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Repairing The Window Motor In A 400GT

This is an article submitted by Fred Paroutaud (Lamboguy) from the forum.

First of all, do not ever "lean on" the switch of a non-working window motor. It's not that hard to fry the motor windings on these motors. I had that problem in 1983 and had to rewind the motor, which I did myself. But you're better off not getting into that situation to begin with. Treat these window motors with care as they are not at all like the robust US car window motors. Also, keep in mind that leaving the windows up when not driving will put less strain on the window spring over the life of the car (as well as keep the cats and cridders out).

Regardless, once the motor (C) stops working, or is working poorly, the first thing to do is check that you are getting voltage to the window motor. Remove the door panel, disconnect the two motor leads on the junction block (A) -- leaving the 2 leads for the switch -- and check that you get battery voltage with window switch engaged. If you do, the problem is most likely the motor. If you don't get battery voltage, look closer to the switch for a broken wire, or check the fuse.

After it is determined that the motor is at fault (as was the case with mine), you'll want to remove the window motor. You'll probably have to remove the window frame to gain access, however it may also be possible (I think, but maybe not) to remove the motor itself. I didn't try this, but think about disconnecting the arm to the window (B) and running the motor to its extreme down position. Obviously, you'll have to use the window crank for this if the motor doesn't move at all. At this extreme travel the large window gear (behind D) will be disengaged from the small window motor gear. If you can lock the large window gear/arm mechanism in the "unengaged" position (maybe by using vise grips as illustrated below), it might be possible at this point to remove the motor without having to deal with the window frame. Keep in mind that the window return "assist" spring (E) is very powerful and by all means you want to prevent any associated damage to the glass window. Again, I didn't try this. I only thought of it after I had removed the entire mechanism (including window frame) as I will now describe. Either way, I think the following might ultimately be a safer method because of the powerful window spring.

First use some soft-jawed clamps to lock the window glass in the up position:

Then mark (outline) the frame position in relation to the door brackets for repositioning when you're done. Then remove the 6 screws holding the window frame in position -- one at the base of each frame leg, and 2 where each frame meets the top of the door.

You'll have to remove the aluminum covers to access the top screws. The front cover is pretty straightforward. The rear cover is a bit of a trick. First, the 4 screws holding the latch in position have very thin slots. I used a .035" feeler gauge as a screwdriver to make sure I had the slot fully engaged, in order to prevent marring the screws.

These polished aluminum plates and associated hardware are designed to "look pretty" -- so try and avoid any scratching or marring of parts.

It's difficult to get the actual latch through the hole in the aluminum door cover. First step may be to put tape on the polished aluminum around the latch to prevent scratching. I didn't, but probably should have. Then make sure the latch is in the locked (down) position as far as it can go, and carefully maneuver the hole in the plate around the latch to remove. Just go slowly and carefully and the plate will come off.

The upper frame screws are tricky too because they will probably be corroded into place. First I sprayed a bit of WD40 on the screws and let that sink in. Then I used a big screwdriver with perfectly matching blade to screw slot, and vise grips on the screwdriver for torque. Pushing very hard down on the screwdriver then turning with the vise grips managed to snap the screw loose in each case.

After the screws are removed the frame should pull straight up with little difficulty. Leave the window up with the clamps in place, then undo the motor screws and remove the motor.

To remove the motor assembly from the window winder mechinism, you'll need to move the winder arm into its extreme down position, which will disengage the winder gear from the motor gear. Here you'll be fighting the window return spring, so be careful not to hurt yourself. It's deceptively powerful. Once disengaged, the winder arm can be locked against the backing plate with Visegrips, and the motor safely removed:

Unscrew the motor from the window mechanism, remove its plastic cover, and look at the commutator and brushes. They are probably heavily worn as mine were.

Then remove the commutator from the motor frame, being careful to keep the brush springs from flying across the shop. What you want to do next is turn the commutator (brass rotor that the brushes ride against) in a lathe. If you don't have a lathe you can try sanding it down with some emery cloth, but that will not accomplish the goal of making the commutator run true.


Notice that I've used a piece of brass or copper sheet to cushion the armature shaft from the chuck jaws. And once trued, the commutator isolation slots should be cleaned out with a knife or similar tool.

Reassembly is pretty straightforward. When you reassemble you may want to grease everything that moves in the window winding mechanism. I used a very thin art/putty knife to get grease into the hard to reach areas such as between the big gear and its associated backing pads and washers.

While the assembly was apart I also spent a bit of time polishing the aluminum door plates and screws, and doing some subtle (and probably ineffective) window-alignment adjustments. This is one of those projects that might benefit from doing a bit at time, over a longer period than anticipated. I spent a couple of weeks, doing one step every few days.

The only problem now is that this window (passenger) works so much better than the driver's window, so I'll probably have to redo that one too.

Good luck!


This page was last modified on 03/12/2014

This page was last modified on 09/06/2014