Tips & advice



Never be tempted use inferior parts on these cars, they simply do not work as well and and can cause long term dammage.

If you do not want to go to mercedes for filters etc use Mann filters, they were standard fitment on Mercedes for many years and are a superior product. Always use Bosch spark plugs, they are not expensive and work the best in these engines.


These cars were designed to use.....they do not generally like short trip, start stop work and being unused for long periods. For this reason it is always a good idea to take them out on a decent long run from time to time to "clear them out" and "stretch their legs".

Sun roof

If there is one job i really really hate doing it's repairing sunroofs on these cars. The problem lies not just in repairing the workings of the roof but in disturbing the roof lining and trim which due to it's age often falls apart and seldom goes back according to plan. Old cloth, old glue = DISASTER AND EXPENCE.

The earlier cars up to 1986 had a relatively simple sun roof mechanism, the 1986 onward cars had the tilt facility with a much more complicated mechanism which now these vehicles are getting older cause problems such as slow operation and sticking.

The easiest thing to do is take the roof all the way back as far as it will go thorougly clean all the runners and use a light spray grease on the contact areas, work the roof backward and forward and repeat the process if necessary.

If this does not work...purchase a large industrial welder and weld the roof shut , but please i beg you , do not bring the car to me :-) evil grin !

Seats and Seat Switches

It is very unusual for the electric seats to stop working and it is seldom the fault of the motors within the seats. In most instances the problem lies within the door mounted seat switch itself. As these switches get older certain parts of the swich will become dirty internaly and stop working. Most of the time these switches can be stripped and cleaned internaly and this cures the problem. This job is not for the feint hearted and should be left to someone with experience.

Drivers seats are prone to collapse and can be repaired, the seat will require removal, the base cushion removing and repairing from there.

Water ingress into the font footwells

I often get worried customers telling me they have spotted large amounts of water collecting in the front footwells (normally passanger side on right hand drive cars)

Under the front dash panel behind the radio speaker is a body seam which for some reason always seem to rust and split open. This allows rain water that is normally collected at the base of the windscreen and discharged by means of srategic drain tubes enter the car. It is very difficult to get to and repair.

Another side effect of this is to fill up the relays that contol the heated seats (where fitted) with water and fuse them, this in turn can, and does switch the heat seats on when the car is not being used which kills the battery. These relays are placed under the front seats and sit flush with the floor pan making them an easy target for water.

Boot Area

Sec's are well know for rust problems in the boot/rear screen area. This is caused mainly and nearly always in my experience by rear screens not being regularly re sealed. When these screens are fitted they are usually fitted with new rubber seals which are soft and pliable thus giving a better chance of sealing. As they get older they harden. On top of this a small amount of sreen is sealer applied in tube form should be used (not silicon).

As the boot wells are covered with carpet and trim it is not always possible to see the water collecting under them, usually a good indication is condensation build up on the underside of the boot lid. Boots need to be kept dry or irreversable dammage will result in a short space of time. Remove boot well side carpet trims and check boot drains are unblocked.


Heres is a good tip, when changing a wheel, use the wheel pin tool that should be in the original tool kit. (if it is not there buy one and place it in your glove box, they are cheap) This small pin screws into the hub so that the whell can be guided onto the hub without spending ages trying to align the wheel bolt holes.We use 2 at a time in our workshop and it makes replacing wheels a breeze especially if you have oversized or aftermarket wheels.

Tyre pressures

The correct tyre pressures can be found at a glance inside the petrol flap as in most Mercedes. Keeping the pressures correct will make a difference in fuel consumption, these are heavy cars.


We are often asked how to check the transmission fluid level.

The level is always checked with the engine running and in park on a level surface. There are two distinct marks/lines on the dipstick, the lower is the cold level and the upper is hot.

When adding oil it is important to remember that it is easy to obtain a false reading due to oil still travelling down the dipstick tube so it is advisable to wait until it has settled.

It is most imprtant that these levels are correctly maintained, as it will affect the shift points and the harshness of the shift.

Seat belt presenters

There are several reasons for belt presenters not working, it is unusual for the presenter itself to be faulty although the gear drives sometimes strip. Gears can be replaced seperately and when faulty make a loud whirring sound.

For the most part it is usually the relay fitted to the rear of the presemter that is at fault, these can be costly from Mercedes so diagnosing the problem correctly will save you money. Swapping relays from the other side can often help.

Windows and motors

Window operation becoming very slow on these cars is often blamed on the window motors but for the most part we have found it is the runners/guides inside the door poorly adjusted/worn or simply a build up of moss and dirt in the top door to glass seal, this also causes the vertical scratches you often see on the SEC side window glasses.

Car cutting out ?

Non start or cutting out on the 126 model is in most cases due to the following reasons :-

1 Fuel pump relay. (causing intermittent start and stop), normaly located next to the fuse box on RHD. Tapping this relay can sometimes cure the problem short term ( get home) as they suffer from dry internal joints on the circuit board) it is possible to repair them but as they are not expensive , new is a good bet.

To be safe, always keep one of these relays in the glove box as a spare, they take seconds to fit and can save you time and money.

2 Ignition Module. This unit (bolted to the right hand front inner wing) never usually gives much warning of impending faliure, it overheats internally and just dies, (loosing ignition spark). It will need a replacement unit as these are not generally repairable. When replacing these units it is imperitive to cover the base of the unit with hear sink paste.

3 Crank position sensor. This is the main pick up sensor that leads from the ingnition modle (above) to the flywheel. This is quite a hardy little sensor and they fail in my experience very rarely, again causing no spark.




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