The gearbox shift mechanism consists of a ratchet type footshifter that rotates a quadrant plate. The quadrant plate in turn moves the shift forks by means of slots in the plate. These slots guide the shift forks to the correct position to select gears sequentially.
Each gear position (1st gear to 4th gear) has a corresponding notch along the edge of the quadrant plate which will exactly align and engage with a single detent ball fixed in the gearbox casing when that gear is correctly selected.
The purpose of the adjuster screws are to act as physical "stops" that set the amount of travel of the footshift pedal for upshifts and downshifts. The gears are correctly adjusted when the footshift travel allows a quadrant plate notch to exactly align with the fixed detent ball located in the gearbox casing. Too much travel will allow the quadrant plate notch to rotate past the detent ball and jump out of gear. Too little travel will not allow the the quadrant platee to travel far enough to engage notch with the detent ball, and will also result in gear jump out or no gear engagement.
Symptoms of jumping out or gear, or not selecting gears can be caused by both too much, or too little travel of the footshift lever. It is therefore recommended that if severe problems are experienced with gear shifting, that the adjustment procedure commence as follows -
The UPPER adjusting screw controls the DOWNSHIFTS and the LOWER ADJUSTING SCREW controls the UPSHIFTS.
1) With the gearbox in neutral position, loosen the lock nut on the upper adjusting screw. Screw the adjuster screw in (clockwise) until 1st gear cannot be selected when shifting from neutral to 1st gear. Then slowly screw the adjuster screw out (counter-clockwise) until 1st gear engages when shifting from neutral to 1st gear. From this point turn out the adjusting screw 1/2 a turn.Lock the lower adjuster locknut.This setting should allow the detent ball to fully engage and align with the 1st gear notch in the quadrant plate.
2) With the gearbox in neutral, loosen the lock nut on the lower adjuster screw, Screw the adjuster screw in (clockwise) until 2nd gear cannot be selected when shifting from neutral to 2nd gear. Then slowly screw the adjuster screw out (counter-clockwise) until 2nd gear engages when shifting from neutral to 2nd gear. From this point turn out the adjusting screw 1/2 a turn.Lock the lower adjuster locknut.This setting should allow the detent ball to fully engage and align with the 2nd gear notch in the quadrant plate.
This adjustment procedure sets the correct travel to select gears for both upshift and downshift, and will usually resolve any footshift problems. If the problem still persists during road tests adjust the screws in 1/8th turn increments. If the problem persists despite adjustments the problem could be a weak detent ball, or excessive play or damage to the quadrant plate mechanism.To confirm that the shift problem is only due to adjustment of the foot shifter, it is possible to select a gear using the handshifter on the right side of the gearbox. If no gear jump out is experienced after selecting a gear with the handshifter it confirms that the problem is due to incorrect foot shifter adjustment.
The Phoenix CJ750 is fitted with a 4 speed twin shaft "Type 331" gearbox with a reverse gear. Gearshift is carried out by means of the left side foot gearshift lever. A handshift lever is fitted to the right side of the gearbox which is usefull in quickly selecting neutral gear.
Adjustment of foot shift lever is identical for both type 331 and type 52 gearboxes
The gearshift is adjusted by means of two adjusting screws located on the back of the foor gear shift cover.
Upper adjusting screw
Lower adjusting screw
Image of shift quadrant plate and detent ball (with rightside gearbox cover removed).