Projects Setting caster & radius rods

Ok, I'm new here so go easy. I'm redoing the front suspension setup on my 1940 Chevy pickup. I've got new tube axle, spring,shackles,brakes,whatever. I'm looking at radius rods. I know I have to mock it all up with weight and tires on to properly set caster before I weld hairpin mount to frame. Maybe a stupid question, but when I lower off the jack stands how I keep from pivoting on the shackle mounts?

 

From your pic, it looks like you are going with a traverse (early Ford) style set up?

 

You want the spring to stay straight while the axle settles to it's right caster angle with the weight on the tires before you totally tighten the spring perch nuts. Otherwise you will put the spring in a bind.

What you are going to end up doing is set it at your "that should be about right" setting. then setting it either on it's tires with all the finished ready to drive weight on the tires or setting the axle on stands with that same weight on the axle and the rear axle at the right height to match and checking the caster again to see if you got it right or need to make adjustments. When you have that squared away you can either finish tightening the nuts or loosen the nuts do a few bounces on the front suspension to settle things out so the spring is where it wants to be in relation to the axle rather than in a bind with the axle. Then tighten the nuts and get ready to drive it.

I'd say that the biggest mistake guy make on suspension and that includes those of us who did suspension work for years is to tighten nuts and bolts on bushing or piece that may end up in a bind in the process without the vehicle's weight setting on the tires or having the suspension at it's final position but on stands.

 

Thanks for the replies, yes it's a traverse spring front axle, suicide if you will, Ackerman will be correct. I'm leaving everything somewhat loose on mock up. I'm sure I will not have tons of adjustment, planning on Kurtis style 36" radius rods. And yes, I would say close enough but dont want to have to cut and grind and reweld the rear mounting point.

 

And to add, as it hangs right now frame supported on stands it's at 8 degrees of caster. If I let it down with wheels on its gonna want to really tilt more without the hairpins holding it back, hell it will probably flip up it's got the engine weight on it.

 

What Mr48 is saying, youll have to get it close, clamp or tack things in place, set it down and then go from there. Once its close and on its own weight youll be able to adjust as needed to get it right, then weld it in place for good

 

Thanks guys, you all have tons of experience on here. I smell what you're cooking, I'm going for it. I might need a loan on money, dang, hot rods are expensive to put together.

 

Looks like we might get through this without anyone mentioning the tube axle and hairpins thing.
Oh..... oops.

 

Now you done it.

 

Personally, I do things different than most people but seems to work for me. I like to set the Chassis at what I intend to be final ground profile on stands at the 4 corners. I never work with a full spring pack be it the Front end or the Rear. I generally only use the Main Leaf so things stay in proper position, and I can raise or lower the Axle with screw jacks to where I intend things to stay once the Spring Pack is built to carry the load at that given point. Makes controlling angles much easier. I also often use some kind of stabilizers to hold said angles in place till needed control arms are in place. As mentioned, Never tighten hardware past keeping it in place till final assembly.

 

Just curious here. Where did you buy that front end set up?

 

4" drop tube axle and machined 47-54 chevy spindles from Speedwaymotors.com

 

Thats how we did every build in the shop and how my buddy does them to this day in his shop building everything from 7 second doorslammers to some badass hot rods

 

I would bolt up the radius rods to the axle, but not connect or build rear mounts. Then set the car on the ground with the radius rod rear ends blocked up. Check the caster, and try to get around 5-7 degrees by changing blocks under the back end. Once it's within spec you can measure the frame to radius rod end center, and build mounts to fit. Be sure before you start to adjust the joints at the front out about halfway, so you'll have enough adjustment when done to fine tune the caster.

 

One mine, I set the castor at the leaf-spring perch and rotated the axle to match that way there is no bind in the shackles. Frame mounts for the hair-pins were in line with the up and down arc center of the front axle

 

Good looking digger

 

If there's no weight on the front spring ,then isn't the spring to long ?

 

Axle stays put and with weight the spring gets longer and that gets taken up by the shackle rotating around the axle perch. Right now on the table, where this spring sets, its easy for the shackles to flip. Once the car is down with weight, the flattening of the spring (making it longer) will rotate the shackle lower thus preventing the shackle from flipping. Further note is that the spring is the way I bought it from Speedway, and was designed for the weight of a "T-Bucket" w/ V8 engine on top of it. This Dragster is much lighter, the engine is further back, and a much lighter, 4cyl ChevyII , I have since during mock-up , have removed the extra spring pack so its just the single lower spring. if it proves to need more, I will add another leaf to it

 

Build the desired caster into the front crossmember with the frame set up at the desired height and angle to start with.

 

They sell a variety of transverse spring wedges to allow you to correct spring/shackle bind as you adjust caster. Some even have a slot in them so you can slide them in place without completely removing all the hardware.

 

Very key info right there. Key words are "Center of Arc"! If you don't get that right you won't like how it works.

 

If you build it right you won't need any correction wedges.

 

So , what will control the lateral movement of the axle ?

 

Triangulation of the radius rods,, wider at the axle then the mounts on the frame and the Bat wings will be tight even with them bolted on, as I did not want to weld on the axle
, and since this is center steer and the left to right balance is equal , the front spring. Any side to side is very minimal

 

Shackle angle also will limit how much if any side movement you might have. The more horizontal they are the less it can swing.

 

Using bones instead of hairpins.

 

Fords original design had significantly more radius arm triangulation than your design & still deemed it necessary to spread the frt spring in order that it be mounted in tension to avoid side to side movement .

 

Marty, Will you give Josh1940 a quick version of the trick to mounting the Bones and getting them correct as in your posted photo?

 

Same triangular configuration, Draw a straight line down the radius rods and where they intersect is the pivot point, Just further back then the normal wishbone pivot would be. Ford also used a single ball for the pivot for which the side to side motion travels in an arc and the leaf is what limits that motion but there was some give to allow those cars to traverse different terrains, bumps and potholes and other irregularities , something this car will never see
Every "T" that uses this type of set-up has no track bar on it and relies on the spring. I am using an English Ford Anglia axle so I am pretty stuck with the original design. The front spring was the shortest commercially available so I am using that as my start point. Once the car is complete and on the ground, at that point I can determine if the spring wants to be shorter and at that point it is an easy correction to have it shortened.

 

Mike, this is a simple as I can make it. Whether the car it in a fixture or on the floor, I always determine the ride height and angle. Then, after locating the front axle, at the desired wheelbase, and caster setting, I make the perch. Then, if using bones, I usually windup wedge cutting the front, to raise the rear to the desired height, as I don't like them hanging down and farther than necessary. When using a pre-made hairpins, that can make the job a little more difficult, than fabricating some custom to the job.