How to repair the forward / backward seat adjustment gear.
The common problem when the seat will not move forward or backward and the adjustment motor is running is that the plastic gear on the large worm screw is either worn or broken.
These instructions are the same for both worm screw mechanisms.
1. Remove the seat cushion by removing the two long bolts with a Phillips screwdriver. Then snap the cushion up and pull out frontwards.
2. For ease of access, remove the black bar bridging the front up / down adjuster. Use 10mm wrench. See first picture.
3. Remove flexible coupler to adjustment motor. This coupler can be compressed and then slipped off the motor shaft and gear housing shaft.
4. Remove large pin by first removing outer circlip and then wiggling out the pin. It is easier if you pry out the plastic sleeve at the side where you removed
the circlip. If you damage or break the circlip, a common 1/2 inch circlip from the hardware store will fit fine.
5. Now you can lift up the gearbox enough to remove the four torx bolts. Use a T30 bit. I found these bolts to be very tight due to generous loctite application.
6. Slide the gear housing off the shaft and you will see the plastic gear and the large nut holding it. Use a 17mm socket to remove the nut. I had to grip the
worm screw with vise grips to hold it.
7. Pry the plastic gear off.
8. Fit the new gear on the shaft. I used a 15mm socket and a rubber hammer to seat it.
9. Place the 17mm large nut back onto the shaft.
10. Add some new grease into the gear housing and fit it onto the shaft. It will not mate flush with the plate because there is a spring in the shaft housing.
11. Fit the four torx bolts. Tightening these bolts will close the housing.
12. Re-insert the large pin with its plastic sleeves and fit the circlip. You might have to turn the gear to position it. Make sure that both worm screws are
equally extended or the mechanism will be skewed and the gears will bind.
13. Refit the flexible drive coupling.
14. Test seat for smooth movement.
15. Refit the black up / down bar.
16. Refit seat cushion and scew in the two large holding bolts.
17. Relax with favourite beverage and pat yourself on back for a job well done and all the money you saved by repairing this yourself.
Note: I obtained my replacement gears from:
BENZ Seat adjustment gear-1 - Hong Mei Trading Co., Ltd.
The common problem when the seat will not move forward or backward and the adjustment motor is running is that the plastic gear on the large worm screw is either worn or broken.
These instructions are the same for both worm screw mechanisms.
1. Remove the seat cushion by removing the two long bolts with a Phillips screwdriver. Then snap the cushion up and pull out frontwards.
2. For ease of access, remove the black bar bridging the front up / down adjuster. Use 10mm wrench. See first picture.
3. Remove flexible coupler to adjustment motor. This coupler can be compressed and then slipped off the motor shaft and gear housing shaft.
4. Remove large pin by first removing outer circlip and then wiggling out the pin. It is easier if you pry out the plastic sleeve at the side where you removed
the circlip. If you damage or break the circlip, a common 1/2 inch circlip from the hardware store will fit fine.
5. Now you can lift up the gearbox enough to remove the four torx bolts. Use a T30 bit. I found these bolts to be very tight due to generous loctite application.
6. Slide the gear housing off the shaft and you will see the plastic gear and the large nut holding it. Use a 17mm socket to remove the nut. I had to grip the
worm screw with vise grips to hold it.
7. Pry the plastic gear off.
8. Fit the new gear on the shaft. I used a 15mm socket and a rubber hammer to seat it.
9. Place the 17mm large nut back onto the shaft.
10. Add some new grease into the gear housing and fit it onto the shaft. It will not mate flush with the plate because there is a spring in the shaft housing.
11. Fit the four torx bolts. Tightening these bolts will close the housing.
12. Re-insert the large pin with its plastic sleeves and fit the circlip. You might have to turn the gear to position it. Make sure that both worm screws are
equally extended or the mechanism will be skewed and the gears will bind.
13. Refit the flexible drive coupling.
14. Test seat for smooth movement.
15. Refit the black up / down bar.
16. Refit seat cushion and scew in the two large holding bolts.
17. Relax with favourite beverage and pat yourself on back for a job well done and all the money you saved by repairing this yourself.
Note: I obtained my replacement gears from:
BENZ Seat adjustment gear-1 - Hong Mei Trading Co., Ltd.
