C-10 / C-20 Trailing Arm, Coil Spring Perch Rebuild

Posted: December 29, 2015 By: JamesR

Just about every 2 wheel drive Chevy Pickup from the early 60’s to the early 80’s came equipped with trailing arm rear suspension and coil springs. Comparing this set up to the typical leaf-over-axle configuration found in most trucks, the trailing arm setup provided a much better ride while still being able to haul a load when needed. This setup was preferred in the 2 wheel drive trucks for its ability to accomplish both tasks well, which is why it was a sought after option for so many years. Since then, newer more effective suspension configurations became available and this type was phased out.

Even with its mass popularity it had one major flaw, each trailing arm was constructed out of two pieces of C channel then bolted together in multiple places with plates welded on the top and bottom in the rear where the springs and axle were connected.  Structurally the arms were very strong but the two piece design allows water to become trapped between the two channels and rust from the inside out. If the two were fully welded on both sides, top and bottom they would not be a problem but 40+ years later its rare to find a truck with rust free trailing arms.

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Photo thanks to http://67-72chevytrucks.com/vboard/showthread.php?t=255644

The rusty trailing arms on my 1963 C-20 were about as bad as they come, so much so I could reach my hand through some of the rust holes.  About a year ago I stenciled out 3/16″ plate and welded them on both sides of the arms in order to regain structural rigidity so I could drive it safely.  As you’ll see in later pictures I have yet to weld in one of the plates but it is already cut and will be welded in soon.

 

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When it came time to install lowering springs I noticed yet another catastrophic rust area.  The factory welded plate where the spring is bolted to the arm was rusting from the bottom up and actually separating the spring from the arm.

 

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Only adding to my list of problems was the upper and lower spring retainer bolts which were rusted so much that the first tap of my impact broke the heads clean off.  Essentially leaving me with a headless bolt that was rusted through the entire trailing arm.  No amount of Penetrating Oil would have saved me here because the same thing happened on both sides.

 

When Cutting Or Removing Coil Springs Make Sure The Spring Is Fully Decompressed, Springs Can Store A Lot Of Energy Making Them Very Dangerous To Remove Or Cut. If You Are Unsure If Your Spring Is Fully Decompressed, Do Not Attempt To Remove Or Cut The Spring.

 

Now having to re-plan my attack I decided my best option was to cut the spring out giving me direct access to the top side of the bolt and more room in general to work.  I did not have any plans to reuse the springs so cutting them was not an issue. In order to get the spring decompressed I jacked up the rear of the truck and placed large jack stands on the frame adjacent to the front trailing arm mount. I then lowered the rear down on to the first set of jack stands then continued to lower the rear axle until it was suspended.

 

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I checked the stability of the truck and slightly lifted the rear so its weight was supported by the jack. I then proceeded to remove the lower “pan hard bar” connection and moved it out of the way.

 

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The “pan hard bar” is unique to trailing arm rear suspension because unlike leaf spring, double wishbone and coil-over strut setups, there is no hard connection that keeps the rear axle centered under the vehicle.  Once the pan hard bar connection was removed I lowered the rear axle back down to where it was suspended.  I placed a second pair of jack stands under each end of the axle and raised them until they were almost touching the axle but not yet supporting any weight, ensuring the springs were still fully decompressed.  I also left the jack under the rear differential and raised it to just make contact, in a situation where there are soon to be cut springs and a couple hundred pound, 3/4 ton, rear it’s always better to be safe than sorry.  This setup allows the rear to evenly and easily drop down onto the jack stands without falling to the ground and potentially kicking out the front jack stands which were supporting the rest of the truck.

 

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To remove the passenger side spring I chose to use my Versa 40 Plasma Cutter, even though it is only rated to 3/8″ steel I was able to make a pass from both sides of the spring in order to cut  through the 1″ diameter spring. It took multiple passes and made a lava hot piece of spring but it got the job done quicker than any other method.

 

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Once both springs were cut and the axle was resting on the jack stands, I used a cut off wheel on an Angle Grinder to remove the old spring retainer and spring perch leaving me with the remainder of a rusted bolt still left in the trailing arm. The amount of metal to remove will greatly depend on the amount of rust that is present. I was able to get away with a only removing about 3 inches on either side of the spring mount.  I then cut out the remainder of the rusted top plate revealing the tops of the trailing arm.  About an hour later, a ton of Penetrant and a large drift pin I was able to remove the remainder of the stuck bolts.  I cleaned up any remaining surface rust with a Flap Disc on an Angle Grinder.

 

Rebuild Time!

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Instead of just welding in a new plate on top of the trailing arm and calling it a day, I decided to beef up the spring mount and back section of the trailing arm. After going through my stock of metal, I came up with a design that would “sandwich” the rear of the trailing arm between two pieces of plate and for extra strength I will be adding a 1/4″ wall tube through the trailing arm and welding it to both plates.  Now water will not be able to get trapped inside the bolt hole and rust itself fast.  I made short work of measuring and cutting the top plates using my Versa 40 Plasma Cutter, it was a big help making square cuts when I removed the rusted out plate.

 

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With the top plate cut and tested for fitment, I marked the center of the bottom plate and drilled it out to the outer diameter of the pipe size using a Step Bit, make sure to take it easy and use some type of cutting fluid while drilling because it can be very easy to burn out the bit.  When drilling thick metal with a step bit, it helps to drill a series of pilot holes increasing in small increments.  Step bits can wear quickly if used to heavily so it’s best to only take a small amount of metal at a time.

 

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After drilling out the bottom plate I used two welding magnets to hold the piece of tubing at a perfect right angle and used my TIG 200 DC to weld the two together on the top and bottom sides.

 

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The tubing was slightly larger than the previous mounting hole so it also had to be drilled out for the pipe to slide all of the way through to the top side.  Luckily I had a large enough drill bit because it would have been a long day with a round file.

 

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I test fit the lower piece set the top plate where it will be welded in, using a marker up through the bottom for hole to get the exact placement of where the upper hole needed to be drilled.

 

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After drilling the top plate I once again test fit all of the pieces and found that I needed longer Grade 8 bolts to compensate for the added material.   I also used a Flap Disc to bevel the edges to create a stronger weld. I confirmed that all of the holes were in the correct location and again removed them to be coated.

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I applied Rust Encapsulator to the inner faces of the bottom piece and hammered it into place, I then coated the bottom of the top plate with Rust Encapsulator and set it into place.

 

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I passed the longer bolt through both pieces and tightened it down by hand, then tack welded both edges of the top plate. Since the trailing arm was slightly bent from too much weight being loaded on the weakened trailing arms, I used a Ball Pein Hammer to straighten out the remaining metal to meet the new plate.  After straightening the old metal, I used an impact driver to tighten down the bolt so the two edges met, then finish welded the rest with my MIG 175.

 

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Proper penetration on these types of welds is very important because this is a structural weld supporting the entire rear of the truck.  All Eastwood MIG Welders have infinitely variable controls which make setting them up super easy and accurate.

 

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I then used a Flap Disc to go over all of the welds to create a smooth finish, I wiped down the area with PRE and then brushed on rust encapsulator to seal the welds and any exposed metal.  .

 

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Removing the top bolt was easy and only took a few minutes since it was not rusted nearly as bad as the bottom.  I still had to use a cut off wheel to remove it but once the nut and spring retainer was cut off, the bolt was easily driven out with a hammer.

 

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I removed the rust with a Flap Disc and brushed Rust Encapsulator on the top and bottom mounting surfaces then bolted in the lower spring retainer.

 

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After waiting a few hours the Rust Encapsulator was dry and I was able to instal the 5 Inch lowering springs. I still need to go back and weld in a new side plate in front of the E-brake cable mount but that’s a job for another day.

 

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Not only is the truck sitting low, it now has super strong rear spring mounts that will most likely last longer than the life of the truck.  Can’t wait to get the engine and trans back in to see the final ride height   Keep checking back for more build progress on this 1963 Chevy C-20.

 

Check out the Eastwood Blog and How-To Center for

 more How-To’s, Tips and Tricks to help you with all your automotive projects.  If you have a recommendation for future articles or have a project you want explained don’t hesitate to leave a comment.

– James R/EW

 

 

 

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