Gentlemen,

I’m a first-time Benz owner, and I’m hoping you can help me diagnose a problem.

I have a 1968 250 sedan (114, carbureted I-6 with column-change automatic. 100K).

Having recently come out of the garage from winter storage, it’s developed a problem in the last couple of outings: It starts fine, and requires a couple of minutes to warm up. Once underway, it feels a little “loaded up” on acceleration, and when I come to a stop, the brakes feel very firm (almost “pushing back”), and the engine strains against the brakes. The RPM dips until the engine almost dies. I’ve managed to keep things going by shifting into neutral at stops, but something’s clearly not right. Even in neutral, it’ll run roughly until I accelerate again.

I suspect a vacuum problem, and this is a system I have little understanding of, and the Haynes manual doesn’t explain thoroughly.

The oil pressure stays close to the peg, and the temp stays in the normal range. The brakes (at the wheels) are relatively new, the fluid level is fine, but I suspect the booster and the vacuum line to the manifold are original.

Coolant’s fine, brake fluid’s fine, oil’s fine. New bimetal “clock springs” between the intake and exhaust manifolds.

Can someone point me in the right direction until my service manual CDs arrive from MBUSA?

Matt

P.S.: This forum’s been a fantastic resource so far – thanks everyone!

Sounds like a booster leaking vacuum when the brakes are pressed. It's a common problem, luckily the boosters are available at ********.com very reasonably. Try removing the line to the booster from the manifold, plugging it and driving it judiciously again (get a feel for the non-power brakes first) I drove mine for quite a while without power to the brakes and it stopped just as well with a little more effort.

I think your stalling problem will subside, but I suspect that may be only half of it. Even with a new booster your car should be able to sustain a reasonable momentary drop in vacuum. Your carbs may be in need of some choke enrichment/fast idle adjustment. There is also a dashpot which pokes the throttle if the idle gets too low, such as going from park idling into drive idling with the auto. It's a nice feature of the zeniths allowing the idle to be set nice and low with all else (including ignition) being up to snuff. It may need some adjustment as well but after the brake booster I would look into the chokes first because that thing may just fall into line after the other adjustments are correct. Again, all this is assuming your ignition gear is in good shape.

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1967 230S automatic
Boston, MA

I agree with todds. Definately start with close observation of the carbs. Get the jamiekoop manual from links on this forum. Then read and understand the entire manual before you do any adjustments.

And if yer bringin it outa winter storage does this mean the fuel is 6 months old?

Gents,

Thanks for all the great advice!

A little more background: The fuel is new. The car had been running nicely for a couple of weeks after coming out of storage, and I was able to fill it with a new, fresh tank of fuel.

Since I first posted, I gave the engine compartment a good cleaning, including the carbs. It's running more smoothly, but still stumbles a little under braking, like at a light. Better than before, definitely.

I ordered a replacement vacuum hose (complete with the check valve). I fear the one it has on now is the original. I'm thinking that's a good first step before I go after the brake booster. It looks original, too.

I'm only the second owner, by the way. The car was well taken care of, but I haven't had enough time with it to develop any familiarity for what feels right or wrong, if you know what I mean. But I'm getting there, and you guys are helping a lot!

Matt