Boss 302 Staggered Shock Mount

The Boss 302 was the best handling Mustang to be produced by Ford when it was introduced in 1969. The Boss 302 was developed to compete on the SCCA Trans-Am circuit. Boss 302 Mustangs dominated the competition and won the championship in 1970. Much of the success was due to significant chassis differences from typical street Mustangs.

Chassis Performance Features Included:

• 5/8" Rear Sway Bar
• 15/16" Front Sway Bar
• Reinforced Front Shock Towers
• High-Rate Springs
• Koni Adjustable Shocks
• Staggered Rear Shock Geometry

The staggered rear shock geometry greatly improves rear axle stability. Staggered shocks simply means that one shock is placed in front of the axle and the other is placed behind the axle. This configuration is more stable under all conditions and reduces wheel hop, spring wrap up etc.

The staggered shock configuration was added to all Boss 302 Mustangs, Shelby GT 500's, and 428 Drag Pack cars to support their high performance demands. The shock that trails the axle is mounted to additional frame structure that was welded into the floor pan just in front of the gas tank above the rear end. This frame structure consisted of 3 sheet-metal components that reinforced the floor and welded to each frame rail. In addition to the frame structure, the lower shock mount plate for the left side is designed with the mounting point coming out behind the axle. Also both left and right are thicker and have more material around the shock-mounting hole. These plates are marked with identification 428L and 428R.

Reproduction Boss 302 Lower Mounting Plates - I sell these for $275 Painted or $285 Powder Coated

There are several options to pick from when looking for lower mount plates. Original Boss 302 plates have been going for $500-$600 lately. The above reproductions are the next best thing. The Boss 302 plates are not only the correct geometry, but they are a lot stiffer than the plain Mustang plates. You can use a right bracket on both sides of the car, but the flexing of the light-weight stock brackets negates some of the performance gained by going to the staggered design.

The picture below shows 4 options.

Top Left: 73 Mustang - Use "Right" on both sides - In 73 Ford went to the heavy brackets on all Mustangs.

Top Right: Reproduction Boss 302 / 428 CJ.

Bottom Left: Stock 67-70 "Right" on both sides - Not nearly as stiff as Boss/CJ stuff.

Bottom Right: Factory Boss 302 / CJ, Easily identified by 428 L & 428 R stamping.

Not Pictured: Best option for the money is to find plates off of a Maverick, these can still be found in wrecking yards for cheap. They are just as stiff as the B302 units. The geometry is almost identical, definitely a good fit.

View of a factory 1970 Boss 302 upper shock mount, from the top.

View of a factory 1970 Boss 302 upper shock mount, from the bottom.

The factory installed the staggered shock configuration after the body was initially assembled. The sheet metal plates were welded in after a clearance hole was cut in the floor pan. It appears that the hole was cut with a gas torch from the roughness of the cut and remaining slag that is left behind.

Visible cut out area from factory installation.

The lower mount welded to the underside of the floor pan was manufactured in 2 pieces and overlapped when welded into the car. This allowed for variations in frame width and adjustment of shock mount location.

Factory staggered shock mounts were welded in using a combination of Mig welding and Spot welding. The ends were welded to the frame using Mig while the floor pan areas were welded together using a spot welder.

From inspection of several original Boss 302 Mustangs it appears that the bottom side was painted with green primer and the interior portion was painted the same color as the exterior body. This was done after the seam sealer was applied.

Sanco Specialties manufactures an upper staggered shock mount that is nearly identical to the factory 1970 Boss 302 unit. Below are pictures of the Sanco mount and factory 1970 Boss Mounts.