Seats move slightly on acceleration or braking
This issue occurs because the rubber bushings on your BMW
Z3 seat rail would have degraded by time and need replacing. Each seat consists of 4 bushings of about 3mm thickness each and because these bushings would become nonexistent they will cause the seat to wiggle / slide with the weight of the seat and occupant as your BMW
Z3 accelerates or brake.
This $20 part will solve the rocking seat issue on your BMW
Z3, together with half a day of labour.
Parts and Tools Needed
- Z3 Seat Bushings kit (4 per seat)
- 13mm Socket
- 16mm Socket
- 17mm Spanner
- T25 Torx
- T50 Torx
- Flat Screw driver
- Old bed sheets, clean cardboard or a car cover
- 2 x long wires (2m) wires. (see step 13)
Step by Step
- Remove hardtop / or put the roof down
You will be taking the seats out of your car and the battery would be disconnected in later steps. Having no top would make maneuvering the seat out of the car much easier.
- Remove Front seat bolts
Slide seat to the back and remove 2 x 13mm bolts. It's Important to start with the front bolts because this will give us clear access to the T50 torx in Step 7.
- Remove Rear seat bolts
Slide seat to the front and remove the 2 front 16 mm bolts. Straightforward as the previous step, just a note that the one near the centre of the car is the hardest to get to.
- Disconnect battery
Disconnect battery to avoid the airbag fault light. Removing negative terminal is enough. Note that If your airbag light does come up, assuming all is connected it can only be removed by an advanced OBD2 tool such as the Autophix ES910.
- Unbolt seat belt and disconnect wire harness
Tilt seat forwards to disconnect the wire harness. The number of plugs depends on which side you are working on and if your car is equipped with heated seats. Irrelevant of this you would need to disconnect them all. Do not worry about placement, as each one has a distinct connector and can only be connected in one direction.
- Remove the seat out of car
Once out of the car flip the seat upside down on a clean smooth dry surface to avoid any damage to the leather while working on the underside of the seat.
- Remove 2 x T25 Torx on the face of the rail, and top T50 torx
Once the 2 x T25mm Torxs have been removed the railing would move freely giving you clear access to the T50 torx. Note that I have a common toolbox and did not have a T50 torx available but still managed with a 6mm allen key. In addition please mark the position of the mount to the railing. This is useful when coming back to fitting and aligning things back in place as the position of the slider mount is important.
- Remove the seat runner
This can be done by simultaneously moving the slider and seat runner in the same direction, eventually taking out the runner on its own.
- Inspect old bushings
From this point you can clear inspect what the issue is and how the old bushing has degraded by time and use. Before you unscrew the part tape off the current position on the slider. This is to ensure correct alignment when you are putting everything back together. Note: Other guides suggest you to count the number of turns it takes to take the part off.
- Fit the new bushes in place
The new bushes might be needed to sanding down in order to fit snugly. Use vise and a random socket to align things into place.
- Place runner back in place
If you used the number of turns technique or tape as a guide make sure the mount is in the correct position and put it back into the slider. Use the inspection hole and a flat screw driver to ensure the runner is connected into the cable.
- Repeat the above steps for the other railing and eventually other seat.
- Putting it back together
If you have arrived at this step, I'm sure putting things back together would be straight forward. The only tip I give is to test the power seat out of the car. After putting the seat back together outside of the car, test the front and back power movement by momentarily giving power to the green/blue power seat motor connector. This can be done by directly connecting 12v power from the battery to the motor - direction does not matter as it only changes the movement of the seat. If the aligning has been done incorrectly (Step 9), the motors would struggle to slide the seat - the T25 Torx is the key here. Also using lock nut on all bolts to prevent nuts getting loose by road vibrations.
While the above information is good to have printed and in hand while doing the work, here is a visual explanation from the manufacture of the bushings
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