There is a wealth of information available in the original WW2 Army Motors published by the Technical Service Division, Holabird Quartermaster Motor Base, Baltimore, MD If your brake and clutch pedals don’t have enough of it start yelling for your company mechanic.
They may call you “silly boy” when you bend over and touch your brake and clutch pedals before starting out on a trip — but don’t worry about it. They may even call you crazy or superstitious. But when you check your pedals for free play this way, you’re playing safe.They may call you “silly boy” when you bend over and touch your brake and clutch pedals before starting out on a trip — but don’t worry about it. They may even call you crazy or superstitious. It’s a good, little driver trick and the best way to guarantee that you won’t fail to get over a hill because of a slipping clutch — or that your brakes won’t lock up when you’re in a hurry. Free play is the pedal travel you get before any action takes place. It’s kind of a safety margin and more than just that, it ‘s your assurance that the linkage hidden beneath the floor-boards is in adjustment. On the 1/4-ton jeep, for instance, the free play of the clutch pedal should be 3/4 of an inch. The clutch pedal should travel down 3/4 of an inch from its “up” position before it makes contact and action starts. Less than 3/4 of an inch free play — or no free play at all — means trouble: the clutch throwout bearing may be in constant contact and you won’t be able to fully engage the clutch at any time. You won’t get over that hill. On the other hand, if free play of the clutch pedal is over 3/4 of an inch. the clutch wont release compIetely – you can’t make a clean gear shift. The gears clash and have a hard time meshng. They growl like a dog. The brake pedal — free play of the brake pedal is just as important though not so well known. Some people don’t believe in it. some ignore it. But if the brake pedal doesn’t travel downwards 1/2 inch (on the jeep) before the linkage makes the push rod engage the piston in the master cylinder, why, then when your foot’s off the brake pedal, the piston may not be able to return to the full-release position where the cup clears the by-pass port in the cylinder. Some of the brake fluid in the lines won’t be able to get back into the reservoir above the cylinder and you’ll find your brakes dragging or even locking. You’ll go nowhere fast. Now don’t be hypersensitive (haw!), don’t confuse true free play of the brake pedal with the travel of the piston in the master cylinder before the brake shoes make contact with the drum. This kind of pedal travel has to be adjusted at the brake shoes — true free play is a11 in the pedal linkage. But in any case, whether you’re driving a jeep or a tractor, your little game of tag with the pedals will start your trip right. (The free play specifications mentioned above, are for the l/4-ton jeep; consult your maintenance manual for the free-play specs of other trucks). Note: From Army Motors, Vol 3, page 237.