The advertising tag-line for the Mercedes-Benz SL was 'Engineered like no other car', and we reckon it's justified – especially at today's prices
Text: Richard Kilpatrick
The SL launched in 1989 with three engine options. Two 3.0-litre straight sixes - the M103 and M104 with 190bhp 12v and 231bhp 24v respectively, and the robust 32v M119 5.0-litre V8. The 300SL and 300SL-24 were available with a choice of manual or automatic transmissions, the 500SL shipped with an old-tech four-speed automatic only. In 1992, the V12 600SL joined the range with the M120 48v near-400bhp engine, reinforcing the SL’s move upmarket.
As with the previous SL roadsters, the R129 shared a basic platform with the mid-range saloon contemporary - in this case, the W124 series. Featuring an advanced five-link independent rear suspension, recirculating ball steering and strut suspension up front. As a Grand Tourer, however, the SL excels - with relaxing, stable handling, perhaps the best seats ever designed (with electric adjustment including the seatbelt) and enough cabin space to carry a significant amount of luggage.
The M119 32V 500SL is responsive, with a 6 second 0-60 and a top speed limited to 155mph, yet will return around 30mpg at motorway speeds. The old-school automatic gearbox impacts urban economy.
Seen as a large car at launch, it fits into modern traffic surprisingly well, and is easy to place on the road. The flat rear deck and square cut boot, combined with either the large rear window of the soft top or the standard equipment hardtop make for rearward visibility that is the envy of most modern hatchbacks, let alone convertibles - and yes, the rear view mirror is electrically adjustable.
Straight-six models are, by comparison to the 500SL, adequate. The manual box shares a ponderous, detached shift feel with the Mercedes saloons the car is derived from, and the 300SL engines are surprisingly subdued, getting on with the job quietly. Economy is not significantly better, but you will be beaten to 60 by some very mundane vehicles indeed, particularly with the auto.
The greatest sacrifice in the straight-sixes is losing the sound of the M119 V8 at high RPM. The 500SL might be a relatively tame beast, yet it carries the heart of a Le Mans winner; the Sauber C9’s fortunes having been reversed with the update from an M117-based engine to the M119.
A PRACTICAL PERFORMER
Mercedes-Benz’s over-engineered approach extended to accepting the limitations of the folding roof. It is not a substantial, heavily lined item, and the design does include some inherent security weaknesses that are indicative of the occasional use intended for it.
The vacuum locking system, therefore, extends to the rear seat cubby boxes, the door pockets, the centre console - anywhere you might want to hide things is locked with the doors. For models without rear seats, the platform behind is large enough for a couple of typical weekend bags, the boot is large and includes space for storing a wind blocker.
All SLs have an oil pressure gauge; it should read '3' nearly all the time, it may drop to 1.5-2 when hot, at idle. If it’s low when driving on a car with under 150-200,000 miles, walk away. If the gauge is non-functional it may be a cluster or sensor, which is mounted in the oil filter mounting. Check for leaks around the sensor as well.
Pick of the bunch is the 500SL. The 320-326bhp M119 V8 is engineered to the highest standards Mercedes achieved before their mid‘90s cost-cutting phase, and it is remarkably tolerant of abuse, capable of incredible mileages, and is relatively easy to maintain. Nevertheless, the quality of the items attached to the engine varied during the car’s production run, giving rise to a few problems that can frustrate owners - particularly when seeking bargains.
Engine management and injection systems evolved, with the earliest cars using a mechanical fuel injection (K/KE-Jetronic), changing to sequential LH Jetronic in October 1992 then Motronic. Ignition on earlier cars uses two coils and two distributors, one set per bank; service items are cheap but you need two of them, a tolerable compromise. The spark controller ECU can be expensive if it has failed.
Oil starvation can cause problems with the camshafts, initially due to hydraulic lifters failing to pressurise - kits to replace the seals are available and easy to fit, if a methodical approach is taken, though plan for aged hoses and pipes cracking when disturbed and ideally replace the timing chain guides whilst the covers are off. An independent specialist will charge upwards of £500 for this job. The plastic components go brittle with age and break down; on a car with more than 150,000 miles look for this work to have been done.
Maladies common to most modern cars can also affect the earliest SLs, such as failure of the crank position sensor; the costs come from diagnosis rather than replacement and if considering any ‘90s Mercedes, a £50 code reader and 38-pin cable is as relevant a purchase as a used-car inspection.
The M103/M104 engines in the earlier (pre facelift) SLs are similarly robust, needing merely consumables and maintenance to keep running for 300,000-400,000 miles. The reliability of these units has been demonstrated in cars like the 300TE; they may not suit the character of the SL quite as naturally, but they are reliable. From 1995 the M104 was offered either as a 2.8- or 3.2-litre, before being replaced with a V6 in 1999.
Post ’93, problems can be found with wiring harnesses on all models of SL (and to an extend, all Mercedes cars). Insulation breaks down inside the loom, with many unrelated issues making diagnosis fun - the engine wiring harness for an SL 500 is £714 from a main dealer.
The V12 M120 engine not only suffers the same problems with wiring, the cost of consumables and densely-packed engine bay make regular maintenance less pleasant than the V8. The trade off for this is unparalleled refinement and a true classic, albeit one that comes with a significant premium over the V8 in purchase and maintenance costs.
POST 1998 MODELS
The 306bhp M113 V8 replaced the M119 in 1998. This twin-spark, SOHC design was all new, driven in part by DaimlerChrysler’s desire to reduce costs as well as produce a new, efficient V8; it has reverted to a quad-cam 32V configuration in current models. The M112 V6 in the 1998 onwards 280 (204bhp) and 320 (224bhp) is a variation of the M113, retaining the three-valve per cylinder twin-spark head design. Both of these engines coincide with a reduction in Mercedes-Benz's quality overall, with the increased servicing costs (12 plugs in the V6, for example) and higher initial purchase price of these younger cars makes them a poor relation in the R129’s history.
Of note, V8 and V12 AMG models also graced the R129 range. The V8 SL60, which uses a 6 litre, 381bhp version of the M119 V8 and was produced between 1993 and 1998, the very rare 1997 SL70 with 7-litre 496bhp V12 and the 525bhp SL73, which uses the same basic 7.3 litre engine as the Pagani Zonda and other AMG V12-based supercars. Finally between 1998 and 2002, the SL55 AMG was offered, with 5.4-litre M113 serving up 354bhp; a precursor to the R230 SL55 and indeed, to the greater volume AMG would enjoy in the 21st Century. SL60s come up relatively frequently, albeit with a substantial premium.
Other tuners, notably Brabus and Renntech, also offered tweaked R129s - these should be bought very much on their own merits and provenance.
Initially launched with a four-speed automatic in the V8/V12 models, an option of 5-speed automatic in six-cylinder versions, and Mercedes’ agricultural manual five-speed box as an option on six-cylinder models only, in 1996 the range was updated to receive the electronically controlled 5G-Tronic automatics.
The manual is reliable, but the simple, tough four-speed boxes are a better ownership proposition when buying at the budget end of the market - if it works when you buy the car, keep on top of fluid changes and it should keep on doing so. The 722.3 600SL gearbox was sufficiently strong that Brabus used it in their 7.3-litre V12 models unmodified!
Six-cylinder R129s got the 722.5 five-speed automatic prior to the 5G-Tronic - this is a revision of the four-speed with an electrical control for overdrive; it is still a hydraulic unit.
The five-speed 5G-Tronic 722.6 was initially treated as a sealed for life unit (including the frustrating decision to replace the dipstick with a tamper-proof cap - a red tab indicates it has been serviced, a black tab that it has either never been checked, or has only been touched by approved Mercedes service centres), which Mercedes-Benz has subsequently revised and recommended fluid changes every 40,000 miles.
There are economy and performance benefits to be had by opting for the later gearbox, but it’s necessary to be aware of leaks into the wiring loom from the electrical connector (look under the car at the multiplug, signs of dampness and residue are a useful early warning) and ideally, look for history with evidence of correct fluid and filter changes. The loom issues can cause the car to shut down whilst driving, and are an involved repair.
Drive with the roof down, and listen for noises from the rear drivetrain. Shifts on the four-speed are slurred, but swift - if delayed changes (without kickdown) or jerky downshifts in particular are present, check the oil level and for the usual burnt, brown fluid indicative of poor maintenance. The 5 speed automatic will hold the lower gears until the car is warmed up, and shifting can be more obvious under power, though any hint of slipping should be a warning.
With the manual, look for vague, notchy gearchanges. If it has them, it’s working fine. Should there be issues with the clutch, release bearing or props, look for general Mercedes specialists rather than SL ones - underneath, the car is no more complex than a W124 300E.
SUSPENSION, STEERING AND BRAKES
When looking at an R129, think 'shoes' - as the car’s values have decreased, the popularity of aftermarket rims and fake AMG rims has increased. What you are looking for are genuine Mercedes part numbers, so if in doubt, remove the wheel and look at the back; plenty of online sites can give you a cross-reference for design, finish and part number, that’s what a smartphone is for. Tyres should be an appropriate brand and rating for a 4500lb car that can comfortably achieve 150mph, skimping on these implies skimping elsewhere.
The steering is precise, but detached, a variable-rate power assisted system with recirculating ball. A worn steering damper is frequently overlooked, inexpensive and can cause vague response, vibration and wandering.
True gluttons for punishment can opt for Mercedes’ Active Dampening System. This option, standard from 1993 on SL600s, provided a CitroΫn-esque hydraulic suspension with height control, active correction when cornering and load leveling. Controlled by yet more of those ‘90s-era ECUs, the recipe for high repair bills is spiced up with the application of nitrogen spheres and a lack of specialists and experience in the UK, particularly as the cars have dropped out of the main dealer network.
Spheres are inexpensive and should be replaced every five-six years, but most problems occur with the valve blocks and sensors. For the determined and competent DIY repairer, it should be simple to maintain; for those who just want to pay for the car and enjoy it, vital components of the ADS system are four-figure modules. Naturally for UK owners you can add the delights of salt-assisted corrosion to any attempt at maintenance.
For more from the historic car world, try Octane magazine.
Subscribe today and get 3 issues for £5