Front suspension

After a month break, I’m back to work on the W109!  I’ve got three days this week and hope to make some good progress.

The most important work to be done is the front air bags.  The driver’s side bag is leaking badly and the passenger side isn’t far behind.  This job is one of those that goes much faster after you do it once or twice.  The order in which you remove things is pretty critical to making things go smoothly.  This is well documented in the factory service manual, but sometimes I need to figure things out myself first!

So, heres how it goes:

  1. Disconnect the tie rod from the steering knuckle.  A proper popper (thanks Daniel) makes it possible to not destroy the boot on the joint.  I can’t see how you can get the air chamber out of the car unless you get the tie rod out of the way.
  2. Disconnect the air line.
  3. With a piece of wood (I used a short 2×4), press the bag up and away from the piston mounted to the lower control arm.  Do this before the removing anything else!
  4. Once with piston is free from the bag, disconnect the 5 bolts holding the piston to the control arm.  There are 5, not 4 as I initially thought!
  5. You should be able to pull the piston out now.  You might want to disconnect the sway bar to keep it from holding up the control arm to give you more clearance.  Or, it helps to have both sides of the car jacked up with the wheels off.
  6. Now, remove the three bolts at the top of the subframe and the assembly will fall out.  Remove it from the back.

Thats it!

Actually, thats not it.  Now you need to remove the bag.

112 320 00 17

To start, I use a wire brush and some penetrating oil to clean up the tops of the screws and the nuts.  The locking tabs (A 112 327 01 73) need to be bent down to expose the nut completely.  Do this carefully, and you can reuse them.  I ended up replacing 10 of them, since this is what the dealer could get me when I originally ordered up the parts.  There are 24 total on the car.  To remove the nuts, start with a good quality thin 13mm wrench and get the nut to turn.  Once it moves, use a nice #3 philips screw driver to remove the screw while holding the nut.  I didn’t find it necessary to hold the chamber in any special way when doing this… I just put some cardboard down on the floor to avoid scratching the paint.

After all the hardware is removed, pull off the bag.  It might help to blow some compressed air into the chamber if its really stuck.  Don’t pry anything between the ring and the chamber… this is part of the sealing surface!

The hardware just after removal is see here.  I cleaned everything up to get all the dirt and grime off.  I also lightly cleaned the air chamber, ring, and the sealing surfaces of both.

As you can see, the old bags were pretty beat up.  This one is from the passenger side that wasn’t leaking!  Its also interesting to see the bag rests in a position it would be in with the suspension completely collapsed, as it sat for many years.

Installation is reverse of removal.  Getting the new bag on the ring is a bit of a challenge, but some soapy water helps.  I tightened each screw and nut slowly to minimize the amount of distortion on the ring before it was fully seated.

I installed an air valve (A 112 320 06 58) and filled the chambers to check for leaks.

Here is the chamber filled with about 50psi.  I submerged it in water to check for leaks, then reinstalled it in the car with new seals at the air line.

While the air chamber was out of the way, I cleaned up the front suspension.  Years of old grease was caked up and covering most of the components.  I started with a large screw driver to pull away the larger pieces, then used a wire brush with some WD-40.  Heres a picture during the cleaning:

I can do more here, but the goal was just to clean things up to make greasing easier, and to help the guys when its time to get an alignment.  I greased everything with good chassis grease when I was done.

And finally, before reinstalling the air chambers, I replaced the bump-stops on the lower control arms.  Since the car was sitting on them for 20+ years, they took a bearing.  These are part number A 112 333 02 65.  Removal wasn’t so bad.  A pry bar with a 2×4 sitting on the control arm removed them with only a little effort.

While I didn’t get the finish the job completely today, I did get quite a bit accomplished in 6 hours.  I still need to clear up the driver’s side suspension and reinstall the air chamber there.  I’ll post pictures of the “before” state to show how dirty it is tomorrow.

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