Since debuting in September of 1979, the W126 generation of the Mercedes-Benz S-Class was the premiere and quintessential full-size luxury sedan of the 1980s. Not only was it a top choice among oligarchs, world leaders, and celebrities alike, the W126 was the ultimate summation of Mercedes-Benz quest to make the best car in the world through innovation, technology, safety, and mechanical excellence, setting the yardstick for every other car manufacturer to follow.
The previous-generation S-Class, the W116, laid the groundwork for this recipe, but the W126 perfected it. Even after its production series ended in 1992, the W126 remained beloved among enthusiasts for its timeless design, cost-no-object build quality, and relative simplicity. (The W140-gen S-Class that followed was comparatively complex and electronics-laden.)
The W126 is often called the “last true Mercedes-Benz.” Underneath, the car is essentially a structurally modernized, lighter, and more refined W116, sharing very similar engineering. This commonality makes them drivable everyday classics with the same long-lasting and impeccable and durable fit and finish, relative ease of serviceability, and polished driving dynamics
The W126 pioneered many features that are taken for granted in cars today, such as traction control and the “Supplemental Restraint System,” or SRS, where seatbelt pretensioners are coupled with front-occupant airbags..
“Compared to the W140 after it, the W126 was always a much better car mechanically,” said former Mercedes-Benz master technician Jim B. “There’s less to go wrong and they’re easier to work on and fix. They’re not as simple as the [previous] W116, but they’re still solid cars.”
Current Mercedes-Benz master tech Dave Klink, who’s been around Benzes since the late 1970, agrees they’re special cars. “The W126 in a lot of conventional senses was a lot more refined than a W116,” said Dave Klink.
If you’re heart is set on one of these rolling bank vaults of German luxury, we’ve created a handy guide to run you through the most important things you need to know about the W126.
W126 S-Class sedan and S-Class coupe
Mercedes-Benz reintroduced two-door versions of its big-bodied flagship as the famed and most desired C126 “SEC” models alongside the W126 sedans, for the first time since the “stacked headlight” W111 and W112 two-doors from the 1960s.
The equipment and powertrains of the coupes are identical with the sedans but with a shorter wheelbase than the sedan and two bucket rear seats versus a three-seat bench. The coupes also feature pillarless doors and no B-Pillar, so there’s a big wide-open space for all occupants to enjoy the breeze when all the windows are rolled down.
Coupes are further distinguished by their “one-piece” headlights with fog lights integrated into the lower front fascia.
Pre-facelift vs. Post-facelift
The W126’s mid-cycle update for the 1986 model year is one of the most distinctive changes throughout the car’s lifecycle. The refresh introduced a variety of cosmetic, equipment,and powertrain upgrades across the model range (including a four-speed automatic transmission) that catapulted the series into the contemporary era.
Pre-facelift cars, from 1979 through 1985, are distinguished by their recessed headlight assemblies, ribbed plastic underbody cladding, and standard use of Bundt-style 14-inch Fuchs alloy wheels.
Post-facelift cars are the most desirable of the breed, from 1986 through 1991, and featured newer-style headlights with lenses sitting flush with their plastic surrounds. The ribbed plastic underbody cladding gave way to flat panels and larger 15-inch, “platter” style alloy wheels. A driver-side steering wheel-mounted SRS airbag became standard after 1986 for all cars, and standard for both driver and passenger beginning in 1988, replacing the dashboard glove compartment.
All cars 1986 and up also received an updated gauge cluster, a more reliable automatic HVAC and cruise control system, improved switchgear, retuned suspension and steering, and ABS as standard.
“The first run cars of the W126 were some of the worst of the Malaise Era cars,” Klink said. “But it’s all relative. They were still better than almost anything from America. They were pretty sluggish, detuned for early emissions and meeting CAFE regulations.
“For the update, we finally got higher-compression motors with high-flow cats and greater power output. Those were good times,” Klink recalls.
Like the previous-generation W116 body, the series numbers and succeeding letters depicted the engine displacement as well as “S” for “sonderklasse,” or “special class” in German, and “E” for “einspritzung,” or “fuel injection” in German, and “L” or “lang” or long-wheelbase.
“The short-wheelbase cars are really cool, but the long-wheelbase cars all ride better,” Klink noted. “They are absolutely just night and day.”
For its introductory run in the U.S., the W126 had no six-cylinder variant, so the V-8-powered 380 SE short- and 380 SEL long-wheelbase models were the range’s entry point.
Powered by the same M116 3.8-liter V-8 as found in the R107 380SL, rudimentary emissions equipment and lower compression choked and bogged V-8 this engine down to 155 horsepower and 196 pound feet from the European model’s output of 201 hp and 232 lb-ft. The result was a 0-60 time of around 11 seconds versus the European car’s 9.8 seconds and an average combined fuel economy rating of around 19 mpg.
“Everyone thought 380s were gutless, but they’re not,” said Klink. “When everything’s adjusted nicely, they perform well. For example, the transmission control pressure cables would often stretch terribly, resulting in a lot of pedal travel before it would kick down. It’s important to make sure they’re properly adjusted to get the right performance from a 380—people hardly got them adjusted right.”
Buyers will need to be wary of early 380 models up through 1984, though—these cars had weak single-rail timing chain designs. (We’ll get to that more in a bit.) All 380 SELs also came with a power reclining rear bench, like the flagship 500 model, with an option for heated seats.
The W126 300 SD utilizes the same legendary “OM617” turbodiesel 3.0-liter inline-five as the prior generation car, albeit with updated power figures of 119 hp and 170 lb-ft. In August of 1984, power increased to 123 hp and 184 lb-ft, despite new exhaust-gas-recirculation emissions gear. Like previous 300 SDs, acceleration is leisurely, let’s say, taking around 14.5 seconds to hit 60. But, in exchange for the sluggishness the 300 SD returns average of around 23 mpg and up to 25 on the highway.
Like the previous W116 300 SD, the W126 300 SD maintains a reputation for being as stone-cold bulletproof if cared for; high-mileage examples make up most of the W126 300 SDs on the used market today.
Succeeding the outgoing 450 SEL and 450 SEL 6.9 was the flagship 500 SEL. Replacing the old cast-iron 4.5-liter in the 450 was a completely revised “M117” V-8 with an alloy construction, an increased displacement up to 5.0 liters, and a revised K-Jetronic (CIS-E) electro-mechanical multi-point fuel injection system.
Like the entry-level 380 model, the 500’s bigger V-8 only mustered up 184 hp and 257 lb-ft of torque compared to the European version’s 500’s 240 hp and 299 lb-ft, taking around nine seconds to hit 60 for the U.S. car. Euro cars did it in a much quicker 7.7 seconds. Fuel economy comes in at a combined average of 15 mpg.
Unlike the 380, only the long-wheelbase 500 made it to U.S. shores.
Both the 380 SEC and 500 SEC coupes are based on the sedans and utilize the same engines and equipment. These earlier models are often hard to come by, because many of them met their demise from neglect or rust. Later, more updated examples of these coupes with the newer engines and equipment remain the choice models.
1985-1991 300 SE/300 SEL
For the refreshed W126, Mercedes-Benz reintroduced a base gasoline six-cylinder model featuring the new-at-the-time SOHC “M103” inline-six—the shorter 300 SE and long-wheelbase 300 SEL. The U.S. received only the 3.0-liter 177 hp version with 188 lb-ft, the same output as the European models thanks to significantly improved fuel injection and emissions equipment.
“The M103 is a fabulous engine,” says Klink. “Combined with the short wheelbase, they’re just really great cars. The 300 SELs are also very much worth keeping.”
The result was a 0-60 time similar to the 500 SEL of around 9.7 seconds but with much better fuel economy rating of 18 mpg combined.
The 300 SDL replaced the short-wheelbase 300 SD, while receiving a completely new “OM603” turbocharged inline-six good for 148 horsepower and 195 lb-ft of torque. The result, like previous diesel S-Classes was a very leisurely sprint to 60 in 13 seconds. But the upside was a combined fuel economy rating of around 22 mpg. All W126 diesels through the mid-cycle update were long-wheelbase.
The diesel-powered S-Class experienced a hiatus for three years as Mercedes-Benz reworked its “OM603” straight-six to meet new U.S. emissions regulations. Sadly, these specific models don’t have the grandest of reputations. Displacement increased to 3.5 liters, but that seems to have reduced the effectiveness of the engine’s head gasket design. Adding insult to injury, the cars were fitted hastily with trap oxidizer exhaust filters mounted on the exhaust manifolds, causing running hotter conditions and eventual warping of the motor’s aluminum alloy cylinder heads. Yikes.
This situation led to a slow head gasket leak, allowing coolant to seep into the combustion chamber, resulting in a slow bending of the engine’s connecting rod. This bending would also prematurely wear the cylinder walls and cause them to “oval,” leading to poor running engine by loss of compression (on top of a bent rod) in the worst-case scenario.
As a result, these 350 cars are nicknamed the “rod-bender” in W126 world. Many engines had rods replaced under factory warrantied service bulletins, but newer and beefier rods plus updated head gasket designs that fix these issues didn’t arrive until years later. When working optimally, these early-’90s diesels produce 136 hp and 228 lb-ft for a 0-60 time of 13.4 seconds, and an average combined fuel consumption figure of 24 mpg.
If you do consider a 350 SD or SDL, Klink suggests doing extra research to make sure the rods and head gasket were replaced by the newer versions. If they misfire under a cold start accompanied by a louder-than-usual clattering sound and blue and white smoke, the rods are bent.
After the mid-cycle update, the 420 SEL replaced the 380, arriving stateside exclusively in long-wheelbase form. The V-8 benefited from a displacement bump to 4.2-liters (from 3.8) resulting in more power, up to 201 hp and 228 lb-ft of torque. (Plus a very important duplex timing chain upgrade.) The result was a similar 0-60 sprint as the older 500 SEL of around 9.8 seconds and an average rating of 16 mpg.
U.S. emissions equipment and lower compression still kept power down from the European car’s figures of 221 hp and 240 lb-ft and 8.3-second 0-60 time.
The big-daddy 560 SEL was the range topper of the S-Class range. The M117 V-8 engine increased to 5.6-liters for its final variation, the largest during the W126 era. Capable of a healthy 238 hp and 287 lb-ft of torque, it was still down from the European’s output of 275 hp and 317 lb-ft, but the North American cars sprint to 60 in a respectable 8.5 seconds. Being the most powerful W126, fuel economy is clearly not a priority given its combined rating of 15 mpg.
Not only was this the greatest S-Class money could buy at the time, but it’s the one that ended up in most driveways of those who could afford it, mainly because it came with all the bells and whistles. Such extras included a standard power-adjustable reclining rear bench seat, heated seats all around, a self-leveling rear-suspension, and a limited-slip differential. If you wanted a baller-spec Benz sedan in the late ‘80s or early ‘90s, this was the one to get.
For the final run of coupes, Mercedes-Benz sold only one version, dropping the 380 SEC from the lineup completely: the 560 SEC. It is the most desired model of the entire W126 series, featuring all of the same kit as the sedan, without two doors and the power-reclining and heated rear bench.
Klink recommends most the 1986 and 1987 560 cars, either as a sedan or a coupe.
“One big change that I think ruined the 560s in model-year 1988 onward for U.S.-spec cars, both in coupe and sedan form, is that they eliminated the unique anti-squat and anti-lift suspension geometry in the rear axle while adding softer shocks and half-inch narrower wheels,” Klink notes. “It just ruined the body control and the way the 560 handled. They were a paragon of high-speed stability, but the removal of that clever geometry turned them into this marshmallowy thing that defied your every effort to drive the car smoothly. It did make them ride nicer. But 1986 and 1987 model-year cars are just much better to drive.
“1988 on, they just suffered from too much rear squat under acceleration and lift under braking. If you’re up for a project though, you can find the rear axle assemblies from an ’86 or an ’87 and it’ll bolt right onto the ‘88s and up,” says Klink.
What you’ll pay for a W126
Values for all models hit their rock bottom around 2009 and remained unchanged through 2018, which is when the uptick began.
The updated cars from model-year 1986 through 1991 are more desirable owing to more creature comforts and significantly improved powertrains, and as such hold slightly higher values.
Sedans peak in value at around $47,800 for a #1-condition, Concours-quality late model 560 SEL. We’ve seen a few 420 SELs in Concours condition go as high as $27,000, but those were likely one-owner, low-mileage cars with a flawless service history. But these are very far and few in between—these old S-Classes are often driven like they’re meant to be. As expected, the 350 diesels aren’t worth much, peaking at $13,100.
Most of the market’s upper echelon consists of #2- (Excellent) and #3-condition (Good) cars ranging anywhere between $12,000 to $25,000 for a well-cared for example with around 80,000-120,000 miles.
The rest consist of #4 (Fair) cars, ranging from $3000 to about $10,000. Anything cheaper are flat-out beaters. There are, however, some exceptions: there’s always the random chance you can discover decent-condition late W126 sedan for cheap at the rice auction or from a flash estate sale.
The two-door models higher values overall. We’ve seen late-model coupe prices go as high as $74,200, but that’s for incredibly rare and highly collectible AMG versions from when the tuning house was still independent. Most 560 SEC coupes in #1 and #2 condition hover between $18,000 to $30,000 with no more than 100,000 miles on them. Cars in #3 condition can be had for around $12,000-$15,000 with similar mileage, while #4 cars bottom out at around $8000 to $11,000.
European specification vs. U.S. specification
Like the previous W116 generation, U.S.-spec W126s have distinct differences to Euro-spec cars, but they’re not as apparent as the W116. U.S.-spec W126s feature longer plastic bumpers than the Euro-spec “short” bumpers while the U.S. headlights feature separate low-beam glass lenses with plastic surrounds and integrated fog light lenses. Euro-spec cars feature much better headlights with a singular glass-pane lens and deeper orange-colored amber turning signals.
The other differences come down to equipment, options, and wheel choices. It’s not uncommon to find a Euro-specification car on U.S. shores—a lot of W126s were imported for the grey market.
What to look out for
The W126 cars share similar maintenance and trouble spots as the prior W116, and W126s are often found in a better state. Still, with the newest W126 nearing 30 years old and the oldest cars being now 40 years old, many rubber suspension and body parts are past their expiration dates. Rust is also a point for concern, mainly at the rocker panels and at the wheel wells. Avoid the cars with the chrome wheel-well covers, as that was not a factory option. Besides ruining the W126’s clean look, the conventional wisdom is that the chrome covers often hide wheel well rust.
“All W126s suffered from sensitive balance issues in the driveline, especially when they introduced the larger 15-inch wheels on the later cars after 1986,” Klink says. “It was so bad when new that Mercedes-Benz almost bought back a ton of cars. Newer tire technology and wheel balancing helps minimize the issue. But it’s still important to make sure everything balanced to avoid prematurely wearing things down.”
Sagging seats, headliners, cracked or broken wood trim and dashboards, and worn leather seats also serve as common wear spots for the interior, and the older Becker radio head units before 1988 often get finicky from weak soldering points.
Still, there’s nothing that isn’t repairable or rebuildable, and upkeep is similarly not as expensive as one would think for a premium automobile. That’s because the W126 is still a relatively simple vehicle designed for ease of maintenance, particularly when compared to the succeeding W140. The W126 shares parts with Mercedes-Benz’s other models of the era, as well, so they are readily available and easy to come by from original-equipment manufacturers and even Mercedes-Benz directly.
All gasoline W126s came with some form of K-Jetronic CIS-E electro-mechanical fuel injection. Fuel distributors and pumps can see aged seals, which could lead to fuel leaks under the hood and underneath the tank. Rebuild kits are readily available and a Bosch pump costs about the same as a W116 gas model, at around $150 to $200. The diesels have similar maintenance spots as the W116, including leaky vacuum lines, worn diesel injection pumps, and malfunctioning glow plugs.
“Despite their reputations for being paragons for ultimate reliability, that wasn’t always the case. Fuel pump relays are a common failure point on all W126s,” says Klink. “High-pressure A/C hoses, if original, also have a habit of exploding in high-temperature conditions on earlier cars. And never let water-contaminated fuel sit in the system. If it passes through, that’s OK, but if it sits, you’re looking at more expensive issues.
“Watch out for weak plastic upper radiator necks and coolant expansion tanks on all models. These cars are getting old and that plastic gets brittle,” Klink says. “And the worst things for any of these cars is if they sit for a long time.” So get out there and drive, people!
Only the 560 SEL sedans and 560 SEC coupes came with the Citroen-esque hydropneumatics self-leveling rear suspension. The accumulators are common maintenance items and should be replaced every 100,000 models for around $1500 at a reputable specialist. Some even go as far as deleting the system altogether for a spring and shock arrangement, but many contend that modification ruins part of the charm of the cars equipped with the system. When sorted, it will last another 100,000 miles with properly timed hydraulic fluid changes.
The M116 V-8 engines in the 380 and the 420 have suggested timing chain service intervals at 50,000 to 70,000 miles, while the M117 V-8s in the 500 and 560 models are suggested at 100,000 miles. The chains are known to stretch while tensioners and upper plastic guides wear out, necessitating their overhaul in a timely fashion to avoid a catastrophic engine failure. Rebuild kits are readily available but be ready to flip over around $1200 to $1500 for the job at a good Benz shop. If you’re wrench-savvy under the hood however, it can be done at home for a quarter of the price in parts.
Early 380 cars are more prone to timing chain failures, as they featured single-rail chains as opposed to duplex chains on the later 380 and 420 engines and the larger M117 500 and 560 motors.
“The timing situation with the 380 was bad with these cars when new, they could grenade themselves almost any time. But many of these cars had the issue fixed under warranty,” Klink says. “If you pursue 380, go after the 1984 through 1985 models as they changed over to the duplex chains, solving the issue altogether. If you happen to get an earlier 380 with the single rail timing chain, make sure it’s been serviced or converted.”
Watch out for weak head gaskets on the 300 cars with the gasoline “M103” straight-six. They often leak at the back of the block on the passenger side of the car and can eventually lead to seeping oil into the coolant, resulting a frothy mixture in the expansion tank and poor running if ignored. But once replaced, the issue is entirely remediated with revised gasket designs.
Lastly, keep an eye out for the cars with “ASR,” or Anti-Slip Regulation, optional on cars in 1991 only. Essentially the industry’s first rendition of electronic traction control, late W126s came with it as an option. It’s not terribly difficult to troubleshoot, but it is just another maintenance item to be worry about on an otherwise mechanically simple automobile. An ASR-equipped car comes with a yellow indicator lamp in the center of the speedometer with an exclamation symbol surrounded by an arrowed circular line. A system fault is indicated by an illumination of ASR light at the bottom of the cluster and that center indicator. The cause of fault is often a worn wheel-speed sensor and at worst, a faulty throttle position sensor or brake sensor tied into the ABS system. Should the system malfunction, the car defer to “limp-home” mode and acceleration and speed will be starkly limited, necessitating the need to restore the system.
BenzWorld.org – A popular online forum for Benz owners, old and new.
MBWorld.org – Another online forum similar to BenzWorld.
PeachParts.com – The official forum of parts retailer PelicanParts.com, PeachParts is a forum oriented more towards mechanical, technical, and DIY work for vintage Mercedes-Benz models.
Oldtimer.tips – A German-based online community, resource, and forum strictly centered around Bosch’s D-Jetronic and K-Jetronic fuel injection systems that apply not only to the fuel-injected S-Class models, but other vehicles with the same system. This is for the serious engineer, mechanic, and troubleshooter.
MB126.com – A resource and guide dedicated to U.S. market W126 and C126 models.