Replacing the Rear Seat Belt Inertia Wheel

An article written and kindly provided by Simon Claringbold

A common problem with the W140 are the rear seat belt tensioners. They tend to hang up and not retract properly. Simon has a procedure that looks very easy.

Symptoms of the problem was that the seat belt retraction was delayed or did not happen at all when the seat belt was in 'Comfort Mode' (CM). The seat belts are in CM when the seat belt tongue is inserted into the buckle - a switch in the buckle detects this - and the ignition is on.

In CM only a weak spring retracts the seat belt. From various contributions to forums I've seen it seems fairly common that once the seat belt reel reaches 10 years of age there is a tendency for the weak spring to become so weak it can't retract the extended seat belt. So when the seat occupant leans forward then back, the seat belt remains dangerously slack. On one of my rear belts this slack could be taken in by unbuckling the seat belt, then re-buckling it again (obviously not a recommended practice while the vehicle is moving). The other rear seat belt would not retract reliably at all.

I have heard that some people have cleaned the inertia reel mechanism using an air gun and lubricating spray to get it working again. Having pulled one of my old inertia reels apart I think this may help only if the seat belt has picked up fluff in the belt reel. It might be worth a try (apparently the factory manual says that the inertia reels should NOT be lubricated). The spring and servo mechanisms are sealed quite well and the springs work directly against the reel. The inertia reel is a sealed mechanism, any disassembly is not recommended. Once disassembled or tampered with in anyway the seat belt would probably become illegal for road use (this is certainly the case in Australia).

1) Remove and unplug the C-Pillar interior lamp. Pull it out by gently prying it out.

2) Pry out just the top of the C-Pillar trim working from the front to the back. If you look inside the trim as it is coming off, you can disengage the clips without breaking them.

3) Remove rear seat base. Two tabs under the seat disengage and the seat lifts up at the front, then pull forward.

4) Remove 17mm floor anchor bolt for belt.

5) Remove top 10mm bolt for seat belt slot that is mounted to the C-Pillar, loosen bottom bolt (I used a 10mm ring spanner). I believe we call this a box-end wrench in the US.

6) Remove 17mm bolt holding the reel on, remove reel, unplug comfort servo wires. Old reel and belt can come out.

7) Slip in new reel (it is side specific - not interchangeable), bolt in with 17mm bolt. Ensure metal clip engages slot in inertia reel housing.

8) Thread belt through slot and trim, tighten up 10mm bolts holding slot.

9) Fix seat belt end to floor using the 17mm anchor bolt.

10) Refit seat base ensuring all seat belt buckles and centre belt are in the seat slots. Rear of seat must engage in the mounts in the seat belt base. Front of seat pushes down until clips spring back in place - you will hear a click when this occurs.

11) Push lamp wiring through C-Pillar trim and carefully refit the c-pillar trim working from rear to front. Keep looking in side as it goes back on so you can line up the slots and clips.

12) Plug in C-Pillar interior lamp and clip it back into position.

It only took 30 minutes to do the job, much quicker than for the first time when I did the other side. None of the parcel shelf trim or the first aid kit has to be removed when you use the procedure above.

Thanks go to Simon for this fine write up!

If you have an article you'd like to submit for inclusion on this site, please contact me.

Was this info helpful? to help keep this site up.

I found all the diagrams I needed with my Alldatadiy.com subscription. If you sign up for the service using the link below, I receive a small commission which helps me cover the costs of administrating my site. Thanks!

Alldata.diy is running a special!  Only $14.95 for adding a car and Renewals!
Enter Promo Code "8001292" (less quotation marks)

10% Off New Vehicle Subscriptions!
Enter Promo Code "Repair10" (less quotation marks)

If you can't see the Alldata image above, click here.