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Massey Ferguson 8250, 8260 gearbox - Power shuttle

MF 8100-8200 Series Tractors Repair Operations

Massey Ferguson 8260, 8250 heavy gearbox with Power shuttle comprises 32 forward speeds and 32 reverse.

The transfer shafts and output shafts are supported by tapered roller bearings and are drilled as necessary to pressure-lubricate the bearings, the idler gears and the Hare or Tortoise synchronization system.

The layshaft is supported at cylindrical roller bearing and at the rear, by two tapered roller bearings.

(1) Input gear (2) Washer (3) Nut (4) Lube tube (5) Snap ring (6) Spring (7) Transfer shaft (8) Bush (9) Bearing cone (10) Bearing cup (11) Shim(s) (12) Thick shim (13) Driving pinion (2nd) (14) Synchromesh cone (2nd) (15) Synchro ring (2nd) (16) 1st - 2nd synchro (double cone) (19) Driving pinion (1st ) (20) Bearing cone (21) Bearing cup (22) Bearing cup (23) Bearing cone (24) Driving pinion (4th) (27) 3rd - 4th synchro (double cone) (28) Seal ring (30) Synchromesh ring (3rd) (31) Special washer (33) Bearing cone (34) Bearing cup (35) Driving pinion (3rd) (Hare) (36) Bearing cup (37) Bearing cone (40) Tortoise gear (41) Locating pin (43) Bearing cone (44) Bearing cup (45) Shim(s) (46) Rear bearing (47) Output shaft (48) Screw (49) Bearing cup (50) Bearing cone (51) Layshaft (52) Nut (53) Shim (54) Bearing cone (55) Bearing cup (56) Circlip (57) Driven pinion (3rd) (58) Spacer (59) Driven pinion (4th) (60) Spacer (61) Driven pinion (1st) (62) Spacer (63) Shim(s) (64) Driven pinion (2nd) (65) Washer (66) Snap ring (67) Needle roller bearings (68) Gearbox housing (69) Hare / Tortoise synchromesh (double cone) (71) Progressive sensor (72) Nut (75) Cover

On MF 8250, 8260 tractor gearboxes with a Power shuttle, 1st and 2nd gear synchromesh gears (16) and 3rd and 4th gear synchromesh gears (27) are double cone type as well as the Hare/Tortoise range one.

When the Hare/Tortoise synchromesh gear (69) is moved to the rear, it makes the Tortoise pinion rotate and doubles the four speeds to give the eight basic speeds.

All pinions have rectified teeth and are helically cut. They are in constant engagement.

The drive shaft of the direct drive clutch traverses the layshaft. The input unit assembly located at the front provides four input ratios into the main box.

Gearbox Description

MF 8260, 8250 gearbox drive is provided by input gear (1) integral with transfer shaft (7). The two hubs of synchromesh gears (16) and (27), as well as gear (1) are hard-mounted to transfer shaft (7) by splines.

First gear (19) and fourth gear (24) are idler gears on shaft (7). Second gear (13) is an idler gear on bush (8), which is hard-mounted to shaft (7) by splines. Third gear 3rd (35) is installed on tapered roller bearings.

All the pinions on layshaft (51) are splined to and rotate with the latter. The gear teeth on shaft (51) mesh with tortoise gear (40) which idles on the output shaft.

Low range (Tortoise)

A synchronized gear is engaged by moving of one of the slides of synchromesh gears (16) or (27) for engage transfer shaft (7) in one of the four idling pinions.

Irrespective of the speed selected, the movement is transmitted to layshaft (51).

Output shaft (47) is driven by the gear teeth machined on the layshaft intermeshing with tortoise gear (40), engaged to output shaft (47), by moving the slide of synchromesh gear (69) rearwards.

High range (Hare)

This range is selected by forward movement of the slide of synchromesh gear (69), which establishes a direct drive between third gear (35) and output shaft (47).

Consequently in 3rd gear, layshaft (51) is passive.

The other gears are obtained by moving the slides of synchros (16) or (27) as for the Low range.

Lubrication

The lube oil is supplied from tube (4) connected to the input unit. It circulates in a series of axial channels, one of which crosses the transfer shaft while the other is blind, machined in the output shaft.

Radial channels feed the various pinions, the bearings and the Hare/Tortoise synchromesh. Needle roller bearings (67) are lubricated by an oil film circulating between the direct-drive shaft and the layshaft.

An oil deflector "C" maintains the oil near the bearing mounted at the back of the input unit.

The shaft-end bearings on shaft (51) are lubricated by an additional oil flow from the drive bearing of the hydraulic pumps located on the rear-axle intermediate housing, via radial ports drilled respectively in shim (53) and the shaft.

On Massey Ferguson 8250, 8260 gearboxes with Power shuttle, all gears are synchronized including the Hare/Tortoise function. The synchromesh gears are all double cone items.

Hare or Tortoise synchromesh gears double cone

Locking position

Axial displacement of slide A provides a thrust against ring K, which in turn bears on synchronization brake B, pushing it towards Cone J through the action of balls D, springs F and pressure system E.

When the corresponding pinions are at the required speed, the slide meshes with the coupling flange C of the candidate gear.

The operating principle is identical for 1st - 2nd (16) synchromesh gears and 3rd - 4th synchromesh gears (27).

Advantages of the double cone synchromesh

- better reliability
- increased stress strength

Overhaul (double cone)

- If needing to disassemble synchromesh gears (16) (27) and (69), check the wear on synchronization brakes B.
- Proceed by stacking coupling flange C, cone J, synchronization brake B and ring K.
- Position brake B correctly by alternately rotating it through a few turns and applying finger pressure.
- Using a set of feeler gauges, measure dimension at three equidistant points. Take the average of the three readings.

Value of dimension

- on a new synchromesh gear, dimension must be 1.6 mm minimum;
- after operation, if this dimension is less than or equal to 0.60 - 0.80 mm, replace the synchronization brake B.
- Repeat the measurement of using the same process.
- If dimension remains incorrect, also replace ring K and cone J or the complete synchromesh if required.

Specifications

A and B - Details, D - Semi set-right adjustment, G - Groove oriented towards the Hare or Tortoise synchromesh gear, O - Port for synchromesh lubrication (Tortoise side)

A - Tighten at 30 - 70 Nm progressively. Rotate the shaft a few turns. Then, complete tighten at 100 - 150 Nm, with Loctite 270 plus mechanical lock. B - Selector rail support.