Lucas DR3 wiper motor
- Why my wipers would not park correctly
- Removing and refiitting the DR3 motor assembly

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When after nearly three years of ownership I investigated why the XK150 wipers would not park correctly, I got a surprise. My car was fitted with a type 75309 Lucas DR3 wiper motor with a 130 wheel, set up for a LHD car. The 75309 variant is, in standard form, not suitable for a RHD XK150 because the 75309 tries to park the wipers on the left side of the windscreen.

A RHD XK150 should have a type 75319, with a 110 wheel and the parking switch positioned closest to the wheel.

A DR3 in an XK150 LHD car has its parking switch closest to the adjuster knob.

DR3 model variants list (partial)

The sweep angle 130 was greater than needed, but meant only that the wiper arms were down on torque at the wheel box shaft, or the motor was drawing a higher current. I was able to fit a 120 wheel from a spare DR3. It's not easy to find a 110 wheel and when found, the cost is quite high.

Getting the wiper motor out and refitted

1. Remove both wiper arms.

2. I made a 650mm (26") long steel prop from 10mm (3/8") dia galvanised steel that would hold the bonnet up without using the normal prop, which usually impedes access when working on the carbs or the wiper motor. The top end of the stand-in prop was ground into a rounded point, a collar fitted to avoid the pointy bit hitting the underside of the bonnet, and the lower end was fitted with a 10mm rubber tip.

The prop was used by placing the bottom end of the prop on the water jacket manifold, beside the right-hand cam cover, and then the pointy top placed in the usual prop's socket. The top 100mm of the prop was bent through 10 for a better fit in the socket.

3. From within the cabin, remove the three #10-32 setscrews holding the wiper motor angled mount plate to the body.

4. Disconnect the six wires associated with the wiper motor, and any ground connection. If necessary, label each wire before disconnecting.

5. Loosen but do not completely undo the 3/4" AF nut holding the rack tube to the motor. Then ease the motor and the rack a little way towards the front of the car. Maybe 10-15mm.

6. Being careful to not over-bend the rack itself, rotate the entire motor assembly to get access to remove the three hex nuts that hold the motor assembly to its mount plate, and then extract the mount plate and associated rubber bushes from the car. Place a soft rag under the motor. Then use a pair of small screwdrivers to push the two ends of the small circlip off the shaft of the main wheel that drives the rack connecting link. The circlip should land on the rag, and avoid loss. Also keep any shim washer behind the circlip.

7. Rotate the entire motor assembly a small amount the other way to gain access to the four hex-head self-tapping screws that hold the aluminium cover on the gearbox part of the motor. To undo the front right side self-tapper might require a special spanner comprising a small 1/4" drive 1/4" AF socket and a 100 mm long flat piece of steel or aluminium as the wrench handle. There might be a grounding wire eyelet under one of the four self-tapping screws. Remove the cover.

8. Now you are in a position to ease the connecting link pin out of the crosshead by pushing the lower end of the wheel shaft upwards, simultaneously pulling on the crosshead end of the connecting link to disconnect the rack from the link.

9. Now the 3/4" AF nut can be completely removed from the wiper motor, the rack separated clear from the motor, and the motor angled out of the car.

Note: In my car, the pin attached to the rack crosshead that actuates the parking switch was partially broken away from the crosshead, meaning a brazing repair or a new rack. I had ordered a new rack as a precaution, and it was definitely needed. The supplied rack was 150 cm (~60") long. I trimmed its length using a bench grinder to 96cm (38"), including a tapered end to ease getting the rack through the wheel boxes later. Also, if you remove the rack, then when re-inserting the rack, remember to place the aluminium ferrule on the rack before re-inserting the rack.

10. At this point, examine the wiring entering the commutator end of the motor. Invariably, the insulation on some of these six wires will be worn away and bare strands visible. At this point, decide whether these six wires will be replaced. A fully color-coded set is available. If you decide to use standard PVC-coated wires, then make them a little longer than the originals to ease the task of reconnecting them to the main loom later. The excess length can always be tucked away behind the motor when the repair job is finished.

11. After carrying out whatever cleaning, servicing and re-lubricating of the armature shaft ends and gear section of the wiper motor, replacing brushes etc, refitting the motor is the reverse of the removal steps. When getting ready to refit the motor, position the parking switch as far away from the crosshead as possible. If you wish to bench test the motor, use the jumper lead links specified on the annotated DR3 circuit diagram.

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