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1951 Mercury No Limit Engineering Installs Trailing Arm Rear Suspension - Mercury Rising (And Dropping)No Limit Engineering Installs Trailing Arm Rear Suspension On A '51 Merc From the April, 2010 issue of Rod & Custom By Kev Elliot Photography by Rob Fortier
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I'm a big fan of trailing arm rear suspension, especially under customs. Not only does it offer a smooth ride with great handling and traction, but there are no upper arms to worry about, or even the upper section of a ladder bar. This means they'll fit under the floor of a custom with minimal or no modifications, especially advantageous when dealing with low cars with scant room underneath! I've installed this setup a couple of times, including on the Rod & Custom project '49 Chevy. This type of suspension also has the benefit of no wheel hop, unlike the parallel leaf systems they usually replace, and is the type of setup widely used in NASCAR racing. It's rugged, simple, and it plain works. With the exception of the... With the exception of the replacement rearend and axle saddles, here's everything required to swap the Merc over to airbag-equipped trailing arms. No Limit Engineering also likes the trailing arm system, offering a number of kits for '37-57 Chevy cars as well as '47-54 Chevy pickups, available with airbags or coilover shocks. They recently undertook a trailing arm install on a '51 Mercury chassis belonging to No Limit Owner Rob MacGregor, and while previous kits have used Chevy pickup arms, and even fabricated tubular arms, No Limit Engineering kits will use the box section arms, as shown here, in the future. In addition to being adjustable (before they're welded) for length depending on application, the box section arms eliminate the need to transition from a tube to a flat section for the axle mounting pad, but also offer more rigidity when it comes to axle wrap, reducing the possibility of pinion angle change under acceleration and braking. The comprehensive kit comprises the trailing arms, axle saddles and U-bolts, Panhard rod and brackets, shock absorbers, airbags, front and rear mounting crossmembers and hardware. Though obviously easier to install on a bare frame, there's no reason this job couldn't be undertaken with the body in place, and with the exception of a new driveshaft and brake plumbing, should be an easy weekend project, offering improved ride quality, air suspension, updated brakes, and modern wheel stud pattern all in one fell swoop.  With the bare frame sitting...  With the bare frame sitting on jackstands, it was checked to ensure it was level in all directions before work began. Shims between the frame and the stands would rectify any issues, but were not needed in this instance.  Though the stock axle was...  Though the stock axle was removed, the leaf springs were left in place. Using a plumb-bob hung from the chassis rail and aligning it with the axle locating pin on the spring, the axle centerline was transcribed to the inside of the chassis rails. The springs and hangers were then removed.  Axle saddles are available...  Axle saddles are available from a number of suppliers, but are designed for parallel leaf springs. In order for them to be used with trailing arms, where they are not perpendicular to the axle tubes, the front of one side of the U-section and the rear of the other, where they'll be welded to the axle, had to be clearanced. No Limit Engineering supplied the pads that were made for the angled trailing arm mount. They supply all of the parts and little, if any, mods are required.  No Limit Engineering uses...  No Limit Engineering uses these huge pivot ball bushings at the front of their fabricated trailing arms. Modified versions of off-road joints, No Limit has them manufactured with urethane inner bushings for street applications.  The arms were bolted to the...  The arms were bolted to the front mount and the assembly set up level on a couple of lengths of box section on the floor. Note the axle tubes on the 9-inch that will be used have been relieved of the stock bracketry and ground clean. The observant amongst you will also notice the axle saddles are placed on the opposite arms in this picture!  Switching them side for side,...  Switching them side for side, the saddles were temporarily tack-welded to the arms at this stage, ensuring the mounting holes were aligned. You can see here how the axle tubes can now sit in the modified saddles at the required angle.  Tack welding the saddles to...  Tack welding the saddles to the arms meant the rearend could be manhandled around and located centrally without worrying about dislodging the saddles.  From above it's clear how...  From above it's clear how the rearend sits in the saddles, and how the Panhard bracket will place the Panhard rod perpendicular to the centerline of the car.  With a straight-edge clamped...  With a straight-edge clamped to the front mount/crossmember, Michael and Owen checked to ensure the rearend would be square in the chassis.  Diagonal measurements were...  Diagonal measurements were also taken, which ensure it'll be central. You can't take enough measurements when modifying components that will effect a car's wheelbase and tracking, as it'll never handle correctly if the front or rear axles are mounted offset or at an angle!  A couple of shims under the...  A couple of shims under the pinion yoke brought the pinion angle up to match that of the transmission output shaft, before rechecking the measurements.  With all measurements deemed...  With all measurements deemed acceptable, the rearend was tacked to the saddles.  With the axle and trailing...  With the axle and trailing arm assembly squared and tack-welded, the front mount could be clamped in place on the stock X-member.  Again, diagonal measurements...  Again, diagonal measurements were taken to ensure correct location before welding. If the front mount is misaligned, the rearend will sit crooked in the car once mounted.  Once Michael was satisfied...  Once Michael was satisfied the mount was located correctly, Kim tack-welded it to the X-member.  The trailing arms could now...  The trailing arms could now be bolted to the mount. The high angle of the joints used at their forward ends allow the brackets to be welded to the plate at 90 degrees, meaning all four are the same, cutting down on production time and costs.  The shock absorber top-mount...  The shock absorber top-mount crossmember, which also mounts the airbags at its outer ends, is made in three pieces, the center tube sliding inside the outer sections, allowing for it to be easily installed on a chassis with the body in place. Note the righthand side is tack-welded, while the left will be once everything's located in the chassis.  No Limit provides this hole...  No Limit provides this hole in the end plates of the shock crossmember for location purposes, though it's not actually used to hold the crossmember in place. The end plates will be welded to the inner framerails.  Here's the bolt used for location...  Here's the bolt used for location purposes, passing through an original hole in the frame. The crossmember locates just before the top of the rear chassis kick-up, in front of the stock shock crossmember, which remains in place.  Once located correctly and...  Once located correctly and adjusted for the correct width, the end plates were tack-welded to the inner rails, and the center tube tacked to the end sections.  With the rearend lifted into...  With the rearend lifted into position it was attached to the trailing arms using a pair of U-bolts, in the same manner as a Chevy pickup. In fact the U-bolts are the same size as Chevy ones, but are the correct length for this application.  With the axle bolted in place,...  With the axle bolted in place, and measurements taken once again to ensure everything's square, all that remained was to fully weld everything and install the Panhard rod.  Once the Panhard bar was bolted...  Once the Panhard bar was bolted to the bracket on the end of the lefthand trailing arm, and set to allow some adjustment, Michael welded the bracket to the underside of the righthand chassis rail.  After everything was tacked...  After everything was tacked in place, the whole assembly was torn down again for final welding. Here, the axle saddles were being fully welded.  Included in the components...  Included in the components is this gusset for the Panhard bracket, required to prevent side loads from tearing the bracket from the chassis.  The endplates of the shock...  The endplates of the shock and airbag crossmember were welded solidly around their perimeter, shown here midway through.  With a hole drilled through...  With a hole drilled through the trailing arm, which was then sleeved, the airbag simply bolts in place. The upper mounts come pre-drilled for the 'bag mounts and access to the air fitting on the top.  Fully welded and with the...  Fully welded and with the airbags plumbed temporarily and inflated, here's the suspension at full height...  ...while here it is at full...  ...while here it is at full drop. With 9 inches of travel, this system offers an improved ride and adjustable ride height, yet is simple and above all, safe.  No limit Engineering offers...  No limit Engineering offers the same style of trailing arms for use with coilover shocks, shown here under an early '50s Chevy with urethane bushes at the front of the arms, and a different crossmember design to suit the wider chassis. Note the coilovers mount to the rear of the trailing arms, with the Panhard rod bolted to a bracket on the axle tube.
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