Frame Rails really this weak? - PeachParts Mercedes-Benz Forum

bbeardb · #1 11-12-2005, 09:18 PM

Here's some shots of the rust...

All the way through on the bottom where it looks like a single layer connects with a thicker (double?) layer.

Brian Carlton · #2 11-12-2005, 09:29 PM

Quote:

Originally Posted by bbeardb

Here's some shots of the rust...

All the way through on the bottom where it looks like a single layer connects with a thicker (double?) layer.

That's not good.

But, it's not too difficult to fix. You need a doubler plate on the underside and an additional plate on the outside. 1/8" plate should be plenty.

pawoSD · #3 11-13-2005, 01:03 AM

On my passenger side it looked just a tad worse than that, I ground off all the rust and undercoat over a huge area, treated it, ground it again, had our friend weld a 1/4" thick steel bracket (this thing was a beast!) onto the whole section, retreated it, and then undercoated it several times. Its ultra strong now.

The other side I just finished today, it had rust, but only surface rust thankfully, I heavily scraped and treated it with the rust converter stuff, then today I undercoated it heavily, all is solved now......for the time being..... I also sprayed a bunch of crud inside there too to inhibit futher or future rust. I will fight the evil michigan salt to the bitter end!!!

t walgamuth · #4 11-13-2005, 03:47 AM

posts are good.

those huge heavy looking sub frames are really not all that thick. they get their strength from the shape. they really arent designed to jack the car up with. if you look in the owners manual you will not find that they recommend using them to jack the car up.

i do it all the time too though. i do use a board too. you will note that your failure is at the weld. the heat generated there makes it a little more prone to rusting.

if you make a pattern of cardboard that folds around the subframe tightly about 12 to 16 inches long you could apply it over the affected area and secure it with self tapping sheet metal screws every two or three inches. stay away from the corner of your subframe as that is where the stress is greatest. apply liberal amounts of roofing cement under and around the edges. this will be simple, wont require welding and will last as long as you want to drive the car.

tom w

Brian Carlton · #5 11-13-2005, 09:44 AM

Quote:

Originally Posted by t walgamuth

those huge heavy looking sub frames are really not all that thick. they get their strength from the shape. they really arent designed to jack the car up with. if you look in the owners manual you will not find that they recommend using them to jack the car up.

if you make a pattern of cardboard that folds around the subframe tightly about 12 to 16 inches long you could apply it over the affected area and secure it with self tapping sheet metal screws every two or three inches. stay away from the corner of your subframe as that is where the stress is greatest. apply liberal amounts of roofing cement under and around the edges. this will be simple, wont require welding and will last as long as you want to drive the car.

tom w

The owner's manual for the SDL utilizes a jack that is fitted to the jacking point directly above the frame rail. This tells me that M/B believes that these rails are strong enough to support the weight of the vehicle. Furthermore, the manual also refers to jackstands, although they do not specifically state that the jackstands should be utilized at the jack points. However, I do believe that the conclusion can easily be made that this is the proper location for the jackstand.

Adding cardboard with roofing cement to a structural member would be akin to filling a rotten header with plastic filler and sanding it smooth. It looks great on the outside but the structural integrity has not been restored.

Welding is the proper solution.

Hatterasguy · #6 11-13-2005, 10:26 AM

I always use the jack pads when I can because those are the best places to jack the car up from. However when I need to use a jack stand I want it under those pads, so I will jack the car up from those rails. I have used this method for years on the SDL, as long as you use a good block of wood you won't have a problem. I find the right under the rear shock is a great place to jack the rear up btw.

However I tried the same method on the SD and one of the frame rails started to crush!

That thing is pretty rusty so I am in the process of ignoring it.

t walgamuth · #7 11-13-2005, 11:47 AM

guys, i was up by accident at 330 thinking it was 530 and i neglected to say that the cardboard was a pattern to be taken to the sheet metal shop and have a part bent out of the thickest steel that they can bend (abnout1/8", i think).

(those sheet metal screws wouldnt hold much in cardboard!)

you guys must have thought i was losing my mind there!

tom w

RUN-EM · #8 11-13-2005, 08:49 AM

Quote:

Originally Posted by pawoSD

all is solved now......for the time being..... I also sprayed a bunch of crud inside there too to inhibit futher or future rust. I will fight the evil michigan salt to the bitter end!!!

Rust always wins

Move south. TEXAS is a big state....sure we can find room fer ya !

Regards

Run-em
1983 300 S D -aka.- SPARKY THE DIESEL

Pete Burton · #9 11-14-2005, 09:07 AM

Quote:

Originally Posted by bbeardb

Here's some shots of the rust...

All the way through on the bottom where it looks like a single layer connects with a thicker (double?) layer.

ooh. nice frame rails, wish mine were that nice. Soon though they will be. I've just welded the doors and quarters, the frame rails are next. - BTW, the metal on those rails is pretty thin, less than 1/16" everywhere I measured it - but overlapped at the front bottom corner.