|The MGA With An Attitude
WIPERS, TWO SPEED DR3, As Used For Sebring MGA's -- ET-219D
MGA DR3 Two Speed Wiper Motor Conversion - by Colyn Firth
At 10:50 AM 3/23/2014 +1100, Bob Somerville wrote:
"The two-speed wiper motor used on Sebring MGAs and other competition prepared MGs was the Lucas DR3. This is the square bodied motor very similar to the single speed motor used in production and uses the same mounting bracket and rack mechanism. It is distinguished by a more substantial cover plate and a five-wire connection emerging from the body. You need the correct switch, rotary or toggle types are available. These motors are readily available as they were commonly used on most of the higher spec British cars of the 1950s such as Aston Martins, AC Cobras, Bentleys, Humbers, most Jaguars from XK140 through to Mk2 sedans, some TRs, etc".
This one appeared on eBay in March 2014. Lucas model number 75310A. It has five wires.
See also articles ET-219E - ET-219F - ET-219G on following pages for a
rotary switch, toggle switch, and relays that can work with this 2-speed wiper motor.
Addendum, January 17, 2017:
position. This is accomplished with an eccentric cam on the wheel's crank pin. This makes the wipers park in a lower position than the lower limit of the normal wiping stroke. Therefore, there is a different model number for a wiper motor for right hand drive or left hand drive (because wipers park on opposite side).
Below is a slightly later production version of the DR3 2-speed wiper motor, Lucas model number 75361A, produced February 1965. Center picture shows the parking contact, more robust and easier to adjust in situ. The mating contact (ground connection) is on the slider that is driven by the connecting rod (not in the picture). Third picture shows the thermal cut-out switch that will switch off and stop the motor (temporarily) if it might overheat.
There are a couple of tricks to this wiper motor. First, when you switch it off, the switch reverses polarity of power to the field coil to make the motor reverse (run opposite direction) until it hits the park switch to disconnect and stop. Second, when running in opposite direction there is about 5/32-inch (4-mm) difference (addition) in the extended stroke of the cable as it approaches the park
To modify the motor to park on opposite side requires reversing polarity of either the armature or the field coil to make it run in opposite direction. It is apparently easier to swap wires on the field coil. Move the park switch wire and the red wire from RH terminal to LH terminal. Move the two blue wires from LH terminal to RH terminal.
Below are pictures (compliments of Bruce Murray) showing swapping of the armature wires.
Wired for Left Parking Wired for Right Parking
Wire colors in the motor may be different. There is one where all wires in the motor have a green tracer stripe (with braided cloth insulation). Wire colors from top to bottom in the diagram would be, Green/Green (solid), Red/Green, Yellow/Green (in place of Orange), White/Green, Blue/Green, Brown/Green.
The item labeled "Resistor" is a length of resistance wire wound around outside of the field coil. Here are photos of the field coil. The yellow covered wire is the resistor. When the resistor is switched into series with the field coil, it reduces current and strength of the field magnet. This causes the motor to run faster but with less torque. When connecting wires, it may be useful to know the resistance of the field coil is 8-ohms, while the resistance of the resistor wire is 12-ohms.
This is the connecting rod. The eccentric cam will rotate half a turn to change length of the connecting link when the motor reverses. This extends the cable farther for parking.
When the link hits the switch finger it will break the ground connection to stop the motor in the park position. The thumb screw is an easy external adjustment for parking position.
Photos below show a strip of paper inserted into the isolated grounding contact. To make the wiper park on opposite side, when changing from left hand drive to right hand drive, in addition to swapping two wires for the field coil the parking switch needs to be flipped over and positioned to switch when the link and cable are retracted rather than when extended. This is why original LHD and RHD motors will have two different model numbers.
Photo left, retracted (as when running) but with park switch in the extended position. Center photo, parked in retracted position. Photo right, the reversible part of the parking switch. Illustration below shows striker at the driven end of the cable that will trip the parking switch.