Buyer’s guide: Mercedes-Benz SEC (C126)

By Malcolm McKay

| 2 Aug 2019

Classic & Sports Car – Buyer’s guide: Mercedes-Benz SEC (C126)

Why you’d want a Mercedes-Benz SEC (C126)

Derived from the flagship W126 S-Class of the late 1970s, the two-door SECs were uncompromisingly majestic powerhouses with super-confident pillarless styling by Bruno Sacco.

They are not the gas guzzlers they appear, benefiting from Mercedes’ ‘Energy Concept’ programme that claimed to improve economy by 25% on the big V8s.

Mercedes’ focus was on safety and it pioneered airbags: the driver’s was optional from the start and standard on the 500/560 after the facelift, while the passenger’s became optional in 1988. Traction control was available, along with seatbelt pre-tensioners. Heated and power-adjustable front seats featured, along with a display for the outside temperature and sophisticated cruise control.

Launched as the 380 and 500, the former grew into the 420 and the 560 was added at facelift time in 1985. A few coachbuilders offered convertibles and AMG modified 500SECs: two raced in the 1989 Spa 24 Hours, but neither finished. American versions had huge bumpers, a lot less power and worse fuel consumption, so beware of imports.

The 420 was the rarest, with just 3680 sold, followed by the 380 at 11,267. The 560 sold 28,929 examples, remarkably only just behind the much longer-lived 500 at 30,184, showing that most Mercedes buyers went for the top of the line. Only c6500 of the 500s were built after the 560 was added to the range.

Rust, while often not widespread, is specific, which can be difficult and expensive to access and repair. Mechanically the cars are extremely strong and most have covered high mileages – if properly maintained, this need not be a concern.

Cars that have passed through a period of neglect, even if covering low mileages, are more likely to give trouble than ones that have been continuously used but professionally maintained, so check the service history.

Prices are rising, but remember that Mercedes parts are top quality and far more expensive than for ‘lesser’ marques. Virtually everything is available (though often on back order), but buy a scruffy car that needs many parts and you will be in for big bills. It could easily take the service-plus-purchase costs high above what you would spend for a really nice example that’s had all that work done already. It doesn’t take long to spend £10,000 fettling an SEC, and a full restoration could leave little change from £50k.

Images: Will Williams

Mercedes-Benz SEC (C126): what to look for

The SEC is a perfect grand-touring car, whether hammering down autobahns or cruising the French Riviera with the pillarless side windows down. It exudes sturdiness and quality of build, rather than lounge-lizard comfort – and despite its bulk, it is lighter and more fuel-efficient than you might expect

Bodywork

See above for trouble spots

Engine

The all-aluminium V8 engine will run for ever if given basic maintenance. Unlike most classics, many SECs have a full service history; if not, pay less. If there’s a clack from the timing chain when starting, expect a £1200-1500 bill to replace it; more if the clacking continues, meaning the cams are worn.

Steering

A special tool is needed to replace front bottom balljoints: rattling over bumps can be the bottom arm thrust link. Steering box rebuild costs c£300.

Gearbox

The gearbox is strong; reverse clutch is usually first to go. Select reverse and if it takes several seconds to engage, expect a £1500 rebuild bill.

Interior

Trim is robust, though velours fade and headlining can sag, which some specialists won’t attempt to fix. A faulty sunroof can be a nightmare.

Check rear screen seal for cracking, parcel shelf for trim damage, and underneath (inside the boot) for poor repairs to this notorious rust spot.

Mercedes-Benz SEC (C126): on the road

Owned for 30 years by Mercedes specialist Tony Montalbano, this car (fitted with a Lorinser front spoiler) is for sale. Visit roberthughes.co.uk

The SEC should feel planted, capable and well controlled, with a strong surge of acceleration whenever it is needed. Handling and steering are not the sharpest, but if the car feels tired, it probably is.

The engine will need a new timing chain by 100,000 miles, and a worn chain can break the plastic guides and damage the head. Check in the oil filler for score lines on the camshaft – worn cams make a clacking noise and new ones can take some sourcing, with four different specs for the 500 alone.

Smoke when idling and under acceleration is usually valve-stem oil seals, which can be replaced without removing the heads. It’s worth replacing the cam oiler tubes, too. Check for oil leaks from the head gaskets, which is several days’ work to replace, and look for collapsed engine mounts.

The fuel-injection systems are designed to keep the engine running even when faults arise, so they don’t get fixed. You can expect to pay c£800 to rebuild the metering head and warm-up regulator, which commonly fail on cars left unused for long periods. Front brake calipers do, too, especially on pre-facelift cars. Cruise-control failure can be expensive to fix; automatic seatbelt guides break, as do belt buckles.

A clonk from the drivetrain is usually a worn propshaft centre mount. Rear axles get whiny and leaky, but go on for ever. Self-levelling rear suspension, if fitted, goes hard when the spheres fail. Hydraulic lines rust and are often poorly repaired – likewise fuel and brake lines.

Mercedes-Benz SEC (C126) price guide

380

Show: £18,000
Average: £7200
Restoration: £3000

420/500*

Show: £25,000
Average: £12,000
Restoration: £5000

560

Show: £30,000
Average: £14,400
Restoration: £6000

*Early 500s 20% less, AMGs significantly more

Mercedes-Benz SEC (C126) history

1979 W126 S-Class saloon introduced

1981 380SEC announced in September alongside the 500SEC, which boasts 231bhp, 299lb ft torque, 7.9 secs 0-60mph and 142mph

1985 Facelifted bumpers, side mouldings and alloys; electronic ignition added in KE-Jetronic; 420, with 215bhp and 135mph top speed, replaces the 380; 560 model joins the range; 500 is increased to 242bhp and 143mph

1991 Production ends

The owner’s view

Owner Tomasz Byrtek has so far spent about £15,000 on his 500SEC

Tomasz Byrtek has owned his 500SEC for three years: “I paid £2000 for it as a project; it had only done about 100,000 miles and I drove it back from Twickenham to Liverpool. Restoration was going to be a slow process but, once I started, I couldn’t stop!

“I’ve spent around £15,000 so far: I’ve rebuilt the bodywork and had it resprayed, replaced the interior, the dash wood, the suspension, and fitted a custom exhaust and wheels. Parts are getting hard to find and can be expensive.

“I’ve stripped a few for spares and, in return for helping me, I’ve helped Mark at Mercedes Classic Parts restore a couple. I’m never satisfied: I’ll be fitting new discs and calipers and it’s going to Poland in October for a complete £6-7k engine rebuild. I do love my SEC!”

Also consider

BMW 635CSi (left) and Jaguar XJ-S are alternative buys

BMW 635CSi

More sporting, the great-looking 635CSi is now highly sought-after, particularly the high-value M model. But beware of rot and neglect, which bring big bills.

Sold 1978-’89 • No. built 86,216 (all 6s) • Price now £7500-50k

JAGUAR XJ-S

Great value new and now, the V12 XJ-S was quicker, thirstier and as refined as an SEC, but lacked the Merc’s build quality. Few have been maintained as they should.

Sold 1975-’96 • No. built 115,413 • Price now £5-20k

Mercedes-Benz SEC (C126): the Classic & Sports Car verdict

They’re not as cheap as they once were and can be expensive to restore, but find a good SEC and you’ll have a wonderful classic

A few years ago you could pick up a Mercedes SEC with a valid MoT for less than £1000. Most cars bear the scars of those days, when low values often led to owner neglect.

With prices now on the rise, fewer examples are being broken for spares and used parts will soon be gone. New parts are expensive, so buy a project at your peril: the highest-priced car you find may in fact be the best bet in the long run, financially.

FOR: Built to the highest standards and immensely durable, a good SEC, given proper maintenance, will give decades of reliable service

AGAINST: A neglected SEC will drain your wallet faster than its fuel tank, with rust repairs and replacing missing, worn out and damaged parts

Mercedes-Benz SEC (C126) specifications

Sold/number built 1981-’91/74,060
Construction steel monocoque with aluminium bonnet and bootlid
Engine all-alloy, single-overhead-cam-per-bank 3839/4196/4973/5547cc V8, with Bosch K-Jetronic (1985-on KE-Jetronic) fuel injection
Max power 201bhp @ 5250rpm to 296bhp @ 5000rpm Max torque 232lb ft @ 3250rpm to 335lb ft @ 3750rpm
Transmission four-speed auto, driving rear wheels through a limited-slip diff
Suspension independent, at front by double wishbones, coil springs, telescopic dampers, anti-roll bar rear semi-trailing arms, coil springs, telescopic dampers (optional hydro-pneumatic self-levelling struts)
Steering power-assisted recirculating ball
Brakes servo-assisted, dual-circuit 111/5in (284mm) ventilated front, 11in (279mm) solid rear discs, with ABS (fronts later 114/5in)
Length 16ft 11/3 in (4910mm) [US 16ft 71/5in (5060mm)]
Width 5ft 111/2in (1816mm)
Height 4ft 71/2in (1407mm)
Wheelbase 9ft 41/5in (2850mm)
Weight 3494-3858lb (1585-1748kg)
0-60mph 9.8-6.7 secs
Top speed 130-155mph
Mpg 17-25
Price new £36,255 (420) / 40,400 (500) / 49,700 (560)