Trailing arm reinforcement

[Aaron Burkemper]

What have some of you done for reinforcing rear trailing arms? I am putting a new set on my 71 C20 2WD. I see the factory had a small plate mounted to the top for extra strength. It doesn't seem like it would do that much, frankly. I was considering boxing in a portion before I put them on. Any previous experience? Pics would be great.

[mikecaddy500]

Mine were rusted out from someone doing that previously. I opted to spend the extra money for tubular arms.

[nightrider388]

What I have seen a lot of people do is weld all the seems on top and bottom and it basically makes them a solid box and keeps moisture out.

[Aaron Burkemper]

There sure are a lot of options for upgraded arms and the like. I couldn't see spending that kind of money on a rusty farm truck.

[pappy 2]

stich-welded top and bottom seam.

[FirstOwner69]

Originally Posted by Aaron Burkemper

What have some of you done for reinforcing rear trailing arms? I am putting a new set on my 71 C20 2WD. I see the factory had a small plate mounted to the top for extra strength. It doesn't seem like it would do that much, frankly. I was considering boxing in a portion before I put them on. Any previous experience? Pics would be great.

I believe only the 3/4 ton trucks had reinforcing plates. There were two plates, one riveted below the trailing arm and one above. The half tons used the same trailing arms without plates. Based on that, I'd say you probably do not need the plates unless you do some heavy 3/4 ton type hauling.

Here are pictures that show the top and bottom plates.

[Aaron Burkemper]

That is correct. It's going on a C20, but I couldn't find specific C20 arms. I guess you buy C10 arms and add plates yourself. Or some other reinforcement. I don't know if it would really make a difference if you aren't working your truck like a 3/4.

[68c10airstream]

Was there trailing arms on c20's??? I thought they were only on c10's, but not sure now!!

[indymachinist]

I too stitch welded my trailing arms. I have heard you want to stick with the I-beam style (dont box them in, dont do tubular, etc) for best performance. The fact is these NEED to be able to flex. Its part of the design. You just don't want the 2 halves to separate.

[GASoline71]

Originally Posted by 68c10airstream

Was there trailing arms on c20's??? I thought they were only on c10's, but not sure now!!

Sure are. My stepson just acquired an 1969 C20 that has a D60 and trailing arms with huge coils

Gary

[SCOTI]

Originally Posted by indymachinist

I too stitch welded my trailing arms. I have heard you want to stick with the I-beam style (dont box them in, dont do tubular, etc) for best performance. The fact is these NEED to be able to flex. Its part of the design. You just don't want the 2 halves to separate.

The beam style works in factory form because they can twist (by design) & the front rubber bushings allow for some flex.

Stitch welds won't inhibit the ability to flex. Aftermarket 'tubular' arms offer increased rigidity but will bind sooner vs. factory arms unless some sort of different front bushing is used. That's why those that 'get it' build their T/A's w/some type of spherical joint up front for articulation.

[hounddogs!]

I blew apart a set of 1/2T arms and started there. Got the two sides clean and coated, then basically followed the factory spot weld pattern to reconnect them. I had new plates cut to beef up to the 3/4T design. The attached PDF is the drawing I used to have new top/bottom plates cut. I used the axle u-bolt to locate the plate, then clamped and plug welded. The rectangular piece in the lower right was for patch panels in the vertical web. Those are visible on the arm on the left below.

All the joints are slathered in seam sealer - I am not going to let these get full of dirt.

[FirstOwner69]

Originally Posted by 68c10airstream

Was there trailing arms on c20's??? I thought they were only on c10's, but not sure now!!

Coil spring rear ends were standard on Chevy 3/4 tons with leafs as an option. I've read that leafs were standard on GMCs with coils as an option.

[Tom Vogel]

I used the Early Classic Enterprises top and bottom reinforcement plates. They are really solid now. Good product.

[Shaky]

I was on a budget early on in my C20 project. The arms were still good, but rust was forming in between the reinforcing plates and the arms. I drilled the rivets, made new plates, and bolted it back together.

You could do something similar to make 1/2 ton arms into 3/4 ton arms.

[special-K]

Is any of this really necessary? Just asking because I've never done anything and never saw a reason to. I don't see rust being an issue on a pleasure ride. Plenty of originals out there still not rusted, too.

[Tom Vogel]

In my case, running high horsepower and sticky tires, yes. In many cases , no.

[Shaky]

Originally Posted by special-K

Is any of this really necessary? Just asking because I've never done anything and never saw a reason to. I don't see rust being an issue on a pleasure ride. Plenty of originals out there still not rusted, too.

Depends on your truck/situation, yes?

You can:

1) Run your rusty ones (I know people who do);
2) Find better used replacements;
3) Rebuild/reinforce your old ones;
4) Run 1/2 ton arms on your 3/4 ton cuz you don't carry heavy loads;
5) Buy aftermarket tubulars.

I wanted to rescue mine before the rust got worse. Probably didn't need the reinforcement, but I'm keeping my C20 all 3/4 ton and might tow with it occasionally.

[indymachinist]

Originally Posted by SCOTI

The beam style works in factory form because they can twist (by design) & the front rubber bushings allow for some flex.

Stitch welds won't inhibit the ability to flex. Aftermarket 'tubular' arms offer increased rigidity but will bind sooner vs. factory arms unless some sort of different front bushing is used. That's why those that 'get it' build their T/A's w/some type of spherical joint up front for articulation.

The spherical joint in front is not what limits the flex. It is the tubular construction itself.

Flex in these truck arms is required for articulation. If they were truely solid and would not flex, you would end up with basically a hinge for rear suspension. If one wheel went up or down, the other would have to follow exactly the same motion. This is not ideal at all.

Look at the nascar truck arms... they are I-beam, stitch welded, and have spherical joints in the front. They WANT the arms to flex, on purpose.


FWIW, I am using stock arms with no plates added, stitch welded, and with Hotchkiss spherical front joints. Pretty budget friendly, and more than adequate for my uses.