Mercedes-Benz 250SL

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Mercedes-Benz 250SL

1966 - 1968
6 cyl. overhead cam, mechanical fuel injection
2496 cc
150 bhp
4/5 spd. MT / 4 spd. AT
Top Speed:
124 mph / 200 km/h
Number Built:
5 star
Mercedes-Benz 250SL
Reviewed by Unique Cars and Parts
Our Rating: 5


Although many changes were made throughout the life of the M129 SL body shape, the major changes were only to be an increase in engine capacity - and although the 250SL's power was almost identical to the 230SL, its larger capacity motor did have more torque. Safety improvements also led to 4 wheel disc brakes being fitted and a softer "pressure absorbing" steering wheel being fitted.

The 250SL was only in production for one year, and was soon replaced by the larger engined 280SL. This has lead to some debate amounst Mercedes fans as to which model is the more collectable, the superior performing 280SL or the low volume 250SL. Certainly from a rarity point of view, the honours must go to the 250SL.

Owning a Pagoda

Some of the most popular classic cars going today are the "Pagoda Roof" 230SL, 250SL and 280SL sports coupes. These are of course not as scarce as the earlier 300SL's nor as valuable (especially in the case of the "Gullwings") nor are they as thirsty as the 107 model which succeeded them. Thus they can make excellent choices for the Mercedes fancier, even if they come at a price. The Team @ Unique Cars and Parts have been keeping a keen eye on prices - and they are inevitably going up. The Pagoda, provided you are prepared to look after it, makes a brilliant long term investment.

Of course these later cars lacked some of the outright sportiness of the legendary 300SL, and some motoring enthusiasts were, understandably, disappointed by the new car. But for space, comfort and roadholding the later car was a definite improvement, while its classically simple but elegant looks were instantly appealing. That this Mercedes-Benz coupe has stood the test of time so well that its styling is as fresh and clean today, nearly twenty years after it was first shown, is a remarkable testimony to good design.

It Started With The 230SL

The 230SL was the first of the Pagoda's, first shown at the 1963 Geneva Show and it used chassis components similar to those of the 220S and 220SE saloons of the period. The rear track of 4ft 10.5in was identical but the wheelbase, naturally, was shorter at 7ft 10 in. The same front double wishbone suspension was used, with the single-joint low-pivot swing axles for the independent rear end common to Daimler-Benz products at that time. The wheel size went up an inch to 14 inches, which in conjunction with a higher axle ratio gave more relaxed cruising with a 19.6 mph per 1000rpm final gearing.

The 230SL's 2306cc engine was obtained by increasing the bore of the 220 by 2mm. A six plunger fuel injection pump fed nozzles in the cylinder head ports and the compression ratio was increased to 9.3 to 1 - high for the time. Although 170bhp was quoted, its true output was probably more like 150bhp. Otherwise, this six cylinder unit had overhead valves operated by a single chain-driven overhead camshaft via bucket tappets, but at this time the crankshaft was carried by only four main bearings.

Although a manual gearbox was available, most SL's exported by Daimler-Benz were equipped with the four speed automatic gearbox with fluid coupling - although the later, improved torque converter gearboxes came with the 280 saloons, this was never fitted to the SL's in this series which finally ended in February 1971. So too, though a rather heavy and low geared manual steering was available, the optional extra power steering was generally preferred making it, probably, the first sports car to be so equipped. Clearly one of the model's most delightful attributes was its adaptability. Originally the 230SL was offered as a roadster or a closed coupe but, again, most cars delivered to export markets came with the most desirable option of the three, a hood and a removable hardtop. Thus, during the summer months, the owner could enjoy fresh air, with the hood available as protection from showers, but in the winter fit the hardtop which had the added advantages of improving visibility and enhancing the lines of the car generally.

A New Engine For The 250SL

If the body was to remain essentially the same throughout the life of the model, the engine was subject to revision. Four years after the initial launch, and again at Geneva, the 250SL took a bow. A new cylinder engine with seven main bearings for greater refinement was the order of the day and the stroke increased from 72.8mm to 78.8mm bringing the capacity up to 2496cc. Other changes saw the rear drum brakes of the 230SL's replaced by disc on the 250, while vestigal rear seats were fitted on the coupe model. Barely nine months after this, the engine was bored-out to 86.5mm to create the 280SL. Many believe this to be better than the engine fitted to the 250SL, mainly because of the extra power and greatly improved torque. Around town there was not much between them, but on the open road the larger capacity engine made the SL more flexible and easier and more restful to drive.

Even a motor car as superbly engineered as a Mercedes-Benz 250SL cannot be expected to be faultless. If you are considering buying one, be prepared to spend money on it unless it has undergone a thorough restoration within the previous decade. It should also be said at this point that the SL's were expensive playthings when new, so if you fancy yourself as a playboy, or playgirl for that matter, you must be prepared to treat the car in the manner to which it should have been accustomed. That means, inevitably, that servicing and parts will be greater than for a Morris Minor, but they are nowhere near as horrific as popular legend would have you believe. The main advantages, though, are that the car is made to last, made to be used hard, and when you do need parts, even body panels, they are available from the factory. And that really is a plus point.

Measuring carbon monoxide output from a cars

Bodywork and Chassis

Such is the truly excellent build quality of the SL's, and indeed all Mercedes-Benz products from the 1960s, that corrosion problems are minimal on any but the most poorly cared-for and abused examples. Less remembered these days is how rust would devour a car from this era - unless that car was fibreglass. Mercedes-Benz cars were different. As well as the metal of the basic shell, the paintwork and bright metal was also of above average standard with very good lasting qualities.

But inevitably with time, even the best engineered metal objects will rust - and that goes for the 250SL. If you are buying one, or simply keeping an eye on your pride and joy, places to watch are along the seam on the top of the front wing, its inner panel, the sills (inevitably) and the corners of the boot floor if the rubber seals have been letting water through.

On poor examples the box section just behind the radiator can rust and, more seriously, the chassis by the rear axle mountings. Of course you might be prepared to take on a poor example at a lower price and carry out a full-scale restoration, but those not wishing to do this and opting to pay the full price for a good condition car would be well advised to take with them a magnet. The high prices and desirability of the model brings out the worst in some people, and some good looking SL's may just be full of skillfully applied "bog". You do not want to pay over the odds for a full-scale rebuild that you had not budgeted for.

If your SL does need work done, then body panels are still available. But one of the more expensive to replace are the front headlight and rear tail-lamp assemblies. If you are considering the purchase of an SL, then we would recommend you also commit to keeping an eye out for second hand lights if only to keep as spares. Another item becoming scarce as well as expensive is the chrome trim, but there's nothing to stop you having it re-chromed by one of the many specialists. Also the strip of wood veneer on the fascia, particularly in open cars, may deteriorate with age but can be refurbished by the amateur quite successfully. The hood, naturally, should be checked for tears and for proper operation and the hardtop for a good fit and A1 condition seals, otherwise leaks and wind noise will result.

Engine, Gearbox and Back Axle

The engine was designed for a long life and plenty of hard use, and bore life was in the 80-100,000 mile region, though most went well beyond that figure. The four bearing crank found in the 250 (and also the 230SL) may need a regrind and new bearings before bore wear reaches the embarrassing stage. The oil pressure gauge is slightly pointless as the needle shoots up to the maximum 45psi reading upon starting up the engine and there it should stay at all normal running speeds. Suspect anything less even when warm at above 1,500rpm.

Unfortunately this model tends to be a second car or used for short journeys, which can do more harm than good and lead to a more rapid bore wear than is correct. A good "thrash" every now and then is said to do wonders! However when the dreaded day comes that an overhaul of part or all of the engine is necessary, then prepare for bill shock. A top overhaul with new valves, freshly cut seats, and the cylinder head skimmed will be expensive. A set of new pistons will set you back about the same amount, while if you are unlucky enough to require a short block, you can double the cost.

The SL Fuel Injection Pump and Gearbox

Fortunately the fuel injection pump has a very long life, about the only problem being that the pump rack can stick causing over-rich running. The unit can be overhauled if there are any problems - the only difficulty is finding a mechanic capable of doing the job. As with the engine the gearbox is a reliable unit in automatic form. It has four speeds and is of the fluid-coupling type - the torque converter gearbox was not fitted to this model in some export markets. Ask any SL owner and they will tell you the gearchanges are not the smoothest around but there should not be any shocks transmitted.

Naturally a check should be made for leaks, and a good test for whether the box may need an overhaul is to remove the dipstick and smell it. There will be a quite distinctive smell of burning in the oil if the news is bad. Of the rarer manual boxes there are both four and ZF five speed versions, with the latter being the most desirable for long-legged cruising. However parts for it are more difficult to obtain and pricey, when you can get them. There are rarely, if ever, problems with the back axle which is extremely robust. Just watch for excessive leakage.

Suspension, Steering and Brakes

The front suspension is generally trouble-free, but problems can arise from faulty servicing, especially if this has not been carried out by an approved agent. Often missed are the two grease nipples on the top wishbones. If the top knuckles have been starved of grease they will usually squeak when the front of the car is pressed down or the car goes over a bump. In bad cases a whole wishbone assembly may be needed. The bottom knuckles can seize too, but are easier to deal with. The trackrod ends are not adjustable. Kingpins and bottom bushes can be checked with a jack under the wishbone to take the weight off the car.

At the back end, two bushes on the swing axles can wear and make for strange handling through rear steer effect - the tyre lever check is really the only way if you are not sure. Front back suspension is aided by telescopic gas-filled shock absorbers manufactured by Bilstein or Fischel & Sachs and should be watched for excessive leaks (they all weep a bit) and changed when no longer functioning properly. There were a number of proprietory makes of shock absorber around too and if these are fitted there is no real problem.

On the steering is a damper - like a small shock absorber - which should be checked for leaks and efficiency. Failure here will transmit an unacceptable amount of road shock through to the steering wheel. The steering box and pump have a very long life being permanently lubricated - just watch for leaks again. The brakes on the 230 had adjustable rear shoes, but those on the 250 (and 280SL) had an all-disc system. The hydraulics are tandem operated, and Mercedes-Benz recommend annual renewal of fluid for maximum efficiency.
Mercedes-Benz 250SL
Mercedes-Benz 250SL
Mercedes-Benz 250SL

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Also see:

Mercedes 250SL Specifications
Mercedes SL Heritage
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