Projects Dynacorn truck arms

I am in the process of collecting parts in the build of my 40 Buick. Plans are to convert to an open rear using the GM truck arms. I have researched all of the previous threads on this subject, so I would like to stick to the title topic. I have a set of decent original arms, but with the usual corrosion prevalent. Dynacorn makes them, probably off shore. Has anyone purchased these, and what did you think?

 

I had a set of good ones I sold years ago, this may not be the internet of your post, but if I had that set again for a pattern they would be able to be made easily from some box tubing and flat iron.

 

I put a set on my '69 El Camino awhile back, with no issues. I thought the quality was good.

 

Well, they "look" right !
I hung a Quick Change under my Stude a few years back with Chevy truck arms. But like you, the arms are '''just" usable.

I'm not going to use the round tube arms, they don't react to the twisting motion correctly.
I'd measure the material thickness of your current arms, (in a non-rusty area), call or e-mail Dynacorn and ask them if they would measure the thickness of their arms.
NOTE - I just called Dynacorn. They do not sell to private parties. But they will hook you up with a dealer nearest you that deals in their product.

If VERY close, or the same, I'd go ahead and buy.
I may look into this myself.

Mike

 

The original arms on those Buicks were designed to work with a torque tube, and are far to light weight for an open rear. If the Dynacorn arms are like the Chevy truck arms they would probably work fine.

 

On my 48 chev I had two good sets of 60's chevy truck arms. There is a place called hotrods to hell in Anderson, CA. The did the truck arms for farm truck. Steve is the guy that runs the place. I bought my adjustable panhard and mounts for shocks from him.

 

I built my own truck arms out of 3/4 ton truck composite leafs for my Chevy II.

I have about 425HP and I have driven it hard for almost a decade.

 

like the watts linkage !

 

The original design of GM truck arms allows for the inevitable lengthwise twist of the arms in normal suspension movement while retaining the ‘beam’ strength required. Square, rectangle and round tube arms resist that torsional twist, which unnecessarily stresses the arms, while providing no benefit to suspension control. (Cue a chorus of “I’ve used homemade box/round tube arms for years and they worked for me!”).....

You CAN make the back to back C channel design arms too....if you wish to “roll your own”.

Ray

 

You could make your own of round or square tubing if you change the front mount to allow for twisting. I would use the rubber donuts that Ford used on their twin I beam truck front suspension.

 

I used Chevy type truck arms to make the ladder bars for my'40. They were used NASCAR arms I bought at a place called Second Chance Race Parts, or something like in N.C. They have Heim ends in place of bushings. Also, I bought a couple of pair, some were built with an extra amount of angle in them. Gene.

 

I have a 40 Ford coupe with an original cross spring. It has tube shocks
and utilizes a set of Chevrolet arms from a pickup. They are identical to
the ones in my sons 65 c-10. There is a linkage that appears to be made from
a steering component that attaches to the chassis and the rear axle
housing at the opposite side. It seems to work well and would plant
the tires under robust clutch engagement from the 371 Olds, J-2
motor. I will transfer this assembly to a 9 inch rear to replace the Olds
in there at present. The arms do hinder exhaust routing to the rear of
chassis.

 

Tin Works out of Eldridge, Iowa makes nice ones.

 

Good point right there.

 

I appreciate all the replies. The Dynacorn arms, part number 1158 and 1158A, appear to be made identically to the GM ones. They are a fairly new product, and sold through Speedway Motors. I have contacted Dynacorn with questions about the metal thickness and bushing design. I could roll my own , but considering the u bolt tunnels, rear kick up angle, and bushing mounts that have to fabricated, it is hard to beat their price. Once Dynacorn replies, I will post it.

 

I think if you carefully study the anchor points and the movements of the axle in relation to the chassis, you will probably conclude that the Ford bushings would not fully compensate for the twisting forces involved. It was not for nothing the GM engineers designed the arms as they did for the application.

Ray

 

I have thought this was a good design for years.

 

I think the GM truck arms as designed offers the best option in my case, but will be really tight where they converge in the x member. I am studying the idea of splitting them, shortening them up 2" in a staggered joint, and reassembling. I have an engineering buddy calculating the reduction in "twist" ability this creates, but does put the bushing end mounting distance apart closer to what GM did, and gives more driveshaft room. The other option I am looking at is using the coil spring mounting hole as a u-bolt hole, shifting the whole arm back since my car mounts the springs behind the axle. I would use the rear hole to mount the coil spring pad.

 

I realize that you were asking about Dynacorn's torque arms, I can't answer about them because I have never used them, but personally I wouldn't buy anything that was made by Dynacorn! I have dealt with their products in the past and found them to be lacking in quality and there appears to be no quality control. If it were me, I'd build my own!

 

We used the Ride Tech truck arms in a Buick once. Replaced the torque tube set up.
As far as twist, on a lowered set up like we used em with, I doubt it ever needed to twist as designed for a factory height truck.

 

Reviews of Dynacorn products are all over the map, hence my original post. Since a fairly new product, I doubted anyone has purchased them yet. I requested product information from them, we will see what they say.
I also have looked into several other options such as parallel and triangulated 4 link kits, only to go back to the truck arms. Anthony Myrick has a good point about the amount of twist vs. travel. There are several companies that make a variation of the truck arm, and research continues.

 

There aren't too many Customs crossing a pasture with a load of fence posts or bales if hay in the back either. I don't think the ability to handle extremely uneven ground is going to be an issue with banginggoldtin's (sp?????) Buick. Fixing uncle Fred's 69 long bed so he can put the camper back on it and go up in the woods to his favorite fishing hole. then it is an issue.
I've got the whole back half of a 70 long bed's frame under a trailer that I have that I built after I rolled the truck that I am thinking about robbing the truck arms out of for my 48.

 

Just a thought; the truck arms are used in Nascar cup cars and when on a road course and under severe braking the rear tires will hop around losing traction/braking and control in general. May apply to street use too but I have no hands on. Same may be true with traditional ladder bars but I don't think I've noticed a complaint of wheel hop under hard braking on the street. Some one go test!!

 

Wh not just build a 4 link and be done with it?

 

Thought I would give an update to this saga. I contacted Dynacorn and another company (CPP), both which are selling new arms. Neither of them could answer my questions of metal thickness, bushing design, and how the halves are put together. The only response I got was "they are reproductions of the original". Going to pass on both and find some decent originals.

 

Interesting idea. Have you ever measured the rear axle wrap under hard acceleration?

 

OK guys, an update- The two companies that manufacture these arms, Dynacorn and CCP, could not provide metal thickness and construction details. I wound up shortening an OEM set 3", by removing a 3" section on each side in a staggered 6" joint. I put a thin copper strip between the halves before welding so they would stay separated, and removed the strips after. The new length will allow the x member to stay intact. I just need to clean them up and paint, but I thought I would share pics to show what I did before that. Tin Works also said they would make a set in their design to my length, but I decided to try this.

 

No, but after twenty thousand miles of hard driving and spinning a pair of 315 rear tires every chance I can I'm still pleased with the results. I built this as a street/track day car and having spent time as a driving instructor I think it handles quite well.

 

I installed a 46 Olds X-member with OEM trailing arms in a friend's 42 Chevy PU frame and added coilovers with a 9". I stepped up the frame etc. The driveshaft loop and panhard bar weren't finished. Reinforcing plates removed any torsional twist. Arms were open 'top hat' style' that could be boxed if necessary. Measure twice, cut once to ensure geometry and pinion angle are correct