Wiper questions, electrical and mechanical, for Elvis (1947 DeSoto Custom Sedan)

[Racer-X-]

I need to get the wipers working.  With the drivetrain swap (GM LM7/4L60E), the wiring in the car now is all 12V negative ground.  I understand the car was originally 6V, positive ground. So there's going to be a conversion issue. 

 

Were these wipers simple on/off.  Or I guess it was two speeds, I'm told, Off/Slow/Slower.  Did they have a "park" feature that returned them to a fixed position when you shut them off?  Or did they just stop wherever you cut the switch off?

 

Will they tolerate the motor running backwards?  This is an important question.  I have a 6V "buck converter" with 20A capacity for this.  I was planning to use that to step the voltage down.  Now that I'm looking at it, it's wired with the ground for both the input and output circuits wired together.  Those wires (both black) are definitely connected inside the converter.  That means that it would be much easier and safer to wire it for 6V, negative ground, even if that results in the motor running backwards, as long as that doesn't destroy anything. If the system is just "on/off", it may be fine.  If there's any "park' feature in it, I suspect I'm going to have problems.

 

It would also be handy if there was a diagram of how the wiper motor is supposed to be mounted.  Ours is hanging loose, rattling around, with a very loose bolt on it.

 

Here are pics, with notes about what I see as issues in these pics.

 

^  You can see the loose bolt in this picture. It's at an odd angle through that bracket.  Also, I'm guessing that the two slotted screws across from each other with the motor shaft bearing cover in the center, are the two power feeds.  Is this correct?   How does that work? Power to one is "slower" and power to both of them makes it run "slow" (the faster speed).  Or is only one screw terminal powered in each speed?

 

Another pic.  This one is a slightly different angle, same end as above.

 

And this:

That's a view of the wiper transmission mechanism.  I think the really old cloth covered wires may go to the wiper motor?

 

This is a different angle on the loose bolt. 

 

I'll try to get better pics tomorrow, but it's tough getting the camera/phone up in there to take better pics.

Edited January 4, 2023 by Racer-X-

[SteveR]

Here's a diagram. It looks like a 2 speed motor Look at page '8' for the diagram

http://www.route66hotrodhigh.com/TechSheets/pdf/Desoto1946-48.pdf

The above is found to be corrupted. Do not use!

Edited September 7, 2023 by SteveR

[Sniper]

When I converted my 51 to 12 negative ground the wiper motor still worked, but it was much faster.  Mine does have a park function, but it doesn't seem to work properly  Now I wonder if my motor is running backwards and that is why park doesn't work properly?

 

Newport Engineering makes a 12v electric wiper motor for 46-48 Dodges, poking thru the Mopar master parts catalog appears to show that all Dodges, Desotos and Chryslers use the same setup in that time frame, 1941 thru 1948.  So it appears that the kit Newport lists for 46-48 Dodges should work on your Chrysler.

 

https://newportwipers.com/product/1946-48-dodge-and-plymouth-wiper-motor-clears-stock-radio-replaces-factory-electric-wiper-motor/#wiper-motor

 

Of course, they do not have a picture of it.  You may want to poke thru the parts catalog and verify my findings though.

[Racer-X-]

2 hours ago, SteveR said:

Here's a diagram. It looks like a 2 speed motor Look at page '8' for the diagram

http://www.route66hotrodhigh.com/TechSheets/pdf/Desoto1946-48.pdf

 

That's an awesome link.  

 

It answered my question yesterday about the cowl vent as well, with a diagram and part numbers for the parts on page 2 of that PDF.  

 

And it answered an upcoming question, at least partially, with the alignment specifications and the diagram on the last page showing the front suspension parts. 

 

And it does show the wiper wiring in the wiring diagram on page 8 of that PDF.

 

Which makes me feel like "that guy," the one who always asks for more and is never satisfied.  Because it doesn't show a diagram or part numbers or any of that for the wiper mechanism. 

 

But I've bookmarked that and saved a copy. 

 

2 hours ago, Sniper said:

When I converted my 51 to 12 negative ground the wiper motor still worked, but it was much faster.  Mine does have a park function, but it doesn't seem to work properly  Now I wonder if my motor is running backwards and that is why park doesn't work properly?

DC motors reverse direction if you reverse polarity.  So it's likely running backwards.  And "park" functions vary in complexity and design, but none of them like to run backwards.  There's usually a lever that triggers a switch to stop the thing in the "parked" position, at least for ones where the wipers are exposed when parked and park within the normal range of motion while operating.  Often running those backwards will bend or damage, possibly even break the piece that triggers the switch. 

 

The ones that "retract" to park are even more complicated and usually self destruct if you try to run them backwards.

 

Thanks for the link to Newport.  I'll keep that in mind.  The contract for this one has an "inclement weather" cancellation clause, so the wipers are more me trying to get them working, less about the car's weekend jobs.  Although it would be nice if it didn't have to cancel for light rain, or if it wasn't parked where it is if there's unexpected rain. I'll talk to the owner about it and see if working 12V wipers are worth that to him.

[Sam Buchanan]

1 hour ago, Racer-X- said:

DC motors reverse direction if you reverse polarity. 

 

So why does the starter and heater fan motor on my P15 not run backwards since the car has been switched from positive to negative ground?

Edited January 5, 2023 by Sam Buchanan

[Racer-X-]

13 hours ago, Sam Buchanan said:

 

So why does the starter and heater fan motor on my P15 not run backwards since the car has been switched from positive to negative ground?

 

OK.   You got me there and I had to look it up.  Because I actually know you are correct about most (not all) starter motors.

 

There are several types of DC Motors.  Permanent magnet DC motors reverse direction when you reverse the polarity of the power supplied to them.  Electromagnetic DC motors use field coils for the magnetic field and can be connected internally a few different ways.  Starter motors are typically of this type, and are "series wound."

 

Series wound DC motors always rotate in the same direction, no matter the polarity.  The direction can only be changed by changing the polarity of one set of windings, rewiring the motor internally.  Typically, the armature coils are reversed to reverse one of these motors, if that's necessary.  Series wound DC motors have the highest starting torque and are excellent for starter motors, so that's probably what the starter motor is on yours, and it'll spin the same direction with either positive ground or negative ground.

 

For heater fans and wipers and other applications, both permanent magnet types and electromagnet type motors are used, depending on the application and the choice of the manufacturer. It seems that electromagnetic types do not change direction if you change the polarity at the main power feed.  You change the armature polarity to reverse all of those types, and some will also reverse if you change the polarity of the field coils. If you reverse both (switching the main power leads), they operate in the same designed direction.

 

Also, I learned that reversing the direction of a DC motor that's designed to spin only in one direction can cause excessive wear of the brushes.  Motors that are designed to be reversed have the brushes beveled on both ends, so that they operate smoothly in both directions.  Motors designed for one specific direction have the brushes beveled on one side only, and will have excessive friction and wear out quickly if they are operated in the "wrong" direction.

 

TIL much.

 

Reference links:

https://electronics.stackexchange.com/questions/159509/why-motor-continues-to-rotate-in-same-direction-even-after-changing-the-polarity

https://www.prorichmotor.com/how-to-change-the-direction-of-a-dc-motor/

[Sam Buchanan]

1 hour ago, Racer-X- said:

Series wound DC motors always rotate in the same direction, no matter the polarity.  The direction can only be changed by changing the polarity of one set of windings, rewiring the motor internally. 

 

You got it.

Excellent post.  ?

Edited January 5, 2023 by Sam Buchanan

[JBNeal]

On 1/4/2023 at 2:31 PM, Racer-X- said:

...

^  You can see the loose bolt in this picture. It's at an odd angle through that bracket.  Also, I'm guessing that the two slotted screws across from each other with the motor shaft bearing cover in the center, are the two power feeds.  Is this correct?   How does that work? Power to one is "slower" and power to both of them makes it run "slow" (the faster speed).  Or is only one screw terminal powered in each speed?

those two slotted screws run the length of the motor and hold the transmission housing to the motor.

 

On 1/4/2023 at 2:31 PM, Racer-X- said:

...And this:

That's a view of the wiper transmission mechanism.  I think the really old cloth covered wires may go to the wiper motor?

those cloth covered wires are part of the park circuit...I have a write-up pending that goes into detail about this electrical circuit, with issues to address, a supplemental wiring diagram, and repair details.  In short, these wiper motors can be rejuvenated fairly easily by dismantling, cleaning critical areas, rewiring the park circuit with fresh conductors, and filling the transmission with fresh lubricant.  There is a leather seal in the transmission that is very tricky to replace, but I think I have that issue solved through trial and error.  In total, for less than 20 bucks in materials and some common mechanical and electrical tools, refurbishing these Autolite 6V wiper motor units can be a satisfying weekend project.  ?

[Racer-X-]

@JBNeal  I look forward to seeing your write up on this. 

 

Does it matter if the 6V supply to these motors is positive ground or negative ground?   This is going in a 12V Negative ground system, using a "buck converter" which shares ground (and therefore shares ground polarity) between the 12V input and the 6V output.

[JBNeal]

The brushes are offset on the commutator so I do not think polarity is an issue.

[SteveR]

In my 37 Plymouth, it has been changed to 12vdc negative ground. I have had no problems with the starter.

[andyd]

Here in Oz most if not all Oz mopars came with electric 6v wipers, my 1940 Dodge certainly did, however the small internal/external spline washers that held the wiper arm to the wiper shaft had stripped and at the time.......40 yrs ago.............lol..... I was unable to find them anywhere, the wiper had a voltage resistor wired in the power line as the car was 12volt, (V8 etc) so I installed a 12 volt BMC cable driven wiper motor between the glove box and cowl side, as it is cable operated the 90degree wiper transmission fittings can be mounted to give either "wave your hands" or "clap your hands" wipers.......I chose the latter, 40 yrs down the track they work fine still, from what I understand the Newport Engineering wiper conversions are also the cable operated type........my Oz 2 cents worth................andyd   

[Sniper]

6 hours ago, andyd said:

Newport Engineering wiper conversions are also the cable operated type

 

They are not.  Here's the setup for a 40 Dodge

 

[Dan Hiebert]

FWIW, I had a '52 Ford F3 many years ago.  It had been converted to 12v negative ground and had the original 6V electric wiper motor and starter.  When I first got it, for a few months, there was no power converter.  The wipers ran like gangbusters, almost scary how fast they ran.  I put an inexpensive converter in that I got from JC Whitney (this was so long ago it was from the print catalog, there was no internet as we know it at the time.)  No polarity change, and the wipers ran just fine, afterwards.  All I did with the starter was put in a 12V solenoid.  It cranked faster than normal but fired up in one or two turns.   

Edited January 21, 2023 by Dan Hiebert

[andyd]

Sniper.......I stand corrected......I contacted Newport 20-25yrs ago and at the time was told that they used a cable operated wiper.........I was considering replacing the BMC cable wiper at the time but decided to stick with it..........although I do admit to purchasing a pair of wiper arms from Newport about 3 years ago to replace the BMC arms which had a few issues .....the Newport arms are top quality and so far have worked fine..........andyd

[JBNeal]

On 1/4/2023 at 2:43 PM, SteveR said:

Here's a diagram. It looks like a 2 speed motor Look at page '8' for the diagram

http://www.route66hotrodhigh.com/TechSheets/pdf/Desoto1946-48.pdf

I was following up on this and it appears this link has been corrupted ?

[SteveR]

5 hours ago, JBNeal said:

I was following up on this and it appears this link has been corrupted ?

I just clicked on it myself and yep it was corrupted. I don't go on those sites.