Working on the wipers.  Have the motor and assembly out of the cowl.  Cleaned up the harness connectors when I put a new harness grommet on.  Reconnected the harness to see if it still worked.  Wiper motor worked perfectly two times.  The third time the motor started humming loudly in the off position on the switch while the ignition key is in the ACC or On positions.

Ideas?

Edited October 2, 20177 yr by kunzma
clarity

OFF doesn't just turn off the power.  It actually sends a signal to the wiper motor relay that then tells the motor to operate in reverse until the output gear in the wiper gearbox reaches the PARK position.  I think you've either pooched the relay or you've got a mechanical obstruction in the system that's preventing the motor from operating in reverse.  Do you have the wiper blades installed?

The motor is not attached to anything.  Just had it sitting on the cowl.  1/1971 240Z if it helps.

Edited October 2, 20177 yr by kunzma
additional information

Possibility #1is that you somehow hurt or confused the wiper relay during your original tests.  The humming noise could be one of the contacts inside the relay vibrating as it tries to close.  Put your ear close to the relay can and see whether that's where the hum is coming from.  If it is, then a deft whack with a hammer might coax the relay back into operation.  Or not.  If the hammer fix doesn't work, you could try opening up the relay can and poking around to see if you can coax the thing back into life.  Probably better, though, to just replace it.  If it failed after 2 tries during bench testing, it'll probably fail again after you put everything back in the car.  Probably when it's raining .

Possibility #2:  The worm gear in your wiper motor's gearbox may have jammed.  I don't know how this would have happened, but the fact that you got two successful cycles on your original test before you ran into trouble suggests that possibility that the gear jammed at the end of the second forward cycle (maybe when the motor tried to go into auto-reverse?  or maybe something broke off inside the gearbox housing and got lodged in the gears?).  It'll be hard to fix this by trying to move the motor and the output shaft by hand, because it's essentially impossible to rotate a reduction-type worm gear system from the output end.  You might be able to free things up by loosening off the load-adjustment screw that's located on the outside of the gearbox housing at the bottom of the worm gear shaft.  If that doesn't work, you'll probably have to take the cover off the gearbox to see what's going on.

Possibility #3:  This is a WAG.  Maybe, by some impossible coincidence, you stopped the motor at the end of the #2 test at the point when the reed switch for the 'PARK' position was j-u-s-t beginning to open, and now it's electrically hung up between 'off' and 'on'.  To check, you can try moving the 'Park' switch to a new location.   Look on the underside of the gearbox casing and you'll see a pie-tin shaped cover that's held in place by three screws.  The cover has two wires coming out of it (from the reed switch). The edge of the cover has five or six notches and there's an indexing mark stamped into the gearbox housing to serve as a reference.  If you loosen the three screws, you can rotate the can to change the location of the reed switch.  Try rotating the cover by one index mark.  Re-tighten the screws and hook up your power source again for another test.  If this works, make sure you return the PARK switch to its original setting before you button everything up.

Let us know what you do next.

I will give those a go.  Thanks for the quick response and detailed reasoning.  I will report back soon. 

Ok.  

1.  Humming is definitely coming from the relay that is strapped to the wiper motor.

2.  Couple of whacks with the hammer didi not eliminate the humming.

3.  Disconnected the wire harness to the wiper motor.  Removed the bolt holding the strap on the relay.  Removed the two screws holding the relay cover.  Inspected the internal workings of the relay and found all the connections looked secure and there was no sign of any corrosion or arcing.  I did find one of the contacts was missing on the side of the tabs that touches when the switch is off.  When the relay is de-energized these tabs are held in contact there by the spring on top of the relay.  I slightly bent the tab with the missing contact so it would touch more firmly.  Reinstalled the cover and strap on the relay.  Bench test result is ....no humming!  (I find out later from a reliable source that I shouldn't have bent this tab.)

While I have this disassembled should I put on a new silver contact?  Thought I read in the forum that they are silver and not regular electrical solder.  Was there ever a contact?

Thanks Namerow for your help! 

Edited October 7, 20177 yr by kunzma
finally had pics downloaded to computer and new information from a reliable source

Steve or Dave Zs-on-da-Brain can advise.  I'm a mechanical engineer and only understand hammers

... although I'm pretty sure that solder is not going to get the job done (not for long, anyway)

Edited October 3, 20177 yr by Namerow

kunzma, Can you take a pic of the area of the relay where the contact is missing? I'm not sure silver was needed in that application. Maybe silver in color, but not Ag in composition? Probably tin alloy.

In any event, a blob of solder might get you out of the woods for a little while, but it probably won't last long. And I doubt that even "silver solder" would contain a high enough silver to lead ratio that it would last.

Was the original contact rattling around inside the relay cover when you took it off?

 

Finally got the pics onto my computer.  First pic shows that the 3 copper tab all have silver contacts on the side that is pulled to the electro magnet.  Second pic shows the spring side of the copper tab that doesn't have the silver colored contact.  I didn't find the contact rattling around inside.  The third is the tabs removed from the relay and the spring side missing the contact.  The fourth pic shows the magnet side of the tabs with all three contacts.  

Edited October 7, 20177 yr by kunzma
additional photos taken and description

Good eyes. That's definately a problem. Those contact buttons are supposed to be welded in place, and it looks like yours just came loose and fell off!

Unfortunately, I think the best long term solution would be a replacement relay. Only other possibility I got is... Are they making use of every contact elsewhere in the relay? If the answer is 'no', and all the arms are identical (and maybe even symmetric top to bottom?) maybe you could swap wires or even contact arms around. In other words, maybe move the missing contact to a position that isn't being used anyway?

Long shot, but thought I would mention it.

A used relay would be the easiest solution.  Whether you can get one without buying an entire wiper motor/transmission is another matter.  Used relay?  Five bucks.  Used Z motor?  Either cheap or expensive, depending on who's selling.  The big vendors say, 'NLA'.  A Honda motor may be your best bet. $90.

Still, it's just a relay.  Go to the local pik-n-pull and buy a dozen.  You should be able to find a piece to swap in.  Nobody will ever know.

I'm not that confident about finding a simple replacement in a junkyard. The triple pole thing has me skeptical.

Agreed.  I was thinking that he could extract a suitable contact point from some non-Z relay (pref. a from an older Nissan product) and then transplant it into the relay from his Z.