Refurbishing your wiper motor
The wipers on my car have never been terribly powerful – probably something to do with the wiper motor being some 35 years old – but it was something I’d accepted especially as I don’t deliberately take the car out in the rain (However events like the Le Mans Classic, in the middle of the summer, can force this on you!) At last year’s MoT one of the advisories was that the wipers were poor, so, with this years MoT approaching, I thought I would show willing and try to do something about it.
When building the car I powder-coated the wiper frame and greased the wiper spindles but never split the wiper motor or its gearbox for fear of breaking them. However, if you are careful both can be dismantled, refurbished and reassembled.
On dismantling my wipers I found the gearbox grease had dried solid and was no longer touching the gears but the biggest culprit for the lazy operation was a dirty commutator giving poor electrical contact between brush and winding, reducing motor power.
I initially cleaned the commutator with an eraser but found I had to resort to fine emery paper to get it back to a shiny finish – if you follow this guide, go easy, you don’t want to rub right through the thin metal. There was plenty of life left in the brushes.
The clean commutator coupled with a regreased gearbox has transformed the wipers which now start eagerly each and every time and operate with much more torque. Whilst the unit was out of the car I also took the opportunity to reverse the side on which the wipers park. (most Chesils park on the passenger side; only in their final year did Chesil start swapping the wipers over to the drivers side to improve visibility when in use.
How To Guide
I’m assuming you, like me, have the late style dual-speed motor, and have removed the mechanism from the car (and that the wipers were in their park position when removed). If not, you are on your own I’m afraid!
After making a note of the orientation of the actuating arm (for later reassembly) on the gearbox, undo the nut (A) attaching it to the gearbox, and the three bolts (B) that hold the gearbox and motor to the frame.
Remove the four screws (C ) holding on the rear plate of the gearbox and remove the plate and gasket.
Push through the spindle and large plastic cog from the front (look out for the thrust washers) and clean away the old grease on the cog and within the gearbox.
Remove the two screws (D) noting their two nuts that are held in slots on the side of the casing and that will fall loose.
To avoid the potential of three springs flying out of the motor, grip the worm drive tightly with your thumb whilst pulling off the casing to ensure that the rotor stays in place (later motors, as shown in disassembly photos, with a white base plate appear to limit travel of the brushes which should prevent the springs from flying). Note a guide at the top of the rotor may either be on the rotor or still in the housing.
Then the three springs can be carefully removed by bending the outer retaining tabs outward (E) and releasing the springs from the rear.
The rotor can now be safely removed and the commutator cleaned. Again there will be a guide at the end of the worm drive.
Reassembly is a reverse of disassembly – put in the rotor (with guides lightly oiled) before carefully reinserting the springs and bending back the tabs (bit fiddly).
Again hold the worm drive in the gearbox casing tightly when putting the motor casing back on as the magnet attraction will put it out of position again, sending the springs flying.
Hold the casing nuts in place with thin nosed pliers whilst refitting the screws.
Before replacing the large cog & thrust washers pack the gearbox casing tightly with grease.
Before replacing the actuating arm reconnect the wipers to the car wiring and run the motor to its park position. This is important as the point in the arc of wiper travel that the wipers stop at in the park position is determined by the orientation of this actuating arm. Putting it back rotated 180 degrees from its original position swaps the park position (Orientation as shown in the first photo will park on drivers side).
If you do decide to swap the side the arms park you’ll also need to buy new wiper arms with the opposite crank (or try bending the existing arms). I sourced mine (my wiper spindles are the type with a through bolt) from Tex Automotive (I actually bought the collet type; removed the collet from the arm; then drilled a 6mm hole through from the rear, so that I could bolt them down).