A.E.C. Regal Mark IV with Synchromesh Gearbox
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THE A.E.C.. Regal Mark IV under' fioor-engined chassis is now beih produced with a plate dutch and fourspeed synchromesh gearbox, as an alternative to the fluid coupling and preselective erpicyclic -gears._ A modification shortly to be introduced to the 164t. 4-in.-wheelbase-Mark "IV chassis is an increase in frame depth from 8 ins. to 101 ins.
. To avoid the somewhat complicated linkage usually associated with clutch operation on -underfloor engined vehicles, a hydraulic system is used. 'the 'clutch pedal is directly attached to a hydraulic master cylinder fitted . to the chassis frame immediately tinder the driver's footplate.
Pressure is eonimunicated to a cylinder mounted on the Clutch housing and operating :directly on to the clutch withdrawal fork. As linkage pins arc avoided, the withdrawal mechanism calls for no adjustment.
The clutch and gearbox are connected by'a -short finiVersally jointed. shaft. Gearbox. ratios. are 468, 2.62, 1.57 and 1 to 1 forward, with a 4.17 to 1 reverse.
Gears of the straight-spur type, with . ground profiles few silent operation, arc used. All forward speeds are engaged by involute-spline dog clutches sliding on splined shafts, the engagement 'being protected by inertia-Jock synchronizing rings. A portion of the profile of the male spline is relieved, so that slight annular movement of the collar can take place after the gear is engaged and, by fouling the edge of the relief, be prevented from-sliding out of mesh.
.13y increasing the frame depth by 2j,, ins., the channel-section flitches previously used will no longer be required. The extra depth has been added to the top of the frame so that the front wheel-arch no longer . exists. In the majority of cases, the deeper frame will not raise the floor height.