115 Steering box frame attachment

[pizzachef]

I just picked up a '74 240D a few weeks ago, and its at the mechanic now for inspection. He's an independent European car mechanic and he's helped me out with my wagon in the past, and he seems pretty knowledgeable with the older Mercedes.

He said that the steering box attachment to the frame is broken, and Mercedes used to sell a repair kit for it, I guess it was something that was fairly common. Well, he said the dealer has no record of this steering box issue or the repair kit.

He's going to look into it, and see if he can weld something together to repair it, but he said the kit came with some longer bolts that may be hard to find just anywhere. I'm not really familiar with the steering box on this car, so I'm just repeating what he said. Has anyone dealt with this on the 115's? If so, I'd appreciate any tips.
Thanks.

[Mike D]

Common problem on the W114-115 chassis. The exterior side of the frame rail rusts. The inside doesn't, especially on a diesel, because it is indirectly lubricated by power steering seepage/leaks and the occaisional slopping of oil from filter canister removal.

Easiest fix is to remove the bolts, make a paper template of the area, pop on over to the nearest metal working shop, have them cut a 1/8" thick plate using their plasma cutter (look for a place which makes ornamental iron fences or gates).

Treat the interior of the frame rail using Waxyoil or substitute, wire brush the exterior area as clean as possible, treat the rail and back side of the plate with a quality primer and paint with some POR-15 or it's like. Trace the outine of the cut plate onto the frame rail. Use a grinder to remove the paint along the lines for welding purposes.

You might have to grind the metal retainer on the top-most rear nut flush to the frame. I suggest you do not "recess" the lower rear bolt. Have a 12MM hole cut to replace the large hole currently in the frame and use a longer bolt with a thick flat washer in the existing bolt's place. Install the bolts through the plate holes, tighten to about 25 ft.lbs, do any final forming and weld the plate into place. Prime and paint the welded area and re-tighten to the recommended specs.

Use ONLY hardened bolts (marked "10.9") and do NOT re-use the bolts, ever! Most of the time you can find the bolts at any decent hardware store but you can always get them (at a premium) at a specialty fasteners shop. I believe the long bolts are M10X1.5 X 80MM. I forget the short bolt's (lower front) length.

Don't be surprised if your steering wheel is off center. This repair won't affect the alignment but it can change the mount position on the steering gearbox.

Don't spray the inside of the frame rail with foam or undercoating. The rail acts as a drain and getting clogged up is what usually causes the rust.

Did I miss anything guys?

Oh yeah, weld the plate slowly and try to keep the heat transfer down due to the waxyoil INSIDE the frame rail. You could apply it after you weld but it's a little trickier to do. Use the usual caution when welding. Keep wet rags on the inside of the fenderwell and between the frame rail and any lines (brake, power steering, fuel, vacuum, electrical, etc). Have a fire extinguisher at close hand.

[pj67coll]

It's not just the 114/115. The 108 I had some years ago snapped it's steering column because the frame rail to which the steeing box was mounted was so rusted out and the mounting bolts had worked loose over time (I didn't know you had to torque them at regular service intervals) that there was so much twisting in the steering column that it just snapped one day while I was parking the car. Unless there was a sudden and severe quality decline at the time of the 108/114/115 series cars, or a major design change in the way the steering box mounts to the car I'd say this is a problem that can occur on any older Mercedes. I have also never heard of a Mercedes factory "fix" for the issue though so I'd be interested in hearing about yours.

- Peter.

[pizzachef]

Great, thanks for the info. The mechanic said that the "repair kit" from Mercedes basically contained a new plate and some new bolts. I guess the plate was already fabricated to the correct dimensions, and now he'll just have to make one himself to match the old one. I wish I could weld because its probably a lot cheaper than to have him tinker around with making a new plate to fit. Well, that's that I guess. I'm glad to know its a common problem and can be fixed without too much difficulty.
Thanks.

[pj67coll]

Originally Posted by pizzachef

Great, thanks for the info. The mechanic said that the "repair kit" from Mercedes basically contained a new plate and some new bolts. I guess the plate was already fabricated to the correct dimensions, and now he'll just have to make one himself to match the old one. I wish I could weld because its probably a lot cheaper than to have him tinker around with making a new plate to fit. Well, that's that I guess. I'm glad to know its a common problem and can be fixed without too much difficulty.
Thanks.

I'm not really sure just how "common" the problem is and would actually like to know more about it's frequency as it seems to be a major flaw to me. Two things might have a bearing on it.

One. I lived in Durban, South Africa at the time which is a severely rust prone location. This had an effect on the car in my case.
Two. I found out later that the steerint box mounting bolts are supposed to be torqued at regular intervals. I wonder how often this is actually done, particularly on cars that are now thirty to forty years old.

- Peter.

[Mark DiSilvestro]

Though rust can contribute to the problem, It's primarily a metal-fatigue issue, aggravated by loose bolts, underinflated tires and cranking hard on the power-steering during parking manuvers.
The frame-rail cracked at the steering box on my '72 W114 250 sedan. Though there was plenty of rust elsewhere on the car, there wasn't any at the steering-box area.
I wound up fabricating my own repair kit from 1/4" steel plate, with longer grade 10.9 bolts from a local steel supplier. I fastened the plate on the outside of the frame rail so as to not change the position or alignment of the steering box. The repair bought me a couple years until the other rust ultimately caused me to retire my 250.
Note that there can be liability issues with repairs of this type to frame and steering systems. I've heard of shops refusing to work on these kinds of problems.

Happy Motoring, Mark

[Mike D]

Here's some pics of somebody's repair on my '74 280C project car. Not the way I'd have done it but it seems to serve the purpose.







This is an Arizona car which has been in Arizona all it's life. I'm the second owner and I know the original owners. So, I'd have to agree with Mark about fatigue compounding the rust problem.

The splooge and streaking are from some rust buster stuff I sprayed while replacing the subframe.

I would have left the lower hole open so I could spray some Waxyoil and I would have treated the plate with POR15 or at least some spray-on rust proofing. This WILL be amended when I am done with the subframe replacement.

Mark, 1/4" plate? How did you get a good bead with the thin frame rail metal? You're a better welder than I, of course that ain't saying much!

[Mark DiSilvestro]

Originally Posted by Mike D

Here's some pics of somebody's repair on my '74 280C project car. Not the way I'd have done it but it seems to serve the purpose.

Attachment 54554

Attachment 54555

Attachment 54556

This is an Arizona car which has been in Arizona all it's life. I'm the second owner and I know the original owners. So, I'd have to agree with Mark about fatigue compounding the rust problem.

The splooge and streaking are from some rust buster stuff I sprayed while replacing the subframe.

I would have left the lower hole open so I could spray some Waxyoil and I would have treated the plate with POR15 or at least some spray-on rust proofing. This WILL be amended when I am done with the subframe replacement.

Mark, 1/4" plate? How did you get a good bead with the thin frame rail metal? You're a better welder than I, of course that ain't saying much!

I didn't weld it. I made the plate oversize so it would straddle the thicker, stronger area where two sections of the frame rail overlap. I fished two heavy threaded anchor plates inside the frame rail, through a convenient hole made by a chunk of frame rail breaking off at the lower steering box bolt. The anchor plates were then pop-riveted in place. With the 1/4" plate bolted to the three steering box bolts and the two additional anchor plates it was quite rigid.
Ironically, my first Mercedes, a '61 Ponton 180b, also experienced failure of the threaded inserts where the steering box bolted to the subframe. I fixed that one by installing a new subframe special-ordered from Mercedes for $168 - quite a hefty sum for me back in the mid '70s, but less than half what a local indie Mercedes repair shop wanted to try and weld the old one.

Happy Motoring, Mark

[Dopey-p]

My 1974 280C Mercedes has the same problem with rust at the steering box. Does anyone have a template for the repair plate?

I am relieved to find that i don’t have to cut into the frame and replace with a section from an unrusted W114/W115!

Or a part number for the Mercedes kit?

[Sugar Bear]

What about cutting a piece out of a good frame and using only the flat vertical section of it that's rusted on yours. Use new longer bolts with Threadlocker on them.
The bolt holes will already be drilled and in the correct location.

Good luck!!!

[pj67coll]

There is a channel on Youtube called Mercedes Maintenance. It's an english guy living in Northern California who has several 108/109's that he's working on. He has one video showing how he fabricated a strengthening plate for one of these cars which was apparently an approved Mercedes solution to the problem. I think he used 16 gauge steel. Worth taking a look at.

- Peter.

[Tony H]

He is/was a member of this forum but I have not seen him post for a long while. I lived a few miles away from him in Ca. He bought several 6.3's from Wa I think.

Originally Posted by pj67coll

There is a channel on Youtube called Mercedes Maintenance. It's an english guy living in Northern California who has several 108/109's that he's working on. He has one video showing how he fabricated a strengthening plate for one of these cars which was apparently an approved Mercedes solution to the problem. I think he used 16 gauge steel. Worth taking a look at.

- Peter.

[Admiral Ahani]

My w114 has the factory repair plate on it. It was there when I purchased the car so I don't know what exactly was involved with its installation, but I can tell you that it's not welded.