The Mysterious No. 7 Auto Patrol

The first Caterpillar self propelled grader was introduced in April 1931 with model name “Auto Patrol”. At year end 1931 it was renamed “No. 9 Auto Patrol”, probably because Caterpillar had a lineup of Auto Patrols on the drawing board. The No. 9 was powered by the 4200G engine, 4-cylinder 4” x 5 ½” engine (the same engine as the TWENTY tractor). In June 1932 the “No. 7 Auto Patrol” was introduced (concurrent with the No. 9 production). It seems strange to introduce a machine with lower model number given the No. 9 and No. 7 had the same power and blade options.

Research shows the No. 7 was a “de-featured” No. 9. They both have identical engines, powertrain, chassis, steering, brakes, wheels, tires and blades. The key difference is the No. 9 has a 5 handle power control box (L lift, R lift, sideshift, circle, scarifier), whereas the No. 7 has a 3 handle power control box (L lift, R lift, sideshift). The No. 7 blade could be angled by releasing the lock, stabbing one end of the blade in the ground, and driving forward or backward. Also the canopy was standard on the No. 9, but an attachment for the No. 7. The rear bumper and fenders are shown in the parts books as an attachment for both machines, but all photos I have found show No. 9’s with bumper/fenders and No. 7’s without. Apparently in this time frame (depression years) there was marketing pressure from municipalities for a lower cost grader. A total of 125 No. 7’s were produced (6D1-6D125). In 1933 the No. 7 and No. 9 were replaced by the newer No. 10 and No. 11.


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thanks kent!

Very interesting history. I never knew the about the 3 handle control box. The older machines relied a great deal on the operator's skills, especially the No.7 with the "stab and unlock" blade angle control.
Thanks again for posting this Kent,
Craig