Someone posted a thread about their rusted frame rails not too long ago. Mine are all dented up as it looks like someone used it to jack up the car. Are these frame rails really that weak? I mean, it is a frame. You'd think it'd be pretty beefy.

I'm kinda scared to pull back the undercoating to see how bad it looks. Might have the same rust problem as the previous poster.

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B
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1983 300SD

What happens is that someone puts jack stands under the frame rail without a block of wood. The jack stand puts a very high point load on the frame rail and does some localized damage. The frame rails are not structural steel..........they are simply stamped sheet metal.

So, a word to the wise. If you have the typical jackstand, make sure there is a piece of wood on top of it. The wood makes all kinds of cracking sounds but it evenly distributes the load onto the frame rail.

I've jacked the SD about 20 times using this method over the past five months
(two times today. )

Another word to the wise, be very wary if your frame looks like this too. My car was "rust free.'' I scraped back the undercoating to find some ugly cancer right in that area. ugh...

I'll post a pic soon.

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B
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1983 300SD

Welcome to the wonderful world of unibody

I've found that if your car has no rust, you can put a small piece of wood on top of your jack and jack on the rubber bumpers underneath the holes in which the tire jack would go.

Never had problems so far. I just can't conciously jack on unibody frame rails when there is a diesel engine hanging off the front of the car

So I use the little pads

Actually from my experience your front rails do not look that bad. Certainly probe them when checking them out. If pretty good I would spray a mixture of grease and oil into them. Generally after that they will not deteriate or at such a slow rate the rest of the car will disinegrate prior to any trouble from them. They of course gain their strength from the shape the metal is punch pressed into while not having particular great strength over a small load bearing area and as previously mentioned they bend and deform a little even if in good condition if load is not spread when car is jacked up at or resting on them.

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.

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B
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1983 300SD

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.

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!!!

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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

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

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

Quote:
Originally Posted by RUN-EM
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

I have lived down there.
Galveston, Texas = salt water RUST
Corpus Christi, Texas = salt water RUST
Don't forget the fire ants, killer bees, scorpions and random Hurricane to make life fun.

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.

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.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

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

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Whew, that does sound better. I was starting to think roofing cement must be some kind of liquid steel!

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B
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1983 300SD