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Mercedes-Benz SL R129

Mercedes-Benz SL R129 Published: 29th Jan 2018 - 0 Comments - Be the first, contribute now!

Mercedes-Benz SL R129
Mercedes-Benz SL R129
Mercedes-Benz SL R129
Mercedes-Benz SL R129
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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 your car for years to come

A lot more sophisticated than the R107 it replaced, you can still do a lot to a R129 at home with little more than basic tools and knowhow. Apart from being excellent value, there’s a good number of R129 specialists around dealing in new and good used parts to keep costs containable. Also, check out the many forums such as Kent-based R129. com, R129 for latest parts and accessories from the US and

Engine output

Mod/h5> An AMG derivative of the M104 was offered in the C36 and rare E36 AMG. If you could find one, in a breakers, the entire combo should fit and mate with existing electronics, for 280bhp. A simpler tweak is to fit a crank pulley from Elbe Engineering – reported to have a notable benefit once the stock ECU self adapts around the new parameters. Price is from £800, at
Mend/h5> All can take it easily but six pots aren’t exactly popular for tuning as if you need pace the V8 is obvious route although you can speed a six up a little by ancillary upgrades such as performance air filters, sports exhausts and an ECU reboot. Try Superchips or, better still, Mercedes specialist Celtic Tuning based in Cornwall (.(JavaScript must be enabled to view this email address)).

Bottom end

Mod/h5> While the option of forged piston and con rods are available; try, there’s little else that can to be done to improve the bottom end of the straight six and V8 apart from the usual overbore. Fresh, quality coolant is essential to avoid premature internal corrosion.
Mend/h5> The (M119) engine that powers the V8 500SL is the sturdiest of them all and is generally fine so long as the timing chains are kept well serviced. The straight six engine suffers from the typical weeping head gasket probs. Oil leaks are a major problem on V12 cars, particularly the front cover; if left unattended it will soak the right side of the engine ruining the alternator and any coolant or air hoses in the vicinity over time.

Front suspension

Mod/h5> Bilstein sells upgraded B6 dampers suitable for AMG versions of the R129, but there’s no reason why the smallerengined variants can’t benefit too. A £700 spend buys a pair from Larkspeed Performance Centre, while DC Performance sells a combined and mated set of front and rear lowering springs for £402.34; don’t go overboard advise Merc specialists.
Mend/h5> Front shocks and wheel bearings are prone to become noisy with age and miles, while tired anti-roll bar and steering idler bushes are known to lead to a feeling of sloppiness; even stock replacements and let alone uprated items will tighten the feel up again. Front springs have been known to break – always replace in matched pairs either new or used.


Mod/h5> Brabus markets upgraded steering angle limiters for fitment with especially wide wheels, to prevent them from rubbing against the inner wheelarches. Smaller aftermarket steering wheels may be of help if you feel that the power steering is a little too light for your tastes although there may be airbag (thus insurance) issues so check first.
Mend/h5> As with most Mercs of this era, the R129 uses a steering box rather than a rack-and-pinion arrangement. These can wear and become sloppy, but this can be rectified. It’s not a DIY job unless you know how, as over-tightening the box can cause internal damage. The steering damper is often worn, check before you touch the steering box.


Mod/h5> Some late SLs had five-speed (722.5) autom, and it’s possible to retrofit this to the earlier four-speeders; £1500 should secure from www. for example. This will give better acceleration and cruising, owing to the improved ratios plus open options for other axle ratios for smarter pick ups. Pelican Parts has new bushes to cure sloppy selector action, a cheap fix.
Mend/h5> Mercedes automatic boxes (by far the most common) are long lived, though treat to a flush and refill of Dexron 3 as a basic first move. It’s surprising just how few autos ever get the fluid changed, and yet it will dramatically improve the shift quality. If you get a rare manual, again and the service history is patchy, change the gearbox oil sooner rather than later.


Mod/h5> Europerformance offers a big brake conversion kit, from £2278 for the fronts and a further £1978 for the rears. While these won’t be necessary for UK-legal road speeds, they may be worth it if you plan track work featuring 10 pot front calipers and six pot rears, with 340mm front discs and 330mm rear discs. Otherwise start with EBC wares.
Mend/h5> For the majority of SLs, refurbish the original calipers rather than spend unnecessary money replacing – it’s just as good, but cheaper. Some owners report of a soft brake pedal feel although they work fine. Changing the pads with quality OE spec plus a full bleed is said to help and you further improve matters by fitting braided brake lines which are stouter.

Rear end

Mod/h5> Uprated rear springs are available, as are Bilstein B6 shock absorbers for the back. Bank on £400 for a pair of B6s. Couple this with the full suspension refresh listed below and the rear end should be usefully tighter than factory spec although specialists warn it’s easy to mess things up with mix and match parts and make the car handle worse than before. What can make the car better all round is breaking the bank on quality tyres and a full chassis geometry realignment.
Mend/h5> Rear control arms and bushes wear put, and usually lead to a feeling of looseness. This wandering is difficult to identify when casually inspecting the rear end, so why not do it as a precaution rather than waiting for obvious probs? Delphi kits are available for under £250. Biggest concern is the special Adaptive Damping System, where fitted, which features involved hydraulics and though usually reliable, is expensive and technical to repair.

Body and chassis

Mod/h5> In common with many other Mercs, there’s no shortage of custom bling for this car although are a matter of taste and certainly can affect resale values if done wrongly. AMG’s bodykit was factory approved and you may find one from around £1500 second-hand, but there’s plenty of other choices on the market for less including replica stuff although quality varies.
Mend/h5> Rust may be an issue – after all, the earlier SLs are now almost 30 years old plus that famous build quality was starting to slip a bit by then. The bulkhead ventilation plenum chamber is said to be a major issue as it can rust out, leading to major water leaks into the front foot well area. Wheel arches front valance (where there’s box section that’s particularly vulnerable) deserve regular checks.


Mod/h5> There were plenty of options available throughout the R129 range, from full leather to heated seats, uprated radios, and special interior colours as part of the Mercedes Designo range. Any of these items sourced from cars being stripped, or from eBay, will make your SL even nicer.
Mend/h5> Second-hand trim isn’t too difficult to source from specialists. Hoods are triple lined, automatic and very costly to replace – like the thick end of £5000. The roofs for all R129s are not entirely interchangeable as later models have a much larger seal around the A-pillars and surround.

And another thing…

Check the wiring loom periodically, because on pre-1998 cars they were biodegradable and as a result their dialled in ageing can lead to unusual electrical quirks affecting performance and driveability. New looms can cost up to £1300, but if you’re good and experienced with wiring you can repair them or fit a new one yourself but it’s not for the novice. On the other hand if you intend on keeping the car, then it’s not a bad idea to have this done as preventative maintenance. Finally, if you’re not yet a member then do join the official Mercedes-Benz Club, the oldest one in the World as help from fellow members can save you a lot of time, money and aggro plus there’s a fine social scene into the bargain.

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