Massey Ferguson 5400 - Issue 1.a
05A02.9
General - GBA20 with Power Shuttle Operation
B . Construction and description
Construction
The GBA20 gearbox with Power Shuttle consists of
three gear trains fitted to:
- mainshaft,
- layshaft (or transmission shaft),
- output shaft.
It allows to obtain eight basic synchronised gear ratios:
- four gear ratios: 1st, 2nd, 3rd, 4th;
- two range ratios: Hare and Tortoise.
Its main characteristic is its assembly of three double
cone synchronisers.
The main gearbox consists of four synchronised gears.
An pinion idle-mounted to the output shaft and
controlled by a synchroniser allows to double the four
initial gears to obtain the eight basic gears.
The mainshaft and the layshaft are carried by tapered
roller bearings.
The output shaft is fitted on two taper roller bearings
and one needle bearing.
The mainshaft bearing cups are fitted up against the
housing.
All pinions have helical teeth and are continuously
meshed.
To ensure optimum gearbox reliability, the bearings are
fitted:
- with preload for the mainshaft,
- with clearance for the layshaft.
The output shaft may be set either with a slight clear-
ance or a slight preload.
Lubrication
The lubricating oil of the lower shaftline is supplied
from the tractor hydraulic system via a 1.5 bar valve. It
crosses a channel in the mainshaft and output shaft.
Radial bores direct the oil to the pinions, bearings,
rings and synchronisers.
The splines of the Hare / Tortoise synchro hub are lubri-
cated via a radial bore drilled in the output shaft.
The oil flowing inside the layshaft lubricates the taper
roller bearings and needle bearing (62). These bearings
are fitted respectively at the ends of the shaft.
Description (Fig. 2)
Drive is transferred from the main unit by the driven
pinion (67) which is permanently meshed with the
driving pinion of the input gear train (Power Shuttle).
The driven pinion (67) is secured to the mainshaft (69)
by splines.
The two synchroniser hubs (11) (23) are splined to the
mainshaft (69).
The 2nd driving pinion (14) is idle-mounted on a
ring (8).
The 1st (7) and 4th (18) driving pinions are
idle-mounted directly on the shaft.
The third driving pinion (29) is fitted on needle
bearings (28). It is also fitted with a needle thrust
bearing on each of its faces to absorb any axial pres-
sure.
The hub of the Hare / Tortoise synchroniser (31) is
secured to the output shaft (44).
The driven pinions (55) (56) (59) (60) drive the
layshaft (54) by means of splines. The rear teeth of this
shaft are constantly meshed with the Tortoise
pinion (36) idle-mounted on the output shaft.
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