The M103 oil pressure sender can be found on the side of the oil filter housing at the back of the engine.   Most of the threads you’ll find on the various forums are referred to the W124.   Apparently on the W124 space is tight and it is a paint to remove the sender.   I can only imagine how hard it must be on the W201 then.     On the W126 there is loads of space, as can be seen in the photo.

With the right spanner, you could probably remove it with the oil filter in place.   I elected to remove the oil filter first.   It made it dead simple to disconnect the wire, and then unscrew the sender unit with a 17mm spanner.    As can be seen in the photo below, there is loads of room without the oil filter in the way.

I went with a new VDO sender.  VDO are the OEM brand.   There are also Meyle sensors availabe, which are much cheaper.  Meyle is a brand I try to avoid.   There was somebody on one of the facebook groups complaining they have replaced two sensors in as many years.  I bet they used Meyle.   Comparing the new M103 oil pressure sender, the original one was still on the car.   It was dated 7/86.   I put a new 9/19 unit on.   Still made in Germany.

Re-installation is even easier than removal.   There is a little washer that goes back on.  In my case it had remained stuck to the housing.   The new one is certainly a lot cleaner!

I then fired the car up.  I expected to see the oil pressure reading jump to three.   But it didn’t.   Instead, the pressure was the same as before.   Around the middle of the gauge after a cold start.

Clearly there was nothing wrong with my older sender.   I think my next step will be to take the car to a mechanic to hook up a mechanical oil pressure gauge.   This will eliminate the wiring, gauge etc and check the actual oil pressure of the car.

I can think of a few possibilities in order of likelihood.

• Oil pressure relief valve stuck
• Faulty Gauge
• Bad wiring to gauge or sender
• Worn Oil pump

I think the oil pressure relief valve is built into the motor on the M103, so not a quick change to see what happens.  The mechanical gauge will at least determine if there is a problem.

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1. The odometer was reading 10% low.
2. I could hear the gears, especially in cold weather.

In addition, some time after I repaired the odometer, one of the bulbs that illuminates the instrument cluster at night failed.   The fix for all these things required the removal of the instrument cluster.  The procedure to remove the cluster and the speedometer is covered in my previous article.

The low reading was attributed to having the wrong gear.   There are a few different gears based on the different W126 odometer units.    The standard gears for a KM/H cluster are both 12/48.  (12 notches on the inner gear and 48 on the outer).   On closer inspection, one of my gears was 13/48.

The 13/48 gear is the green one.     It was a simple matter to replace the inner gear that I installed back in 2017 with the green one.    The replacement gears are made of a much harder material than the original VDO gears.  This means they should be much more durable.   The downside is increased noise.   My hypothesis is that I can lubricate the plastic gears to reduce this noise.

I used a little rubber grease on the gears.  I’ll have to see how well greasing the gears reduces the noise.    While I had the speedometer out, I was able to change the bulb, which are contained in housings beside the speedometer.

Over time, the markings on these speedometer units fade.   With the speedometer disassembled like this, the original colour can be seen in markings between 50 and 60.   The needle is also supposed to be this colour.    Some people choose to repaint the needle while the speedometer is exposed.   Since all the markings are faded, I chose to leave it as is to keep them consistent.

I have not yet checked the accuracy of the odometer, but it is working and I can’t hear it so far.  I also have proper illumination when the headlights are on.

The post 300SE Odometer Repair Update appeared first on Classic Jalopy.

The most common point of failure is a set of small gears that connect the electric motor to the odometer.   They are made from a very soft plastic to ensure noise is not transmitted to the cabin.   Over time, they loose teeth which stops them from working.     Replacement of the gears is a fairly simple procedure.   There are a few different companies who can supply the replacement gears – I got mine from Garagistic.

Removal of the instrument cluster

The W126 instrument cluster is simple to remove.   The cluster is only friction fit in the dash, and unlike some models the steering wheel does not need to be removed.   The official procedure calls for two special hooks to drag out the cluster.  Some people have made their own copies of these hooks. I found it easier to remove the drivers side speaker and simply push it out from behind.    There are many different connections to the cluster, and the trickiest part is removing the ones with the least slack first.  I found this was the vacuum line for the economy gauge.  That line is friction fit into its rubber tube.

Dismantling the instrument cluster

The speedometer is removed from the rear.    The outside temperature gauge is removed first.    There are after market replacement units available although I do not know their quality.   They are available in Celsius and Fahrenheit.

Next the plastic housing is removed.   Care needs to be taken with the speedometer face and needle!   This allows access to the rear of the speedometer.    It appears that the circuit board can be removed from the speedometer, but it doesn’t easily.   Its not really necessary, as once the back cover is off, the odometer gears can bs seen on one side and their cover removed.     From here the Garagistic instructions are useful, even if they are for a BMW.

Replacing the gears

The gears are easy to remove, and my small gear was pretty much disintegrated.   The only slightly fiddly job is that there is a metal bushing that also needs to be removed as the new gears do not need it.  The first photo shows two of the three gears removed and the second shows the new gears installed.

Some people recommend some grease to ensure the gears are silent.   I didn’t have any on hand, so I’ll need to see if they are annoying and I need to remove the cluster and add some.   There was also a 4th tiny gear in the pack I didn’t seem to need.   I am not sure if this is for another model, or I missed it.   Re-assembly is simple and only takes a few minutes.

UPDATE September 2018.   The repair above worked.  However, one of the gears was the wrong ratio, causing the odometer to run low.  I also chose to lubricate the gears to try and reduce noise.   For more details click here.  I also fixed the Odometer in my 560SEC using the same procedure.

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