1986 300E power seat won't move forward and tilt up & forward
 

I own a 1986 300E and the power seats are not functioning correctly. I did a search on power seats and some people on this forum were able to fix their problem by changing or cleaning the switch.

My driver's seat will not move forward, nor will it tilt up & forward. All other functions work including the head rest. When I press the switch forward, I can hear a single click under the seat, but nothing happens. I don't think the motor is bad because the seat will adjust in all other directions fine.

I am confused and don't know where to begin trouble-shooting this problem
1. Does the "click" mean that the switch is engaging the motor?
2. Does the motor moving the seat backward also power the seat forward? I hoping it's just a cable or something.
3. Does anyone know how many motors are on these power seats?


I'ver tried cleaning out the switch w/contact cleaning solution from radio shack but it has not helped.

Is there a way I can manually move the seat forward?

Please advise...


Thank you,

jrmd01@yahoo.com

I'd still suspect the switch as the culprit. I would take the switch out, and then, on a bench or table, over a large cloth, take it apart and clean it thoroughly. It's full of little springs and BBs, but just be careful and you should be fine. Clean all contacts and see if that doesn't do the job.

Your post implies you think there is one motor. There are separate motors for each function. One could be bad and the rest fine. However, if the seat moves back - for instance - but not forward, the motor is likely fine.

On our 102, the right/left switches could be swapped (though the switches now controlled different things). This allowed verifying that the switch was the culprit in our case.

Steve

Here's a hot tip...
 

...The Range Rover guys buy MB seat switches because they are cheaper than their OEM, apparantly. Here's a link to an article on cleaning one: http://www.disco2.com/howto/homemechanic/seatswitchclean/

I know I found a better article somewhere, but this is close. And, there are posts on cleaning MB switches here too. Good luck!:)

O.K. here is an update, nothing fixed though...
 

I own a 1986 300E. The driver's seat will not move forward, nor will tilt up and foward. All other functions work fine, even the headrest.

I did a search and many have solved their power seat problems by cleaning the switch. I have also been advised by Forum members Dakota, Sbourg, and Donbryce to check, clean, and replace the switch.

I took out the switch (I didn't disassemble it) and sprayed it with contact solution from radio shack. Problem still existed.

To double check if the switch was the culprit, I put the suspected faulty driver side switch on the passenger door and it worked fine. That means the switch is good.

I put the good switch from the passenger door on the driver side and get the same sypmtoms...I hear a single click under the driver seat, but nothing happpens.

Since the switch proved to be good, it must be something involving the motor or the cable.

Sbourg, you mentioned that if the reverse works, then it probably isn't the motor. Do you know if the motor moving the seat back also moves the seat forward? If so, then I suspect it's the cable (I don't know if that's good news or bad news).

Do I now remove the driver's seat to find out what's wrong or can I still trouble shoot this problem without removing the seat? If I have to remove the seat, which (and how many) bolts will I have to remove?

...can anyone advise me on my next steps?

Thanks in advance for any help/opinions.

jrmd01@yahoo.com

There are three motors and three cables for these seats. If necessary, removing the seat is not difficult (four 10mm nuts and a cable harness) but you might need a helper to help lift it out of the car. Once on a bench, you can easily access the motors and cables. But if the seat does not go forward/reverse, getting to the mounting nuts is a b**ch

However, it is easier to check the switches first, if the front of the seat goes up, the front up and down motor is fine, if it goes back, the forward and back motor is good, etc. and you just need to clean the switch contacts.

Good luck

jrmd, it sounds to me like you have thoroughly eliminated the switch. So now maybe it's time to take the seat out, but as vnoronha said, it may be tough. There is a bolt thru the seat track at each end. I don't know how you can get to the aft ones. Are they visible or have you moved the seat all the way back? I'm thinking that I would try to see if the motor is getting power in all modes...you may have to trace the harness to get at it upstream, but that may not reveal the problem if it's downstream of where you test. How about in the door area? Any breaks in the wiring from the switch to where it jumps between the door and the jamb? You may need a schematic. Let me know and I'll try to dig one up if you need it.

My '86 300E has a tendency to get the drivers seat back stuck if i recline the seat. -Only response is a click from under the seat!

First time it happened i had the seat FULLY reclined and did not want to drive around like that. So i pulled and yanked the seat while activating the switch and all of a sudden it worked.
I have since found out that if i lean a little bit forward while activating the switch, it works fine.

Maybe you could try to push/pull the seat before taking it all apart?

Freestyler

I recall that the seat back in my 380SE was reclined way back when I first looked at the car, and it was upright when I purchased it from the second owner, but the switch never worked right. The guy I bought it from told me that he unplugged the connector and somehow polked around the female plug with a length of wire until he made the connection that turned on the motor to bring it back up. When I eventually got around to checking out the problem, there were 2 breaks in the seat springs that had chaffed the wires, causing a short and an actual break. Everything worked fine after I fixed the wiring. Perhaps a broken wire or short is causing your problem too. I'd try using a jumper wire to move it forward/backward to get at the bolts, remove it, and do a thorough examination on the bench. Worse that could happen would be a blown fuse, which mine did every time I tried using the switch.

I'll try all of your suggestions this weekend
 

Thanks to everyone who responded.

From everyone's suggestions/experience, it's seems more likely that something is wrong with the wires. I'll try to probe around the wiring harness to see if I can get the motor some "juice".

If that fails, then I'll remove the whole seat and inspect it. Hopefully I can still get to the rear bolts.


By the way, I was just wondering...since I can hear a click, is it possible that a gear or cable is stuck? I'm hoping the motor is good and not stuck, since the seat will move backward. (Assuming the motor that moves the seat forward, also moves it backward).

I'll post an update on Monday, but I'll still check this website for anymore advice / experience anyone had with this particular problem.

Sincerely,

jrmd01@yahoo.com

I think the click you are hearing is a relay. The switch connects/disconnects a low amperage wire that powers a relay coil, in turn making/breaking a higher amperage connection to the motor. Like a power window motor, the switch and relay swap the motor + and - terminals to make it run forward or reverse. I'd be looking at the wiring to the motor from the relay.

Update: I give up...
 

I tried to remove the seat today (Sun 11/23/03) and I can't get to the rear bolts, it's nearly impossible...I give up.

I know it's not the switch (see my previous post). I have no choice but to take this to a mechanic. Hopefully it won't cost too much to fix. If I couldn't get to the rear bolts, I have NO IDEA how the mechanic will be able to get to those bolts. It's so frustrating...I guess I'll have to bite the bullet.

Thanks everyone for your input.


jrmd01@yahoo.com

What did it turn out to be?

Dave

UPDATE:
 

UPDATE: I tried to take the seat out to look underneath, but it's impossible to get to the rear bolts.

I have access to the wires infront of the seat, but I am clueless to which wires control the motor to move the seat forward.

I don't have enough money to take it to a mechanic, so I'm just using some cushions for now. Anyone have a ballpark figure on what this might cost me?

jrmd01@yahoo.com

update - mechanic's assessment
 

Well I took my car in to a mechanic. He said that he thought it was the relay because he can still hear a click when he presses the button. He will replace the relay and I have my fingers crossed that it'll work. A new relay is around $600, I opted for a used one at $100.

I trust this mechanic because he only works on mercedes. He's a german guy who's worked on mercedes for MANY years.

He told me that he first suspected the switch because that is usually the part that goes bad. I told him I eliminated that possibilty by testing the switch on the passenger side.

I'm having other minor work done on the car. When I get it back I'll keep everyone posted on how it went.


jrmd01@yahoo.com

Finally power seat problem solved
 

Just wanted to update everyone.

I just got my car back and now all power seat functions work. In my case, the problem was the relay under the seat. This is an easy fix as long as you can still remove the seat. The mechanic had a hard time getting to those bolts and charged me accordingly ($$$$$). Damn it. That's o.k. I had other misc work done too, and I'm satisfied.

Anyway for anyone with similiar problems, follow these troubleshooting tips:
1. Don't play with the switch if you know it's not working properly
2. Don't move the seat all the way forward/backward (it'll block the bolts holding the seat), you may have to take the seat out to check the relay, motors, cable, etc. under the seat.
3. First check the switch (most probable cause of the problem 90% of the time....according to my mechanic. This is an easy 2 min DIY job)
4. Remove the seat and check the relay
5. Elimininate other causes ie. cable, motors, etc.


Thanks to everyone who tried to guide me in the right direction.

Unfortunately I could not fix this problem myself. I became frustrated and gave up when I could not remove the 2 rear bolts...it was nearly impossible to get at. Like a dumb @ss I kept messing with the switch and the seat got stuck all the way back, hence blocking the rear bolts.

Hopefully my experience will save someone $$$$$ and lots of headaches.

jrmd01@yahoo.com

Do you have details on which relay was replaced? Is the part number on the invoice?

Sorry the part number is not listed on the receipt
 

Sorry, the part number is not listed on the receipt. It was a used one so that's probably why he did not list it. He just listed it as "replaced seat relay w/used one".

If you look under the seat, you can see it. It's kind of big...rough estimate 6"X8". It looks like a flat rectangular black plastic box. According the the mechanic, a new one is apporx $600. He sold me a used one for $100. I should have asked him for the old part, but I have no use for it, so I never bothered.

Everyone, please check your switch first because 90% of the time this is the culprit (2 min DIY job). For the remaining 10%....good luck....hopefully it's something as simple as mine --- the relay.

jrmd01@yahoo.com

part # of seat relay
 

I went back to the mechanic to pick up the old relay. The part number written on the relay is 124 820 00 26

Hope that help.

This thread is done.


jrmd01@yahoo.com

Seat switch fixed at last!
 

When I bought my 90 300D sedan in 1999, the seat would not always slide back. I thought it was a problem with the seat motor and therefore did not mess with it. A mechanic told me I would have to remove the entire door panel to mess with the switch. I didn't want to pay him $300 for three hour's work, plus parts, and I was too lazy to mess with it.

There are two kinds of switches: the one with a memory has tewo small 1 and 2 buttons on it. Mine was the forgetful type, which is cheaper.

Then my neighbor drove the car for a while and in a totally unrelated incident the front of the seat was tilted all the way down and would not rise up at all. The switch seemed loose as well. So I decided that perhaps the entire problem was in the switch.

So eventually I finally got around to checking this forum. jmcd01 in Hawall discussed how he actually removed the switch, took it apart, cleaned the contacts and put it back together. His instructions were excellent.

The only problem was that three of the teensy ball bearings had somehow vanished. I cleaned all the contacts with a small Dremel grinder. The contacts are brass thingies about 3.8" wide in the shape of a vee with a flat spot on the bottom. The contact points are the flat part of the vee and the two little blobs on the underside of the end of each wing. These rock back and forth under a combination of ball bearing-spring-ball bearing. There are four switches: the two with the white inserts are for the seat back and the center of the seat, where it controls the back and forth movement of the seat. Two other plastic switches don't have a white insert and go on each side of the seat slider. All four of these (four plastic switches, eight springs and 16 teensy ball bearings will all fall out when you open the silly thing. A brass axle the diameter of an old thin ballpoint pen refill runs through the hole in each of these four plastic switches.

I was short one axle and three ball bearings and could not locate any ball bearings anywhere, so I gave up and bought one at Finish Line here in Miami for $82 ($87 with the FL state sales tax). They are a good local place to get filters and mats and such. If you try to find them in the phone book, they had a fight with Ma Yellow Pages and after three years of her posting the wrong address Finishline removed their ads. But they are open Mon thru Sat from 9 to 5:30 at 5760 SW 8th Street, 305 266 9687, 800 842 7851, in the event you need a Hengst of Mann filter for $6.00 right away.

I was thinking that there might be a way to magnetize the top ball bearings to get them to stick atop their springs. I was about to go out ansd get the recommended diaelectric grease when I decided than my lack of ball bearings would prevent me from fixing the thing. I guess the missing balls need to be inside the door somewhere, but I was too lazy to open it up.


The headrest switch is more polite and might not come loose. To clean it, just pull it upwards and clean the inside of the vee switch and the two contacts on the outside of the wings of the vee.

I am posting this in the event that it might make it easier for someone else to fix their seat. It is really great to be able to move it without fiddling with it for a couple of minutes to get it forward or back.

Many thanks to jmcg01.

relay
 

How did you test the motors? Can the relay be tested?

Well I know this is a very old thread but jrdm01's posts did indeed help me diagnose the exact same problem that he had. My drivers side front seat won't go forward or back but does everything else. I too hear a click under the seat when I press the appropriate button so it must be the relay. Luckly my seat isn't all the way back and I can tilt the seat and the backrest forward to expose the back bolts. I just applied some liquid wrench on one of them as it is pretty rusty so we'll see what happens when I get the seat out. Hopefully I'll be able to find a cheap used relay to replace the one that is there.

I just wonder if it's still possible it could be the wiring going from the relay to the motor since I hear a click, but then jrdm01 heard a click to and the relay had to be replaced. I am not even sure how to test the wire going from the relay to the motor.

Any thoughts anyone?