The Right Way To Reinforce Trailing Arms

[Vanapplebomb]

So I have been thinking about how to reinforce a pair of trailing arms I have. I want to make them nice and beefy, but I don't want to deal with all the unsprung weight that the regular box kits have. To be honest, I really don't think that those box kits make the best use of the weight of material there.

I think I could fabricate my own "boxed" trailing arms that make better use of a given weight of material.

I have seen light weight tubular, but I don't have a tubing bender to fabricate my own, and the kits are on the expensive side, and so I will pass on that option.

Here are my general observations about the arms.
-The strait portion of the trailing arm rarely bends, but is much more easily twisted along its axis.
-The region between the bearing carrier and the spring plate mount is the most likely length to bend.

My opinion of the box kits on the market.
-There is a lot of extra material along the strait portion of the arms.
-The sheet metal doesn't seam thick enough near the outer bend in the arm.

Alright, with that in mind, its time to think about how to loose some extra metal, and add it to where it is more needed.

What's In The Red Box?

Too much, thats what! Keeping the straight portion from twisting doesn't need that much material. Actually, those four joints will leave it weaker than if it was tied together with three. This triangular shape will be better than the box shape. Two 1/8th inch plates should be more than enough if welded together in the center, and tied to the top and bottom lip of the trailing arm stamping. This eliminates some of the extra plating found in the box kit. When that portion is reinforced, it would look something like this.

Here is a picture I found where someone made a brace like this. This picture is better than my sketches.

The Green Stuff

Alright, now that the twisting issue is solved, time to tackle that bending problem. To do this, a heavy plate should be used to tie the end of the trailing arm, to the midpoint of the strait away. 3/16-1/4 inch plate would really bullet proof this week spot.

So as you can see, the combination of the two comes together to make something like this. I made the green corner gussets see through so you can see whats going on.

Now for the shocks. We need something to mount the shocks too since the old mounts are gone. I Think a good chunk of 1/4 inch steel starting on top of the spring plate mount and continuing over the top corner gusset will do nicely. This will also help strengthen the joint between the trailing arm and the Spring plate mount.

And here it is! What do you guys think? Good idea?

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1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[Mal evolent]

mine go to the sandblaster this weekend. when they come back I will do them the AEH way:

stock shock mount, stock rubber bumper, reinforcement without reengineering.
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73 Beetle Baja, Ghia front brakes, Type 3 rear brakes, 2220 ( 94 X 80 ), Weber Progressive, Bosch SVDA, '97 Mustang seats

Baja Bugs for Volkswagen Virgins: Index

[joescoolcustoms]

My 1 X 2 tubular arms weigh very close to a stock, unaltered arm. And the tubing does not have any bends, all straight pieces. They do seem expensive, but I bought mine used for $ 150.00.

Those old design, heavy looking diagional arm brace kits have remained unchanged for a very good reason. They focus the strength on the most vulnerable point on the arm, right in front of the bearing housing, which is what bends on a stock arm. The whole idea of strengthening the arm is to increase the load the bearing carrier can take before bending the metal arm in the weak curve of the stock arm.

The part of the arm between the spring plate mount and the pivot point is not subject to twisting on the axis. The pivot point moves and does not apply a twisting force on the arm. The reason the plates run from the bearing housing to the pivot point is to focus the bending energy the length of the complete arm as a solid package. Just like the shortest distance between two points is a straight line, the strongest member is a straight member. When the bearing housing tries to bend, it has to distribute the force around the stock curve towards the straight postion of the arm. By making it straight, the compressive fource runs in a straight direction from one end of the arm to the other end of the arm. If that is not made straight, the fource has to travel which ever way the metal is shaped.

The inner "Bridge" plate is just that, a bridge member to steady the top and bottom straight plates. If the top and bottom plates were left by themselves, they could bend when under compressive forces. This middle plate connects them to each other and makes a solid box that is super strong.

In the end, how much weight do you really save eliminating one plate of steel? Three pounds between the two arms, maybe? Weight can be saved elsewhere where strength does not matter as much like undercoating, sound deading, headliners, rear kick panels, carpeting and so forth.

Trying to save unsuspended weight has very good pay-offs concerning handeling and response.

The design you have is strong, but the old design is stronger. Your design will focus the bending force at the end of the green plates, which is in the middle of the arm. What is your intention with the arm? How hard are you going to bang on these arms? I am too old and hurt to much to bang on my off roaders any more, so most of my braces are for looks anyway.
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Bad News Racing 2018 NORRA 1000 3rd in Class
Best Day Ever Racing 2022 NORRA 1000 2nd in Class and first All Female team to complete the race

Everyone is gifted. Some just do not open the package.

Looks like it was painted with a live chicken,polished with a brick and buffed with a pine cone

[joescoolcustoms]

Here are pictures of my tubular rear trailing arms. Notice the straight run from the bearing housing to the center pivot point. Having just moved them around to take pictures, I do not think there is much more than a pound difference between these and a stock arm. These are 1 X 2's,

_________________
Bad News Racing 2018 NORRA 1000 3rd in Class
Best Day Ever Racing 2022 NORRA 1000 2nd in Class and first All Female team to complete the race

Everyone is gifted. Some just do not open the package.

Looks like it was painted with a live chicken,polished with a brick and buffed with a pine cone

[Vanapplebomb]

It's not as much about reducing the unsprung weight as it is about putting more material where it is needed...just being more effective with the materials. I think there is a lot of useless metal on the strait aways that would be better off near the bend in the trailing arms.

[larryvance66]

Here is what I've done. Light and effective. Stock length dosn't need much beefing up. It's when you start lengthening things you need more.[img]

[/img]
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I got a Volkswagen for my wife....Best trade I ever made!

[SlipshodPhotog]

Here's another option:

Jeff, at the Kaddie Shack in Pasadena, CA, just started selling these kits that are designed to beef up a stock arm.

[77charger]

Can never overdo the arms.Seen many ripped apart at glamis most were tubular type that break near the bearing carrier
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[AZ-BUG]

Mine...

[Stingray250]

3x3's

[Vanapplebomb]

[mr_bill]

here is a look @ the arms & shock mount on my 11 Car......

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see ya' on the trail........

"Mr Bill"
Dos Perros Motorsports
Orange, CA
1972 Class 11x/Stock Bug
'60's era "vintage" Tunnell-Buggy

"...no one here....get's out ALIVE...."

Motor = electric
Engine = internal combustion

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[Vanapplebomb]

What are the eye holes welded to your bearing carriers for? Towing ropes for getting pulled out?
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1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[Mal evolent]

or trailer tie down
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73 Beetle Baja, Ghia front brakes, Type 3 rear brakes, 2220 ( 94 X 80 ), Weber Progressive, Bosch SVDA, '97 Mustang seats

Baja Bugs for Volkswagen Virgins: Index

[SamT]

Here is how I build them:

The secret to shaving weight from arms is no tosion bars. If you run a air shock or coilover mounted above the bearing carrier the arm doesn't have to be bullet proof. The torsion bar makes the arm constantly try to rip the entire torsion housing off the frame all the time, even somewhat when sitting still!

[AZ-BUG]

[mr_bill]

[Vanapplebomb]

I messed around today with some cardboard and my stripped down arms. This is what I came up with. I would still like to add gussets to the spring plate tab and bearing carrier. Anyways...it's a start.

In the first picture you can really see that I came up a tad bit short on the pivot end. That will be fixed, don't worry

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1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021

[joescoolcustoms]

From an engineering standpoint, that is a good design. Should be strong.

One additional plate to add to take it to darn near bullit proof, is to add a plate closing the area in just in front of the inside of the bearing carrier. In the last photo, on the right side identified as 1/4 inch plate, box the area in just forward of the carrier. This one piece can be done in 1/8 plate. It wil tie the top and bottom plate together and keep them from flexing in a hard impact situation.

Nice work!
_________________
Bad News Racing 2018 NORRA 1000 3rd in Class
Best Day Ever Racing 2022 NORRA 1000 2nd in Class and first All Female team to complete the race

Everyone is gifted. Some just do not open the package.

Looks like it was painted with a live chicken,polished with a brick and buffed with a pine cone

[Vanapplebomb]

Thanks for the input Joe, I will definitely consider doing that!
_________________
1800 Type 4 Berrien 295

http://www.thesamba.com/vw/forum/viewtopic.php?t=487021