(Copied from unknown source)


Optional Equipment on:
FORD ’85’, PASS. CAR MODELS (1938-39-40-41
LINCOLN-ZEPHYR, HB (’37). 86H (’38), 96H (’39)
LINCOLN, ZEPHYR & CONT’L. 06H (’40), 16H (’41)
MERCURY, 99A (’39), 69A (’40), 19A (‘41)


NOTE:- This axle provides low axle ratio for power and acceleration (with planetary gears locked out) and a higher ratio to reduce engine RPM at high speeds (with planetary gears operating). Do not confuse this type with the Ford Two-Speed Truck Axle which operates differently.

Model Changes – Two-Speed axle used on all models is same design and operates in same manner. Minor differences in control units and installation procedure will be found on the various car models listed above.

Lincoln 1941 Overdrive – Warner Type R10 Overdrive unit (mounted on rear of transmission) also available for 1941 Lincoln models (both Overdrive Transmission and Two-speed axle may be found on some cars). Refer to Warner Overdrive article for data on Overdrives.

TYPE:-Consists of a planetary gear reduction unit built in a special differential assembly case which is installed in place of the regular Ford or Lincoln-Zephyr differential (furnished) with new right hand axle housing which replaces original housing). A vacuum cylinder mounted on the axle housing operates the planetary gear clutch and is controlled by a valve assembly linked to the clutch pedal and to a control button on the instrument board. An adaptor (two-speed gearbox) is provided for connection in the speedometer drive cable and is linked to the control button so that the speedometer drive ratio is changed for overdrive operation to insure speedometer reading accurately at all times. NOTE – Some 1939 cars have a speedometer drive gear assembly mounted on the axle housing. These cars do nor require a separate adaptor.

With the dash mounted control button pushed in (for direct drive), the sliding clutch in the rear axle locks the sun gear and the differential case (in which planetary pinions are mounted) so that the entire planetary gear system (sun gear, pinions, and outer internal gear) rotate as a unit and the ring gear drives the rear wheels directly. When the clutch is released and the control pulled out to the overdrive position, the vacuum cylinder pulls the sliding clutch out so that the differential case is free and engages the stationary clutch plate so that the sun gear is prevented from rotating. The ring gear then drives the differential case and pinions, and the rotation of the pinions (on the stationary sun gear) causes the internal gear and the axle shafts to revolve at a faster ‘overdrive’ speed.

INSTALLATION:- When Overdrive axle is installed the regular Ford or Lincoln-Zephyr axle should be dismantled (center pinion mounting housing need not be removed but torque tube should be blocked up so that it does not hang on the universal joint ball housing). Right hand axle housing, differential case (right and left halves and bearing on right half), differential pinion spider, and ring gear bolts and nuts should be discarded (replaced by over-drive axle parts). Overdrive axle assembly should be assembled on pinion housing using original cap screws, except for top front hole (special long cap screw and copper washer furnished wired to hole in which it should be installed). Original right hand axle shaft should be filed smooth for distance of 8" back from side gear to remove all scale and high spots, thoroughly cleaned, and dipped in regular axle lubricant (5" at side gear end). Then insert shaft through overdrive unit (these instructions for shafts without speedometer drive gear only). Original differential pinions should be assembled on new spider, bronze thrust washer installed on spider in back of each pinion (lubricate washers with axle lubricant before installing), and inserted in overdrive differential case so that spider engaged in slots in internal gear case and pinions properly meshed with side gear. Original left hand axle shaft should be threaded through new yellow bronze side gear thrust washer and original ring gear, washer tongues entered into slots in differential case through which differential spider was assembled, and ring gear bolted to face of differential case with new cap screws. Left hand axle housing can then be assembled. Important – See that ring gear and differential are clean and free from all nicks to ensure gear running true, tighten mounting screws evenly and securely and lock screws with lockwire. Make certain that side gear thrust washer tongues do not slip out of slots in case while gear is being installed.

Control and Speedometer Adaptor (Ford):- Control valve is mounted on bracket bolted to top of left hand frame side rail ahead os steering gear (back center hole engages rivet head, other holes must be drilled for bolts). Special clip should be bolted to lower end of clutch pedal and connected to bellcrank on control valve by rod. (see adjustment below) . Forward vacuum tube connection on valve should be connected to manifold spacer installed between carburetor and manifold (manifold studs must be replaced with new longer studs when spacer installed). Vacuum connections at rear of valve should be connected to vacuum cylinder by rubber tubing and copper tubing running along left hand frame side rail (connect ‘low’ top connection on valve to right hand end of cylinder, ‘high’ bottom connection to left hand end of cylinder). Control button is installed in drilled hole in instrument panel (2 ½" up from starter button) 1-3/8" from left of instrument cluster), and control cable taken through drilled hole in dash (3 ½" from left edge). Connect cable wire to lever on top of valve, see that lever is in forward detent position and that control button in forward position against instrument panel, then tighten cable clamp on valve.

Speedometer Adaptor:- Adaptor screws directly on speedometer head (install square key furnished for connection between adaptor and speedometer before mounting) with regular speedometer cable connected to adaptor and short control cable (from control button connected to adaptor lever).

CAUTION – Button & Valve Assembly (Lincoln-Zephyr:- Control valve mounted on steering gear housing cover plate. Connected in same manner as Ford except as follows: Clutch pedal rod clip clamped to shaft at clutch pedal end and inside edge of engine mud pan notched to provide clearance for rod, control valve vacuum line connected to windshield wiper connection on manifold with special adaptor, control valve mounted on lower edge of instrument panel 2 1½"to right of starter button.

Speedometer Adaptor:- Adaptor should be mounted on left side of dash and connected to speedometer by special short length of cable taken through 15/16" hole drilled in center of dash. Regular speedometer cable should be looped up on left side of engine compartment and connected to adaptor.

ADJUSTMENT:- Control Valve Clutch Connection – Adjust clevis on valve operating rod at control valve end so that valve plunger is depressed 1/8" minimum, ¼" maximum with clutch pedal depressed to floor. Valve travel must not exceed ¼".

Control Button – Cable conduit should be positioned in clamp on valve body so that valve lever is in forward position (stopped by detent) with control button pushed in towards dash and fastened in this position by tightening clamp screw.

SERVICING:- Axle Lubrication - When first installed, axle should be filled with 4 ½ pints (Ford), 6 pints (Lincoln-Zephyr) recommended axle lubricant and car should be run with rear wheels jacked up (transmission in high, overdrive in low) for 5 minutes to circulate oil through overdrive unit. Axle should then be refilled to level of filler plug in overdrive case. Always fill to level of overdrive filler plug for this purpose.

Vacuum Cylinder Lubrication – At 10000 mile intervals, remove vacuum cylinder, lubricate leather piston cups thoroughly with Houghton Cosmolubric #1000 hydraulic oil or equivalent.

Speedometer Adaptor Lubrication - At 10000 miles, or sooner if noise develops, remove adaptor, take out small plug on side and repack case with Alemite lubricant by hand - do not use pressure.

TROUBLE SHOOTING:- If overdrive axle does not shift properly, check all vacuum lines and connections for leaks, check tubes for kinks, sharp bends, or flattened spots, make certain that rubber tubing is not cut or torn so as to obstruct opening at valve and copper tubing connections. Check valve settings (see adjustment setting above).

OVERHAUL:- See Ford and Lincoln-Zephyr Rear Axle articles for axle servicing data.

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