Vacuum seat latch controls on 69 280SE convertible

[dpreston Virginia]

Having my interior redone and found out my car has vacuum hosses that control the latch on my front seats.
The main hose had a screw in it. I have owned the car for 13 years but had never taken out the seats.
Any body have experience getting the system to work? The vacuum controls are under the seats with cables attached.
Thanks for any help finding parts and getting it going.
Diagram is attached.
David
Sorry the photo is upside down. Always happens when I post from my iPad.

[wwheeler]

Hi David,

I know a fair amount about this system as my '68 coupe has it. It is complicated for what it does; but what isn't on these cars.

On my car, the vacuum source is a nipple on the rear of the intake. I believe it is on the same take off as the auto trans vacuum line. There is then a check valve as the tube goes to the firewall. At the firewall, it splits left and right. These L&R lines go into their respective kick panel area where they split again. One hose goes to the seat diaphragm and the other to the door vacuum port. Somewhere the lines splits yet again and now goes to the black buttons on the rear side panels.

There are (4) main parts. The vacuum tubing itself, the diaphragm under the seat, the door vacuum port and the rear seat vacuum relief button. The worst part is under the seat with the wire cables and sliding lock bars. I have not really gotten into that. Basically the system works with a vacuum. When the vacuum is high, the seat back is locked via the diaphragm and sliding bar. When the vacuum is broken, a spring under seat overcomes the diaphragm and forces the sliding bar to release the seat back. The way to break the vacuum is to 1) open the door 2) turn off the engine and 3) push the rear seat button. All of this matches your picture. The point is to lock the seat back when driving. These seats have a non-locking tilt mechanism which is why the lock is needed. Your seats probably do not lock now?

There are two door vacuum ports that I know of. Original on mine is a spring loaded plunger on the door jam that contacts a rubber pad on the front door frame. When the door is shut, vacuum is high. When the door is open, vacuum is broken. The other type is the replacement from Mercedes and is a spring loaded plunger with internal seal. It does not require the rubber pad on the door.

The parts I have from Mercedes are:
Diaphragm element under seat #111 800 55 75 - This is a replacement for a later car (3.5?). The diaphragms are correct and you have to reuse the other parts and rebuild it.
Door vacuum switch #000 821 17 52 - I believe these are the later switches but fit just fine and do not require rubber door pads.
Back seat vacuum buttons#114 805 00 73 - these are the original type.
Door rubber pad #115 987 07 40. The ones Mercedes had were years old and were crumbly. Let me know if they made new ones.

I think that is everything. Let me know if you have questions.

Wallace
 

[dpreston Virginia]

Wallace,
Thanks for all the great information. I am not sure my seat has the correct latch to lock its at the upholstery and I'll dig in when I get it back.
Have you gotten yours to work?

David

[JPMOSE]

Great write up Wallace.   Be forewarned...the vacuum diaphragm units are expensive!  Last I checked (I replaced one in 2010), they were about $400 each!   In the case of my 3.5 (with D-Jetronic), idle speed (when in park) would fluctuate up and down (after about 3-4 minutes of engine running from cold).  A vacuum leak is the typical cause.  I traced it to this vacuum pod. 

[wwheeler]

Yes in fact, the system can cause all sorts of issues. One is that when I set my idle speed and the door is open, I have to make sure to hold my finger on the door vacuum switch. Otherwise the idle will speed up just a bit when the vacuum drops. Probably changes the timing also.

When I bought my car, the rubber buffers in the door where missing. These are the "plugs" for the door vacuum switch when the door is closed. Therefore, the seat backs were never locked because of the break in vacuum. To replace, I used a chrome hole plug (with the fingers on the backside) and glued a thin piece of rubber of the flat side. Works like charm. Keep in mind, some later cars may have the door switch that has the seal built inside and does not need to door buffer. Other than that, the system works OK. I do need to lube the sliding bar lock as it get s a little sticky in the cold.

I am curious if anyone knows what cars came with which switch? My '68 280 SE had the earlier ported vacuum switch.