Will it retract when you put slight pressure on the mast? Clean the mast with a DRY cloth to remove road grime. If you are mechanically inclined and don't want to spend money on a new antenna assembly, remove the assembly from the vehicle, remove the cover, and clean the clutch mechanism with a greaseless cleaner like break cleaner to remove the oily film from the brass disc ONLY.
Run the antenna through its cycle a few times as you are cleaning the clutch. This removes the material that causes the clutch to prematurely slip before the mast is fully retracted. If you need to, you can disassemble the clutch entirely and clean it. If the mast is straight and smooth this procedure should help, unless there is a more complex problem with the motor/drive. Good luck!
Replacing the Antenna Mast
Two techniques are listed here with the second being most likely the easiest
As you will find, most power antenna problems are related to the antenna mast. Either the plastic has broken, or the teeth are stripped.
An easy way to check to see if the power antenna motor is still working is to listen when the car is being turned off. If the radio was on and you don't hear the power antenna motor, then the problem may be in the motor itself. If you can hear the motor, then you probably have a mast problem.
My mast was halfway deployed and wouldn't raise or lower. I could hear the motor working, so I bought a mast off of eBay for $18.99 shipped.
You should also know before you start that if the seal between your car body and the antenna isn't recently new, then it will probably get damaged during this process. The good news is that the retail price of the seal (at my Mercedes dealership) is only $2.11 and is part# 126-827-14-98.
If your mast is deployed any further than the top picture here, then you may have a problem removing the antenna from inside the trunk.
Start off by removing the antenna from inside the trunk. Pull back the carpet to expose the power antenna control unit.
It's secured by one screw down low, the antenna lead, grounding screw and control wires up top. Remove the lower screw and slide the unit out.
Remove the grounding screw, unscrew the antenna lead and detach the control wires. That should make the power antenna unit completely disconnected from the vehicle.
The next step is to open up the control unit. There are several tabs (14) along the sides of the control unit. Using a slotted screwdriver, press down into the tabs and loosen the cover.
Loosen the two on the straight end last. The cover should pop right off.
Inspect the inside of the control unit for any obvious problems. I've heard that the drive belt can break, although I've never seen that. If it has broken, that could certainly be causing your problem.
It may be easier to remove the mast if you remove the two screws and the plastic cover along the rounded edge of the control unit. This is where the mast meets the teeth of the drive unit.
I understand that earlier units may not have teeth at all.
I didn't take any pictures while removing the mast and installing a new one. You can turn the drive belt by hand to aid in the mast removal and installation.
You may be able to connect the control wires and let the motor pull the mast back in, but I wasn't so bold. Once the mast is in, installation is the reverse of these instructions. Good Luck
Brand new antenna mast ready to take its place in the Mercedes.
A broken antenna mast has no business on a Mercedes! Hopefully your radio works the antenna like it is supposed to.
You don't need to remove the power cover but I did to show you the guts. Pretty ingenious how it works.
The original antenna plastic cord is smooth, but I opted for the upgraded and better toothed cable. The friction roller is knurled and works great if kept clean.
If you have any plastic shavings in the housing, vacuum or blow them out before installing the new mast.
With the radio off take some pliers and unscrew the antenna and pull it up until you expose about this much of the shaft. Then have your friend turn the radio on and gently pull it out as the motor feeds the cable out.
Take the new mast and insert the cable into the hole with the toothed notches facing the front of the car and push it all the way in until it stops. Then have your friend turn the radio off and the motor will grab the cable and suck it in. Gently guide the mast down and tighten the antenna back and your done.
Not having a friend helping as I didn't, requires you to turn the radio on and run back to the antenna and try to guide it in.
I did this several times until the cable grabbed correctly.
If I had a helper, then I could have focused all my attention on the cable and not trying to dodge the jack stands on the floor.
Use the old antenna as a fishing pole or just throw it away like I did.
New mast ready for another 20 years of service.
Yes those 4 jack stands were my obstacle course. It would have been easier for me to have just moved them but then that would just be the easy way out!!!...
Good luck... Enjoy!
SAVE BIG $$$$$$ IN REPAIR AND MAINTENANCE COSTS!!!