1979 Mercedes-Benz 450SEL 6.9

This car, Lot 382, sold for $41,193 (€36,300) at RM Sotheby’s Online Only European Sale Featuring the Petitjean Collection, June 3–11, 2020.

I judge a Mercedes by its engine bay, and this is just an average example. In fact, I’d rather see a dirty engine compartment with original hose clamps, spark-plug wires and finishes hiding under grime than a clean one with a plethora of errors.

Speaking of errors, let’s list the obvious ones:

• American-style hose clamps on the upper radiator hose.
• Non-insulated generic spark-plug wires. (A correct spark-plug wire presentation involves running the left and right ignition wire loom through a tube of heat insulation. Said heat insulation costs about $4 from Mercedes.)
• A splitting high-pressure air conditioner hose, indicating the a/c may not hold refrigerant.
• An incorrect windshield-washer pump, with a fabricated wiring harness.
• A clamped-on positive battery terminal. (A correct terminal from Mercedes is $6.)
• A broken fan shroud that has been repaired.

These issues are easy to deal with and could have been rectified with little effort. Small errors are frequently an indicator of bigger ones, and there are plenty of challenges waiting to neuter the egos of prideful mechanics on the 6.9.

Key differences for America

The U.S.-market 6.9 represents a “safe choice.” U.S. cars were supplied with a detuned engine (250 horsepower), exhaust emissions system, automatic climate control, hydraulic but non-height-adjustable suspension, and alloy “Bundt” wheels. They are excellent cars, but the Euro version is the purest manifestation of the form.

European-market cars are more than just those pretty, slim bumpers. They had higher compression and stronger 300-hp engines. For starters, electronic climate control was optional outside of the U.S., and few buyers selected that option. (Some 6.9s weren’t even optioned with a/c!) The majority of Euro-market 6.9s seem to have velour upholstery (even some U.S. cars were optioned with it), which is not as well-liked as leather. Finally, the hydraulic suspension on Euro-market cars is height adjustable, a feature axed to meet U.S. regulations.

All of this is to say that despite the fact the auction catalog made it clear that this was a U.S.-market car, some bidders may have thought they were bidding on a hairy-chested Euro-market 6.9, thanks to those bumpers. Indeed, our U.S.-market subject car is masquerading as a Euro-market 6.9.

When it left the factory, it not only had the giant (but highly effective) U.S.-spec bumpers, but also a speedometer and odometer calibrated in miles. Although the auction catalog implies that our subject car’s metric speedometer is original, hopefully the correct mileage was transferred to the new speedometer, or this 450SEL may have a mileage discrepancy. The catalog also implies that this car has anti-lock brakes (ABS was first offered on the W116), but there were no U.S.-market W116s offered with ABS, and thus the ABS light on the instrument cluster would never have been present.

Suspension issues

Some 6.9 owners complain about the complexity of the hydraulic suspension. The question is whether the suspension is reliable and serviceable. Years ago, pundits would mock the 6.9 because a suspension failure would basically render the car worthless. But well into the 21st century, the Internet has solved most of our issues. A suspension failure is still expensive, but Martin Werminghausen at 600AirSuspension.com has generated a rebuilding program for the hydraulic components on the 6.9 and similar W126s with this system.

Shamefully, Mercedes itself stopped supporting the 6.9 and hasn’t supplied the self-leveling shock absorbers and hydraulic hoses for a long time. The hydraulic accumulators are still available, which is key in refining the ride quality of these cars. The rear leveling valve is repairable using a kit from Mercedes, but for the front and main leveling valves, a third-party rebuilder is needed.

Broken HVAC systems

Another area where the 6.9 struggles is the automatic climate-control system. The Chrysler-sourced unit is notorious for vacuum leaks and failure of the climate-control servo, which lives under the hood. The most effective solution for the servo is to buy a new one. Mercedes does supply these, but there is a catch: The version for the W116 lists for over $2,000! However, the version for the W123 is only $900. What’s the difference? I still haven’t figured it out, but the cheaper one works.

While I have tried using rebuilt servos, they never work for long. While many rebuilders complain that the plastic body of the servo cracks, this is not the main issue. The real issues are internal vacuum leaks, a seized electric servo motor and a leaking internal hot-water valve — all items the rebuilders never seem to deal with.

Another major issue that will shut down the whole system is failure of the in-dash vacuum actuators. These actuators are buried in the dashboard, with the defrost actuator actually requiring its removal. When this actuator fails, if the system still works, all of your a/c will end up coming out of the defrost vents.

A 6.3 at half off

For those of us who admire the 6.9, this sale might be interpreted as a clear market signal. For detractors who consider the 450SEL 6.9 an inferior sibling to the 300SEL 6.3, this sale might be interpreted as a fluke. The 6.9 is, at best, a $40k car. This sounds cheap, especially when you compare these to the 300SEL 6.3, a car that seems to frequently trade hands for twice that. The 6.9 used to be a $5k–$10k car at best, and if you must have one, you can still buy a decent one for this kind of money.

I think our subject car sold for $10k above its value — just look at those re-dyed seats — showing the demand is there for good 6.9s. Great low-mileage examples will cost this kind of money to purchase and sort out, and the 6.9 is more reliable than the 6.3. While it may not be as iconic or sexy as the W109, our subject car represents the kind of cash the market is willing to dish out for a no-excuses 450SEL 6.9 — or at least the perception of one. ♦

(Introductory description courtesy of RM Sotheby’s.)