450SLC - Transmission Won't Kick Down (Bad Solenoid??)

[finleymac]

I have a 1977 450 SLC. The transmission was working great until a few days ago when I tried to floor it, and it didn't kick down. Since then I haven't got it to kick down at all. The transmission still works fine and shifts through all gears, and you can still shift down with the shifter.

I checked the Kick down switch under the gas pedal and it was working properly. Where the wire from the kick down connects to the transmission; there's power when the switch is down.

I located the kickdown solenoid on the transmission, and when the KD switch is down the solenoid clicks. I removed the solenoid from the transmission. I tested using a 12V battery; when I applied power the solenoid clicked, and a rod or pin moved down slightly. Does anyone know if that's what it is suppose to do?

If it isn't the solenoid could it be anything else, or is the transmission itself in trouble?

I looked online to purchase a new solenoid, but I couldn't find anyplace that sells one. All I could find was the seal for the solenoid. Do I have to buy this from Mercedes?

Any suggestions on how to fix, or where to buy the part would be greatly appreciated. THANKS!

P.S. I had this in the Vintage forum because it is a SLC, but it looks like the SL forum isn't just for convertibles.

[BobK]

I had to replace the solenoid in my '88 SL. Would not drop to first gear when pedal was depressed or if shift lever was moved over to "B" position. Solenoid read ok with a meter, but new solenoid worked, after a few tries. (and Oh what fun to try!). Bought coil and bolt/valve from dealer. Think it was less than $100 all totaled. On another car ('83 300D) the wire going to the solenoid had worn thru at the crossmember and just needed to be repaired.

[finleymac]

Originally Posted by BobK

I had to replace the solenoid in my '88 SL. Would not drop to first gear when pedal was depressed or if shift lever was moved over to "B" position. Solenoid read ok with a meter, but new solenoid worked, after a few tries. (and Oh what fun to try!). Bought coil and bolt/valve from dealer. Think it was less than $100 all totaled. On another car ('83 300D) the wire going to the solenoid had worn thru at the crossmember and just needed to be repaired.

Thanks for the info. When you said it wouldn't kick down into first was that also true for the other gears? Also do you remember what your solenoid did when you tested it (clicked, moved down)?? I did some research on the solenoid and it looks like it is suppose to move back and that release pressure. Mine does move back, but I'm not sure it is far enough.

[BobK]

I did not test it with 12 volts for actuation. I just put the meter to it to see if it showed reasonable resistance. Car would kick down once from the vacumm or whatever, but would not go the extra gear when you floored it like my SEL did. (also had an '87 560SEL). Car would not go into first gear if I shifted to first manually. After replacing the two parts, all was better. Car is back in the serious fun category. Don't know how similar your car/transmission is to mine.
'88 560SL has a 4 speed automatic that starts out in second unless you stomp it (and have a working solenoid).

[Strife]

Mine wouldn't work-I discovered this when building my first gear start. There were TWO reasons:

1. A "mechanic" (At MB dealership!) pinched the wire between tranny pan and transmission, causing short/fuse failure when engaged;

2. "B" switch was not adjusted properly (required a little bending and forming, then a little lithium grease on the "B" gate.

I bought a $66.00 solenoid BEFORE I discovered this.

[finleymac]

The 450 SLC transmission looks like it differs a lot from the 560. As you probably know it is a 3 speed, and always starts in first gear. And when you floor it the car is suppose to only shifts down one gear. I'm going to try buying a new solenoid, and if that doesn't fix it, probably the car will run like this forever. Also does anyone know if the Vacuum modulator value could be causing this problem?