engine compartment brace weld W114

One of the two diagonal frame braces at the top of the engine compartment on my 1974 250 sedan (W114) has broken at the weld at the firewall. It is the brace on the driver’s side, which here in Australia is the right.

What is the standard repair procedure? I will not do the welding myself, but I want to make sure the mechanic I bring the car to is giving me a straight story (a history of multiple attempts at various repairs by Mercedes specialists leaves me wary).

What other, possibly-related problems should I look for?

A previous owner seems to have had firewall corrosion attended to. My evidence is the new sound-deadening blanket on the firewall. The car also has an ‘exchange’ engine, a 2.3-litre unit in place of this model’s original 2.8-litre unit. I would not be surprised if the brace got bashed during the engine swap (experience indicates that some mechanics in Australia have a habit of creating new damage while conducting repairs). In addition, when I got the car, the driver’s side door (the right side) had a large shallow dent in it. The car had also had a lot of putty work done on the roof, trunk lid, and hood, and it has small ripples in the topsides of the fenders. My suspicion is hail damage (not rare in this country) rather than collision damage.

I am wondering if this frame break has been causing the funky steering. The steering has always felt rubbery on the highway during my ownership (last six years). The car seems to oversteer on long left-hand sweepers but not right handers. The steering box has been adjusted to have no play in it. Suspension bushings front and rear, rear springs and shocks, and steering bushings have all been replaced.

At this point, I will not even start on the 14-month tale of getting the Weber carbs mounted (38 DGAS’s, which are too large). The engine runs smoothly, but ….

Any insight on the frame repair would be most welcome. Thank you.

Will R.
Sydney, Australia

[Mark DiSilvestro]

I would get that brace welded. If the rest of the steering is sound, another area to check is the frame rail around the 3 mounting bolts for the steering box. A fatigue crack in this area of my 1972 250 allowed the steering box to rock, especially at parking speeds. Have someone turn your steering wheel while you watch the steering box to see if it wiggles. Ultimately one of my 3 steering box bolts broke causing really loose steering. After 3 times replacing bolts, adding washers, etc, I finally had to install a 5" by 8" by 1/4" thick reinforcing plate to stop the frame rail bending.

Hope this helps,
Mark DiSilvestro

Mark,

Thank you for your reply regarding repair to the frame brace on my ’74 250.

My concern right now is how to make sure that the weld repair is done properly (after many faulty repairs in the past on various bits). The weld beads on the original joints (the ones at the firewall) are pretty hefty. So, I want the repair to be strong. I am not sure that just cleaning up and rewelding the broken pieces will do it.

My questions involve –

Should a piece angle iron be welded to the firewall to strengthen the joint?

How about putting a sleeve over the end of the brace itself and welding to that?

What kind of welding is preferred – arc, gas, brazing? Does it make a difference?

As you suggest, the steering box bolts and that weak section of frame they go through really cause hassles. I should have mentioned that I have had that fix done four or five times, mostly inadequately. One mechanic claimed to have welded in a reinforcing plate, but the next one said that none was present. A highly recommended old-Mercedes specialist had the repair done once by his body shop guy, then the box loosened up within months. Apparently, the weld still had a ridge on it on which the steering box rocked (these sorts of problems are one reason that I want details on the currently needed repair). That ridge has now been ground down, and the bolts seem to be holding up. I am hoping that some mechanic somewhere can put their hands on the reinforcement kit.

So, thanks again for your thoughts. Any more ideas about the details that concern me?


Will

[Mark DiSilvestro]

I'm part of the pit crew for a friend who vintage-races a 1965 V8 Sunbeam Tiger. It had originally, a similar pair of struts between frame and firewall. Another crew member, who is an excellent welder, added an angle steel brace across the firewall to reinforce this area. He uses a Heli-arc welder.
Get the best welder you can find for an opinion on your problem. This wlll be difficult to solve via E-mail.

The kit I designed for my steering problem mounted to the outside of the frame rail so there were no 'ridges' to displace the steering gear. I put additional plates inside the hollow space to further reduce flexing.
The whole arrangement is now bolted in place with 7 bolts instead of just the original 3.

Good Luck,
Mark

Mark,

Thanks for those details on strategies that you have experience with. They help.

Now, to find an expert welder ....


Will