Restoring Mercedes S124 side window frames

Restoring Mercedes S124 side window frames

Today we start to fight the bogey opponent of every station wagon driver as well as every potential buyer: the rear side window frame of a S124 T-model. You can find this rust potential in every good buying advice, mostly accompanied with spine-chilling pictures. When you see it, you should better run and not look back. But like any other damage it is possible to maintain the side window frame. But you have to aware that this endeavor takes a lot of time. We talk about quite an effort, only the preparation, pull apart the trunk, fire prevention etc.


Firstly let’s start to examine the full amount of damage. In order to do that you have to remove the aluminium frame which is fixed with 2 cross-head screws or 2 torx screws. We start to remove the frame with a wedge and a flat screwdriver starting from the back.  Please be gentle, due to the fact that the frame is made out of Aluminium it is easy to bend it!

Remove these 2 screws and start to pull the frame from below



Now we are able to remove the window. Just press the window out of the seal from inside in the hight of the junction from the cross beam to the D-plillar. Don’t be afraid, it can’t break! Pull the seal out of the seam, carefully along the window. Now you should be able to fully remove the seal, working it into the direction of the rear lights. Use a bit of pressure and the window plus seal is popping out of the frame!

If you dipped a bit deeper into your purse and have ordered the parts at your local dealer, you will be able to speed up the process. Just place a tiny cut right and left on top and the window is coming out immediately.






How bad it really is

First of all we have to remove the old sealing and get the area dryed. This can be done by eiter using a heatgun or simply letting it dry out by itselve. Once this is done we clean out the complete area and start taping the surounding & intact areas in order to avoid it from further damages by power tools.


Under the use of an anglegrinder with wire wheel brushes im starting to work out all the rotten areas. If holes get bigger nerver mind, it would have happend anyhow later on. Welding will be unevitable! Once all the rust spots are clean we can see how big the area is that needs to be replaced. The car shown here was used on purpose as this is one of the baddest frames i ever saw.


As our model here needs major work, lets proceed…



Fire prevention

Before starting the weling machine some points in advance that cannot be repeated often enough. We linked the newspaper article to an welding desaster before but just to remind you once more: garage fire . Im sorry for all you english speaking people, but i guess the pictures speak for themselves. What does this mean for us? Even under professional circumstances accidents can happen that wont only harm your car, but also your life. Due to this welding always needs to be done only when the danger of fire or explosions are kept as low as possible. There are some easy things to achieve this:

  1. All trims and panels around the respective area must be removed. The wheelhousing panels need to be out before welding. Carpets and insultation bruns like hell and before you know it your work goes up in flames.
  2. When welding little beads having 700-800 degrees celsius will fly around. They will not only burn carpets in no time, they also harm skin, eyes and so on. So being prepared with suitable clothing is a good idea.
  3. To prevent the inside of car from fire it helps to coat it with several blankets. Special fire resistent equipment is way to expensive for unregular use so we need to find a different solution. I use several layers of blankets with the ones below being a little wet. This prevents these beads from burning the interior. Using single-use blankets with foil layers come in handy as they prevent the water from moving into the interior as well. They also help you from preventing dirt moving into the car.

As we have the fuel tank sitting on the right side it hopefully doesnt need to be mentioned that this area needs special ventilation. Having explosive gases in this area will be a certain death. If in doubt, do it outside with all doors open.


Getting it done

Depending on the proogress of damage it might happen that the welding will have to take place in the viewable area. Even though visiting your local paint shop is inevitable this needs to be done as perfect as it can be. As with all other craftmanships the preparation is crucial for the final result. Saving time here will result in more time to be spent in the paintshop, it is that simple. This means that welding overlapping sheets is a absolute no go, unless you want to avoid large amounts of filler. This means more time for getting the sheets fitting but it will be a more sustainable work.

The highest precept: prevent the metal from large amounts of heat. Metal sheets will deform when being heated to much which will result in wavy spots. A very helpful tool is the Bosch PMF which works with oscillation. Cutting metal works pretty nice and generates no heat at all. Disadvantage: Terrifying noise. Make sure your neighbours arent at home.


With a special cutting device we start to remove all rusted areas. Make sure to have straight lines drawn on the spots to avoid more work than needed. Freestyle cutting looks cool but will take you additional time for preparing the new metal sheets. The edges on both the car and new metal needs to be free of any paints for better grounding.

Next step is to prepare the new sheet. Our patient is a total mess and building the sheet on your own would need special equipment like sheet benders. Im a lucky guy as i always keep some scrap cars to have things like this area onhand. Once removed from the scrap car we start matching it to our car. Be careful, only grind down small spots and check for fitment before proceeding. Slowly work your way to 100% fitment, dont rush it. Nothing would be more desastrous than having the new sheet being grinded too much. This would result in more work and specially more heat to close the areas where the sheet is too small.


Finally. Welding it!

Here we go. Make sure the welding spots are as far away from each other as possible. This avoids the sheet from deforming. Wait for the welding to cool down before setting the next spots. Work your way through the repair sheet until the welding bead is closed. A helping hand could also be useful with cooling the welding from the inside with compressed air. Do not directly aim onto the welding spots, cooling it too quick can be harm the bead as well.




Spots that are to small for anglegrinders can be processed with special beltgrinders. Most suitable for our work are models with belts being 300x10mm. With these even the most difficult spots can be reached.

The result stands for itself, no major deformings! The underpart now gets several coatings with an aerosol based primer. The visible also get primered, im using Brantho Korrux nitrofest for this, a german based paint manufacturer. Of course you can use whatever is available on your market. Pay special attention to the folds and make sure to have them filled up with primer several times. Once they stop taking more paint you can be sure that water will be kept a away for a long time!







Next stop: Paintshop!


With repair weldings where only small areas are replaced preparations will need fillers or tin-lead, this cannot be avoided. Using tin-lead is the best way but there arent many people left that are proficient doing this old craftmanship. Luckily we found a paintshop that still does this way. Ten days later the car is ready for pickup again and we can proceed putting it back together. The inside of the frame gets a shot of silk matt black to have it looking like it left factory.

How lovely is that? 🙂


For getting the windows back in place there are several ways to succeed. I prefer it the following way. Clean the old seals if you want to save the money and pre-mount them with the window. For installing the windows i prefer using Vaseline. Its not only helping to smoothen the rubbers surface, it also has preserving characteristics. Then place it onto the frame and start to pull the seals lip towards the cars inside. Work your way through the whole frame. It helps to have the rear parking break tool onhand, can be acquired via Hazet (4964-1)


Customer was willing to have the right side done as well. No the back of the car is back in full gloss!


Once all windows are back in place we need to check the car for being waterproof. Just having it steam jetted wont be sufficient as it wont simulate heavy rain. Even though many of you wont like it, im taking it to local car wash with the inside trim to being installed. This is the best way known to me to identify where water is accessing the inside of the car. If there are spots, eradicate them with sealings like Teroson or anything else being available. Just make sure it wont have glue like characteristics. This will make it a mess if you need to rework this area in the future.

If everything is done and all trims are back in place you can add more rust preventing materials like fats or waxes. Just make sure to have no contact to the window seals as most of these substances harm rubber. Specially the inside of the wheelhousing can be protected from further rust so dont be too ascetic here.



We hope that this documentation helps some of you, have fun preserving your own waggons. We look further for your feedback and input, here or on facebook!



Facebook Like