Power Seat Motor brushes - 1993 Lincoln Mark VIII

[thecoolmajor]

Hello everyone!

Well, my driver's side power seat won't go frontwards or backwards anymore (the seat tilt and the up and down still work). I could hear the switch click so I knew it wasn't the switch so I took all three motors apart and cleaned them. I believe the middle motor controls the frontwards and backwards motion.

They weren't all that dirty but my the frontwards or backwards didn't still didn't work. Then, I switched 1 and 2 stators to see if the problem followed and it didn't so if it wasn't the stator, it was the brushes. The brushes are very worn and wondered if anyone knew where to buy some. I can't even find a new motor online much less brushes.

I may find some close enough and see if they work or if all else fails, switch the brushes with the motor that controls up and down so I at least have frontwards and backwards motion.

Thanks!
Mike

 

[marked8]

Found a related post on TCCOA:

http://forums.tccoa.com/16-interior/126892-power-seat-motor-rebuild.html

I dug into this recently. What I found is that the motors almost never go bad. I opened up the gearbox by drilling out all the rivets. (It is a pain to disassemble the unit.)

The seat is moved by worm gears, all of which seem to be pretty sturdy. The only weak link I found is the gearbox itself, which is made of plastic. (Polycarbonate, ABS? Not sure.)

My seat's problem was that it wouldn't move forward or back. When I pushed the switch, it went CLACK CLACK CLACK, but nothing moved. Well, the problem was that the worm gear and matching helical gear were not held in the proper alignment. When the motor applied torque, the two gears moved apart and the gear teeth skipped over the worm. How did this happen?

Well, like I said before, the gearbox is plastic. The forward-back gear set happens to be positioned right along the bottom edge of the gearbox. Over time, the grease in the tracks gets crusty, and it takes a lot of torque to move the seat. Maybe coins get stuck in the tracks. Maybe there is a heavy driver or the car is pointing uphill. Anyway, one day, there is a lot of torque applied to the worm gear set, and the gearbox splits in the area that is supposed to hold the gears in place. It looks sort of like a "greenstick fracture". So every time the seat motor is applied, the broken part of the gearbox flexes away from the rest of it, and the gears skip past each other.

I was able to fix this by slathering a whole mess of JB weld over the outside of the gearbox. It reinforced the area where the forward-back worm gears are positioned. So far, it seems to be working. The best part is, you don't need to take anything apart.

Cleaning and lubricating the tracks are probably the most important thing to make sure this repair holds up ... or, if your seat still works, to make sure that it stays working!

 

[thecoolmajor]

Hi Marked8,

Thanks for your input on this. I had used lithium grease on the rails and when I pulled the seat out, I checked them for coins, etc., but found nothing. The gears all looked fine as well - nothing jammed or broken.

When it was installed, it wouldn't make any clacking sound or any sound at all. For the seat back tilt or the up and down, I could hear the motor engage. For the frontwards and backwards, I only heard the switch engage and then silence which I believe means that the motor was being energized but wasn't working. If it was working and engaged, it would grind or clack. When I reinstall it, I will check that gearbox.

 

[thecoolmajor]

Power Seat Problem RESOLVED

I wanted to update and finish this thread. Marked8, you are correct that motors almost never go bad. I will say I jumped into this and assumed the problem was the motor being dirty and the brushes being bad. But, I took the time to troubleshoot this the correct way and found the problem to be in the Memory Module.

I printed the schematic of the seat I found at this sight: http://www.box.net/shared/zjjdzf3yh4. From this, I found that the forward/reverse wires were the red/white and yellow/white wires coming from power seat switch, through the memory module and then to forward/reverse motor. Refer to the attached pictures for the troubleshooting portion.

First, I connected my multimeter to these wires into the back side of the motor connector and pushed the forward/reverse switch back and forth, switched the leads around and pushed the fwd/reverse switch again. In both cases, the meter showed 0V, which meant the motor wasn't getting voltage. By doing this to the wires of the other two motors, front height and rear height, the meter showed 12v in both directions. To further clear the motor of being bad, I disconnected the motor connector and inserted jumper wires from the rear height motor wires to the fwd/reverse motor wires. When I moved the rear height switch up and down, my seat now moved back and forth.

Next, I connected my multimeter to the red/white and yellow/white wires of the back side of the seat position switch connector. By pushing the fwd/reverse switch and reversing the leads showed 12V in both directions. This meant that the switch was working in both directions and supplying voltage to the memory module but the memory module was preventing voltage to get through to the motor.

So, I will look to buy a memory module but won't pay $250 for it like I have seen on Ebay. Instead, I may just bypass the memory module. If I splice and connect the red/white and yellow/white wires on the motor harness and position switch connectors (picture 2), I can bypass it and live without it.