Rear window seal replacement: 300CD
 

Is it possible to do this job without trashing the rear window glass on a coupe? Mine is in great shape and I'd like to keep it intact.

Should be, a friend did that in his driveway. He replaced the rear windscreen, but with skill I don't have, not a problem.

You might need the right tools.
 

(My first thought is If you have an idea where it is leaking is it possible to carefully pry the rubber away, fill the leaking area with Black silicone sealent, wipe off the excess and avoid taking the chance of busting the window alltogeather. The detractor is that dirt sticks to exposed silicone; take care not to leave any exposed.)
If I were going to tackle the job I would invest in the tools needed to do the job. Harbor freight sells (also your local autoparts should) a tool with a T handle attatched to a thin cable and cutter to separate the sealent from the rubber molding. I cracked a windshied (not a Mercedes but I was still trying to be careful) trying to remove a windshield without this type of tool. After you have separated the rubber molding from the sealentand the rubber moulding is really stiff (and you plan to replace it) it might be easier to very carefully cut it to free it from the bead area of the body than to try to pry it out. (See if you can find another web site that has photos of the job being done and what they used to do the job; even if the car is not a Mercedes.) For installation find out if there is something that other folks us as a lube (maybe dish soap and water?) to help ease the rubber molding back in (is sealent used during installation?). Also if it is the rear window has the elcetric defogger you need to be carful of the connections. Whoever change the window on my car befor they bought detatched the copper sheet metal (where the wires attatch) connectors from the window and I do not at this time know how to permenantly attatch them back on to the replacement window (plan ahead). Please let me know if any of this was helpful. Good Luck.

Thanks, that puts it into perspective a little more - not exactly a job for the neophyte glass changer. I've done the silicone trick before, but it's not usually a permanent fix. I'm getting a little sick of replacing the silicone that I put on the lower part of the window every year or two, so this job would save me a frequent headache and finally keep the trunk dry, once and for all.

Any idea what a shop charges for this (assuming rear window replacement is not necessary)?

About a hundred dollars, give or take twenty five.

But they will not guarantee not to break your glass. I would keep doing the silicone job.

Tom W

I would not use silicone, it causes rust. You can get the proper sealing compound for sealing windshields.

?
 

How does silicone cause rust? Is it just not as good a sealant?

Be prepared for some work, found this on another site when I was going to replace the rear window on mine. http://www.benzworld.org/forums/w123-e-ce-d-cd-td-te-class/1259945-rear-window-rust-repair.html :eek: To remove the glass/seal: From the inside cut the seal at the top of the glass vertically, then take one side of it and peel it apart all the way around the window. The glass should then push out. Takes 2 people, one inside pushing out and second outside to hold. Does this makes sense? Also use only the MB factory replacement seal, not the aftermarket one. Hope this helps some.

If you want a good sealant that won't breakdown, go to any marine store and get BoatLife Caulk, it holds up in the harsh salt water marine environment, even when exposed to the sun. I recaulked all ten port lights on our sailboat and about eight years ago and still no leaks. I don't know if silicon causes rust, but it doesn't hold up well to sunlight - I've seen sailboats that have caulked with it and after a year or so, it turns black and you can peel it off in one long strand - not good!

I cant tell you HOW it causes rust (H2O based?) , but windshield sealing compound is not silicone, do a search or check at your local auto glass shop. I get it in a regular caulking tube at the "Ding Doctor" shop.

Gil,

Not sure where in NH you are, but if it’s any help I have Mark (512-6400) at Mr. Glass in Manchester lined up to do a front windshield replacement for my 82 300D soon (once my insurance company gets its act together). Mark is highly recommended by Brian and Pat at Amoskeag. I can let you know how it turns out.

Charlie

STEVO is correct, silicone will cause rust. heard this at the glass shop 10 yrs ago. thought they were nuts. also some other glass guys said it also.

I have taken my rear glass out twice and the windshield once. not that hard. cut the rubber around the glass on the outside, and then gently push the glass out. no not force it or tweek it any, glass doesnot bend.
think crack.
Then peel off the remander of the rubber. clean up the area and check for rust, the glass man will just replace the glass. so if you drop it off at a shop and get it later, no way of knowing what was under there.

The guy that replaced my rear glass last yr, said MB doesnot use any sealant, just install the rubber dry. I had the gasket replaced because it was leaking. first rain, the trunk was soaked. needed a bilge pump.
so bought a tube of the 3M urethane gasket sealant at the auto supply about $14.00. sealed under the rubber all around the out side edge. now dry as a bone. won`t use that guy again.
His price was $150.00 just to install, and I already had the new gasket.

Charlie

Silicone dose not cause rust but I believe I know what that guy is talking about. If you apply silicone over a uncleand or rusted area the silicone either will not stick and/or it will continue to rust under it and with a water leak around the glass there is often rust inside under the rubber. It may be that sealent made for job may stick to and seal off rusted areas better so I may be a good suggestion to use the correct sealent. If you remove the glass you sould be prepared to at least wire brush of any loose rust and use a rust coverter or antirust paint to keep the rust from continueing its work.
I have found that silicone will not seal well if both surfaces to be sealed are not clean and dry (no oily film). Years ago I installed a water pump and used silicone around the edges (I wire brushed and wiped of the area but it still had an oily film on it). Several months later I found a leak where the coolant had rusted under the silicone. Since then I have gone back to using that old ugly brown permatex when I install a water pump wich seems to be more reliable if the area cannot be cleaned and degreased well or there is previous rust present. When I do use silicone sealent I make sure everthing is clean off and I degrease the area with Brake cleaner and wipe with clean rags or toilet paper.
Lastly there is at least 2 types of automotive silicone sealent that I hav used; the regular one is Ok for valve covers (it also dries up inside of the tube even with the cap on within a month) and shuch while the other type labled ULTRA something (I use Ultra Blue, cost more too) is better for items that need more serious sealing and if the cap is on good takes 3-4 times as long to dry up in the tube and you can depend on having some to use later.