broken 40 Ford rear bones....and a possible solution

Well I've seen my first set of 40 rear bones break...or start to. I didn't build it but I guess I'm fixin it

Funny thing is I've run rear bones split out to the frame and never had a problem. This set was the right way and triangulated. After closer inspection I noticed the 37 to 40 bone is a lot weaker than the 42 to 48 version. Luckily all the cars I've done have the later bones.

Here's the cracked bone. The car only has about 5 miles on it...yes I said 5 miles.



Not sure how I came up with this but if you cut a 40 bone of the opposite side ....it makes a great gusset and adds a third bolt. I would still like to add a little more gusseting up the tube




Right now it's just a thought...but I think it just might work
Clark

 

Nice. Always love seeing old Ford parts modified to make useful improvements!
guy in my club has 40 bones on the rear, triangulated ,and open drive. he broke one clean off, I have yet to repair it, but this is a damn good solution.
I think I'll be doing the more ladder bar type strengthening idea i saw on here somewhere, using a rod that goes from the pivot end to the top plane of the diff, with a plate back to the bone, like a laid over ladder bar.

 

I've got the early set you fish plated....I may use them but if I do I'll have to do the end for the hiem joint. I think the early ones will need more than just the fish plate..was going to do both side but sorta like this idea
Clark

 

Lowsquire....that sounds like the typical Rolling Bones set up.

The rear is in the car and painted...I'm trying to get away without pulling it and having to repaint it.
Clark

 

Guess I shoulda mentioned this is an open drive set up.
Clark

 

I was under the impression that a lot of them (when used split) crack where the tube meets the forged end. Have you ever seen/heard of this failure? Are you going to try to address that weak point?

 

for what it is worth there is an article in the current issue of Car Craft on this very problem and a fix

 

I read an article in the Oct '13 Rod & Custom on repairing and reinforcing broken rear bones. Seemed to me they did a whole lot of work and didn't really accomplish a lot other than move the stress point out further on the tube, maybe it is enough, who knows.

To me, those '37 up rear wish bone tubes don't seem strong enough for both the torque of an open drive rear and the twist imposed on them when spread out to the frame rails.

 

Cornfed....I was under that impression too. I fish plated over the seam on most of the ones I've done in the past.

After these failed I've seen a bunch of this style breaking here.

The Dude... Rod and Custom also did a story on this too. That's what got me started on adding a third mounting point.
Clark

 

Rich...if you really look at the 42-48 bone they are a lot stronger than the 37-40.. I'll have to get a picture for a side by side comparison.
Clark

 

After reading your earlier post, I went to compare the early and late rear 'bones; but only had some '40s in the corner, guess I brought the last set of '48s over to my kid a while back. I was only aware of the shorter length of the later 'bones.

 

I liked "Litttlemans" solution... he used the old fatigued parts for a pattern and built a new set!

I really wonder if "winged" sets don't just delay the inevitable!

 

Torque arm.

 

I originally built my 37 with an open drive and the factory cast ends. I used a Model A wishbone that I split for the radius rods. I welded pieces from an old tie rod so it would accept tie rod ends and brackets to the frame for the rear end to pivot. The cast ends started cracking right away when I started driving it. I v-grooved them and rewelded and they just cracked in other areas. I also noticed that the left radius rod had bent slightly from the torque of the rearend. I rewelded the ends and built them into ladder bars "Rolling Bones" style and haven't had a problem since. That has been about 6 years ago. It wasn't much trouble to modify and looks better than what I had. I think even if you can keep the ends from cracking your radius rods will bend. I can send pictures of what I built if you would like.

 

Clark, we had our 40 bones crack on our 27 Bonneville Roadster. We cut out the old mounts and made new ones with the extra mounting hole from good 5/8 steel plate, and welded them in. We then wrapped the bones with 1/8 sheet from the bracket out 15". This gave us a very strong set of bones. Any one splitting their bones in the rear for racing or drag starts should think about doing this procedure. --TV

 

After numerous post about the weakness of using original torque tube supports as radius rods the answer is, they still wont work. These are triangulation brackets for the torque tube they are not designed to be used as radius rods . The closest that will work are the 35-36 design but they even leave questions as to the internal rust factor deteriorating the quality of the piece. In short you cannot or should not use 1937-48 ford torque tube supports as radius rods, they are too weak no matter what you do.

 

That's a cool idea. If you look at my build thread you will see the Uni ball I used to connect the front of the bones to the frame for an in split look. It has 32 degrees of movement, will let the axle/bones work like they are attached to a torque tube coupler. Should keep them from binding which is part of the reason they break. I'm also using an open drive banjo. I'm thinkin both these ideas together might eliminate the need for the torque rod. I do have a torque rod on mine.

Check post 91-92

http://www.jalopyjournal.com/forum/showthread.php?t=511327&page=5

 

Physics always wins over style. Put a torque arm on it. Run it to one of your bones so you don"t have a conflict or put a shackle on the front. Look in the speedway racing catalog on how the sprint cars do it.

 

After I had the same problem twice,, I finally decided to use a set of Pete and Jake ladder bars,,hated to but i just feel like I did the smart thing.

The bones work fine if they are not split,,the later bones are better for this but they too need reinforcing. HRP

 

Yes, and a hamber with a 32 just called me this morning as he was trying to get to a show.. One of his parallel rear arms broke yet again.

He and I have had many talks on the problem in the past, and despite not wanting to "alter" a 50s built car, I believe he is going to fix it correctly this time.

 

Don't split them out to the frame and be sure to run a torque arm.

 

The solution:

 

Yup, torque arm.

 

thanks, I wanted something that would let them move like they were supposed to. splitting them and using tie rod ends or even heim joints works sort of but those both have their limits and at some point will bind because they arent moving from a central point like they would with a torque tube coupler. the uni ball has 32 degrees of movement in any direction, from cycling the rear end in the chassis and driving behind it while being towed, it will never be close to limiting out. I'm using a Hot Rod works torque rod kit, just wasn't installed in those pics. the Uni Ball, some 36 radius rods and a torque rod would be the shit!

 

He needs the torque arm.

 

Fellas, if you read, I have the hot rod works torque arm installed.

 

I still don't think the popsicle sticks are the best tool to explain it, as the center one is twisting, and he does not mention it.

He seems to mislead a person that can't grasp the stresses, by saying the heims might be beyond their angle limit. That leads a inexperienced viewer to think that a better joint up front fixes everything.



I was trying to discuss this over the phone earlier, and it is not easy. What we need is a video of a steel pipe acting as the rear end, with two other steel pieces welded to the pipe as the arms. Then go through the bending video.

Do the same, but with an I beam type profile to represent a front I beam axle, which can work, because of the I profile which twists very easily.


The best teaching tool "in person", that I know of, is to disconnect a rear split bone mount on a front beam axle setup, and have the car owner lift up or push down, to see how easy it twists the axle, and therefore is not straining the split bone parts.

then explain how it would feel, if the front axle was a tube, like a rear end.

 

If you really think about it most suspension set ups are wrong then. The only correct ones would be with the bones mounted at one point and not split and an independent style.

Ladder bars, 4 bars, parallel springs even truck arms all will have twist. Truck arms are designed to twist.

A torque arm does not stop the twist. The torque arm only helps with the forces of acceloration and stopping.

Riddle me this. We built a car with the bones split out to the frame....I know it's wrong! We used 46 bones with the weld between the forged or cast end and the tube gusseted.

The car has been used and abused hard. Flogged around a dirt track....a bumpy ass ride....sideways. The clutch has been dumped on a sticky ass dragstrip with slicks. AND does not break.

Then there is another car that has the bars triangulated ....the correct way. It has 40 bones. The car is driven 5 miles and not abused and they break.

Where is the logic??

I'm just trying to come up with an easy and safe method to fix a done car. It's not a race car that needs over engineered. It's just a simple hot rod that will not get beat.
Clark

 

This is the answer from someone who knows his old Fords. I use the 35/36 bones and reinforce them by splitting, inserting tube and re-welding. Lots of work but they don't crack under any condition.

 

Its hard to say, luck, some things that arenet supose to work do, and some things that arent supose to work dont!

Is the car that has the gusseted bones a lighter car than the car with the 40 bones? ive got both types of bones and the later bones are a little beefier but not that much, maybe you gusset just worked.

What i would do its thro out the 40 bones and make a pair out of some heavy wall dom tubign and make a larger plate using 3 bolts where they mount to the axle, mill a slot in the Dom tubing so the plate goes into that some, if all that makes sense.