Rear Trailing Arm Modification For Air Springs

[Lakeroadster]

I have seen folks modifying their rear suspensions to use air springs and was curious how this affects the trailing arms.

Here is a photo of one such modification

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This set-up totally changes the loading on the trailing arms. Here is a very basic analysis to determine the load on the trailing arm at the spring location:

Stock

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Spring moved forward 12 inches

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The spring loading decreases due to the increased leverage that is a result of moving the spring toward the trailing arm front pivot point.

Note that this evaluation assumes 1000 lb in the bed of the truck, not an empty truck.

The question is how does this stress the trailing arm? I created a model of the rear trailing arm and then ran a series of Finite Element Analysis, FEA.

Note that the representations are exaggerated visually but the values at the left correspond to the actual stress and deformation.

Model of Trailing Arm

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Stock Trailing Arm Stress

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Stock Trailing Arm Deflection

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Spring Moved Forward 12 inches From Stock, Stress

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Spring Moved Forward 12 inches From Stock, Deformation

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So nothing scary looking with the above. But if you look at the original photo above you will see the air springs are not centered on the trailing arm. So I changed the model to move the air spring 3/4" off center. Here are the FEA results:

Spring Moved Forward 12 inches From Stock, Spring 3/4" off center, Stress

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Spring Moved Forward 12 inches From Stock, Spring 3/4" off center, Deformation

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Notice the twisting of the trailing arm. And the stress levels are approaching a level of concern.

Summary

Moving the spring forward 12 inches produces acceptable results, but care must be taken to have the spring centered on the trailing arm.

Since the trailing arms are made from two separate c-channel shaped components mounted back to back making sure they do not separate is critical. A repair kit is available that basically adds a flat bar to the top and bottom of the arms. This should be used.​

The information posted here is for reference only. Results will vary based on actual dimensions, materials used and the quality of the implementation and fabrication.

 

[Lakeroadster]

Here is a link to a thread that shows C20 trailing arms, they came from the factory with the plates partially along the bottom and top to prevent the trailing arms halves from separating.

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[Rich 5150 69]

I really don`t think you need an engineering degree to fiqure out whats going to happen to those trailing arms after a few months if that let alone the stress he is putting on the mounting points at the front, probably shear the crossmember first...

 

[Lakeroadster]

Yeah, that's what I thought too, that's the reason I did the analysis. But the above shows otherwise IF he moves the bags back to 12 inches forward from stock, which he has said he is going to do.

 

[vwnate1]

Good Info !

And hopefully this will make some kid stop and re consider before he gets hurt or kills someone .

I like the idea of re enforcing the trailing arms , I wonder it the C/20 arms pictured will fit (bolt up) in my C/10 ? might be a wise up grade as I'm considering replacing the bushings anyway .

I tend to drive a bit too fast in the twisty bits and after all , SAFETY KNOWS NO SEASON ! .

 

[Rich 5150 69]

And hopefully this will make some kid stop and re consider before he gets hurt or kills someone .

I like the idea of re enforcing the trailing arms , I wonder it the C/20 arms pictured will fit (bolt up) in my C/10 ? might be a wise up grade as I'm considering replacing the bushings anyway .

I tend to drive a bit too fast in the twisty bits and after all , SAFETY KNOWS NO SEASON ! .

All the trailing arms are the same demensions, just the 20`s were reinforced from the factory, ECE sells plates to reinforce any others or just buy the steel and DIY, they suggest stitch welding as opposed to one solid weld. A lot of Drag racers that are using stock suspension this is the first mod to keep the twisting to a minimum..

 

[Rich 5150 69]

Here`s another example of bad engineering or not understanding the concept of coolant recovery, when trying to explain to owner I got a bunch of flak, ok so when it dosen`t recover the coolant and or the bottle explodes its his truck...I even posted a schematic of one for him. Some people just don`t understand, he was just proud of his JD bottle..

 

[vwnate1]

Coolant Recovery ('puke') Tank

Wow! that's scary ;

I hope no Child or other innocent is nearby when that explodes and sends shards of glass flying.....

 

[vwnate1]

Improved Trailing Arms

All the trailing arms are the same demensions, just the 20`s were reinforced from the factory, ECE sells plates to reinforce any others or just buy the steel and DIY, they suggest stitch welding as opposed to one solid weld. A lot of Drag racers that are using stock suspension this is the first mod to keep the twisting to a minimum..

THANK YOU ! .

Depending on how hard they are to remove (I hear they're bugger-all) I'd just go get some OEM ones as they're plentiful here in So. Cal. and heavier duty is always a good thing IMO .

 

[Lakeroadster]

THANK YOU ! .

Depending on how hard they are to remove (I hear they're bugger-all) I'd just go get some OEM ones as they're plentiful here in So. Cal. and heavier duty is always a good thing IMO .

A flame wrench makes it all easy Nate

The front trailing arm bolts are a bear to remove, mostly due to poor access to the fasteners.