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 engine and chassis modifications were 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.  Some of these modifications were carried over to other performance Mustangs like the 428 Cobra Jet powerd Mach 1's and Shelby GT-350 & GT-500.


Chassis Performance Features Included:

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 4 sheet-metal components that reinforce the floor and are 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.

Lower 428L & 428R Shock Mounting Plates are now reproduced.  The reproductions are excellent and are identical to the originals.  Sanco Specialties keeps these in stock and sells them for $325.00 per set.  Please email us if you need a set.


There are other options to pick from when looking for lower mount plates. Original Boss 302 plates are very difficult to find for sale.  Please send me an email to inquire about availability, prices on original's range from $500-$600 depending on condition.  The Boss 302 lower shock plates are a significantly stiffer than the plain Mustang plates.  You can use a right bracket from a standard Mustang 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 you have for lower plates to use with the staggered configuration.

Top Left: 73 Mustang - Use "Right" on both sides - In 73 Ford went to the heavy brackets on all Mustangs.  (Note: Angle is slightly off for use on left side but will function fine)

Top Right: Reproduction Boss 302 / 428 CJ - $325.00.

Bottom Left: Stock 67-72 "Right" on both sides - Not as stiff as Boss/CJ. (Note: Angle is slightly off for use on left side but will function fine)

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 5-Lug Maverick.  Maverick plates are just as stiff as the B302 units.  The geometry and strength is excellent and nearly identical to the Boss 302 design.  Most of the Maverick plates are marked with "MAV L" or "MAV R".  We sometimes have these in stock, please send an email and inquire.  Price for Maverick plates, media blasted and painted is $150.00.



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 or "Bucked". 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.  Staggered shock assemblies are available either direct from us or through ebay cost is $299.00 including UPS ground shipping to anywhere in the continental USA.

Below are pictures of the Sanco Specialties mount and factory 1970 Boss Mounts.



There were some variations to components complementing the Boss 302 staggered shock installation.  I have studied many 69 & 70 Bosses and there is no 100% clear pattern, but here is what I believe to be correct:

Right side upper shock mount should have a "doubler" installed to make it as strong as the new left side mount.  I have verified factory installation on early 69 Bosses.  It is my opinion that this installation was somehow accidently not completed during the stagger mount installation at the factory on many cars.  Sanco Specialties now produces this part and it is available through ebay or direct for $29.00.


Left side upper shock mount should have a plug installed to fill the hole where the shock would have been installed if it wasn't a staggered shock car.  I have verified factory installation on early 69 Bosses.  Cars may also be found with this plug missing.  Installations I have inspected are usually mig welded in place with 3 small tack welds.  Sanco Specialties now produces this part and it is available through ebay or direct and is included with the doubler for $29.00.  I make this plug as a duplicate of one removed from one of my Boss 302 projects.  However... it looks suspiciously like a knock out plug from an electrical box....


  I have observed two other interesting modifications that are common to staggered shock installations.  I currenly don't have any pictures to show, so you will have to just use your imagination.  I have noted on several cars the standard shock cross member is skip welded with a mig welder, much like panels on the Trans-Am race cars were done in critical area's.  The second thing is a doubler is welded to the floor pan, directly above the pan mounted pinion snubber.  This is a thick, torch cut piece of steel.  Another interesting observation is these modifications are seen on late built (March 1970 & Later) 1970 Boss 302's that had 3.91 or 4.30 gears. 

For More Information contact:

Forrest Sanco

400 North Cherry Lane

White Settlement, TX 76108


Phone: (940) 594-7259


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