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· W163 Crash Test Driver
2008 ML350 (Me!), 2018 GLC300 (Wife), 2010 GLK350 (sold), 2003 ML-350 (Totaled!)
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Discussion Starter · #1 · (Edited)
Hey everyone! When my son bought his 2004 C230K, the parking brake was a complete mess. The pedal was broken, as well as both rear cables. We replaced the pedal and the two rear cables some time ago, but after doing so we realized that the front cable was badly stretched and it too needed replacing. Since we would have replaced literally everything else front to back, we bought a new adjuster/tensioner for under the back seat as it was badly rusted and half broken as well.

Replacing the front cable was easy enough. There are four blue plastic clips in the tunnel that keep the cable away from the drive shaft and exhaust. The WIS says "try to unclip the cable, destroy if necessary". They really should just say "destroy and replace" because they are practically impossible to un-clip. You cannot unscrew these from the inside as you might think by looking either, as they are blind studs. Once you have the old cable out, remove all the blue plastic clip remnants. Then, you just push/force the new clip over the screw.

The tensioner was the fun part. I could not find ANY DIY's on the internet anywhere and strangely there is nothing in WIS either, so we did it by feel, slowly. The three bolts that hold the tensioner are part of and connected to the gas tank and there is no way to unbolt them from below. The two main bolts are fairly easy to clear, but the large, forward third bolt is the killer. There is simply no way to get the tensioner free without partially dropping the gas tank, and thus the three bolts. Best if you have a near empty tank for weight purposes. It sounds scary, but is really very simple. You leave the filler side connected and drop the driver side a few inches. No need to remove any hoses or fuel lines, there is enough slack for this job (whew!). This process will also give you a straight, wide open shot at the fuel filter so if you haven't replaced yours in years, this would be an easy time to do it.

Also very important: You will need an assistant, as someone needs to wrangle the tank from underneath while the other removes/installs the actual mech from above.

This is how you do it:
  1. Lift the back seat and remove the access cover to the tensioner mech.
  2. Remove all three nuts on the tensioner mech.
  3. Detach and remove all three parking brake cables from the mech.
  4. Remove the two large, black plastic under-car covers.
  5. Remove the heat shields (two) from around the driveshaft/exhaust/tensioner area. You'll need to PB Blaster these as they will be rusty. T10 inside torx.
  6. Remove the two large, inside gas tank strap bolts. These are big, 27mm. Ironically this is the exact same size as the oil filter. Not having a true 27mm socket, I was able to use my oil filter socket believe it or not! You WILL need a large breaker bar or impact wrench to get started. Be sure to spray liberally with PB blaster and let it soak in, as these probably haven't been off since the car was built. They are also self locking nuts, so even once loose you still have to muscle them off. It may feel like they are stripping/binding as you unscrew but they are not. This is just the self locking groove fighting you.
  7. Remove the driver side, outside gas tank strap screw as well (ONLY the driver side). Leaving the filler hose side of the tank connected, this frees the tank just enough to allow one side to drop a couple inches and the tensioner to clear the bolts. Surprisingly, you can get the old mech out through the hole from above which is a lifesaver, otherwise you are looking at dropping the drive shaft.
  8. Install the new tensioner through the same hole the old one came out of. Push the tank back into place from below and have your assistant bolt it down.
  9. Re-install the gas tank straps. Big inside nuts are 60nm. Outside screw is 20nm. Not having a WIS article to go by, we re-used the nuts and they torqued down nicely. Proper MB shop procedure is probably to replace these self-locking nuts with new for safety/liability purposes, but I don't know that for sure. After double checking the torque, I am confident they are not going anywhere.
  10. Replace/re-attach the three brake cables.
  11. Test and adjust the tensioner. Other than the pads themselves this is the only adjust point.
  12. Spray the entire mech area with lubricant/protectant before re-installing the cover.. Since it is exposed to the world from below and the old one was badly rusted, stuff does work it's way in there. Best to give it some protection.
  13. Reinstall heat shields and covers.
There you go! At first we thought it was going to be a very difficult job, but it turned out not to be so bad. I'd say it was a 7 on the 1-10 scale due to the under car gyrations. Now, he has a brand new parking brake system from pedal to wheels.

Good Luck!
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