MB380SLC
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- May 15, 2009
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- Your Mercedes
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Having discovered that my seat back restraints were not working, I set off on an adventure of finding the route cause. These, together with the central locking system, are operated by a vacuum pressure system consisting of colour tubes, connectors and four non-returning valves. The “heart” of the system is in the corner nearside front wing against the bulkhead, where all the tubes converge. (Pictures 1&2). Note there are four non-returning valves (blue and black) for each system. These are prone to wear out, but you can check them by consecutively blowing or pulling air through; clearly they are meant to work in a single direction (the black end) Picture 3. If any are faulty they should be replaced and maybe the root cause of the problem.
First we identify the tubes by colour codes as follows. Some cars may have different ones, but below are the ones applicable to my car.
Blue lines Operates the seat back restraints. Under each seat are two pairs of bellows, which when vacuum is introduced, moves the locking mechanism into place. (NB This will only happen when the engine is running and the doors locked). For a detailed diagram of the seat restraint mechanism look at http://www.detali.ru/cat/oem_mb2.asp...SGR=165&SGN=04
Yellow and Green & Yellow and Red lines Operates the central locking system (doors, bootlid and petrol lid). The diagram for this is http://www.detali.ru/cat/oem_mb2.asp...SGR=045&SGN=02
Purple lines Operate the headlamp adjustment mechanism when fully or partially loaded and again the detailed diagram can be seen at http://www.detali.ru/cat/oem_mb2.asp...SGR=015&SGN=01
Note the lights have their own reserve tank under the wing on the passenger side.
The fifteen spheres that comprise the vacuum reservoir tank is located under the front off side fender, above the wheel and normally holds a charge for about 4 hours if working correctly. The vacuum reservoir is charged from the inlet manifold, so if the headlamps and locking are not working, the engine pipes are the place to start looking, you can check the vacuum in any pipe when the engine is at idle by putting your finger over the end or by using a pressure gauge. However, if no vacuum is being held in the reserve, it’s not disastrous, as the vacuum created by the inlet manifold will be enough to run the system anyway.
The Black and Yellow is the line to the vacuum reservoir.
It should be noted that diesel models have separate vacuum pumps and a separate note for diesels is available on http://northernresource.com/mercedes/107-vacuum.htm
So now to get down to finding that leak(s). You’ll need a vacuum pump which can either be purchased through http://www.mityvac.com/pages/products_hvpo.asp
for about £65 or get lucky on Ebay as I did and purchase one of these US made ones as in picture 4. It is also quite useful to have a pressure gauge (picture 5). But you will find plastic golf tees more than useful in blocking up those lines while you go testing individual ones for leaks, so equip yourself with a few of them.
Identify the line that serves the vacuum pressure reservoir and disconnect it and plug the connector with a golf tee. Similarly eliminate the central locking and headlight lines, so that you are only left with the BLUE lines connected in a loop. All open connectors should be blocked off with the golf tees. You might want to go a bit further and isolate a single seat. Making sure the doors are closed (because the blue line is also connected to the light switching mechanism) with the seat restraint forward, start the engine to see if the locking mechanism at the base of the seat moves forward. If not, then there is a leak, either in the lines feeding it or the twin diaphragms under the seat. After checking the lines (you will have to remove the metal covering the wires on the door sill) and taking out the T tubing supplying the seat (picture 6), block off one end, whilst creating a vacuum with the pump on the other end (picture 7). If the mechanism doesn’t work after this, then there is a leak in the diaphragm(s) (top right hand side of picture 8, which will require you to take the seat out, isolate and repair. The most common fault is that the blue line comes away from a connector under the seat (picture 9). In my case, the rubber on the diaphragm had come away from the mechanism, so had to be replaced. I also found two small leaks in the rubber forming the diaphragms which had to be repaired with rubber compound.
In picture 10 the vacuum pump shows holding good pressure on the Purple line that feeds the headlights. You can go through each system testing with the hand pump. In order to find a leak you will need to test before and after each component until no leaks are present. A small leak will affect the overall system, so it is worth doing this job methodically paying attention to detail.
I hope the above helps someone else in finding fault with the vacuum system of their SL model. Good luck and happy motoring.
NB The author does not assume any liability based on the information provided.
PS I'll try and put the remaining pictures up separately after posting this.
First we identify the tubes by colour codes as follows. Some cars may have different ones, but below are the ones applicable to my car.
Blue lines Operates the seat back restraints. Under each seat are two pairs of bellows, which when vacuum is introduced, moves the locking mechanism into place. (NB This will only happen when the engine is running and the doors locked). For a detailed diagram of the seat restraint mechanism look at http://www.detali.ru/cat/oem_mb2.asp...SGR=165&SGN=04
Yellow and Green & Yellow and Red lines Operates the central locking system (doors, bootlid and petrol lid). The diagram for this is http://www.detali.ru/cat/oem_mb2.asp...SGR=045&SGN=02
Purple lines Operate the headlamp adjustment mechanism when fully or partially loaded and again the detailed diagram can be seen at http://www.detali.ru/cat/oem_mb2.asp...SGR=015&SGN=01
Note the lights have their own reserve tank under the wing on the passenger side.
The fifteen spheres that comprise the vacuum reservoir tank is located under the front off side fender, above the wheel and normally holds a charge for about 4 hours if working correctly. The vacuum reservoir is charged from the inlet manifold, so if the headlamps and locking are not working, the engine pipes are the place to start looking, you can check the vacuum in any pipe when the engine is at idle by putting your finger over the end or by using a pressure gauge. However, if no vacuum is being held in the reserve, it’s not disastrous, as the vacuum created by the inlet manifold will be enough to run the system anyway.
The Black and Yellow is the line to the vacuum reservoir.
It should be noted that diesel models have separate vacuum pumps and a separate note for diesels is available on http://northernresource.com/mercedes/107-vacuum.htm
So now to get down to finding that leak(s). You’ll need a vacuum pump which can either be purchased through http://www.mityvac.com/pages/products_hvpo.asp
for about £65 or get lucky on Ebay as I did and purchase one of these US made ones as in picture 4. It is also quite useful to have a pressure gauge (picture 5). But you will find plastic golf tees more than useful in blocking up those lines while you go testing individual ones for leaks, so equip yourself with a few of them.
Identify the line that serves the vacuum pressure reservoir and disconnect it and plug the connector with a golf tee. Similarly eliminate the central locking and headlight lines, so that you are only left with the BLUE lines connected in a loop. All open connectors should be blocked off with the golf tees. You might want to go a bit further and isolate a single seat. Making sure the doors are closed (because the blue line is also connected to the light switching mechanism) with the seat restraint forward, start the engine to see if the locking mechanism at the base of the seat moves forward. If not, then there is a leak, either in the lines feeding it or the twin diaphragms under the seat. After checking the lines (you will have to remove the metal covering the wires on the door sill) and taking out the T tubing supplying the seat (picture 6), block off one end, whilst creating a vacuum with the pump on the other end (picture 7). If the mechanism doesn’t work after this, then there is a leak in the diaphragm(s) (top right hand side of picture 8, which will require you to take the seat out, isolate and repair. The most common fault is that the blue line comes away from a connector under the seat (picture 9). In my case, the rubber on the diaphragm had come away from the mechanism, so had to be replaced. I also found two small leaks in the rubber forming the diaphragms which had to be repaired with rubber compound.
In picture 10 the vacuum pump shows holding good pressure on the Purple line that feeds the headlights. You can go through each system testing with the hand pump. In order to find a leak you will need to test before and after each component until no leaks are present. A small leak will affect the overall system, so it is worth doing this job methodically paying attention to detail.
I hope the above helps someone else in finding fault with the vacuum system of their SL model. Good luck and happy motoring.
NB The author does not assume any liability based on the information provided.
PS I'll try and put the remaining pictures up separately after posting this.
