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Window motor rebuild - How to

33144 Views 73 Replies 31 Participants Last post by  chevymaher
Well I guess I'm the first to discover this, so I'm going to try my hand at making a 'how to' on it. Here goes.

It's pretty common to see people having issues with their power window motors, but now I know why. There is a resistor built into the motor unit, in series with the motor istelf. This is a temperature dependent resistor, where the temperature is determined by the current flowing through it. As the temperature increases, the resistance increases, allowing less current to flow. The problem is, these seem to get more sensitive as they age, resulting in the quite common "Motor stops working and I have to wait to use it again" issue.

All you have to do is bypass the resistor.

First of all, you'll need to get the motor out of the door. Follow your standard trim panel removal procedure (I use a crowbar) to get the trim off, and use a metal drill bit to drill out the rivets holding the motor in. You'll want to put some duct tape running up one side of the window, over the door frame, and down the other. This will keep the window from falling into the door when you take the motor out.

When you have the motor out, you'll need to crack it open. There are three metal tabs that hold on the plastic end cap, I found that a pair of large channel locks worked quite well for bending these.

Then carefully pry off the end cap. The whole thing will most likely be covered in a very sticky grease (marine grease?) that will give you some trouble in getting the cap off. Be aware that the motors brushes are attached to this cap and are under spring tension, so be patient and take your time if you don't want them to fly in all directions when you finally get it off.

Once you've finally removed it, the underside should look something like this:

That copper bar there with the numbers on it is the culprit. All you gotta do is put a dab of solder where the top bar is exposed to the bottom bar:

And just like that, it's fixed. But now comes the hard part: getting the motor back together. Initially I had tried to stick the stator back into the end cap with the brushes, and then stick all that back into the housing. I quickly found out though that the magnets on this thing are quite strong, and will just yank the stator straight out of the brushes. I did find an easier way though. Start by bending all the rear tabs on the brush mounts all the way out. Initially they should look kinda like this:

And you want them to look like this:

Now, you want to pull the stator out only enough to attach the brushes and end cap. But again you'll find that the magnets just want to yank the stator back down. What I did was I took a couple of flat iron bars (from a scrapped transformer) and stuck them down the sides of the housing, where there are gaps between the magnets. This was enough to hold the stator up, and I was able to remove them without disturbing the endcap.

Now you'll need to put the brushes back in. With the stator still pushed up and the end cap sitting on top, push the brushes through the backs of the brush holders. The brushes have a 45 degree cut on two sides, these sides need to go against the plastic end cap. Now put the springs in, and take a pair of pliers and start squeezing the end tabs together, just enough to put some tension on the spring. Push the spring towards the stator to make sure it is in all the way, and finish bending the end tabs back to their original position.

Remove whatever you used to hold the stator up (being careful not to dislodge the endcap), and push the end cap back down to its original place. Then bend the metal tabs back, and you're done!

It should be noted that this resistor was most likely a safety feature, cutting power to the motor when it was unable to move. This fix is done at your own risk.
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Big_kid said:
Nice detail, nice pics. Maybe add an inline fuse or circuit breaker for some protection?
Yeah, that would work. But you'd blow a fuse every time some dope decided to hold the button while it was already all the way up or down.

I made this same fix to the motors on my door lock actuators a few months ago and have had no ill effects. In my professional opinion, there is very little risk. The worst that could happen is a motor winding would burn out with a puff of smoke, and you'd have to replace the whole unit.

I wasn't aware of the existence of low voltage circuit breakers though. Tell me your secrets.
Since I've got the extra motor, I'm going to do so some tests to see what sort of current it draws, and how long it can endure being jammed. I figure 10 seconds at 14.4 volts would be enough to go without a fuse.
So, it seems a 10 amp delayed trip breaker would work well for this. At 14.4 volts, the unloaded motor drew about 2-3 amps, and voltage dropped to 12.3. With the motor jammed, current rose to 15 amps, but I held it for 20 seconds without overheating the windings. it probably could've endured it even longer, but I didn't want to risk damaging it.

So there you have it. A 10 amp slow-blow circuit breaker if you want to play it safe, however since it held up for a full 20 seconds, I don't think it's necessary.
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Just a tip, if you have a multimeter you should use it to verify your solder joints. Measure the resistance over the joint, it should be less than one ohm. If the joint didn't connect, it will read somewhere around 10 ohms.

I can't seem to edit my original post, why is this? I've got some more info I'd like to add to it.
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Ok, thanks.
RECox286 said:
Looks like the P/W fuse is rated for 30a. Fairly heavy ! This must be the reason for the thermal reset protection in each motor. Any chance of bridging the bad boy with a circuit

that includes a remote c/b instead of just shunting the components with solder. I'd be willing to bet that might be a better choice. It would involve a bit more work, but would at

least have a better chance of not smoke checking the motor. What is the amperage draw of a single motor under a stalled loading ? Easy to find out; jam the output gear while

trying to make it go electrically, while you have an amp probe in the circuit. Figure that there are 2 motors in the circuit, plus what ever else the fuse is hooked to, so, perhaps

a bit less than 1/2 of the fuse for one motor, say 10a ? Here's where the testing comes into play. Start with a 10a fuse, and start reducing values until the fuse smokes, then add

1/2 of the failed fuse as a safety factor. I won't say my logic is where it should be, I'm no rocket scientist, but it sounds like a place to start.

Already done, see viewtopic.php?f=76&t=13637&p=145763#p145708
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For the record, I'd like to say that the device being disabled here is most certianly not a bi-metallic strip. It may be difficult to see from the pictures, but the two bars are made from solid copper and are much too thick to have any mechanical action to them. It is also worth noting that during my initial investigation into what the fck was wrong with the goddamn thing that I applied heat to the joint with a soldering iron while measuring the resistance, and saw a steady increase rather than a sudden open circuit.

It is my opinion that this device was originally intended to only be activated in the event of a jammed motor (for example, the window is already all the way up or down), where the short circuit current would be sufficient to heat up the junction, increasing the resistance until it was so high that no more useful current could flow. I beleive that the failure lies within whatever compound is used between the two plates to create the thermo-resistor action. Either with age or use, the joint breaks down and becomes more sensitive, raising the resistance at ambient temperature. These few ohms of resistance are enough to generate heat during normal use, creating a positive feedback loop until, again, the resistance is so high that no useful amount of current can flow.

I hope this makes sense. :shrug:
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