I’ve been slowly tidying up my W123 since I purchased it.  However, I had a couple of last things I wanted to do before the event.

Cleaning the wheel wells

The wheel wells of a Mercedes-Benz of this era should be body colour.  Many people assume they are supposed to be black.  That is mostly because they are normally so caked with dirt and grime.   Some even get painted back due to that wrong information.

It seemed like a good idea to remove the wheels and clean all the dirt and junk out.    I found a toilet brush (that hadn’t been used in a toilet) with its long handle and plastic bristles good for this task.

I had done one of them before when I had to remove a wheel, so I only had three to do.  You can see why these cars rusted out in certain climates.  In both the front of rear there are so many places for dirt and mud to accumulate.  All you need is a bit of road salt for it to eat the car from the inside out.

For example, at the rear there is a sort of ridge or lip that allows a whole bucket full of dirt to get trapped up there. This can’t be easily seen unless the wheel is off.

Removing a stain from the boot lid

I had noticed a stain on the boot lid of my car.  It looked like something had dripped onto the boot and then left a stain.  It was probably either some hard water that dripped from a parking lot, or perhaps bird droppings I had not removed fast enough.

Given there were some swirl marks in other places on the car, I though it would be a good opportunity to give the whole car a bit of a polish.   I started by masking up the rear of the car, before getting out my polisher.

The problem was, I hadn’t used it in 10 years and the fitting to attach polishing pads had perished and couldn’t be used.  So I ended up using a pad in my hand and polishing the boot lid manually.  I think I was able to get it done well enough to get rid of that stain, although I wasn’t able to do the whole car like I planned.

At some point in the future, I’ll do the whole car properly.

Regassing the AC

The AC had become tepid, no good for a drive to Canberra in the height of summer.  I used my blacklight to see if I could see any leaks, and I couldn’t.  With that, I took the car in to be regassed and since it held vacuum, we did.  At this stage I’m not sure where the minor leak is from.  Perhaps under the dash.

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I also noticed that the plugs would stay on for a long time even when the engine was warm when restarting.   I figured the most likely culprit was the relay.   While the best thing to do would probably have also been to test each of the glow plugs, the symptoms seemed very much in line with a bad relay.

I looked up the part number for my car and came up with 002 545 0532.   There were a lot of options for this.  I think OE was VDO or Stribel.  At the time of purchase, neither were available.  As I write this, Stribel seems to be at around USD$255.  There were a few brands available and I went with Huco, which seemed to be made in Germany.  It was about $55USD.

Swapping out the relay made an immediate difference.   The glow time was much shorter and the car still started very easily.   I’ve been driving it around for a few months now and I’ve not had the light come on at random times again.

Interesting, when I start the car from cold, the light goes out, but comes on very faintly when the car is running for another minute or so before going out.   Not sure what this means, but everything seems like it is working as it should be.

The old relay was clearly the original as it was dated 12/80 which is in line with the build date of the car.    I’ve kept the old relay as being original is probably rebuildable.

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Todays job was to replace it.  I had a couple of spares, as this part is shared with the W126.  However, they were a little dull.   While the original part number of 1238800086 is now NLA,  All the sites listed 124880008667 as fitting the W126 and W126.

I understand the preferred way to change the star is to remove the grille.  However, given my star was already floppy, I wasn’t too worried about damaging the old one, so attempted to remove it in situ.   I used a large set of long nose pliars to turn the collar anti-clockwise.   If the collar is turned anti-clockwise and sits on the tabs on the bottom of the star, then it should slide out from the top.   In my case, pulling against the spring tension of the collar to get it to sit on the tabs caused the little metal strip that holds it together to fail.  The collar then separated from the star and I was able to get it out easily.

I had left the new star on my desk at home, so had to drive the 240D back with a star installed.  It is a strange feeling to drive a W123 with no Mercedes Star.  Kind of odd because I drive the C126 and C107 all the time that don’t have them.

Unboxing my shiny new star soon showed that 124880008667 is a little different to 1238800086.   The base of the W123 part is quite a bit larger.   The newer part fits, but it was obvious where the larger star had been there before.

to compare, I got one of my spare W126 grilles and removed the star.  It was the older W123 part with the larger diameter and fit well, but was rather dull.   I then went to look at my 1987 560SEL – it had the newer style star installed. Owning the car for 5 years I had never noticed this.

I have a couple more W126 grilles in a box that could have yielded a better Mercedes Star.  Since it looked good on the 560SEL, my first attempt was to get the new one to work.   I got out a microfiber towel and some quick detailer and after a while, I was able to remove nearly all the evidence that the larger star had been there.

Installing the new one, I was pretty happy with the result.  Its very nice driving the car with a lovely shiny Mercedes star at the front.  The new one also has the staying power to withstand the massive acceleration available from the 240D.

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The A/C worked well until I took the car off the road for a couple of months to fix the fuel system.  After that, the freon had leaked out again.  A further re-gas and having the valves changed basically just gave me my road trip to Brisbane.  Clearly there was a leak somewhere.

I looked with my blacklight, and the issue was apparent.   There was green dye all over the compressor.   This isn’t all that surprising.  A/C compressors need to be run regularly to prevent leaks.  As my car was likely laid up for a while before my ownership, the seals had obviously gone.

My 240D is new enough that it uses the GM ‘pancake’ style rotary compressor, not the York.  My 240D still had the AC Delco compressor with metric fittings these cars came with.  I do not believe these are available anymore.  I bought an Omega brand compressor to replace it with.  Naturally I had the drier replaced at the same time.

I could have stopped there but decided to upgrade the condenser too.   The original condensers designed for R12 don’t work all that well with R134A.   I’ve been very happy with the Klima Design works condensers in my 560SEC and 450SLC so decided to also put one in the 240D.

I noticed in the W123 instructions it mentions that you can paint the condenser black to match the factory look. I reached out to Klima Design Works to confirm that this would not impact cooling performance.   Their reply indicated that their testing hadn’t seen any measurable impact.  I decided to paint mine before I had it fitted.

It was a pretty easy job to paint both the condenser plus the various fittings satin black.  I only painted the front of the condenser.    The back is not visible.

I had the new compressor, condenser, drier etc fitted a couple of weeks ago.   Painting it black made a huge difference in how noticeable it is.   I’ll probably go back and see how much I can paint the condensers I have in the two 126s and the 107.

Its been pretty cold in Sydney since I got the car back.   The new upgraded A/C seems very good, but I’ve not had a hot day to test it with.  I’ll be doing a trip in January for the 50 years of the W123 event, so having nice cold A/C will be a plus for that event.   While I don’t miss most of the features of modern cars, I do very much appreciate cold A/C and these condensers really help.  I won’t know until it gets hotter, but so far I am happy with my W123 air conditioning upgrade.

While I don’t particularly notice it when driving, it is apparent when the compressor kicks on when the car is idling.   The compressor is probably using a decent chunk of the power the OM616 makes at idle.

It is a complete bolt in kit so I could go back to original at any time.  I don’t plan to though. I have kept the original one to go with the car.

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I had assumed I would just put up with it, as the grille inserts available from the usual parts suppliers in America are of horrific quality.   However, a friend who had recently purchased a 280CE mentioned that he got a very good insert from Niemoller in Germany.   I decided to order one, as well as a new auxiliary fan.

When the replacement W123 grille insert arrived, I agreed with him.   Its not perfect but is quite good quality.   The only fault I could find in it is there is some slight evidence of where the plastic has flowed before it hardened.  You have to look quite close to see this.

Changing the W123 grille insert is not particularly difficult.  It is just one of those fiddly jobs that takes a bit longer than you expect it will.   To replace the insert, the entire grille must be removed.  This is quite easy as its held on by six 8mm screws.

Four of the screws are quite obvious, but two require an extension and cannot be seen.  Once the grille is off the car, then the W123 grille insert is removed from the rear.  It is held on quite securely.  The two outer screws holding the grille shell to the car are also holding in the insert, so that leaves another six fasteners to remove.   The easiest one is the Philips head screw at the bottom.  Then the Mercedes emblem below the star also holds on the top centre of the insert and is removed with an 8mm nut.   That is also quite straightforward.

The sides are more fiddly.  There are four clips that hold the insert flush against the grille shell.  The bottom ones hare hidden behind plastic spacers.  These are held on with phillips head screws.   Then, I removed the four clips by rocking them side to side with a flat head screwdriver until they came off.

With the insert removed, the metal strips can be simply slid off.   The horizontal ones slide outwards and the vertical one slides down.  Other than the one held on by hot glue, they were simple to remove and re-install on the new insert.   On closer inspection, my strips are not as good as I thought, and I regretted not getting new ones.  I’ll try and polish them up with metal polish.   While I was there I also transferred over my grille badge.

Re-assembly is the opposite of removal.  While I was at it, I noticed that the blue surround of the Mercedes emblem was a bit faded.  I had a much better emblem on one of my spare W126 grilles, so I swapped it over.  Its not perfect, as some of the white paint on the star has come off, but its in quite good shape. There are also a couple of metal clips to accept the mounting screws in the top left and right corners of the insert that I swapped over to the new one.

The main thing I discovered while re-assembling the grille is that the Philips head screw at the bottom of the grille should be re-installed last. I tried putting it first.  However, there are some plastic tabs that sort of tuck into the grille shell inner rim.  If the bottom of the insert is secured first, they are not property tucked in and the insert doesn’t sit correctly.   I found it better to install the Mercedes emblem first to locate the top part of the insert, and then the sides, then the bottom last.  The metal clips on the sides are the most fiddly, but eventually went on with a flat head screwdriver.

Re-installing the grille was also a bit fiddly.   After a few attempts to line it up, I found it easier to use the two inner screws to locate the grille on the bonnet.  I inserted these with the bonnet in the normal position.

From there, I installed the two outer screws.   For the middle ones, the bonnet needed to be in the service position.  Otherwise I couldn’t put the screw on the end of the socket and then guide it into place.

I’m pretty happy with this improvement.   There are two other future improvements.  I will try and polish up the metal strips, and the star can be a bit limp at times.  On my trip to Queensland it would sometimes fall over at speeds over 100km/h.

Observant readers will notice I made a mistake.   I noticed it when writing up this article.   The tongue for the latching mechanism is not in the right spot.  While I had put it in place when first fitting the grille, when moving it around to fit, it must have fallen out.

I went back the next day to check.  It took a few minutes, but I eventually got the bonnet open.  I was able to use a hook to pull the latch open without damaging the grille.  Since the grille is now screwed into place, It wasn’t just a simple matter of putting the tongue in the slot.  At first, I thought I would have to remove the grille again, but then I noticed that the tongue is easily removable.

In about thirty seconds I had the circlip and pin off.  That then allowed me to re-install the tongue from the front and then re-attach it.

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I had a quick look at the wiring diagram to start troubleshooting.  On the W123 diesel is a pretty simple system and easy to test.  There is the switch on the A/C receiver/drier that triggers a relay to run the fan.  Unlike the petrol cars, there is no trigger for high coolant temperature, the fan is only for the A/C.

My first step was to jump this switch.  When I did so, I heard the relay click, but the fan did not come on.  Seemed apparent that my fan had died.

While I was ordering a new W123 grille insert from Niemoller I also ordered a new fan. It would seem the Bosch fans are no longer available.  Swapping the fan over is not particularly difficult.   It is secured in three places.  On the bottom, there is a small phillips head screw that holds a piece of plastic trim in place.  This trim is a filler piece between the grille and the bumper bar.  That phillips head screw also locates a bracket at the bottom of the fan.  The fan is removed with the bracket attached, as the plasic trim can flex enough to let it past.

The top left and right of the fan are held on with 8mm bolts with little brackets to the diagonal stay tubes.   Unplugging the fan is harder than removing it.  The plug is clipped onto the body of the car in a spot that is a bit hard to get to with the car on the ground.  My hoist is currently broken, but I eventually used a pick tool from the top to remove the clip and then I unplugged the fan from the bottom.

When I removed it, it was amazing how much debris was caught underneath the fan.   I cleaned this up as best as I could.  It was a simple matter to transfer the bottom bracket from the old fan to the new fan.  I was also hoping to re-use the plastic finger guard. However the body of this new fan is quite different and is not compatible.   Given the incompatibility, I think this fan should have come with a finger guard that fits.

Re-installation was a bit fiddly, The bottom mount is easy to fit, but it took some time to get the two side mounts to line up properly.  It was also a bit of a pain to get the plug clipped back in place.   In the end I did, and the fan whirred into life when I jumped the switch on the receiver/drier.

In our hot summers, a working W123 Auxiliary fan is essential to good A/C performance.

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I don’t really like not being able to trust my gauges to be generally correct, so I wanted to see what I could do about this.   The issue seems to be mostly due to grounding.  The whole cluster gets ground from one plug, which then provides ground to each of the instruments, and lights.

A friend of mine with a W123 had fixed a cracked solder joint in his cluster that had made a big difference.  I’m terrible at soldering, so he offered to take a look at my cluster and see if the same solder joint needed repair.

Last week I removed my instrument cluster.  On removal, it had obviously been out before.  Somebody had written an odometer reading on the back, which I assume was done when the odometer was previously repaired.   The cluster was generally in very good shape, except somebody had tried to pull it out from the front before and slightly damaged the front cover, so I had to be careful.

I find the easiest way to remove these clusters is to remove the drivers side speaker and push it out from behind.  The W123 instrument cluster is harder than the W126 version, because the oil pressure sender is mechanical.  For reasons only known to them, Mercedes-Benz give you almost no slack to play with on the oil pressure line and speedo cable.  Even an extra two to three centimeters would make a big difference.

A 10mm spanner is needed for the oil pressure line, but the rest of the connections can be done by hand.

My friend looked at my cluster, and didn’t see the same solder joint broken.  There was some oil inside the cluster, and some of the screws were a bit loose.  Since the oil pressure gauge does not seem to be leaking now, I wonder if it leaked in the past?   Regardless he gave it a clean and also made sure it was screwed in properly.  From what I understand, the screws are important for the grounds.

I also decided to add another ground line.   From reading on the forums, it seems a lot of other W123 owners do this.   I figured it couldn’t hurt.  I grabbed a couple of ground lines with eye terminal from the 420SEL parts car. One terminal went on the other side of the ground bolt behind the W123 instrument cluster, held it on with a washer and nut, also from the 420SEL.  I put the other ring terminal behind one of the screws on the instrument cluster.   The only non Mercedes part was a connector between the two ground lines.

I put it all back together and took the car for a test drive. Getting the oil pressure line on is quite fiddly.  Eventually I got the cluster back in place and tested all the connections.

Today is very hot, mid 30s, so I was curious to see how the temperature gauge performed.   The fuel tank is full, so I will not be able to test that until I have used some fuel.   At least on the 20 minute test drive I did, the gauge seemed to perform very well.  It crept up to about 100 at one point in stop and go traffic, and then when I was on the move again, slowly came down.   It never used to perform so predictably.   I will keep an eye on it, but so far it seems like a big improvement.

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I got the radio back last year, and finally found time to re-install it.    I had also seen on Instagram where anther W123 owner had installed a USB charge port meant for an E36 BMW in place of the factory fader.    My factory fader is still working, but my 240D has two switch blanks on the top console, which is the perfect spot for a charge port.   The USB charge port was quite expensive, but it looked like a really good solution so I ordered one.

To power the Becker 596, I also planned to install another Tranzit BLU Bluetooth Box.   This is the same solution I have used in my 560SEC, 300TE and 450SLC.   I’m very happy with it.   The Tranzit BLU is a small box, about the size of a deck of playing cards that provides a FM signal directly on the antenna wire.   This makes it far less susceptible to interference.  It also provides a handsfree option for calls.

Normally the Tranzit BLU is controlled by a hidden button.  However, I had the idea of using a factory sunroof switch in the other blank switch location instead.   I didn’t have a W123 sunroof switch in my box of parts, but I had one for a W116 or W107, which is good enough to test with.

The installation was pretty simple.  I use the connector for the cigarette lighter to power the USB charge port.   The spade connectors that came with the charge port were too narrow, and not quite long enough so I made some extensions.   In testing the USB charge port, I was also able to easily pull off one of its connectors, so I crimped on a new one.

Since the USB charge port is designed to be added to an E36 BMW, it has been designed to piggy back off another accessory.   Therefore, it already had power and ground connectors for the Tranzit BLU.   I used a relay to trigger the Tranzit BLU from the Becker Antenna trigger.   That relay then powers the Tranzit BLU and also triggers the power antenna.

Instead of the button that comes with the Tranzit BLU, I wired in the sunroof switch.  I used a multimeter to work out which of the four pins are activated when the switch is pressed forward.   Essentially the way the switch works, is when it is pressed, it joins power to one side of the motor, and ground to the other side.   Thus, pressing the switch the other way reverses these connections, allowing the motor to run in reverse.   I assumed for this purpose I just needed to make the connection to trigger the Tranzit BLU.  Turns out I was wrong.

I wired it all up and did a quick test of the system.   I was able to pair my phone and play music through the Becker 596.  However, the switch did not work.   I tried a few more pin options to no avail.   I had assumed that the switch was ‘dumb’ and just made a connection to trigger a press of the button.  However, it was looking like that was not the case.   I got the Tranzit BLU switch and connected that to a multimeter.   On very high resistance settings, I was able to trigger a change in resistance when pressing the button, but it wasn’t constant.    Given there appeared to be more to this button than I anticipated, I gave up and put the switch blank back in place.    The Tranzit BLU button is now on the steering column out of sight like in my other cars.

Despite the failure of using the sunroof switch to power the Tranzit BLU, I am very happy with the setup.   The correct Becker is back where it should be and I can play music through my phone and make and receive phone calls.    I am taking the 240D on its first road trip this weekend, so having music will be great.   The install is totally reversible with no factory wires cut.

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Since I had the car in the air, I used the time to check what calipers I had on the car.   On the front, I had Bendix and on the back I had Girling.   Once I dealt with the fuel delivery issues, I planned to have the brakes sorted out.

Based on what I saw, I ordered rebuild kits for the front calipers, plus pads, rotors, wear sensors and all four brake hoses.  The mechanic I was using to do the job also suggested I get wheel bearings while he was in there.

Having seen the condition of the fuel tank, it is obvious that this car has seen little use in recent years.   It is pretty typical of lower mileage cars that don’t see much use to have binding or sticking brake calipers.   This is another reason to use classics regularly and have the brake fluid changed every couple of years.

I suspect a fair number of seldom used classics could do with a brake caliper overhaul.

It took me a lot longer to deal with the fuel delivery issues than I had anticipated.  The car finally went to visit the mechanic this week.  I also asked him to look at the A/C as it was no longer cold.

I got the car back today and the brake feel is transformed.  He told me that he had to replace three of the four pistons in the calipers as they were all corroded.  After seeing the inside of the fuel tank that does not surprise me.   He also changed a valve in the A/C and recharged the system.

Today was around 40C and the car had been sitting outside the mechanics workshop in the sun for a few hours when I picked it up.   It was a good test of the A/C.   On the move, it was quite good, but the performance in traffic was not so great.  I’m not sure if the aux fan is kicking in enough, I’ll have to look at that.   On the W123 diesel the fan is only connected to the A/C pressure switch, not the coolant temperature like some of the petrol cars of this period.  This means my trick of adding a resistor to make the fan kick in more aggressively is not as easy to do.

I’ll first make sure the fan is actually working properly, and if it is, perhaps add something that causes it to kick in more aggressively.    I know it did before, but it is possible a relay or fuse has blown since.

The 240D is now running and driving better than ever and I am looking forward to using it more in January.

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The main difference between a tank from a petrol W123 and a diesel is the petrol cars had the swirl pot at the bottom of the tank.   The swirl pot allows fuel to continue to flow even during hard cornering, as the return line not only keeps the pot filled, but draws fuel in from the rest of the tank.  Presumably the diesels don’t need this as they flow a lot less fuel and are less likely to do hard cornering.   In addition, an algae outbreak could clog up the little hole in the bottom of the pot.   I’ll be using the biocide additive on my car regularly, so I’m not concerned about this.

When the tank arrived, I was really impressed with how clean it was.  I couldn’t see any rust at all in the tank. The petrol fuel strainer was also quite clean.  Since I don’t want to do this job again, I gave it a clean and was able to get some of the normal residue out of the tank before installing it.   I used my pressure washer to clean inside the tank as best I could, then dried it with my cordless blower.   After that, I used some methylated spirits to make sure I got the last of the water out.

I came back the next day to prepare the tank for installation. I installed a new diesel fuel strainer.   The diesel strainer has a coarse mesh, to allow minor algae to get through and be caught in the pre-filter which is easier to change.   This is part 124 470 01 06.   I also re-installed my fuel sender.   Mercedes thoughtfully made both of these items use the same 46mm hex.   I also had to glue on the rubber ‘foot’ that sits around the strainer and between the tank and the body of the car.

Re-installing the tank was easier than getting it out.   The only slight hiccup was the rubber ‘foot’ had been somewhat dislodged and I had to use screwdrivers to reposition it from under the car.

Once the tank was in place, it was a fairly simple matter to install a new fuel supply hose.  The car was using the fitting from the original hose, with a normal fuel hose clamped to it.  There probably isn’t anything wrong with this, but I bought the proper cohline hose.  It is for multiple cars, so I had to trim a few cm off for the W123 diesel.

Next was the return line and breather hoses.   The EPC states that these hoses are both 120mm.  I cut 120mm hoses, but I found the return hose was too long and I trimmed a few cm off it.   The breather hose was also thicker.   I didn’t actually install the breather hose at first, I waited until I had the car running so I could move it to the hoist under its own power.   I had bought the proper hose clamps for the engine bay and the supply hose, but forgot these two, so had to use the regular hose clamps here.

While I was at it, I also replaced all the hoses and filters in the engine bay.   The pre-filter was quite dirty, and needed replacement.   The main filter probably wasn’t, but I replaced it anyway.  I also used the proper hose clamps that don’t bite into the hoses.   According to the EPC, the hose from the supply line to the pre-filter is 140mm and the hose from the pre-filter to the lift pump is 40mm.

The EPC also lists a special return hose some people refer to as the ‘Cigar’ hose.   This is part number 000 997 51 52.  A lot of people don’t seem to bother with it, but since I was ordering new parts I got one.  I found it to be very long, and I had to push it a long way onto the return hard line so it didn’t kink.

At this point I was ready to refuel the car.  I had 30 liters of diesel I had pumped out of the car through a filter, so I added this to the tank.   I was happy to see there were no leaks and I began to prime the system.

The primer pump felt very odd, and I couldn’t work out why it didn’t seem to be moving much fuel.   After about 30 minutes of trying various things, I noticed that one of my hose clamps was stopping it from going all the way in.   Simply rotating this clamp restored full travel to the primer and I was able to get quite a lot of fuel moving.   I think my issues priming the system last time were due to my blocked strainer, as I was now getting quite a lot of flow.

It still took quite a few times of priming the system, trying to start the car, priming the system, and trying the start the car until it finally roared into life.   It ran well and seemed to be idling better than before.  I wonder if it wasn’t getting enough fuel with the blocked strainer.

A quick test drive around the factory complex showed no leaks and the car running well.   The downside was that the A/C had stopped working, which I will need to attend to.

Since I was happy with how the car was running and there were no leaks. I re-installed the boot trim, and left an Easter egg for a future owner on the fuel tank.

I will check the condition of the fuel pre-filter over time, but I expect that with all this work my fuel delivery problems should now be behind me.

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