2000 V70R - Headlight wiper operation question?

[scot850]

Every time I am at a pick-n-pull if I see a headlight wiper motor, I pull them and then try them when I get home. I can't believe I am that un-lucky that none of them work as I expect, so perhaps I am doing something wrong?

What I do is place the motor on something flat in the engine bay and connect to the appropriate wiper side and then switch the ignition on and cycle the wash/wipe. The original motor with arm attached works fine, but the 'spare' usually only moves (RH in this case) the shaft maybe 20 degrees CCW and then stops. Disconnecting, switching the engine off and on does nothing. I know these motors have an overload resistor that fails in them, but I thought when that failed they didn't move at all. I know the 'fix' but normally return them rather than take them apart (normally breaking many of the tabs).

Do the motors need to be loaded with the arms to make them reach the extremes of the sweep to keep them going?

Appreciate any education I can get on the subject. And before someone says why bother, up here in Canada we do use these when the work as the roads get real messy in the winter.

Thanks again,

Neil.

[j-dawg]

Those ones you're bringing home are probably actually broken. They weren't very durable.

[scot850]

I was thinking that, but having had a 93, 98 and 2000 all with these fitted and all that worked in-spite of the winters and temperatures we get I can't believe they are all bad. What I don't get is if they were bad, why do they move initially then stop? If the overload resistor is kicking in then it happens really quickly and even under no-load (no arm fitted).

At least at $10 I can justify taking it apart to look as it is $10 + to drive down and back. I'll add it to the 'investigate how it works pile'. May get to it sometime in my life!

Appreciate your help.

Neil.

[jimmy57]

They put a protection resistor in the motors to stop the motors from frying if someone washed windshield when headlight wipers were frozen to headlights. The resistor disc is inside the case stuck between contacts that you can trace as one incoming from wire and the other outgoing to the motor inside.
The resistor is thermal and if the motor stalled the high load would heat resistor and it would go from less than 2 ohms to something over 75 ohms. Sometimes the resistor disc and the contacts can be cleaned but on some the disc has failed and has too much resistance and it will only run a few degrees before it goes high ohms and shuts off motor current.
This same resistor disc setup is what takes out door lock motors and makes them have the same barely moves behavior.

[scot850]

Thanks again jimmy. Your wisdom is also appreciated. I'll take apart, take pictures and post back when I get to it.

Neil.

[scot850]

Thought I'd add an update to this thread. I followed a very helpful article on a SAAB web-site that shows how to clean and service a headlight wiper motor unit. What I got from it is that the resistor does not necessarily fail, but as the motor gets older, the grease in the unit dries out, and the motor brushes get contaminated from carbon on the commutator, just like a starter motor. The suggestion it that cleaning the brushes and re-greasing the various cogs the motor will run ok again as the friction that overloads the resistor is removed to normal levels.
Not sure about that, but all I can say, is that having done this maintenance to the spare motor, it now works as it should!! Is the resistor failing a read herring, and by replacing the resistor with foil just allows you to overload the motor allowing it to run? Just a thought.....!

Links I used are:

http://www.saabnet.com/tsn/bb/9-5/index.html?bID=112092

http://www.saab9000.com/procedures/elec ... repair.php

Input always welcome!

Neil.