Mercedes R107 SL

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Do you drive this great classic or are thinking of buying one? Here’s how to ensure that you get the best out of yours for years to come…

Built like a Mercedes should be, W107 SLs are some of the most endearing and enduring prestige classics you can own - and for remarkably low cost if you do it right. This means using genuine (or quality aftermarket) parts and letting a specialist loose periodically to make sure your DIY handiwork is okay. Well engineered, the W107 is a delight to work on. It’s also worth joining the owners’ club; the Mercedes Benz Club has strong links with the company and can handle any technical query going. www.mercedes-benz-club.co.uk, or tel: 08456032660.

Engine Output

Mod:
There’s a select range of tuning parts and the likes of Newman Cams of Kent (even though it doesn’t list Mercedes) will probably re-profi le you sportier camshafts. Plus you can have the heads professionally modified, but that’s about it. The blocks have a degree of over-boring but any tuning work is bespoke and expensive.

Mend:
Rattly V8s from cold, in the region of the nearside rocker cover box, suggest impending timing chain failure. Exhaust manifold gaskets are prone to fail and manifolds prone to their studs welding themselves to heads and breaking. Tappety sixes not serious, nor weeping head gaskets, usually, but all Merc engines seem to leak, and consume oil.

Fuel System

Mod:
Depending upon model, two types of Bosch fuel injection systems are used; Bosch; D-Jetronic up to ‘76, K-Jetronic afterwards, and this means that a limited degree of ECU chipping can be carried out to increase power and drivability.

Mend:
All are injections and are quite reliable although should still be expertly tuned; problems are usually due to poor electrics and connections, although V8s can suffer from inlet manifold air leaks and the fuel fi lter (located near the pump) is often overlooked. Rich running is usually down to throttle or temperature sensors.

Front Suspension

Mod:
As a heavy car, this naturally takes its toll on the suspension. If you’re thinking of sprucing up the suspension, speak to a specialist fi rst, as some damper makes, such as Konis it is reported, don’t seem to work too well on the car. Polybushing will make the car less refi ned but tauter and don’t forget the front sub frame bushes, which deteriorate.

Mend:
There’s a multitude of suspension joints and bushes to maintain but it’s the steering that can cause the most problems. Wear in the box and the idler is pretty common but some of the slack can be adjusted out – a specialist is best to do this. Most concerning though is the steering box breaking away from chassis leg, which mostly relates to pre ’76 models; many have been attended to by now.

Brakes

Mod:
In standard form the SL brakes are good and, for most needs, just uprated pads may suffi ce, while you can always upgrade to V8 brakes if required. A good number of specialists advise sticking with genuine M-B components.

Mend:
There are no real problems if looked after properly, lthough deteriorating front brake hoses can cause soggy pedal and lead to the brakes binding. Because irtually all SL came as automatics, this usually made the arking brake redundant and its lack of use causes the orkings to seize up. So, use yours as intended!

Transmission

Mod:
Practically every SL came as an auto but manuals were available for 280s and 350s, the latter four-speed only. While it’s possible to convert, remember that the change quality was never that precise. Autos were originally four-speed, reverting to a more reliable three-speed (‘72), before going back to four with switchable modes. Some degree of swapping is possible but speak to SL people or owners club on this first.

Mend:
Early four-speeders with fl uid flywheels give trouble. All autos have a couple of seconds delay before drive in reverse, but complete no-go doesn’t mean ‘box failure but a lose nut by the kick-down switch. Regular fl uid changing plus cleaning fi lters and pan helps.

Wheels and Tyres

Mod:
There are shed loads of aftermarket wheel and tyre combinations, so it’s best to speak to and SL expert as going large doesn’t benefi t the car but quality tyres do. Bear in mind replica Mercedes alloys aren’t as well made as the genuine articles and will corrode faster etc. A thorough alignment check can improve the handling a lot (see below) although W107s do seem to wear the outside of their tyres.

Mend:
Still on ‘genuine’ wheels, if car won’t run true even after wheel alignment it could be due to fake rims. Proper M-B ones feature fi ve small holes near centres which facilitate the factory’s steering and suspension alignment tools. Apart from toe-in, camber and caster angles are all adjustable.

Body and Chassis

Mod:
Custom parts freely available - some, notably factory-approved kits, work better than others – but hurt values, so choose bling with care. Fancy trim, such was arch fl ares are rust traps and mask rust.

Mend:
Pay attention to heater air intakes fan, battery tray, door pillars, fl oors etc. Apart from bonnets on some, shell is steel panels available from the factory and aftermarket, although some pattern parts don’t fit as well.

Interior and Trim

Mod:
Never the most inviting of cockpits there are lots of custom trim parts around, such as wood capping and steering wheels, while leather is a popular upgrade. There are also kits available to turn two-seater into 2+2s.

Mend:
Odd trim designs (and there were many) can be diffi cult to exactly replicate. Poor central locking? Well, being vacuum operated, its tank can fall away due to rusting brackets, although problems are mainly due to leaking values (behind the battery). Boot lid springs are known to weaken, made worse if a rear spoiler is retro-fi tted.

Rear Suspension

Mod:
There’s a limited range of upgrades available but, before you go harder on the suspension, remember the SL is more of a cruiser than bruiser. Lowered springs will have a dramatic effect on the ride, for example and make car hard to sell on.

Mend:
There’s not much to say here, except to say that you should look after the normal workings and host of rear bushes (including the subframe) and don’t forget the special bearings that operate the antisquat system, as these can fail and give similar traits as worn springs.

Details

The difficulty is improving an SL without spoiling it. First ensure that your car is good with a thorough service and set up by an expert – it’s surprising how much a transformation this brings, especially steering and wheel alignments. An uprated rad relieves tension of a hot traffi c jam and prevent popping a head gasket. Pre-76 cars had Bosch electronic ignition, albeit with conventional contact breaker points, and it’s certainly worth upgrading to a modern ‘pointless’ set up.