How To Double Clutch!

The synchronizer makes me recall a discussion concerning “double clutching” and whether or not you need to use this method of shifting with the T-84J. First, off, what the heck is meant by, and how do you “double clutch”? Double Clutching, was a prescribed feature of Army driver training. The “purpose of double clutching is to synchronize the speed of the flywheel and the turning clutch disks so that gear shifting may be accomplished with a minimum of clashing of gears.” The procedure?

1. Depress clutch pedal
2. Move gearshift lever to neutral position
3. Release clutch and at the same time depress the accelerator until the engine speeds up and the gear speeds are more nearly synchronized.
4. Depress clutch pedal again move gear-shift lever to the next lower position.
5. Release clutch pedal and at the same time accelerate engine to obtain desired road speed.

…the procedure is the same for shifting to a higher speed, except that the engine is not accelerated while the gears are in neutral, per TM 21-300 page 113. Double clutching is also mentioned in TM 21-305, dated November 1944. However, according to TM 9-803, page 18, para 5c(6): …No double clutching is required… The only time you might want to double clutch is when shifting from 2nd or 3rd into 1st gear. Not a practice that I recommend but sometimes you may find yourself in need of lower gears. Just use caution. I guess you might also find it necessary to double clutch if your synchro is badly worn, too. Don’t rely on this procedure–rebuild that transmission as soon as you can. from USMC Preventive Maintenance Manual, 1943 and Trouble Shooting And Rebuilding The T-84J.