Actually its pretty easy. As Leathermang states, masking tape is your friend! After installing the window/seal run blue painters tape around the metal/rubber seal lip right at the edge of the rubber. The MB sealant tube has a flattened tip with a hole in the center the goop come out of. The flattened tip slips under the seal lip easily and can be drawn along while gently dispensing sealant. If you are careful there is very little squeezed out from the seal. The cleanup can be tedious. Keep moving to a clean section of the paper towel and use a rolling/lifting motion to remove excess sealant. After you are done remove the painters tape and the metal is still clean!

The glass/seal side is even easier as the glass cleans easier. I tried just the seal first and it leaked profusely from the glass/seal side and a bit from the metal/seal as well. The sealant ended all leaks permanently. Yes it takes patience and some care but its not difficult.

RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I've only done a few window installs and have never used sealant. I don't really get the point of it. Go ahead and reply "it's to seal the seal".

Why do you have to seal a window seal to the body of the car on the inside and out? It makes no sense, I thought that's what the seal was for. Sure does make it a pain to remove the old seal (after 20 or more years, they're literally glued to the body), and taking a razor to it just causes paint damage.

I guess it's a longevity thing, I wish I could compare a 20-year old window seal that was used without sealant vs. one used with sealant. I bet the one without sealant would be shrinking away from the body, leaving a gap for water to enter. Looks like I answered my own question.

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

Lets go at this from the other direction. It is often a lot of work to replace a window. It is also RISKY if you are going to have to reuse the old glass... I have broken my share even being very careful... old glass is fragile...
So what would be the disadvantage of using sealer as compared to not using it and having a leak and having to take the window out and redo the job ?
$10-$20 for sealer , and some work to clean up if it gets to places it should not be...
I do not assume that just putting rubber against glass keeps water from getting between the two...but it seems that you do... if it does seal great... but most people will look at the instructions from MB ... who, after all, did MAKE THE CAR.... and it says to use the sealant... giving the exact part number for the seal.... Does not surprise me that people use sealer under those circumstances....
It is called ' fudging your bet' or ' buying insurance' .....

leathermang,

i have to do both windshields soon. my rear window is original. what are my realistic chances of not breaking it on the install you think? i have done zero glasswork before.

what can be done to mitigate the risks?

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

I see what you're saying and agree with you. It does provide a little bit of extra reassurance.

With all that being said, I don't take MB's word as definitive. Just because they made the car doesn't mean that it's not fair to question something they recommend.
MB is fallible just like the rest of us.

dieseldan, putting in a window is really pretty easy, but it's a 2 person job. Requires rope, soap and patience. Oh and I guess it requires special MB sealant

There's probably lots of good DIY info out there. Installing a Mercedes window is no different than any other typical automobile window (front window not included).

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

Well, you know I am a confirmed do it yourselfer... so it pains me to say that I would not try to do an MB front or rear glass. I looked carefully at the FSM .. but that metal trim and the size and tightness of the seals... just out of my league...
I would find someone who has done it before... ask for references.... go SEE the references.... and then pray while they were doing it.

" A man's got to know his limitations" ---Dirty Harry

I broke a lot of things before I sorta ' knew ' mine.... LOL

Now if you are set on doing it yourself... pay some pro who knows how to do it to let you watch them do at least one... that way you can see if there are some special tools and techniques they use. And don't try it in really hot or cold weather and don't let the glass be out in the sunshine while working on it... place pillows on the rear hat shelf in case it falls to the inside... and use a sharp exacto knife to carefully cut away the old rubber.
And be sure you have arranged for fast shipping or a way to store the car indoors if things go wrong.... There is a TSB which applies to many of our cars about replacement of the metal at the bottom of the rear glass.... often rusted through... so read and order stuff for that if called for...

leathermang - thanks for the tips and the cautions. im a little ways off from the job, but ill start pricing it out now and decide how ambitious i need to be.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

leathermang - thanks for the tips and the cautions. im a little ways off from the job, but ill start pricing it out now and decide how ambitious i need to be.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Well in the case of my rear glass I replaced the seal as it was leaking. The new seal, correctly installed leaked badly too! The solution was the MB sealant. So theres the point of it, it stopped the water from coming into my car! I never said it required sealant. I tried not using it and found out I had to. Kudos to anyone who can get the seal to do its job on its own.
RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I agree completely... MB has only been making fine automobiles for more than 80 years... have made millions of them.... have multi million dollar Research and Developement departments... we should never take anything they say at face value just because THEY said it...

Diesledan, Why don't you drive down here to central Texas for Randy's " get together" ( I put that into parenthesis because he is not providing food )... and let Justin replace your windows... we will watch and learn from him....

The typical auto window does not get installed with the metal trim already in the rubber seal... like the MB does...

Justin , Do you understand that on something like the caulk recommended by MB that if you were to go to the dealership and ask for that old part number.... you would get the newest recommended sealant ? NOT some ' new old stock' tube of sealant which has been sitting on the shelf for the last 25 years ? That the stock number will probably have been ' superceded ' based on the newest information they have about the performance of sealants... and will likely come from 3M even if it does not say so on the tube ?

Calm down man I wasn't trying to attack you or say that I am good at installing windows. In fact, I said I've only done it twice. Never had any leaking issues after the fact, but maybe I was just lucky.

Yeah so MB has lots of experience and they certainly know what they're doing, I'm not questioning that. And of course I know they don't sell stale, 25 year old sealant. You might as well just come right out and call me a moron if you're going to suggest that I thought that's what they do.

Let me clarify something for you, all I was trying to say in my comments above is that I have never heard of using sealant on window seal before (aside from the front window), so in my own way I was trying to figure out what it's purpose was. I should have probably just asked that question right at the beginning of this thread. I've learned something new about installing windows, despite the fact that you (leathermang) have managed to make me feel like a total ass.

WRT to the whole "MB isn't infallible" thing, I was just trying to express to you that a manufacturer recommendation does not literally translate to "if you do it any other way but this way, then you're a complete idiot".

What's the MB recommendation for EGR plugging or ALDA fiddling?

Oh and that's awesome that you're going to call me out like WRT to the Texas GTG. Are you just trying to make me feel so dumb that I'll just be too embarrassed to show up or what? Good ol' friendly Texas right?

Have you ever seen a 70's or 80's VW? They used metal trim in the window seal. It's a complete PITA to install. MB isn't the only one.

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon

Justin, I am just having fun... trying to use a method which will cause you to look at your ' apriori ' assumptions... people sometimes have ' niches' or ' parity numbers which don't add up but have not run scandisk lately' or where their backgrounds added things where the physics just pointed somewhere Else in the universe...but not where it should have...
I have a good long time friend who is an expert in one area of things leather... but at the same time he is convinced that contrail from planes are chemicals being spread by the government to keep us under control.... I am sure you don't susbscribe to that.. But lets examine the area of your thinking which for some reason just did not have the historical physics background to be standing on it's own...

It is true that some situations where rubber is placed against a smooth surface it does a great job of keeping water from getting past that junction. Two of those are in your bathroom... one in the tub or sink if you use a flat rubber disc to keep the water in those items... the other in your toilet tank... a flapper which raised when you push on the handle to flush..... Both of these work just fine with no Mercedes Sealant..... but the trick is that the water ( and pressure ) is on one side only. A window seal on the other hand has the pressures ( air ) equalized on both sides of the glass and seal. So unless that rubber has properties whch would cause it to naturally BIND to the glass...it can not be expected ( on its own ) to seal against the movement of water between it and the glass.
It is possible to manufacture rubber which will tend to do that... but it may not be possible without a seal to also have resistance to shrinkage and to UV rays or other things which an outdoor exposed seam needs.

So the question is where you got the idea that simply placing rubber against glass makes a waterproof seal ? I assume the opposite.. that some kind of glue or sealant would be needed... can you pinpoint the time in your past when you got this impression?

I drove VW 's or KarmanGhia's for about 15 years... and replaced a couple of windows...and probably did not use sealant if it was not suggested by the FSM... but rubber gaskets for windows are of all sorts of shapes and configurations... who would know if there were problems ? The factory would be the ones getting the calls from irate customers or their own service departments... thus the next time the manual was printed it would be the place most likely to have the best information. That is why if MB says it in their FSM I tend to trust it more than I suspect it.

I think the truth is somwhere in the middle, gentlemen.

There are quite a few forum-dwellers here who have installed windshields without the sealer and, if you believe them, have not had leaks. My glass installer agreed, and (fingers crossed, don't want to jinx myself) my leak MAY be gone in the front, no sealer used.

That said, I am ready to follow the FSM should I determine that I am still leaking. I plan to use the MB stuff to assure compatibility.

The argument you make, leathermang, is a bit simplified; in fact there is pressure on the joint, the glass itself pushing outward toward the metal, the metal trim squeezing the assembly. The question is whether it is enough. You and MBUSA, among many others, say no, Justin, among many others, says yes. On the 123 windshield, the manual says goop the pillar sides only, not the whole thing. Even MB is of two minds. My guess is that MB errs on the safe side, liability and all that.

There is no definitive proof here at mercedesshop, nor in the world of techs and glass guys I have asked. Do what works.

When I do my rears I may go with the goop. Those windows come out pretty easy (less tightly fit?), and it's harder to know when the water is getting through.

Anybody want to answer my question about the install rope????

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K

Sorry, I knew I had missed that question...
What I have used...and which was recommended to me by others.. is regular old ' Sash cord".... should be called that at the local hardware store....

Another factor on the sealant need or not... is where you get the new rubber gasket from... some aftermarket are not exactly the same ... thus that pressure you refer to might be just fine with a proper one...and leak with some other brand.... on a Subaru I did with aftermarket rubber on the front windshield I had a half inch HOLE to fill at the lower corners...

Thanks, Leathermang,

I watched a glass guy do my windshield, he had what looked like an athletic jumprope, with handles. The rope thickness seemed comparable to sash rope.

Well, any reports from the guys doing their windows?

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K