Building Trailing arm suspension for the Chev thread

Hey guys, just starting this thread to show the new trailing arm suspension we are building for my 54. I should have done this 6 yrs ago when i started the build, but went with the lowered parrellel leaf set up instead thinking it would be easier and still get me what I wanted...Wrong! So now im cutting up my shiney shit to make it rite! Heres some photos of what we are taking out.

 

So at the end of build when I realized I needed air in this i went with a setup that got me thru a year..removed some leafs and ran a air over leaf set up and shock waves up front..it got me thru summer and thats all ill say! We are now making a bigger C-notch, building a crosmember for the trailing arms to mount to, building trailing arms from 1 1/4x3 and tapered them down half way, we made the bushing sleeves from solid 2" stock and milled them out for the metal sleeved bushings from a mustangII lower control arm.

 

I cut the unfinished trunk area out to give the exhaust,Pan hard bar,shocks ext. alll a place to go with still being able to keep the battery,amp,sub a place to hide.
We built new pocket style perch mounts to except the ends of truck arms and bolting them in with three 1/2 bolts
Next was figuring the mount plates for the bags, the lowers will mount as shown to the new arm and the uppers off the new C-notch frame area.

Today we are working on the crossmember and tryin to get that ll wrapped up so we can drop out rear-end and cut the new notches in!

 

Heres a few pics of what we built in the last few days. We installed the crossmember (the pic does not show it finish welded). Made the new C-notches and the new upper bag mounts.Tomorro we will weld them in and cut away old notches..then clean up frame area and install 2 upper crssmembers, the front to support the upper bag mount and a rear to grab the shocks. It sucks cuttin up and workin under my newly finished car but will be worth it when Im done!

 

Got the new C notches welded and cut in into place, built the cross bar for the upper shock mounts..next make the pan-hard bar, get everything painted and cover the hole back up! Then on to the front to install new bag set-up.

 

Nice work!!

 

You do excellent work - my compliments! How did you go about tapering the trailing arms? That was a very nice touch.

Nelson

 

Thanx man..We cut the trailing arms (1.25x3 box) down on the bandsaw then welded in a new finish strip before we used a holesaw to bore the half round for the bushing sleeve.

 

Aside from the fact you are doing very nice workmanship, you're not going to like my comments.....the 'truck arm' suspension is one I think is very good and often underrated/overlooked.........BUT......most I have seen in magazines, vendors ads and on the HAMB are NOT done correctly, in my opinion, and here's why.

The majority of the truck arms are being made from round or box tubing, whereas, the original GM arms were back to back "C" channels, forming a light guage beam that was very strong in resisting axle wind up but was INTENTIONALLY able to twist over it's length. That is very important because when the car body/chassis rolls in a turn and the axle and frame 'twist' in relation to one another, if the truck arms will not absorb that action by doing the twisting, the rear axle housing/truck arm mounts are highly stressed as are the front truck arm mounts. And, the further apart the front mounts are, the worse the twisting/binding becomes.

Ideally, the truck arms would come together and have a single pivot just below the driveshaft front u-joint. But close in to the driveshaft will do if the front bushings have ample rubber..........not delrin/nylon etc.

You may fare better with this since you have gone to the effort of tapering your truck arms and they should be a bit more flexible as a result, but you don't have the front bushings as close as would be most beneficial.

You don't have to take my word for any of this. Just build a small model, using something like a pencil or piece of brake tubing to simulate the axle housing, glue or solder some 'truck arms' to it............hold the front of the arms as though they are attached to the crossmember............and then rotate the "axle housing" to simulate the the leaning of the car in a turn. You'll quickly see the conflict if the arms don't twist along their length.

I was talking to a vendor at the NSRA Midwest meet this weekend In Springfield, MO and he shared a great comment with me............"When there is a conflict between Physics and Style...........Physics ALWAYS wins"

Ray

 

I completely agree with Hnstray's comments.

 

So the difference in arm design seems to make sense as you guys describe it. Because I don't know can someone describe how the Nascar design compared? Was it more like the original GM design or did they use square tube?

 

About 15 years ago, there was a promotional tour that brought 2 real Cup cars to display around the USA. I spotted them set up at the local truck stop...I asked the head guy if I could go under the ropes to look under the Hotwheels car.. I was shocked to see the EXACT C-channel arms as a 60-72 truck...they were 100% the same as a NOS part from GM...riveted together, holes for the trucks E-brake cables, etc.

Somewhere I read that GM sold the rights to the arms so they could be remade for these racecars..so they were identical.


As far as flex; GM used a very large OD rubber front bushing, plus they are very long, so it all helps And I am pretty sure a super heavy duty Chev truck had a stiffener riveted at the entire bottom of the 2 C-channels. So, yes the flexability is a good thing, but making your own should be OK if they are long and have large flexible bushings??

 

you could also verify this theory by dropping one side of the axle with a floor jack and supporting the other side with a jack stand. Watch the front bushing mounts flex or bind up.

 

I recently bought a set from Stock Car Products in Virginia (or W. VA) and they are made in the same manner as the GM orginals. Very nicely done, though not dirt cheap........but few really good things are.

Ray

 

So a guy thinking of using this suspension really could look for a rust free donor and adapt one from an old truck. Thats kind of a joke in my area because there won't be a rust free one anywhere close, but the approach should be solid if the steel is.

I'm actually planning to put a '47 Chevy AD COE cab on a trailing arm type '72 Chevy pickup frame someday. One of my concerns is the condition of the trailing arms, but that is something I'll wait to deal with when I actually start working on that project. Don't be holding your breath its behind several others.

 

I do believe Clark here on the HAMB builds alot of truck arm suspensions for his hot rods.....I think he uses small I beam with holes drilled in them for looks....

 

Hears a 48 chevy pickup with factory trailing arms I did to kinda go with what Hnstray was saying. Sorry not the best pic

 

I'd like to see the results of this. I suspect that there would be enough travel and articulation for a fine ride on a street car.

The arms are long enough that even the smallest deflection at the bushing end will translate to a fair amount of movement at the axle end.

 

Ya, just to clarify im not knocking it, its already in the car, try it out and see how it looks.

 

I didn't think you were.

I am a less theory, more real world evidence kind-of-guy.

Close to half of what I have been told over the years has, so far, proven to be partially or completely untrue.

 

I need to set up the rear of my '52 in the future for bags. I'm curious about how this set up compares with 4 bar. It looks a lot easier to set up. Is the ride / handling comparable?

Pete

 

How much travel are you expecting? I thought the idea was to take as much sway out of the car and have it sit as flat as possible when cornering.
I understand the theories about bend, bind, break, but I don't think there is that much travel.
Scotty.

 

The vast majority of wheel travel on a conventional passenger vehicle is concurrent with the wheel on the other side, meaning that the whole vehicle is going up and down.

You do need the ability to have some non-concurrent movement (just one wheel up/down), to comply with road irregularities. You might be surprised how little that comes out to in the real world.

I drive, daily, a truck that can swing 21", per wheel. The travel gauges show, that even on the roughest paved roads (L3, 65 MPH, I-880 N/S @ Embarcadero Cove), the actual travel is 6" and 8" front to rear, respectively.

 

You've got the relative movement idea right...but...think about what happens at the axle housing/trailing arm junction. IF these trailing arms were jointed at that junction, as in a 3 bar or 4 bar setup, none of this would matter. But, because this junction IS NOT articulated, the small amount of movement at the front end DOES equate to a lot more at the back end and THAT is what is trying to 'rotate' the axle housing about it's own axis. It is as if you had the housing on the ground, the arms pointing upward, and rotated one arm forward and the other back at the same time. The housing tubes won't twist (or shouldn't anyway) and the stress on the trailing arm mount at the housing is incresed by the leverage of the arm's length.

The closer to the center of the chassis the front of the arms are anchored, the less stress is developed, as the amount the arms move opposite each other is reduced, as compared to when they are further apart.

Enough people have installed a similar setup with really stiff arms, and are driving every day, that I can't say it simply will not work. All I'm saying is, it won't work AS WELL as if the geometry is taken into account and accommodated. For my time and effort, I'd like to have the best results available from a particular installation, no matter if it's brakes, suspension, electrical etc. Each builder is certainly free to do it his own way.

Ray

 

That is certainly true, Ray, and a good point.

 

Gimpyshotrods, that set up looks really nice. I like the way you mounted the bags on the arms.

I hope you don't mind me adding to your thread a bit, I think it's a good one and there aren't many out there on trailing arms. I just finished fabbing a set-up in my '50 pickup using stock parts. I put an ad on CL and came up with an entire back half of a '72 1/2 ton plus new-in-the-box bushings, bolts and u-bolts all for $50. I was able to cut the ends off the crossmember (it was too narrow) and weld to some channel that fit perfectly inside the frame rails. My '71 swb rides so nice I've always thought it was a superb suspension. These pics were just a mock-up and don't show it completed but I will have some more soon. It will have air bags in place of the coil springs too.

 

Lookin' good...............!!!

Ray

 

While I do build bag-on-bar systems, I cannot take credit for any of those featured in this thread. They are all from the wisdom of those other than me.

 

A few days away from my computer and I came back to alot of info..First off glad this has turned out to be a informative thyread for future use of other Hambers and not just pics and pats on the back!

Ray thanx for the compliments, it sounds like you have all your info correct and hard to argue or disagree with that nor would I, but as some of the others said some real world does come into effect here too. The box is 1/8 wall 1.25x3 tappered for that reason, we took the measurement off the C-10 outside at the shop for the front spread on arms , they are almost same length too, granted the frames are a bit different in width but not by much. I also used rubber bushings and not nylon for more roll too. The amount of travel back there is 6" and the actual movement of everything is very minimal as we did check over and over to make sure we had no issues along with jacking one side and looking for bind. My buddy who is helping me out with this is well known in our region for building great chassis from hotrods to customs to drag cars so I def trust his imput on all of this. Once again im not disagreeing with you just saying that alot of what you said we did take into consideration but maybe for the next Hamber reading this they will go the C channel route and proffit from all of your advise as it was super informitive! Thanx again

Eric