70 wiper motor resistor

[Joe R.]

Re: 70 wiper motor resistor

Wayne

Just a few suggestions:

1. Do you have a automotive electrical repair shop close to where you live. They may have wiper motors that they cannibalize parts from.

2. Junk yards with older GM cars may have wiper motors that are low cost and back then I would expected this resistor was used on a lot of GM models.

3. Buy a rebuild motor from say advance auto they are about $60 plus you have other parts if needed you can cannibalize from.

4. Our chapter president does rebuild wiper motors as a living call him he may have a part for you. His name is Steve Hack 513-553-2080 give him a call.

Hope this helps.

Paul 18046

You might want to make a note of this. Steve Hack does NOT rebuild the wiper motors! He sends them to Steve Hackel 1 708 687-4183 who knows what he is doing and is an expert rebuilder. You might want to give Steve Hackel a call.

JR

[Paul O.]

Re: 70 wiper motor resistor

Wayne

Spoke with Steve Hack this evening he does have spare resistors if you need one give him a call. Steve also said do not run the motor on a bench test on high for more then a few seconds or damage would result to the motor and circuit.

Joe

I can tell you and I have been at Mr. Hack's shop he does rebuild them watched he do the same. I also know Mr. Hackel he has done work for me when I lived in Chicagoland and when I was restoring my 71. He does great work none better.

Paul 18046

[Joe R.]

Re: 70 wiper motor resistor

I'm having some aggravations with my wiper motor. I had it out and bench tested it then took to cleaning it up but accidently (stupid hat on) damaged the small resisitor on the plug inside the motor. I've checked around and it seems you just can't get a resistor like that so I looked for a modern equivalent. Willcox has a pic of the resistor and labels it as 20.6 OHM resistor and I assume it is "wire wound" type (whatever that is) as it looks like a thin wire wrapped around a piece of asbestos. I called a local electronics store asking for a 20 OHM wire wound resistor and he said they had a variety in different wattages and needed to know what watt range it needed. I dunno. So, is a modern resistor an option to replace the old one? If so, what wattage would be running through that? or grounding or however it works.

Wayne,

I'm a little late to the party, but I am an EE. Let me ask a dumb question, are you for sure the resistor is bad? How many Ohms do you get when you measure across the resistor? It's best to disconnect one lead before checking the resistance. If the resistor is bad, it will measure open circuit (infinity Ohms). Assuming it's bad, even without knowing any of the specifics about the circuit in question, it's pretty safe to say that the most voltage you would see across that resistor would be 15 Volts because the battery is the power source and it should be between 13.8 and 14.5 Volts or so if I remember correctly. Another way to express power is:

P = (V * V) / R

So the maximum power would be:

P = (15 * 15 ) / 20.6 = 10.9 Watts

I like to double the actual wattage to determine the wattage rating. So I would use a 20 Watt resistor in this case.

What are the dimensions of the resistor you have?

Joe

[Ken P.]

Re: 70 wiper motor resistor

So a 20 ohm resistor at 20 watts should work? or is it physical size? When I search 20 ohm resistors on the net they seem to come in every wattage from less than 1 up to
1000.

Physical size.

[Joe R.]

Re: 70 wiper motor resistor

Physical size.

Ken,

Electrically, it needs to be 20 Ohms with a 20 Watt dissipation rating. Mechanically, it needs to be packaged to fit in the space available to it. If it really dissipates 10 W or so, it needs some space around it for cooling and / or it needs to be mounted to a heatsink or a piece of metal at the very least.

Joe

[Wayne B.]

Re: 70 wiper motor resistor

The relay is one inch long and about one eighth of an inch in diameter, exposed tight coil. Willcox has a picture in their troubleshooting paper for a wiper motor, I can post it but it has their name across the pic and I don't know if that would violate any forum rules. I called Willcox about it as I am VERY cautious about copyright infringement and they said they didn't mind (usual "If", I don't change it, take their name off, claim as my own etc). The pic is very clear what it is.

if it doesn't violate rules I'll post it here.

[Joe R.]

Re: 70 wiper motor resistor

The relay is one inch long and about one eighth of an inch in diameter, exposed tight coil. Willcox has a picture in their troubleshooting paper for a wiper motor, I can post it but it has their name across the pic and I don't know if that would violate any forum rules. I called Willcox about it as I am VERY cautious about copyright infringement and they said they didn't mind (usual "If", I don't change it, take their name off, claim as my own etc). The pic is very clear what it is.

if it doesn't violate rules I'll post it here.

Wayne,

How about a picture of yours in its present state? A good electronics technician could possibly repair it.

Joe

[Wayne B.]

Re: 70 wiper motor resistor

nah, that thing is hosed now and I'm sure an electronics guy would laugh me out of the building when there's a part for around a buck that could fix it. If a modern wire wound resistor will work it just makes sense, like the chip in the box on my TI instead of the old boards. Besides, for what it would cost I might as well get a rebuild and canabilize it. Just the same, the new resistors I've seen are very cheap and it doesn't make sense to spend fifty-sixty times as much as you need too...I've certainly had enough of that over the years and don't have money to throw away anymore like I used to

[Joe R.]

Re: 70 wiper motor resistor

nah, that thing is hosed now and I'm sure an electronics guy would laugh me out of the building when there's a part for around a buck that could fix it. If a modern wire wound resistor will work it just makes sense, like the chip in the box on my TI instead of the old boards. Besides, for what it would cost I might as well get a rebuild and canabilize it. Just the same, the new resistors I've seen are very cheap and it doesn't make sense to spend fifty-sixty times as much as you need too...I've certainly had enough of that over the years and don't have money to throw away anymore like I used to

Wayne,

My concern would be that the 'resistor' has some other electrical properties (most likely inductance in this case) that will cause problems if not present. Can anyone provide a schematic showing how the resistor is being used? If you can provide a picture, I can ask some of my technician friends what it would cost to fix. It sounds like an easy job, unless I'm missing something.

Joe

[Paul O.]

Re: 70 wiper motor resistor

Wayne,

My concern would be that the 'resistor' has some other electrical properties (most likely inductance in this case) that will cause problems if not present. Can anyone provide a schematic showing how the resistor is being used? If you can provide a picture, I can ask some of my technician friends what it would cost to fix. It sounds like an easy job, unless I'm missing something.

Joe

Here is a diagram of the circuit for high and low speed. From the shop manual.

Paul 18046

[Joe R.]

Re: 70 wiper motor resistor

Here is a diagram of the circuit for high and low speed. From the shop manual.

Paul 18046

Paul,

Thanks for posting that! It appears to me that a 20 Ohm resistor has an excellent chance of working just fine.

Joe

[Wayne B.]

Re: 70 wiper motor resistor

I'm going to go ahead and put this up, I can't see anything in the FAQ against it, guess I'll find out quick enough.
disclaimer: for educational purposes

[Ken P.]

Re: 70 wiper motor resistor

Ken,

Electrically, it needs to be 20 Ohms with a 20 Watt dissipation rating. Mechanically, it needs to be packaged to fit in the space available to it. If it really dissipates 10 W or so, it needs some space around it for cooling and / or it needs to be mounted to a heatsink or a piece of metal at the very least.

Joe

He was just guessing at the 20W. He doesn't know what watt rating he needs is. I told him to get a 20 ohm resistor of the same style (wire wound) and of the same physical size as the original and chances are that the watt rating will be the same. As far as packaging...well that was part of my same size suggestion.

[Wayne B.]

Re: 70 wiper motor resistor

Here's a new kink. I recieved an email back from a wiper motor rebuilder and they said they replace the old resistors with new ones and that they are 7 watt. I stopped by an electronics supplier in town (not auto electronics) and he shook his head, pulled out a twenty watt resistor and it was huge.

I got a look at a brand new rebuilt wiper motor (autozone) and looked inside and it looks like the exact same resistor as the old style.

[Joe R.]

Re: 70 wiper motor resistor

Here's a new kink. I recieved an email back from a wiper motor rebuilder and they said they replace the old resistors with new ones and that they are 7 watt. I stopped by an electronics supplier in town (not auto electronics) and he shook his head, pulled out a twenty watt resistor and it was huge.

I got a look at a brand new rebuilt wiper motor (autozone) and looked inside and it looks like the exact same resistor as the old style.

Wayne,

Will the wiper motor rebuilder sell you just the resistor? You might ask your local electronics supplier for a 10 Watt resistor. Or spend the money on the Autozone part to cannibalize it. The only other option might be to contact some of the more major electronics houses (Mouser, Digikey, Allied, Newark). Ask them for a resistor in a TO-220 package. It will be pretty small and will dissipate 25 Watts or so. Being able to dissipate more wattage than you really need won't hurt you a bit. Or you might try their web sites.

Joe