Projects Installing Radius Arm Mounts

Need advice on mounting these brackets. Outside, inside, bottom of frame?? How high or low should the arm be from the frame?
Also is there any info out there for this type of type of build?

 

You’ll have to provide a little more information. What kind of car? frame? front axle? Radius rods?how low do you want it to be? That bracket partly determines the caster angle at the kingpins, a very important factor in a safe driving car.
The info you need is on here but searching for it can be a pain. Post more info and I’m sure folks can get you started in the right direction.


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From the looks of them I would think the bottom of the frame. HRP

 

how high or how low kinda depends on your front suspension setup. Are you using them for radius rods? or for wishbones? you need to have you front axle and spring assembled and mocked in position to check and set your caster at the king pin. this will let you know rround about where the mounts need to be. I acutlly used these same mounts on the inside of the frame with a hole in the side of the rail for the tie rod end to go through to mount the wish bone. You can kinda put them where ever you want, and design you front end around that location. I don't recommend just welding them to the bottom of the frame and putting you front end on, they will hang really low and look goofy as shit.

 

how high or how low kinda depends on your front suspension setup. Are you using them for radius rods? or for wishbones? you need to have you front axle and spring assembled and mocked in position to check and set your caster at the king pin. this will let you know round about where the mounts need to be. I acutlly used these same mounts on the inside of the frame with a hole in the side of the rail for the tie rod end to go through to mount the wish bone. You can kinda put them where ever you want, and design you front end around that location. I don't recommend just welding them to the bottom of the frame and putting you front end on, they will hang really low and look goofy as shit.

 

My '30 pickup uses very similar brackets, and yes they install to the bottom of the frame. As the others have said, this is what sets the caster of the front axle, so you need to make your measurements and set them in the correct position. Are you using hairpin radius arms? Hair pins will allow you some adjustment of the caster angle once the engine is installed and you have full weight on the car. The hair pins should be installed so the bottom rail is parallel to the ground.

 

I used a pair of these on a 1934 chassis and a buddy on a 1930 Model A. In both cases mounting to bottom of chassis proved too low (as noted in prior post).

 

Here is what I have right now.




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I see you have them tacked to the frame now. What I would do is leave them that way for now and then come back to them when you have your frame hight and rake finalized and then move or modify the bracket to set the proper caster.

Phil

 

Put those mounts where they look the best in YOUR opinion, THEN, if needed, pie cut the radius rods near the axle and adjust the caster angle to 6 degrees with car at final ride
height. This has to be done with the engine in and the final weight on the car. Then weld the pies.
That type of front radius rod setup while looking cool, works good for drag and circle track race cars but provides a very harsh ride for the street. This is a better alternative for street, autocross and road racing where you are turning both ways and want a softer ride. That is a Kenworth truck tie rod end.
This was a very successful autocross and hill climb car.

 

Very nice Pete. Where can one find more information on that set up?

 

I agree that pie cutting the bones is a great way to set the caster but you want to be a more competent welder than me to do it.

Phil

 

What do you want to know?

 

Well, I was wondering where that joint came from, but now that I look at it, it's a threaded lug or sleeve connecting the wishbones together, with a ball joint threaded into that, and then another mount welded to the cross member with the ball joint attached to that, so that whole thing can rotate with the wishbones right to left, and up and down, giving full articulation. And all fabricated, right?

 

Roger on that. Kenworth truck tie rod end. Looks exactly like the common early Ford tie rod end on steroids. 7 degree tapered stud. Readily available at Kenworth truck dealers parts dept.
I used the same basic setup on the rear except there the anchor point needs to be directly under the U-joint cross and up as close as possible to it. (open driveline)
When used on the rear the radius rods need to super stout becaause not only do they take up the rotational torque from the axle but 90% of the forward driving force is through them. the other 10% is through the spring.