Driving from Maryland to Tennessee in 85 300SD. Got tired about 2 am and stopped to take a nap. Lowered seat back for a nice rest. Woke up ready to go. Seat back would not raise!! Head rest would not move up and down and front of seat cushion would not move. Just fore and aft and rear of seat up and down. Took switch apart, cleaned contacts etc. put all the ball bearings back after many attempts at 3 am and no difference. So I had to drive the last five hours with my no seat back to rest on!! Now I'm home and looking into situation. I can hear a clicking under the seat when I try to move headrest, seatback and front seat up and down. What would happen all of a sudden to cause this. Seat worked perfectly previous to my nap.


Randy
84 300SD
85 300SD

 

Hi Randy,
Several different motors are used to provide the seat functions.
Clicking suggests the function has main (battery) power.
Control module and possibly fuses situated under the seat.
You usually need to be able to move the seat fore/aft in order to gain access to the seat runner bolts so you shouldn't have too much difficult getting the seat out unless the full back backrest hits the rear seat. If it does and the bolts are in the runners you have got a problem.
Since you are obviously DIY minded (trying to replace ball bearings at 3.00 am by the roadside) I would check the fuses (if present) and then unplug the various leads to the controller and replug.

If this doesn't work I'd take the controller off and investigate the relay contacts inside.

Dirt build up jamming in the mechanisms at extreme of movement and age are the most likely cause of a blown fuse / failed relay.

Alternatively you could apply 12v up to 14v directly to the motor terminals and cut out the controller etc to get the seat off the stops. Ensure motor is trying to turn in the correct direction before stepping up the voltage. The motor is polarity sensitive. Clockwise/anticlockwise rotation.

Take care when messing about with powered seat mechanisms. The rise and fall mechanism especially can easily take your finger off (scissor action)

Stuart

 

It was a blown fuse (#5 in the engine compartment box). At 3 am I checked the fuse box lid sheet and saw a description for seat adjustment. I figured since the fore and aft and rear cushion up and down was working it must not be a fuse. But today in the bright daylight I checked again and sure enough the fuse was blown. Replaced and everything works perfectly.

So I'll put the screw the seat back down and go on my merry way!!

BTW, I did try to separate the seat from the adjustment mechanism because I have a broken spring and was going to work at fixing with some tubing or something, but can't seem to figure out how to separate the two. I to two screws out of the front and back of the track and one out from underneath the track. the tracks would slide back and forth when moving the seat back and forth but not come off. does the fore and aft mechanism hold it down somehow?? Is there a better way to take the seat spring/cushion off?

Randy