John Deere stx38 - Manual (Page 190)

5 - 26
3/21/97
THEORY OF OPERATION POWER TRAIN
BRAKE SYSTEM COMPONENT
LOCATION AND OPERATION
IMPORTANT: Early Model STX30 & STX38
(SN —210000) brake linkage differs slightly.
Theory of Operation remains the same.
Function:
The brake system allows the operator to slow down,
stop, or lock the tractor into park position.
Major Components:
• Clutch/Brake Pedal
• Clutch Cross Shaft and Bellcrank
• Clutch Compression Spring Assembly
• Clutch Bellcrank and Tensioning Idler Assembly
• Adjustable Idler Assembly
• Transaxle Drive (Input) Sheave
• Brake Rod Assembly
• Transaxle Brake Assembly
• Park Brake Lever and Locking Rod Assembly
Theory of Operation:
NOTE: Clutch/brake pedal has approximately 127 mm
(5 in.) of travel.
The first segment of clutch/brake pedal travel (N) is
taking-up freeplay in the linkage and start of
compression of clutch bellcrank actuating spring
assembly (D).
The next segment of travel (O) is fully compressing the
clutch bellcrank actuating spring assembly (D) and
pulling the traction drive clutch bellcrank and idler
assembly (E) fully rearward, overcoming the belt
tensioning spring (B) and fully disengaging the traction
drive system. As the pedal is released, belt tensioning
spring (B) pulls clutch bellcrank and idler assembly (E)
forward into the belt, tensioning the belt and fully
engaging the traction drive system.
There is a small segment of pedal travel (P) that briefly
allows the tractor to free-wheel so the operator can
shift-on-the-go before any brake engagement starts to
occur. However, this segment can be adjusted to be
more aggressive, causing more friction (overlapping)
between clutch and brake functions if desired,
especially in the higher gears.
The last segment of travel (Q) is engaging the brake
system and manually locking of the park brake linkage
(C). The brake lever (G), with the bottom cam surface
contour (I), pushes the two dowel pins (J) against the
striker plate (K). The striker plate forces the thicker,
outer friction puck (L) against the brake disc (H). The
two friction pucks (L and M) become compressed
against both sides of the brake disc (H). The brake disc
is keyed to the end of the intermediate shifter/brake
shaft (not shown). When the compression force of the
friction pucks is great enough to stop the brake disc
rotation, the transaxle and wheels stop turning. This
works in conjunction with the clutching system.
With the clutch/brake pedal (A) fully depressed and the
traction drive system disengaged (fully clutched), the
park brake lever assembly (C) can be engaged, locking
the clutch/brake pedal linkage and the brake disc in
park position.