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SLK 320 [R170] - Auto - 2001
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7 Posts
Discussion Starter · #1 ·
Good afternoon,

I am currently replacing all of the rear multi link suspension arms, as well as the coils and shock absorbers. I thought that it would be a good idea to have a look at rust proofing as best I can while everything is out of the way, so I have painted the subframe with rust buster EM121.

The issue that I have come up against is the the rubbery coating underneath the car and in the wheel wells is separating at the edges in several places, and in others seems to have worn away or come off and rust patches have formed underneath. What is the best course of action here? Clean, rust converter, then Dinitrol 4941? Perhaps this is one for a professional?

I’ve never really done anything like this before, so any advice would be greatly appreciated. I have added a couple of photos to show what I mean.

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Registered 2009 SLK200
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5,419 Posts
@Delucas any hints from when you did the 171?
Different cars but possibly similar issues.
Rust its the Devil in Disguise ......
all i can suggest is angle grider or drill with small attachment and get rid of rust ......
use rust eater let it dry etc
then spray with compressed Air with 3M under sealent .
 

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Premium Member 2002 R170 SLK V8 5.0
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5,144 Posts
LOL, here is the answer, I have the same issue on the R&D Car I just bought, it's a right PITA to get off, I've tried Grinder with various discs, Grinder with Wire Wheel, found the easiest way is a 2" Scraper and a rubber mallet it will chip it off.

This is a serious structural issue, left untreated, and without experience of welding :poop: like my pic below, it will write the car off, you can't just patch over the top of it, have to remove sections above, weld into and tie in the structures underneath and finally weld in new metal on top !!

So in a nutshell, a lot of welding needed, (a lot more than I had anticipated), but I own this bucket of rust now, so I either do it properly or break it for spares ;) Thankfully it is localised to these 2 areas only the rest of this Car seems to be in good condition ;)



I have a funny feeling there are a lot more forum Members who will have this problem if they dig about underneath the thick underseal :(

Now I have it all stripped, Subframe Out etc, needs 2 x front to rear Brake Pipes too, I will be posting updates in my Project thread, I'm cutting out today, but also need to make Card Templates before cutting, Target is to get the Subframe back in by Sunday so I can move the car out, then I can do the bits under the wheelarch and sills at my leisure when time allows ;)
 

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Registered 2015 SLK250d
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131 Posts
Under seal is excellent to a point, but as you can see rust can track underneath it and it has to be removed to see what the damage is.
I would not use more under seal on a classic but have moved to the products from Buzzweld and Lanoguard in the UK that protect but allow any issues to be seen.
 

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* Registered
SLK 320 [R170] - Auto - 2001
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7 Posts
Discussion Starter · #6 ·
Thanks a lot for the replies. Looks like rather more work than I was hoping!

I think that I will try and remove as much of the rubbery under seal as I can in the affected areas so that I can have a real idea of the extent of the issue. The welding etc is unfortunately beyond what I'm capable of doing at home, so I'll get some pictures across to a professional to have a look at. Buzzweld isn't too far from me, and it looks like they offer restoration services, so I'll speak with them. Thanks for the recommendation.

I'll add this job to the fairly long list of stuff that needs fixing, and update with any progress that might be of interest to others when I get it sorted.

Dave, I will be keenly following your progress on the R & D car - R170 with a V8 sounds great!

Cheers.
 

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Premium Member 2002 R170 SLK V8 5.0
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5,144 Posts
I hope your car isn't as bad as the one I just bought ;)

Thankfully my 2002 (with the V8) doesn't seem to have this issue, although I will be checking it thoroughly now I know where to look, issue is they have a box section chassis that you can see, but to stop the car from flexing with roof down there are 2 more internal braces inside which have dissapeared due to the old Tin Mice eating them away ;)

Some detailed pix will be in my project thread later.

On the RHS of this one I just got, (V6 Car), there was about 12" to 18" of the internal structure just missing rotted away ;)

Thankfully the LHS doesn't look as bad, just around 3" to 4" up from Sill level, so hopefully when I start that side I'll have a lot less to do ;)

I'm assuming about 7 x 6 hr days to do both sides so £2520 just in labour plus welding consumables, Waxoyl and Underseal etc and that doesn't include the Wheelarch replacement and paintwork which I will be doing later on ........................

Yeah, hindsight and all that, I drove a 700 mile round trip to get this car, and I should have just walked as soon as I saw it and saved up a bit more spare cash for my "Projects Pot", then paid a couple of £ grand for a decent Car ;)
Instead of that I just gave him the £500 and took it away, working on the basis it had a couple of rare and decent parts I wanted for my V8 Car, and I could always get my money back +++ by breaking it.
The seller was, to say the least, very economical truth wise, and yep the last MOT, (4 Days after he bought the car), was definitely well dodgy, it didn't get this bad in 18 months ;)

That said, yeah, I knew it would have more rot than just rear Wheelarches 🤣

TBH I would have broken this Car up if it wasn't for the fact this rot is very localised and the rest of the Car is pretty good structurally ;)
I didn't book any work in for this week, except for 2 small jobs that are waiting on parts since last week ;)
 

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* Registered
SLK 320 [R170] - Auto - 2001
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7 Posts
Discussion Starter · #8 ·
Fortunately mine doesn’t seem to be as bad as yours, I have peeled away the under coat in a few places and the rust appears to just be on the surface and only extends a 2 or 3cm. I have contacted a couple local rust experts to get quotes for sorting it out, hopefully it won’t get in to the £1000’s!

I think mine is similar to yours in that the majority of the issue is just is one place on both sides, and a couple of patches by bolt holes. The main actual floor pan looks pretty solid.

I removed the rear strengthening struts today, and the drivers side one had a massive rust hole in it, so had to order another one, other side is okay, so I’ll just clean it up and cover it in epoxy paint. Fingers crossed there won’t be too many other surprises like this. Really starting to dislike rust now!

New suspension and multi link suspension components are getting delivered tomorrow, so at least I can get that fitted and know that is good for a few years 🙂.

Think this is going to end up being rather an expensive project!
 

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Premium Member 2002 R170 SLK V8 5.0
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5,144 Posts
I have peeled away the under coat in a few places and the rust appears to just be on the surface and only extends a 2 or 3cm.
It's not about what you can see, it is about the extra structure that you cannot see inside the box sectional Chassis .......................

What you need to do is this ...............

Buy a cheap illuminated USB Camera, and plug it into a Laptop or Phone, now take out all the rubber bungs you can see that lead into the Cavities, including the ones at the end of the Sills, take a look in there, that is why I had to cut this much out of my Inner Wheel Arches, so I could get in there and repair it ;) ......................

Simply welding a patch over a hole in the outer steel will pass an MOT, but the lack of structure will mean the Cars Shell will flex over bumps and eventually it will bend in the middle or start cracking :cry:
I didn't think mine was as bad on the left side, (it isn't quite), but I cut it open to inspect and here we go, it needs work, so I'm actually going to replace and strengthen all of this just like I did on the other side :)

This is the Left side now cut open ready to start cutting and welding today, notice inside this chassis section there are 2 more reinforcing rails, the one with the pressed holes and the one behind it ....





This is the right side now gone as far as I'm going to for now to enable me to get the Subframe back in, Wheels on and move the car around ;) ....



I will finish the lower inner Wheel-arch sections and both Sill / Jacking point areas at my leisure, because I don't need Subframe Out just take Wheels off to do these ;) If I had a bigger Workshop with more lifts I'd carry on, but Customers are now queuing up and I need to get the Car off the lift asap ;)

This is the "Jacking Point rot", common on all Mercedes and a much easier repair ;) ....



When this lot is finished I am going to absolutely soak all internal Chassis and Sill sections by high pressure spraying gallons of Waxoyl in through all the Grommet Bungs and Sill Cover Clip Holes ;)

And then, after this is replacing the rear Wheel Arches and re spraying them and a couple of other touch ins :ROFLMAO:

I removed the rear strengthening struts today, and the drivers side one had a massive rust hole in it, so had to order another one,
Mine are all rotten on the V6 Car, I had never realised they are hollow pressings, I plan on replacing all of them, but will fabricate from 4mm Stainless Flat Bar, I will also do all 4 on my V8 R170 as although not as bad, they are scabby and look awful ;)

HTH ;)
 
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