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560sl vacuum actuator/pod defroster

10K views 2 replies 3 participants last post by  rockcrusher 
#1 ·
I am providing this description in the hope it will assist others in their efforts to understand and repair these types of problems. I am not a Mercedes expert so anyone that would like to comment on this do so in hopes that we can create a more definitive process for various repair or replacement options.

My car 1987 560SL but it is the same on many other 107 chassis.

After reading tons of posts on the various boards, I decided to tackle replacing my vacuum pod (part# A000 800 32 75).

How I determined that the pod was bad.

I purchased a vacuum gauge (mighty mite) for about $29.00 at Pep Boys. I used this gauge to test the vacuum going into the switchover valve (part#A107 800 22 78.) Then I removed the vacuum tubes from each port sequentially and tested the vacuum tube that went to that port by using the Mighty Mite to draw a vacuum on each tube. I found that the one going to the defroster flap control numbered 38 on my diagram held no vacuum.
Defroster pod/actuator removal.

At that point I removed the radio and it's mount that allowed me access to the upper right part of the vacuum pod. I removed the input to the upper port and tested directly on the vacuum pod itself and could not draw a vacuum.

Now knowing the culprit I set out trying to figure out how to get it out.

There are many approaches that I have read about and I looked at the possibility of using the ones I had seen. In the end I settled for the following which differed from most all.
Remove the glove box, glove box door(Note: not really necessary but it does make moving around much, much easier.) Remove the steering wheel and the instrument cluster. This gives you access to the left side of the pod. Get a long 3/16" drill bit (12")and just about any portable or smallish drill. Thread the drill bit through the cavity between the glove box behind the radio area to the set point on the rivet that connects the pod to the thrust arm of the defroster flaps. The set point is the small spread area(dimple) where the rivet has been pressed or pulled to set it. The other side of the rivet (left side) is large and flat like a solid washer. Drill out the set side. Be careful it only takes minimal pressure on the drill and a couple of seconds to remove the set side of the rivet. All you want to do is remove enough metal to allow the rivet to fall out the other side. It does not take much.

After that the hard work is done. Pry off the 3 metal locks, don't destroy them they can be reused. When completed the pod will drop right off. It you have rubber washers under the locks save them for reuse.

Now you have two options you can rebuild the pod by using new Diaphragms supplied by George Murphy email:perfanalysis@comcast.net or you can order a new pod from George or any of the online retailers for from $63.00 to $71.00 or directly from Mercedes for $89.00. Obviously your choice.

Disassembling the defroster vacuum pod or any other pod for that matter.

This is so simple once you discover the secret. I took a piece if nylon string about 1/8 in and looped it around the circumference of the pod just below the base of each location where the plastic hooks fit into the next section. Tie the ends together put a small rod of some sort into the loop and twist. it compresses all four plastic hooks at the same time and allows you to simply pull them apart. basically they practically fall apart since there is a spring inside that pretty much does the job for you. Use the same process on the other end. The pod consists of two sections short thrust and long thrust. The two sections are linked via a connector that allows the vacuum in the lower end to partially pull down the top end.

Note: If you disassemble the vacuum actuator you will see there is a linkage between the upper and lower chambers. If this linkage is defective normally indicative of the upper chamber not being connected to the lower, you should probably buy a new unit. I had this problem.

Putting it back together

This turned out to be a little more difficult than I had anticipated. the part of the vacuum pod that connects to the thrust arm of the defroster flaps was about 1/32 in smaller than the one I took off. I didn't check it before I put it in and had to drill it out in place.
Mount the pod in place and put the rubber washers in place along with the locking rings. If you don't have the rubber washers it will work ok but the washers provide you with a tighter fit once you press down the lock rings. I used a 3/16" x 1/4" aluminum rivet to reconnect the vacuum pod to the defroster flap thrust arm.

Note: What looked to me to be enough space to use a manual rivet gun was not unless you remove the ignition switch. Not wanting to remove the switch I pressed the rivet manually with a small C clamp and some creativity. If I had to do this over again I would have removed the ignition switch or used a screw an nut with locktite described in some other posts.

Once this last part is complete all you need to do is reassemble everything that you took apart.

General Comments

This really is an easy job and relatively quick for someone that is handy and familiar with getting around the whole dash area. While you are in there be sure to check the center vent vacuum actuator area. Although you can't see it you can check to see if the area where it is mounted is cracked or broken. Mine was cracked and I made note of it for a later time as it is a much more significant project.

If you plan on maintaining you car yourself the vacuum gauge that lets you draw a vacuum is a very handy thing to have. As many things in these cars work as a result of a vacuum it will pay for itself quickly and provide you with confidence levels for the various vacuum systems and components.
 
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