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SAAB 900 Seat Tilt Mechanism Repair, Pt. 1

With the seat out of the car, we can take it to The Dungeon and find out what's wrong with the tilt mechanism for the seatback.

Here's the seat from underneath.  There are four (!) motors to make it all work.

The motor at the top drives the seatback tilt via two cables.  The motor on the left with the green connectors is for the fore-and-aft adjustment.

The second motor on the left is for the rear of the seat bottom rise/lower, and the motor on the right is for the front of the seat bottom rise/lower.

Here's what is causing the seatback to twist.  The cable housing for the left side of the seatback tilt is broken.  This is a very common issue on 900s with power seats.

The housing is a thick plastic tube.  You can see it has to make a fairly sharp turn when it goes from the motor back to the seatback.  Over time, it can break, which causes the cable itself to bind.  With one side not working, the seatback becomes twisted as a result.

Replacement is the repair - although after looking at the broken housing I would think you could slip a flexible steel rod over the housing and it might work also.

Looking down from the top of the seat, you can see that the left side of the seatback is further back than the right.  The left side has the broken housing - its cable won't move.

The right side can move, and in this instance it was moved forward, twisting the seatback.

The driver's side seat has the same issue...I'll fix that one next.  But first let's fix this one.

I've managed to procure two motors, two left-side and two right side cables in good condition.

You can see how the tilt adjustment works by studying the whole assembly. 

A switch on the side of the seat controls the tilt motor to run in a forward or backward motion.

The motor drives both seatback cables at the same time.  The cable rotates in its housing.  The end of the cable is connected to a gearbox that contains a gear driving a splined bushing, or hub.  The cable thus drives the bushing in a circle.  You can see this gearbox and the splined gear in the shots of the assemblies on the workbench above. 

The bushing fits over a mating splined shaft housed in the bottom of the seatback which runs horizontally.  That shaft is connected to a geared wheel which in turn is attached to the seatback.  The rotation on the cable goes through the shaft, and tilts the seat backward or forward depending on the direction of the motor.

This will hopefully become clearer as we see how everything is installed in the seat.  It's a very simple, yet clever design.  But I still prefer manual seats.  I suppose I am stoopid.

So let's get the assembly out of the seat and replace it.

First thing we do is remove the outside plastic cover.  This takes a T-30 drive.

This is the easiest part of the whole job.

There's a plastic cover over the gearbox.  We need to pull back the upholstery a bit to get to it.

There's a clip holding the side of the seatback upholstery at the bottom.  You can see it here.

Before I started this job, I figured I might need some special tools.  (You can never have enough tools anyway, so this was an excuse to get more).

Here I used a pair of Osborne fabric stretching pliers to pull the upholstery up and off the clip.

On the left you can see the outside of the big gear connected to the seatback frame.  That's what gets driven to move the seatback forward or backward.

The arrows in the picture to the right show where the gearbox cover is located.  It's clipped on to the gearbox itself.  We need to pop that off.

Note the big blue-green spring.  There are four of them which hold the corners of the seat mesh to the seat frame.  I was hoping to not have to remove it when taking the gearbox out.

Silly me.

It's harder to see, but this is a portion of the cover viewed from the outside of the seat.

I was able to push the cover off the gearbox from this side...

...and then pop it off from the rear.

Here's the inside of the gearbox cover after removal.  You can see the three tabs that clip onto the gearbox.

I'm pretty sure that molded "V" on the cover is to point to the top side of the cover to aid in assembly.  Clever.

Or it's just a random artifact from the molding machine.  You decide.

Now we can access the 8mm bolt that secures the gearbox drive to the splined shaft in the seat.  Finally we can see the gearbox clearly.

From this picture you should be able to visualize how the tilt mechanism works. 

This is a very tight clearance - I couldn't get a socket in there, so I used a closed-end wrench.

Tool Note to self:  procure a set of ratcheting closed-end wrenches before you do the driver's seat.


Post a Comment 1 comments:

  • Sven Nyström said...
    August 23, 2014 at 4:32 PM
    Is the molded "V" on the inside of the left cap? And is there maybe an "H" on the inside of the right one? ;)

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