to make a pivoting link (V) in the front of the ladder bars to lessen the spring binding with leaf springs. Anybody try this? Just wondering. Might loose some of the effectiveness of the bars but if look is the goal along with some extra traction this might help. Any thoughts?
I think the key words here are Traditional Gas Class drag car build. I know that things have lightened up a bit but I'm not aware that the '70s have made it inot the definition of traditional yet. Most of what gets built as a trad gasser has to be raced outlaw or on a non NHRA sanctioned track. So I'm not exactly sure that the '70s NHRA rulebook applies here. But I'm probably wrong. carry on.
HJmaniac, As long as the ladderbars are mounted solid on both ends, the spring is mounted solid in the front and the axle bolted solid to the spring, the suspension will bind up some. It has to since the spring changes length thru it's travel (that's why there a shackle on one end). I've seen sliders on the spring mount, spring boxes with sliders in them for the front spring mount and ladder bars with a slot in the front mount. I've also seen suspensions that do bind up that seem to work pretty well, so pick your poison. If you're planning to run a slider setup on the street they seem to make a LOT of noise. Some of them kinda sound like the rear end isc coming out of the car. Porknbeaner, Like I said, I don't know if that rule is still in the rulebook or not. If it is, I'm wondering where you find an outlaw or unsanctioned track to run at. Sure you can get by with it at most sanctioned tracks most of the time. And not all gassers ran the long girder ladderbars, even in the 60's. My Anglia had them on it, but it wasn't the most efficient car leaving the line either. If you'll look in Montgomery's gasser book, there are a lot of cars that you can't see the bars on. The High and Mighty (I know it's not a gasser) even ran a 4 link with short bars back in the EARLY 60's (maybe late 50's) Larry T
Longer is better right up to the point where you gotta start dropping the front mount location for installation reasons and mess up the instant center. At least that's how I know it. I've been wrong before and will be wrong again.
Longer bar moves the instant center forward in the car and that makes the tire hit softer. More horsepower usually requires the instant center to be farther forward. A short bar and big horsepower usually means "Blue Skies" (wheelies) That is the reason for use of 4 links...they allow infinent location of the instant center.
Most cars will use a ladder bar in the area of 30". Some will say that longer bars work better but with proper tuning a 30" bar can act just like a longer bar. If it is something like a long wheelbase pick up than you can use a 34-36" bar. Anything shorter than 30" will usually rotate the pinion too much. Generally the lower bar of the ladder will be pretty close to parallel with the ground with the car at ride height. The actual set up goes something like this; Looking at the car from the side, imagine a line drawn vertically through the front tire contact patch. Now imagine a line drawn horizontally at the center of gravity. These two will intersect at a point somewhere above the front tire. Now visualize a line drawn from the contact patch of the rear tire to the front intersect point. This is called the no squat/no rise line. Now, if the rear suspension instant center (the front pivot point on a ladder bar car) intersects the no squat/no rise line, that is what the rear of the car will do, neither squat or rise on acceleration. If you move the pivot point above the line, the rear will rise causing the tire to hit harder due to better weight transfer and if you move it below the car will squat softening the hit. There is more to tuning that can be done with spring and shock rates, pre load, front spring weights and loads etc. but that is the basic setup for a ladder bar car.
I just went thru this with my Model A. It requires a lot of data to correctly mount the ladder bar at the frame rails. I measured all of my mount points then weighed the car on each corner, then a buddy put the info in a program and told me at what height the ladder bar should be mounted on the chassis. You need to know how much weight is on the front tires and the rear tires when the car is completed.......or cheat and have a common setup that everyone is used to like an 85 Camaro. That an a high dollar set of double adjustable shocks should get us going, I will find out tonight, its the first time I have run the car since the changes. Hot Rod Don's comments above are exactly what I was chasing.
I guess this is the idea I was thinking about. I see Cal Track has alraedy been doing it. Kind of pricey. Any body use these or this Idea. Should be simple to make I would think. CALTRACS Traction Bar System <FORM method=post action=http://order.store.yahoo.net/cgi-bin/wg-order?chucker54+catrbarsy1>Item# catrbarsy1 <INPUT value=http://chucker54.stores.yahoo.net/catrbarsy1.html type=hidden name=.autodone></FORM> Product Description Tremendous benefits can be realized when the CALTRACS traction bar system is installed on a leaf spring suspended automobile. CALTRACS traction bars were developed to achieve specific goals to improve high power traction while staying within hard set NHRA parameters. Each of the two assemblies needed is comprised of three basic components: 1.Front Pivot 2.Force Transfer Link 3.Rear Mount The combination of these components changes the pushing point on the car by redirecting the turning action (spring wrap-up) of the rear axle through the Force Transfer Link into the Front Pivot. The Front Pivot Spring Stop Bolt resists this turning motion and also controls the bending of the leaf spring at its thinnest section. The push into the Front Pivot helps the cars weight shift towards the rear of the car because of a new directed angle of force toward the front of the vehicle. (The "Instant Center" moves farther forward). This is where the system emulates a Four link system. The pinion angle is also maintained. 1. The Front Pivot Two steel plates sandwich the leaf spring sides. Two attach points in the plates provide the user with a selection in which the forward Force Transfer Link rod end can be located. A machined aluminum spring eye bushing and steel insert supports the front of the spring while allowing the plates to pivot. A spring stop bolt controls and restricts spring wrap-up. Spacers are provided for different vehicle applications that control clearances in the front spring eye pocket. 2. Force Transfer Link This is a length of chromolly tubing with CNC machined threaded inserts TIG welded into each end. The front Insert is machined with right hand Threads and a HEX outer shape for Simple wrench adjustment of the Installed assembly. The rear insert is Left hand threaded. Opposite thread Styles at each end provide the means to easily lengthen or shorten the link for desired pre-load adjustment. 3. Rear Mount A welded ¼" steel assembly replaces the original vehicles spring perch and incorporates the mounting provisions for the rear rod end of the Force Transfer Link.
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