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Subject: Power headrest cable repair Author: DavidC (moderator) : member since December, 2003 : 11918 posts Posted on: 2004-02-23 22:03:06

If you can hear your headrest motor running but your headrest doesn't move, the following will show you how to fix it. This is a common problem on many different BMW models, including the E23, E24 and E34, among others.

The headrest is powered by a "worm drive", a small, screw-like gear connected by a flexible shaft to an electric motor. The flex shaft is a stiff steel cable with square ends, enclosed in a rigid plastic jacket. The square ends of the steel cable fit into receptacles in the electric motor and in the worm drive. During operation, the plastic jacket doesn't carry the torque. Instead, it simply prevents the steel cable from twisting.

The reason that the headrest doesn't operate is that the flex shaft shortens over time while the length of the rigid plastic jacket remains the same. This causes one of the square ends of the steel cable to slide out of its receptacle, thus the worm drive doesn't turn. The shortening of the steel cable is analogous to twisting a string, causing it to become shorter. There are several solutions:

1. Replace the flex shaft with a new one. The downside to this approach is that it requires removing the motor and the headrest track mechanism, which is very difficult to disassemble and reassemble because the screws providing access to the worm drive are on the underside of the assembly, meaning you have to pop rivets to get to them. This is not something I wanted to do.

2. Fabricate and install a spacer in the socket of the square end of the flex shaft, where it meets the motor. The disadvantage of this approach is that it requires removing the motor. Though that's not difficult, it is unneccessary in my view and it carries the risk of having to be repaired again in the future if the spacer falls out or becomes dislodged.

3. Shorten the rigid plastic jacket, thus effectively making the steel cable longer. It had the advantages of being simple and easy to perform, durable and it does not require disassembly or removal of the complicated worm drive or electric motor. This is the approach I chose to take.

You'll need the following items to complete this repair:

1. Utility knife
2. Scissors
3. Philips screwdriver
4. Approximately 2"-3" of fuel line hose
5. Two metal hose clamps

Items 4 and 5 are available at any auto parts store, such as Advance Auto Parts, AutoZone or Pep Boys.

To begin, remove the seat back to expose the headrest motor and drive assembly.



Use a utility knife to cut through the black plastic jacket of the flex shaft, at approximately the midpoint of it's length. You only want to pierce the plastic, not cut through the steel cable on the inside.

Once the cut has been made, pull the steel cable out of the jacket and set it aside. It's very greasy. Cut 1/2" from the plastic jacket, using a pair of scissors or a knife.



Slide the fuel line hose over one end of the plastic jacket and secure in place with one of the metal hose clamps.

Insert the steel cable into the plastic jacket, slide on another metal hose clamp, then join the two halves of the plastic jacket by sliding the other side into the fuel line hose. Make sure that the two plastic jacket halves fully meet in the middle of the fuel line hose. Remember, the idea here is that we want the overall length of the plastic jacket to be 1/2" shorter than when we started.



Tighten the other metal hose clamp to complete the repair.



Push the buttons to test your newly-restored headrest. If it still doesn't work, loosen the metal hose clamps and remove another 1/4" of the plastic jacket, then reassemble and test again.

When done, use a nylon strap to secure the flex shaft to the wire frame of the seat, replace the seat back and you're done!

David Cecil
'97 740iL, 117k miles
'86 735i, 91k miles

www.e38.org has links for everything about your BMW 7-series automobile

• Power headrest cable repair (pic) - DavidC 2004-02-23 22:03:06 (31458 views)
  • Re: seat twist repair - toups 2004-04-25 07:17:36 (2409 views)
    • I haven't had that problem yet, so I don't have a fix, but (m) (url) - DavidC 2004-04-26 17:52:31 (1764 views)
  • great pics David...remember this works for the infamous seat twist, too! - Q 2004-04-04 11:23:02 (1856 views)
  • Thanks for this post. I made my friend do it himself and> - kff 2004-03-06 01:45:04 (1673 views)
    • the friend who did it himself here - Chip in PA 2004-03-29 20:21:26 (1403 views)
      • Re: the friend who did it himself here (nt) - Chip in PA 2004-03-29 20:53:02 (1312 views)
        • Re: the friend who did it himself here (pic) - Chip in PA 2004-03-29 20:54:43 (2510 views)
    • Sounds like a familiar story! Please post some pics and/or a description - DavidC 2004-03-06 03:07:35 (1449 views)
      • Chip just bought a 1986 535i with 130K on it and it was... - kff 2004-03-06 20:28:55 (1364 views)
  • Re: Power headrest cable repair - Kevin 2004-02-25 19:57:17 (1770 views)