A nasty rust surprise. A huge hole near the bonnet/hood release cable grommet.

Started by Rimas, 21 May 2013, 02:25 AM

w116john

hi
my fix is temp i will have to get it welded later in the year , it is a really awkward spot to work at especially lhd with the fuse box so close.
hopefully I'm dry for a while, but my floor matting is shot.

oversize i used a coat hanger to find the drain hole pushing up from below it looked just as yours does, then tried to scrap out as much as i could

rimas i was going to drill a new hole but firstly i put in a small tube and some sealant which did not work, so i then dug it all out and put in a larger tube from a garden hose, which looks as if its large enough to take the water.

drilling a new hole is a good idea find the lowest point, i also think putting in a tube is a good idea, you could fashion it from fibreglass?

now to fix the swimming pool in the boot.

Rimas

Quote from: oversize on 15 June 2013, 07:00 PM
Note that I can't see the opening for the hole on the RHS near the fusebox and it's obviously been blocked for years and I think it's rusted through.....

Thanks for the pics, I'll definitely have to check that side more thoroughly too. Yeah I had no evidence of a drain on mine, it was mostly just rust.

The strange thing was that it had also rusted a secondary hole into the firewall just underneath which would have been the end of the car had I not found it. I finished the work today, did a water leak test and no signs of leakage. I did however find a small amount later in the day in the rear of the car. I think my windscreen rubbers would have caused that because I gave them a big soak. So that was a bit of a let down.

I did however get to drive the car again for the first time in about 4 weeks, man was the lack of road noise great with the dynamat and, well, I guess the lack of a big hole in my car! By the way highly recommend dynamat for ease of use. It was great to work with.

Just hope like crazy that I found and properly treated all the rust, it would be a nightmare to pull up all those sticky sheets.

Quote from: w116john on 16 June 2013, 01:08 AM

rimas i was going to drill a new hole but firstly i put in a small tube and some sealant which did not work, so i then dug it all out and put in a larger tube from a garden hose, which looks as if its large enough to take the water.

drilling a new hole is a good idea find the lowest point, i also think putting in a tube is a good idea, you could fashion it from fibreglass?

now to fix the swimming pool in the boot.

Good idea, I was thinking about fitting a pipe with a flange end. I could drill the exact size hole and it would just sit in. Would have to make sure the flange is as flush as possible to the surrounding surface, maybe building it up with fibre glass or just silicone.

I think no matter what, we will make sure that these areas are clean on our cars from now on!

Cheers

Rimas

oversize

I just checked one of my cars (Moby) that appeared to have no rust in this area.  Despite it being an early car, the panels are the same design as the late car (Green Lantern) in the pics here.  I pushed a piece of wire (modified coat hanger) up through the opening from underneath but it wasn't coming through at the top.  So I peeled off the firewall pad around the bonnet cable grommet.  It appears the pads were installed first, followed by the grommet, so the pad is sometimes difficult to peel back.  What I found was that the pad was blocking the hole and as a result IT HAD RUSTED THROUGH THE FIREWALL!   >:( >:( :( :( :'( :'(  The drain holes were only small and it doesn't take much for them to block up.  Compare the size of these holes to the drains for the plenum below the windscreen and you'll see what I mean.

So the moral of the story is that if your car still has the firewall pad in place, it's likely to have rusted out the firewall and allow water into the car.....  If you're installing a new pad; CUT OFF THE EXTREME ENDS BY AT LEAST 100mm or risk a rust disaster later.  Not happy Jan....
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

Oh and if you intended to fix this problem professionally with a steel replacement panel, I reckon it'd be best to pull out the whole dashboard and attack it 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

Oh no!

Pics?

Are you talking about the 'pad' on the engine bay side? This is what I peeled back to discover my problems..

Taking the dash out for that is highly recommended, I chose the "paint brush covered in rust seal, splatter all behind the dash blindly" approach. I hope I got it all!

What will you do about this one?

oversize

Moby is a low priority as he needs lots of work.  But the dash has already been pulled by one of the POs and it wasn't even put back completely so ripping it out again shouldn't be too hard....  I'm just thinking how I'd redesign the panels and drain area so it'll never happen 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

TJ 450

Also, the contact adhesive used probably holds moisture in behind there, causing further problems. The rust appears to spread out in a radius, suggesting to me that the adhesive acts as a wick.

Removing the dash opens up a whole can of worms, one in particular being not destroying it in the process.

One needs to be prepared for the left hand corner of the dash to be damaged during removal, if it is brittle.

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

oversize

If you dash hasn't been replaced recently, it's probably ready to crack too (if it hasn't already).  You'd have to plan for a new one, or recovering it during the job.

I'm starting to think the whole insulating pad should be removed, as I'm worried about rust and not concerned about a bit of extra engine noise....  But I'm sure it'd be an engine out process if you wanna do it properly
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

TJ 450

Yes, I don't like anything that hides sheet metal like that. The only problem is that it almost certainly doesn't look original without it. Mind you, it could be painted black. 8)

You wouldn't need to remove the engine, just all the mechanisms and clips attached to the firewall, including the accelerator linkage.

The remaining contact adhesive will be a PITA to remove though.

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

oversize

I really don't know why they didn't have the deadener on the inside only....  When repairing this area I'm seriously considering completely redesigning the drains and some of the sheet metal.  Having the inner guard meet the firewall in a downward curve is madness and a natural water trap.  Long term even seam sealer won't stop it from rusting due to the harsh environment
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

I'm also thinking there must be a better way to protect the firewall during inner wheel arch duties than just coating it with bitumen deadener....  I'm thinking moulded plastic with deadener on the back to prevent excessive noise and drum
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

I guess as long as moisture or oxygen are removed from the equation, rust won't occur. Bitumen should be fine.

I've found a really good sticky product that dries hard and is a blend of fish oil and tar. Fergusons Knock-Out: http://www.knockout-rust.com.au/information.html

Seems to get into all the hard to reach spots. I did all in my fresh air dam, smelling quite chemically driving to work this morning.  :P

ripley

Hi guys,
could someone send me a MIRACLE PAINT to Lithuania? :) seems like a good stuff.
I could pay extra for helping...
Thanks.

gurrier

Hi. I can't view the pictures. Anyone have an idea what I can do


Quote from: Rimas on 21 May 2013, 02:25 AM
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?  :-\
1973 350SE

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber