Mercedes 300D Highway Bomber - Modernized - Cold A/C - GM Overdrive A/T

1978 Mercedes-Benz 300-Series Base Additional Info:

With a heavy heart I’m listing my beloved W123 highway cruiser. It needs to go to a discriminating new owner; I have a new project car that needs investment. This car has 263,000 miles on the original engine, which runs excellent. This is my daily driver so the mileage will continue to increase for the duration of the listing.

At a glance summary:

1978 Mercedes 300D (non-turbo), 3.0L OM617 5-cylinder diesel engine with 700R4 GM automatic transmission. Laundry list of new parts. Reliable as the tides. Rides wonderfully. New tires, belts, hoses, etc. No oil/fluid drips on your driveway, and doesn’t burn oil or have much blow-by.

Cold A/C, remote electric keyless entry and electric power locks (including trunk). Good interior, marginal paint—could use repaint. Excellent road trip bomber. Pioneer touchscreen stereo with Bluetooth and Sirius-XM. Center console with USB power ports (4).

Needs: Exhaust system needs fine tuning. Also some wear in the steering gear--could use rebuild eventually but still tracks fine on the highway.

This wonderful example of German engineering now has the overdrive it needs to storm country roads and highways, and we have had a blast with this car. Since its major updates we have driven it over 7000 miles (with young children) on 1000+ mile road trips to Death Valley, Mammoth, Central Nevada, Northern California, Route 66, Phoenix and other places with unfailing reliability and comfort. If this car could talk, it would tell you exciting stories of fun at an age & mileage when many Mercedes are ready for retirement. It has an amazing underdog personality and curb appeal that earn it thumbs up at remote roadside gas stations and diners all over the southwest.

The Details:

This particular car has a very rare color combination of Icon Gold Metallic exterior with a Parchment interior. It was a special-order color combination that the buyer personally ordered through House of Imports Mercedes-Benz in Buena Park, CA in fall of 1977. The buyer personally took delivery of the vehicle at the factory and shipped it home. I have much of the original sales and bill of lading paperwork. We named the car “Booger” but actually its a pretty color…it grows on you.

I will bestow upon the buyer a large file of service history, engineering information, drawings, and other documentation that outline this car’s heritage and back story, but for the purposes of this listing I will cut to the chase: This particular Mercedes W123 sedan is a bargain at the listed price.

The car was specifically selected as a candidate for a transmission repowering project (among other improvements) that would give it long freeway legs to keep up with interstate traffic for long road trips and commuting in L.A. traffic. The car has a GM Hydramatic 700R4 four-speed overdrive transmission. For those not familiar with GM powertrains, this transmission is a heavy duty unit used for V8 car and truck applications during the late 1980s through mid 1990s. The particular unit in this car is a nearly new trans that came from a 1992 Camaro. With that said, let me get this out of the way up front—for better or worse if you like firm NASCAR-style upshifts you’ll love this car. If you like your Mercedes to slur its gear shifts like a drunk sloth (basically like the original transmission) this car will annoy you. At full throttle it barks its tires shifting from 1st-2nd which is decidedly uncouth for a Mercedes.

There were myriad mechanical changes that had to occur for the Mercedes to accept this modern transmission. Again, I’ll review this all in detail with the buyer. However you should rest assured that modifications were done to OEM-levels of quality from the weld work to machining, insulation, sealing, corrosion protection and assembly. A couple of finishing items remain to be completed, but it's already suitable for trips and daily driving.

The transmission installation was an engineered job. Solidworks drawings and specs were created for all of the conversion components, and readily-available parts were used for all appropriate locations to make the car serviceable and reliable for daily use. The trans was installed in such a way that it will be as reliable as the original Mercedes powertrain. Many F-bombs were lobbed during the custom fabrication and build of this car. The result is a cool, legendary old Mercedes W123 that cruises happily at 80mph with the engine purring at 2200rpm, right where it likes to be. For any of you who have owned a standard W123 Mercedes diesel you know that at 70mph the engine is usually screaming so close to its redline that it sounds like the connecting rods are about to come through the hood…not very pleasant for long drives by modern standards.

The car itself is a rust-free very sound example. No crash damage or structural repairs. There is a minor dent in the right rear door (see photos) from a previous owner who appears to have rubbed it against a post. The paint is not original but is over 25 years old and is faded. Clearcoat is thin or failing in a couple areas. But it does shine up just fine as a daily driver as the photos indicate. All power windows work. New 3M window tint.

Upholstery and carpeting are exceptional. The original MBTex Parchment interior is classy, and the carpets are in excellent condition overall. However, due to their light color and irreplaceability I keep floor mats over them. The driver’s seat has had upper upholstery replaced at some point and the color is a shade off; most Mercedes aficionados are quick to catch this but most folks don’t notice. The dash has cracks, but original Zebrano wood is in great shape. The center stack and console are completely scratch-built and have matching real Zebrano wood trim/padded black vinyl.

The center stack and console were completely reconfigured to accommodate updated audio and climate controls. The Pioneer touchscreen headunit also has Sirius-XM satellite radio. Sound quality is very good but the car could use new speakers and an amplifier to meet modern performance. The center console has a closing armrest lid upholstered in the OEM parchment MBTex. There are two USB ports inside the console for charging devices. There is a second pair of USB ports in the back of the console for back seat passengers. There are convenient trays for smartphones, coins, etc.

The absurdly complex and unreliable original climate control system has been replaced with an extremely reliable analog system that allows direct control of airflow, 3-speed fan and A/C. The A/C blows ice cold and has been reliable on several road trips through a hot so-cal summer. It has been converted to R134a refrigerant.

Traditionally W123 front door map pockets crack and are near impossible to replace. The front map pockets on this car have been completely replaced with custom-made bins that have cup and pen holders in addition to cubbies for phones and other items.

Another major weakness of the W123 cars are their vacuum-operated central locking systems. The system has been completely replaced in this car with an electrically actuateddoor & trunk locking system that is controlled with a modern keyless remote.

If this car sounds like an amazing value for the listed price, you are correct. The sum of its parts far exceeds the asking price. However the new owner needs to be a fit for this car—it is not really the car you should buy for your child to sendthem off to Berkeley for their Freshman year.

OK then what does it need?

Exhaust work. The one ongoing challenge I have with this car is exhaust resonance. The GM transmission has a torque converter (vs. MB’s fluid coupling) and it amplifies the diesel engine’s vibration into the exhaust system like a tuning fork. This causes a most undignified noise in the cabin at a steady 1200rpm that sounds like an angry cow mooing. The exhaust is resonating at a low frequency and needs some finesse that escape my level of skill. The turbo engine does not cause this resonance—and it would remedy the car's inherent lack of power. My plan was to put in a later turbocharged OM617A engine; but I can’t justify any more expense on this car. The trans has to shift down out of overdrive for even slight grades; the turbo would make it better all around.

Other Items. Aforementioned steering gear has some slop from years of wear. It has new brake pads all the way around but the rotors will need replacement on the next swap. It will also be due for a routine valve adjustment in the next year or so—I don’t think most owners ever get these done, and the engines will keep on chugging without it, but when done routinely it contributes to these engines’ reputation for 500,000 mile lifespans. Rear main seal is starting to get wet. Not dripping on the ground but will start eventually. The reverse light combo switch needs to be installed. Wiring is there and switch set is ready, just needs mounting, fit & adjust. Cruise control is inoperative.

Thank you for considering this unique motor car. I would be happy to answer questions on the car and let you know more about it in detail.

PLEASE READ PRIOR TO SUBMITTING AN OFFER: I can assist with arranging transportation for out of state buyers. Buyers with unsatisfactory (or limited) feedback will have offers rejected. I highly suggest a test drive with this car prior to making an offer.