Tom Plunket wrote:
> Sorry if I'm being a pest. 
I really appreciate all y'all's help.
> The mechanical bits are more up my alley, this vacuum stuff is all
> German to me.
>
> Karl wrote:
>
> > > The only vacuum problem I've noticed so far is that the passenger-side
> > > doors, fuel door, and hatch don't lock when I turn the key in the driver
> > > door. I also can't manually operate the lock on the front (passenger)
> > > door, so I'll pop the panel off and see what's binding, and hopefully
> > > the automatic actuation problem will be obvious.
> >
> > BEFORE you remove the passenger door panel:
> > Your central locking system is single door only. By this I mean that
> > ONLY the drivers door locks and unlocks the whole car. The passenger
> > will only be able to be unlocked IF the door is locked from the drivers
> > door. You cannot lock the pass door if the drivers door is unlocked.
>
> Thanks, I actually discovered that today while playing around with it.
>
> If I lock the driver's door, I can lock the passenger side doors
> manually; the front goes down easily and the back feels like it is
> getting /some/ vacuum assist. If I unlock the driver's door, the
> passenger side doors unlock as they should. ...which means that in
> order to lock my car, I need to turn the key in the driver's door lock,
> then go around the car to lock the other two doors! (Driver's side back
> door operates properly, and I'm not 100% positive but I think the hatch
> auto-locks properly. Fuel door will not lock automatically, and
> manually operating the mechanism doesn't 'stick' in the locked position
> like the doors do, i.e. it just releases as soon as I let go.) Is the
> "can't lock passenger door if driver door is not locked" mechanism
> vacuum-driven as well?
Yes, only vacuum driven. One vacuum line moves the piston one way, and
another vacuum line moves it the other way. What MB calls the vacuum
switch, which is really a valve, is in the drivers door and linked to
the lock. When the driver's door is locked/unlocked this valve
connects the incoming vacuum vac line to either the lock or unlock
line that goes to the other doors.
I can't imagine a mechanical solution to this
> that wouldn't be really ugly, but if it is a fact that as long as the
> driver door is unlocked the passenger door is unlockable, then I must
> have some good vacuum functionality. I know there's a leak somewhere,
> though, since if I leave the car locked overnight, turning the driver
> door lock doesn't unlock the other doors, but they'll pop open soon
> after starting the car.
>
> I haven't taken the door panels off yet (except to reconnect the back
> door plunger knob thinger, after which I forgot to reconnect the window
> switch ugh), and I have discovered that Chilton's is amazingly useless
> on vacuum issues,
I think someone was selling DVD's or books on how to fix MB vac on
Ebay.
are there two lines going to the lock, e.g. a 'lock
> now' line and an 'unlock now' line, or is it one line with positive and
> negative pressure that causes the lock to operate? Would the behavior
> I'm seeing be automatically indicative of bad servos, or do I really
> need to get in there and test the vacuum with the door apart?
My guess is it's probably not related to the servo. First place I'd
look is on the driver's side firewall, near the brake booster, where a
bunch of the vacuum lines go through a rubber grommet. Try pulling
those lines back and forth a bit, work them around. The only two
leaks I had were right there and the lines just snapped when I tried to
move them to find the problem.
Might
> there be another 'tap' to test the vacuum operation, say in the engine
> bay?
The vacuum originates from a pump on the front of the engine. You
should see a hose, about 3/8 coming from it and then getting split off.
Keep in mind that there are check valves along the way to keep one
segment seperate from another. You'll see those in the lines at
various spots.
The line for the driver doors goes from the engine compartment, through
that grommet at the firewall, under the dash, and on to the door via
the hinge area. The hinge area is another areea to check.
I have a decent vacuum pump, and certainly the more I can diagnose
> before taking it apart, the more likely it is I can get the right parts
> before doing so.
>
> Oh- when I open the doors, there's that plastic sheeting in there.
> Clearly I need to remove it to do any meaningful work; what should I use
> to reattach it to the door when reassembling?
Clear package sealing tape works well. If the sheet is shot, you can
just use a clear poly sheet of the stuff these use to cover things when
painting.
>
> Oh again, it typically takes a second or two for the engine to shut off,
> which is not the behavior of the old lady's '85 300D, so I figure that's
> also a vacuum issue that's hopefully pretty easy to rectify.
That could be due to either a vac leak or bellows problem with the shut
off circuit, or there could be other leaks on whatever is shared with
that line. I'd work on the obvious vac problems, like the door first,
as you may cure this in the process.
Today the
> car failed to shut off entirely, but I discovered if I operate the
> windows it will shut right off (and I do know about the STOP lever under
> the hood). Fun times, I actually don't mind all of these issues 'cause
> I used to spend a lot of time working on cars when I had 'simpler' ones,
> and this seems like all stuff that one can figure out without needing to
> attach the vehicle to a computer. (...says the software developer!)
> Maybe I'll go dig out the vacuum pump and try to diagnose the shut-off
> issue in the morning.
The shutoff works via a vac line that runs to the ignition switch,
where a valve turns with the key. From there a line goes back to the
rear of the injection pump, where it works a bellows.
>
> Thanks,
> -tom!
>
> --
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