Author Topic: A nasty rust surprise. A huge hole near the bonnet/hood release cable grommet.  (Read 14860 times)

Rimas

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Hi all,

well I've been learning the w116 ropes slowly and steadily of late. Some of you may know that I have found the typical 116 wet carpets recently and have started hunting for the problem. Here is what I dug up on Sunday.

My silly error was that everyone speaks about the common rust spot as being under the fuse box. My car is an Aus RHD car and I didn't think that most of the advice I was reading was coming from Europe/USA cars.  ::) :P The spot under my fusebox is super clean!  ;D

Having the car up on the jacks for the suspension work I got my first clue:



HMMM, what's going on in here....



Ah, I see! Bear in mind the size of the hole was made worse because I really chipped away with a screwdriver and vacuumed the area out hard after I found it.



Got some miracle paint and rust converter during the week. Ideally I would love to cut this out and start with fresh metal but to be honest my budget doesn't allow for that.

Will anybody hold it against me if I fix this with fibreglass and miracle paint?  :-\
73 350 SE

TJ 450

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Yep, that's a standard rust spot on RHD cars.

One has to be very lucky not to have a hole there.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

ptashek

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Will anybody hold it against me if I fix this with fibreglass and miracle paint?  :-\

I won't, because that's similar to how I have fixed it for now, even though the hole in my car was nowhere near this size.
Once the body is properly restored I will be encapsulating this very area with epoxy anyway, just because it's a never-ending rot story in there.

In the meantime, keep it nice and clean, and make sure the drain hole is passable.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

oversize

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Unfortunately this is very common and getting access to fix it is problematic.  I'd even suggest it's the reason many cars end up being scrapped!  All but the very dedicated take the time to get it fixed.  The front guards are quite hard to remove because they're glued in place and the bonnet and dash need to be removed if you're welding otherwise you risk a nasty fire.

But get it fixed and you'll have a great foundation to enjoy.  After years of leaking you'll probably have a dry interior, rid the car of horrible smells and it'll be worth investing in a new set of carpets plus anything else to make the interior even more comfortable.
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

Rimas

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Thanks Ptashek,
I'll make sure to be thorough in there to avoid these problems spreading.

Oversize I did think about taking the panels off, thanks for the forewarning about the glue! I'm probably going to take your advice and get some new modern insulation, (dynamat maybe? hopefully something that I can mould into shape with heat or something similar?) and then see how bad my carpets are.

Looking forward to tackling this on the weekend. I'll feel a lot better once it's all sealed.

Man it's frustrating how people have no idea to clean their cars in these areas over the years/they just don't care.

Not to call myself a hero or anything (lol) but at least this 116 has been plucked from certain wrecking.
73 350 SE

oversize

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I'd remove the engine bay insulation in the corners as it seems to be part of the problem.  Make sure the corner drain isn't blocked and if you don't have one then drill a hole (there's a couple of threads on this subject).  Protect the edges of any hole you drill with a rust preventer and paint.  Remove the glovebox to improve access from the inside.  Disconnect the bonnet cable at the latch end and pull it into the interior of the car.

Cut out anything that's rusted, removing all the daggy bits.  A Dremel might allow you to get into the tight areas without removing many parts.  Taking the bonnet and springs off might help and it's not that hard if you have someone to help.  Paint the exposed steel with an anti-rust agent to prevent it coming back.  Then I'd buy an oversize piece of sheet steel and bend and hammer it into shape (sounds easy doesn't it?!).  Drill and cut a hole for a new cable grommet.  Once happy with the new panel's shape and fit (test-fit lots) I'd paint it up nicely (both sides).  Then I'd GLUE IT INTO PLACE.  I'm not sure what's the best adhesive to use, but I'm sure there's something out there to suit.  Make sure all the edges are sealed and water tight.  You could then give it all a final coat of paint.  Put it all back together and you're done.  Keep it clean and dry and it should never happen again.

This process avoids the dramas of welding and should be far neater than fiberglass.  If you're not confident in metal working, take the car to an expert to make up the repair patch ONLY.  Doing the rest yourself should reduce the cost substantially.
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

Rimas

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Thanks Oversize!

Great tutorial. I do however think that I'll wing it with some fibreglass for now. I think I'll cut a grommet hole the size of the hood release cable housing and then carefully work up the fibreglass to that. I'll see how I go.

I have a tin of miracle paint and a tube of rust treatment so I will lather the floors, firewall and rust hole in it.

Do you think gluing a piece of metal back in there could invite future rust when the glue perishes?
73 350 SE

oversize

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If all the metal edges are correctly treated and sealed the rust shouldn't come back.  The only problem I can see with the process I mentioned is that after cutting away all the rust, there may be nothing left to glue to, or provide a sufficient seal.  If water's able to get in-between the old steel and the repair patch then the rust process will start all over again
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

oversize

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BTW do you have any pix from the inside?
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

Rimas

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Hey mate,

yeah I'll get in and get a few good pics tonight. I was intending to get in there Friday morning before work to 'soak' the area in the rust treatment product I have. Apparently the stuff dries and you have to wipe of a residue that forms after the chemical reaction.

Cheers for following up on this thread, it helps me a lot!
73 350 SE

oversize

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I'd highly recommend trimming off the badly rusted areas first, because the rough, larger surface area means rust has a better chance of staying untreated and continuing to eat away at your lovely car!   :o
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

ZCarFan

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One of my former 300SDs had a hole big enough to get you hand through there.  Was wondering why my leg was getting wet and cold. :)

My current 280 SE is rusted here too, but only a small amount.  Right now I have the cable and grommet out along with the carpet, insulation and drains.  Need to seal it up soon.

Don't get too discouraged there Rimas.  Just work on the items one at a time.  You need to take a long term approach and realize that after a year or two it will stabilize and you will drive more, wrench less.


marku

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Made me go and look at the 450. No hole!! but it has rusted out behind the ignition module. I have seen others with this problem.
450SE silver green/bamboo velour/green vinyl roof

Rimas

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Thanks for the positive encouragement Zcar, I've started to feel better now that I've done some work.

Here are some pics of what it did to my floor:





I also decided to investigate why this rust had appeared on this side of the car too. The pic looks worse because I have hacked away at the rust a bit already and I treated it.



It was really hard to find how water could get through into this cavity, but I found that it was probably through the grommet near the ECU. I think it goes to the vacuum tank that sits in there (grey hose). This grommet sits right in the path of my waterfall caused by the main rust hole. I played around with a few ways to funnel some rust converter into this area through the grommet until it leaked out where the rust was. Glad I did this because hopefully it will buy a bit of time until I get the panels touched up.

I also decided to check in the fresh air vent and found an interesting sign of buildup and corrosion that everyone should take care with. It's obviously one that is hard to access but I'm glad I did. Will be including this area in my rust treatment/miracle painting.




And finally, after much scrubbing, vacuuming, treating with a rust converter and a fish oil blend I got the first delicate layer or fibreglass on with a good layer of Miracle Paint.



It may look a little rusty coloured in the area, but this was the fish oil blend spray that I was getting into every nook and cranny.

Forgive if the fibreglassing looks a tad dodgy at this stage, it was just really difficult and important to span across the area. This first layer is mainly to create a surface to work with and refine next weekend. The stuff should be hard as a rock because it was already starting to set when I applied it.



It was surprisingly good to work with, I decided that bonnet/hood release grommet hole was too difficult to fashion so I will just seal this cable with the fibreglass and maybe a silicone next time I work on it.

Anyway that's what has kept me busy this weekend, I hope you all enjoyed yours!

Rimas
73 350 SE

w116john

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hi
I'm just after finding something just like that in mine , just under the bonnet release gromet.

I am just going to do what you did to repair it and hopfully keep it dry, did you repair the drain hole?

and if you did any tips ?  my car is lhd and the fuse box is next to that spot and any water build up goes under it,

I'll patch as best i can and later on in the year i have the rust sorted professionally

best of luck with your repairs

john