Prevention is better than cure


They do say that prevention is better the cure, when you own a Mercedes-Benz 'A' Class its also cheaper! and here is a typical example of where they can be true.
The vacuum pump for the central locking is situated in the left hand corner of the boot (rear Compartment ) by the spare wheel It also sits in a recess which is lower than any other part of that surface which means that should water get into your rear compartment it will find its way into the well that the pump is located in.
'Arh' I hear you say but my car doesn't leak when it rains ! It doesn't have to, Mercedes -Benz have put a joint in the pipe work of the rear screen wash that is notorious for coming undone , with the result that whenever you operate the screen wash the water screen wash fluid runs down inside the 5th door and finds it's way into the well
Over time the fluid collects and the pump sits in fluid (water & screen wash ) which causes severe damage to the pump , so much so that it eventually packs up and the central locking ceases to operate , Although the unit is easily replaced it is an expensive item, so get yourself a polythene bag without holes, lift the pup from the well taking care not to damage the small hose connections place the pump into the polythene bag and re site it in the well, either trim off any excess polythene or fold it down in such away that it remains above the level of the recess(well ) any fluid no finding it's way into that area will be outside the bag and not cause damage to the pump. When you clean you car just just a few minutes to check that fluid is not getting into the boot area. it will save you a lot of agro in the future and cost.

For repairs to the rear screen wash hose. main page(24)

This is what you could be faced with if you do not listen to the advise given!


This information and photographs were received from Eddy a fellow owner of an 'A' Class which as you will see had severe problems caused by water getting to the vac pump.

Central Locking Pump dis-assembly


Here's one sorry looking pump.


















Note the line up of the rounded groove all the way down the nylon and ceramic body.
















Remove the three screws from the bottom end.


















Note the four rectangular "slides", these move outwards due to centrifugal force to create the suck and blow. The second outer ring comes off. Remove the four slides ... don't lose them.















I was then stuck as to how the rest came apart but as you can see the top "key" appears to be an interference fit on the semi-circular spindle end and I managed to gently lever it off by carefully inserting feeler gauges between the rotor and the back plate, then gentle persuasion with a couple of screwdrivers helped to ease off the top. The rotor then pulls off the spindle.












This is the reverse of the last ceramic back plate. You may find it has sealant to glue it to the metal plate. Note the two "o" rings These seal the nylon inlet/outlet tubes on the nylon body. Place them into the back plate as it will be easier to fit later. The middle recess holds the bearing.












Note which way the bearing sits when removing it. Also see the two "o" rings ... don't lose them. Remove the two screws that holds the metal plate to the motor body.















The metal plate may come away with the nylon outer casing, it may also have sealant to hold the two together. I didn't do anything with the top end of the motor (brushes etc) from the bearing which fell into the motor body.













Here's my bearing .... well stuffed. I don't know if it was a sealed lubricated unit or solid as this appeared. I basically cleaned all the parts and re-assembled, the pump was not up to scratch and overran, this caused overheating and smoke. I purchased a s/h pump on E-bay and was fitted within minutes and all worked ok. When re-fitting ensure that no sealant gets into the "o" ring holes or the bearing. Make sure the bearing is the correct way round . Fit the ceramic back plate with the "o" rings already in situ. fit the rotor and top cap ... tap it gently in place. Fit the middle ceramic ring .... make sure that the central groove is aligned as Fit the four rectangular ceramic "slides" make sure they are the correct way round ... they should match the rotor slots and not checking that the body groove lines up. It may be prudent to remove volt supply ... I used a battery charger. It doesn't matter which way round the connections are made as it will either suck or blow. I suggest carefully securing the screws with the motor running as you can hear the motor labour if the ceramic body parts are not aligned correctly.




If you are interested here are a few pictures of the circuit board and the connector.
















The top right hand corner component is like a clockwork motor and seems to wind when moved/tapped.


















Note that there are three "o" rings which may stay in the black plastic housing or come off with the circuit board.

+12v (positive) and the control/signal wire.

















Many thanks to Eddy For the photographs and information on this page,

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