[W126 Coupe] Front seat backrest locking mechanism

[Gary]

always amazed   thanks

Dick Spellman <spell.yy at verizon.net> wrote:  Hi Gary:

The rubber cover on the side of each coupe seat covers a plastic plunger 
that has a blue vacuum line attached to the inside. When this plunger is 
depressed the vacuum present at the lock diaphragm in the seat is 
released and the seat back is then free to move.

There is an electrical vacuum switch under the drivers dash area that 
operates (opens) permitting engine vacuum to pull the lock diaphragm 
attached to a metal hook that engages the steel rail at the underside of 
the hinge point on each of the seat backs. When you open a door, the pin 
switch in the door frame interrupts power to the electrical switch under 
the driver's dash which again releases the vacuum locks on the seat 
backs. That's about it. The vacuum is NOT present at the seat locks when 
the seats backs are free to move. So, if the doors were closed, engine 
running the seat backs should be locked (vacuum present).

Dick

Gary wrote:

> hey dick am i to understand that button on the side of the seat works 
> of a vacuum. and if so what does it do. i though you just pressed to 
> move the seat up.
>
> */Dick Spellman /* wrote:
>
> Hi Jon:
>
> Where you just replaced the seat material and the hoses appear to be
> okay, why not lift the rubber cover on each of the seatback release
> points to see if somehow the nylon plunger underneath is partially
> depressed creating a leak. You could inspect further by using a
> MightyVac on the feed (connection under front of seat) to the
> seatback
> to see if one or both hold a vacuum (say 12-15 inches, no more).
> This is
> most likely your problem unless you messed with the electric vacuum
> control valve under the driver's knee bolster (look for a small
> aluminum
> like dome and it will be warm to the touch) or have a faulty door pin
> switch.
>
> Dick
>
> Jon Pridham wrote:
>
> >
> > Hi Everybody,
> >
> > I recently changed my velour interior to a leather interior. In
> doing
> > so, i have found that the backrests now no longer lock into
> place when
> > the engine is running, allowing the backrest to tilt forward
> without
> > pressing the vacum release button.
> >
> > I can only presume that there is a fault in the front seats that i
> > have fitted as the system worked on my previous seats.
> >
> > I have checked all the blue vacum pipework, and all seems in order.
> >
> > Does anybody have an idea where i should look next to recify the
> problem?
> >
> > Thanks,
> >
> > Jon Pridham
> >
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