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Scratch built radius rod questions.

10K views 12 replies 5 participants last post by  Loose Ctrl 
#1 ·
I am planning a scratch built woody wagon T bucket with a supercharged Continental flathead I6 from a 50/60s car.About 140hp and roughly 250ftlbs of torque.I would like to run tubular radius rods front and rear.I don't think the front will be an issues because the torsional loads will be small.The rear however,will be under some torsional stress.My plan was to run hiem joints at the frame in brackets and solid mounts at the axle in kind of a C shape.The tubing I am considering making them from is 1.25 inches in diameter and .25 inch wall thickness.Transverse spring up front and coil overs in the rear with a panhard, or preferably a watts link.I'm not looking to race, or run this car hard,but it will be a driver and see interstate duty.Should I increase my rod size to 1.5 inches in diameter and .50 inch wall thickness?If I scrap this idea,I'd consider braced hair pins front and rear.
 
#2 · (Edited)
Typical racing 4-link bars and standard ladder bars are 1.0" x .156" wall DOM(drawn over mandrel)mild steel tubing, has a .688" bore which is then direct threaded 3/4"-16tpi for a 3/4" rod end(hiem).

Tougher 4130 chromemoly tubing is typically 1-1/8" or 1-1/2" x .083" wall or .062" wall and then has a threaded insert welded in the tube to accept the 3/4-16tpi rod end.

1-1/4" x .250" wall mild steel gives a too large tube ID to be able to direct thread for the heim, and too small an ID to accept a threaded insert for a 3/4" hiem. Wall thickness is certainly overkill as far as strength.....I can't even imagine using 1.5" x .500" wall tube...oooohhffff, that's heavy.

1-1/8" x .250" wall mild steel gives you a .625" bore, which could then be slightly drilled oversize and tapped for the 3/4-16 tpi for a 3/4" heim....if you feel you need the larger OD and thicker wall, either for aesthetic looks or strength.

I will say this...I built my own 4-link, drag race 1" x 156" tube and 3/4" heims....you will have a hard time buying all the bracket and tube material, bolts, nuts, right and left hand thread taps, and heims for the cost of just buying them prefabbed...I'll not do it again to save just $40-50 in the end. Learned my lesson well there.

Tube size and wall is going to depend in your case on what size and style Hiem you intend to run ...3/4, 7/8, 1"??
 
#3 ·
info from the WIKI

stuff I posted a few years ago on the WIKI here on hotrodders on building a T bucket
4 link/hair pinsYou can build your own hairpins from 7/8" DOM (drawn over mandrel) steel tubing. If you have a blower or lots of horsepower you will want to use 1 inch DOM tubing. You can use a Harbor Freight pipe bender to bend the tubing. You have to cut the pieces longer than finished length to work in that style bender. Cut the end that has to be tapped 1 inch longer than the finished dimension, weld a small piece of scrap in that 1 inch area to grip in the vise so you won't get teeth marks on the finished piece. Use a large right angle drill and start with the bit that will just remove a little bit of material then keep changing bits until you get to the size required for the tap. Then, drill out that extra one inch with the bit size to match the OD of your tap. ONLY GO ONE INCH DEEP. This will allow you to start the tap in straight and get good threads. Then you can cut off that extra inch, and redrill with the correct size for the tap, finish tapping to the new length and have good straight threads.

When drilling or tapping use plenty of tapping fluid or thread cutting oil; you can use a tubing notcher that you bolt to a steel table top and tack a piece of scrap angle iron so you can clamp the tubing at the right angle to cut the ends.
The last 2 T bucket chassis built I used the CCR blue prints, easier that when I used to mock up everything with 2 X 4's and pvc sprinkler pipe.
http://californiacustomroadsters.com/index3.html
 
#6 ·
Thank you all for the input.I have done 4 links and ladder bar kits before.I installed a set of hair pins, but that's easy, just bolt everything together.The ones I am thinking of are the old school single rod made from the wishbones with tractor hiems.Oh,and I made the mistake of assuming that DOM tubing was the standard.I didn't know welded seam tubing was still in people's vocabulary in the hotrodding world.I love chromoly.I used it when I was in the aviation field.Expensive tho.

Anyway,here's what I am going for,except I want solid rods.My car won't be in the dirt low.4 inch dropped axle with spring behind the axle up front.Out back it will be coil over mounted behind the axle.

These are speedway units similar to what I want.I'm not concerned about having the taper.I was planing to weld a C made from 1/8th inch plate to connect at the axles.I hadn't thought about hiem size.It would be nice to just thread the tubing and go that route.
 
#10 ·
modified wishbones.

The ones you show should have an I beam front axle to allow some flex in the front suspension. If you use them on the rear the pivot point should be close to the center line of the frame for good handling. If the split wish bones are used on the rear and fastened solid to the rear axle housing the axle tube acts like a rear sway bar with and infinate torsional rate. If you want them on the rear for the old style look they could be part of a 3 link with pivot attachment to the axle housing.

I would go with heavier than 1/8 plate. I normally use 3/8
 
#11 ·
Hair pins, radius rods...I've also heard of them called Curtis rods, after the 50's Curtis midget racers.

I agree 1/8" is too thin for brackets...I use 3/16" as a minimum, 1/4" for heavier duty when making double shear brackets....5/16" and 3/8" for single shear....most of the time it is just looking at the job and making an educated and experience based judgement call, no hard guidelines.....but I feel 1/8" is just too small for anything suspension related other than reinforcement plates, fish plating, or gussets.
 
#13 ·
I had a post written out earlier and the processor in my other computer crapped out.It had pics and everything and I lost them. :smash:

Oh well.Thanks guys for setting me straight on material thickness.I am now thinking of keep the rear outside radius arms and doing triangulated upper links instead of straight bars and panhard or watts link.I have about got this figured out.Now if winter would blow out and I could get the house done.
 
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