I have some photos to see what is inside.

I begin thinking that backlash is deliberate to prevent something...

general view.

input worm shaft 1 drives worm gear 2 that drives gear 3 through articulated lever 4.

there is backlash only between gear 3 and final gear 5.

all gears are made of very hard plastic.

final gear 5 on output shaft was took out.

wiper is mounted on output shaft.

I have some photos to see what is inside.

I begin thinking that backlash is deliberate to prevent something...

Maybe it's to do with lever 4 - to always have an amount of slack in the system so even if the ignition is turned off mid cycle that lever will always fall offset. Imagine if it was stopped at full up or full down stroke, it would take a lot to push/pull it to start it again but if it always settles sideways of that because of the slack in the gearbox it would be easier to start it again.

wiper motor is very powerful and the worm reduction mechanism increases torque a lot also.

in fact lever 4 is made of steel because the motor could break it.

I think the backlash is some sort of damping protection in case that wiper gets stuck from ice.

I had mine frozen on rear glass but the fuse didn't blow?!, the motor was 'humming' though.

maybe other members can describe what happened with their rear wiper stuck.

below I put the wiring, looks there is not just a simple DC motor inside.

the electrical circuit is fairly simple, it's just a changeover switcher, so that the switch has precedence over the wash/wipe relay. The capacitor is there to decouple the motor so that it condenses any electrical noise to ground.

TeflonTom, what happens when wiper arm is blocked?

does the motor reverse rotation?

i dont know, those resistors have a current limiting effect, so i guess it would just stop rather than reversing.

wiper-waggling.