M103 Distributor cap and rotor

Today I changed the Distributor cap and rotor in my 1986 300SE.  I bought the new cap and rotor about two years ago but only just got around to changing it.   Unlike on the earlier engines, the M103 distributor cap is a fiddly job.   Instead of sticking upwards, it comes out sideways as it attaches to the camshaft.

I find that whenever I buy one of these older cars, chances are the distributor cap needs changing.   It is not generally an expensive part on the mainstream engines, and can make a big difference to the smooth and reliable running of the engine.  An old and pitted cap is going to produce a weak, inconsistent spark.    I normally just purchase a cap and rotor when I buy the car.  On the off chance it doesn’t need replacing it is good to have a spare.

My 86 300SE is no exception.   The cap wasn’t in terrible shape but it was clearly worn and ready for replacement.  The contacts were worn and so was the rotor.

M103 distributor cap

The M103 distributor cap differs from the other cars because of how it connects to the camshaft.  To remove the cap, there is a cover for the plug wires that snaps off.   Next, three 5mm allen bolts hold the cap to the engine.   Two of them are easy to see but the third one is underneath the cap and only just visible from the left hand side.   I found it easiest to remove it with an allen socket and a small extension.   Using a 1/4″ ratchet made it easier to clear the Serpentine belt.   I used an adapter for my 3/8″ socket into the smaller ratchet for this purpose.

It is easier to remove the plug wires first.  I found there wasn’t clearance to remove the cap until the plug wires were removed anyway – the fan gets in the way.    The actual distributor cap has a black cover that provides the mounting points for the plastic cover and splash protection for the ignition wires.   On the surface, mine looked ok but on closer inspection I would have preferred to change it.   It has a couple of small cracks in it.    In the picture above, the old M103 distributor cap on the right still has the cover attached.

Once the cap is removed, the rotor requires 3x3mm allen bolts to remove it.   In my case, one of the bolts was rounded off.   It was quick easy to remove with vice grips, at the expense of breaking the old rotor.

M103 distributor cap

I gave the inner plate as good a clean as I could.   Ideally I would have replaced this too.  As can be seen in the picture above it has seen better days.

In total, the job took about an hour to do, including the rounded off bolt.   I had not changed an M103 distributor cap before, so it would likely be faster next time.      Note, that the M104 engine is very similar.   The M104 is basically a DOHC version of the M103.  More power, but also even more prone to eating head gaskets.

Youtube tips – shifter bushing and rounded bolts

Today I did an engine and transmission oil change on the 300SE.   I don’t normally post basic maintenance to this website as it really isn’t that interesting.   In this case, I used to tips I learned form MercedesSource videos that really sped up the job.    MercedesSource are an online parts vendor, who also make some useful special tools.   The owner, Kent, runs a youtube channel to promote the business.  I’ve bought a couple of his special tools over the years and found them quite useful.


The first tip was for removing the bolt from the transmission oil pan.   This bolt uses a hex fitting, which had been rounded off by a previous workshop.   Last time I changed the transmission oil I made a huge mess as I had to remove the pan without first draining the oil.   I obviously didn’t want to damage the bolt without a new one on hand.

This time I had the new bolt ready to go.  The tip is to use a chisel to tap a divot into one side of the bolt and then tap against that divot in the direction to unscrew the bolt.   This technique took all of a few seconds to remove the bolt.   The new bolt was quite cheap.  I don’t remember exactly how much as I purchased it a couple of years ago.

While bolting the transmission oil pan back on, I noticed that my lower shifter bushing was bad.   It had largely disintegrated and the shift rod was no longer snug in the transmission gear selector.   The 70s and 80s cars use a much better design than the 60s models in that there is a clip at the end of the rod that ensures it can’t fall out entirely.  There might be a lot of slop in the lever, but it won’t leave you stranded.     When the bushing failed on my 250SE, I had to use a bulldog clip to make a temporary fix to get the car back into the garage.   Luckily I wasn’t stuck somewhere else.

shifter bushing

I have previously done the shifter bushing on my 450SLC.   There is quite a bit more room to work on the W126.  MercedesSource sell a bushing press that makes installing the new bushings a doddle.  It’s even easier if you use a little rubber grease.     I only needed to do the lower one, the upper one seemed fine.   These are the sort of parts that it makes sense to keep on hand if you own these cars.   They are not expensive and it makes sense to check them each time you look under the car.

shifter bushing

I had also planned to check the distributor cap, but I didn’t get time today.   I’ve not checked it since I owned the car and its a part that is often neglected.   The M103 is a bit of pain to get to compared to other motors.   I also plan to check for vacuum leaks as the vacuum gauge on this car is at the halfway point at idle.   It should be close to the left hand end.   This probably means a vacuum leak.

450SLC Dragging rear brakes – part 3

In part 2, I had been struggling with my new SLC rear Calipers.   As outlined in that section, the new calipers I had on hand are for models not equipped with the anti-squat rear suspension.   This was because USA models were not so equipped.   The hard lines were too short to fit properly and fouled on the suspension bump stops.    I dropped the car off earlier in the week to have new hard lines made up that fit, and to change the flexible hoses.

I have since found out that I made a pretty stupid mistake.   Instead of checking the new parts properly, I used the old ones to determine how they should fit.   In this case, I fitted the calipers based on the position of the old ones.   If I had checked the part numbers properly, I would have seen they were on the wrong sides.   Additionally, if I had used even a modicum of common sense I would have seen the bleeders were facing down, not up.     Why is this a problem?   Having the bleeders facing down means it is pretty much impossible to bleed the brakes.   Instead of pushing the air out, the fluid will just run out leaving air in the calipers.

The brake shop first put the SLC rear calipers on the right sides.   Then they made up new hard lines for the rears to go from the hose to the caliper.     After that, they changed the hoses.   The fronts were not much of a problem.     They had the same problems I did with the rears – no matter what they tried they could not undo the fittings.    I suspect that due to the extreme heat from the sticking rear calipers, the metals were almost welded together.

Stubborn rear hoses - needed for the SLC rear calipers

In summary,  I have an entirely new rear braking system.   New calipers, rotors, hard lines on both sides and hoses.    I also have a new master cylinder and front hoses.    The brakes feel great, and now the brakes are not dragging, the car feels more lively.

Incidentally the shop I took the car to has recently done some work on a 50,000km 450SLC.   They commented that mine rode better and seemed to have more power.   Not bad after 300,000km.

Rover P5 Coupe parts car update

My old Rover P5 Coupe parts car is almost completely dismantled.   It is being parted out to aid in the restoration of three other coupes.   These coupes are in much better condition but needed certain parts to return to the road.    Last I saw the car there were still key parts on it, but all that is left is the engine and transmission.

Rover P5 Coupe

The car is now in a rather sorry state.    It was never in great condition, but it did make the drive back from Canberra to Sydney after the Flynn auction.  Not bad for such a cheap car.    It looks like the bonnet has been used as an outdoor painting bench!

DG Box

The engine is being kept in reserve for the restoration, but the owner will probably sell the DG automatic gearbox as the restoration projects are all manual/overdrive.    It is a shame to see such a rare car parted out, but at the same time this one very rough car is being sacrificed to get three very nice ones back on the road.   This P5 coupe parts car was originally stone grey with a red interior.   When I bought the car it has a poor quality vinyl roof that is unlikely to be factory.

Rover P5 Coupe restoration update

I recently stopped by the workshop where a friend of mine is restoring three Rover P5 Coupes.    Over the last couple of months there has been quite a lot of activity, although that is somewhat hard to see from the photos.   Rover P5 restoration is quite time consuming – they are not simple cars.   The photos from my visit in April are available here.

Rover P5 restoration

Firstly, all the electrical work is completed and tested.   This is an important milestone and something that needs to be right before the interiors can be installed.   The electrical work includes sensible upgrades such as relays for the headlights.   The blue coupe in the picture below has also been pre-wired for driving lights.   It is hard to see from the photo but the blue coupe pictured has been upgraded to Halogen lights.

P5 Restoration

Hard to see because they are covered for protection, but the bumpers have all been re-chromed.      Next, the engines are being readied for their first start – hoses, belts, fluids and the like.

Rover P5 Restoration

The picture above shows the somewhat unusual arrangement of the combined generator and power steering pump used in the P5 3 litre.     Finally, some of the interior is starting to take shape – starting with the boot.   The P5 came with a nice arrangement of tools on the passengers side of the boot which can be seen below.

Rover P5 restoration

The other two cars also have more of their interiors installed.    The Yellow MKIII has the dashboard more completed and the other blue car has the doors trimmed.

Rover P5 restorationIt was good to see the progress on the Rover P5 restoration.   I am looking forward to visiting again in the new year to see further progress.    The three cars should be magnificent when finished.

450SLC Dragging rear brakes – part 2

A couple of weeks ago I started investigating the dragging brakes on my SLC.   I found both of my rear calipers had been overheated and were in poor condition.   I ordered a set of rear calipers, and decided to change the rotors too.   Mine were still in spec, but on the lower end.    The hoses I had purchased last time were also not right.  I needed hoses with two female ends but the other hoses were male/female.

450SLC brake calipers

The first thing I found was that it was quite hard to remove the old rotors.   Not only were the rotors rusted to the hubs, but the old rotors was catching on the handbrake shoes.   I was able to turn the wheel by hand, but I think it was dragging a little.   It took a couple of huge whacks to free the rust on the hubs, and a lot of pulling to get them over the shoes.


I used a wire wheel to clean off some of the rust on the surface.  After that I applied some copper grease to stop it rusting in place next time.     Putting on the new rotors was almost impossible.   The handbrake shoes fouled on it quite badly and I had to adjust the handbrake shoes quite a lot.  Not just a few teeth, but probably a full turn.   I wonder if this was also part of the dragging?     Before I had adjusted the handbrake, I could not turn the new rotor at all even with two lug bolts at a long pry bar.     After the cleaning the braking surfaces, I was able to fit the new rotor.

450SLC rear caliper

At this point I also bent and fitted the new hard line I had damaged in part 1.   The lines do not come pre-bent and I so purchased a bending tool.  It is important to do more than minor bends with the tool as you can kink the lines and impair brake function.

New brake line for 450SLC rear caliper

The new 450SLC rear caliper fitted quite well, but there was a problem.   The new caliper had a slightly different place for the brake line than the old one.   Other than that, it was almost identical.      I did some research and found the source of the problem.

For one reason or another, Mercedes-Benz decided not to equip North American 450SLCs with the anti-squat rear suspension.   I imagine the decisions was based on the lower power output of those engines.   It is a strange decision though, as while the power is lower, there is still plenty of torque that is the main cause of the squat on acceleration.    Not equipping the cars with this suspension also meant a different arrangement for the brakes.   On the rest of world SLCs, there is a brake hose that connects the hard line from the car to another hard line that brings it to the 450SLC rear caliper at the front of the rotor.   This is the system that my car is equipped with.    On the North American cars (and the 350SLC, 280SLC etc), there is the normal arrangement of a hose from the hard line right into the caliper.

This is why the brake hoses I purchased first time around had a male/female arrangement and these new calipers had a slightly different arrangement for the brake hose.   The brake calipers I have, are part number 1234200583 and 1234200683.   The new correct brake calipers for my car have a 126 part number.   These calipers are far more expensive than the 123 part number 450SLC rear caliper.

On the passengers side I was able to get the hard line to connect to the caliper.   I am a bit concerned that it is very close to the bump stop.   On the drivers side, I was not able to bend it the way I wanted and it rubs on the bump stop.   I don’t think this is very safe as a large bump could damage the line.

From looking at the caliper, I think a new (slightly longer) line could be fabricated that clears the bump stop and connects to the caliper.   I don’t really have the ability or tools to do this, so I will take the car to a brake specialist.  This should be the best way forward rather than getting a new set of calipers.   I was also unable to get the hose off the drivers side, so will have them do that at the same time.  What they found and the w9ork they did is covered in part 3.

I bled the brakes, first with my vacuum pump and then had a friend help me bleed the brakes further with the traditional method.   There must be a small amount of air left in the system as the pedal is a little spongy.  I didn’t re-bleed as when the new lines are fabricated they will need to bleed in any case.

I also tested the handbrake and it is able to stop the car and is not dragging.

My final task was to fit my new MBCNSW grille badge.   I put it on the opposite side as my Mercedes high mileage badge.   Looks pretty good.

MBCNSW grille badgeFor what should be a simple job, this one has taken a long time.   I’ve probably spent more than two full days on it.

560SEC Climate Control repairs part 1

When purchased, my 560SEC did not have working climate control.   Not only did the A/C not work, but the heater had a mind of its own, occasionally bursting in to life and turning on full heat.  Curiously for a car that has been in Australia since the early 2000s, the car had not been converted to R134A.

My first step was to see if the system could work.   Overseas readers may not know that in Australia it is illegal to sell freon to the general public.   R12 has not been available for many years.   Therefore, I booked the car into a mechanic who does A/C work to have the system converted and gassed up with R134A.   First steps were quite positive, when the Klima relay was bypassed, the system would blow quite cold if you jiggled the ignition key a little.    That left some obvious repair items though.   I had a new ignition switch (the electrical part) fitted, and ordered a new relay.   I also ordered a rebuild climate control unit.

The old Klima relay and ignition switch

While the ignition switch was out of the car, I planned to put in a new tumbler.   It used to be possible to purchase these from the Mercedes-Benz classic center.   They would then set them up to use the right key for your car.   The part has been NLA (No Longer Available) for years on the W107, but I purchased it for my 300SE about 18 months ago.   In that time, it is now NLA for the W126 except for the 1990/1991 models.

The new freon had dye inserted, so I was able to check if the system was holding pressure.   In general, it was, but there was a small amount of dye around the compressor.   In particular, between the two halves of the compressor.   The mechanic who gassed up the system had seen success with a product that can be added to the A/C system to seal up minor internal leaks.  We added that component and I waited for the relay and climate control unit to arrive.

The Climate control unit is quite easy to fit.   I have done this job on my 300SE when I was troubleshooting its climate control system.   First, the ashtray is removed, then the radio.   The dash panel can then be pulled down and out to expose the climate control unit.

560SEC Climate control

it is easier to remove the connections to the other switches first.   Care must be taken to keep the fiber optic cable with the switch, so the back lighting will work when it is re-attached.

In the series 2 cars, the climate control unit is screwed into the back of the wood panel, and there are two big connectors that connect the unit into the cars wiring harness.

560SEC climate control

I am getting quite fast in removing this part of a W126 dash after doing it quite a few times on the 300SE.  Taking the dash apart also allowed me to fix a few other annoyances.   The first was the illumination of the gear selector when the lights are on.   It is a tiny 1.2w bulb that slots into a hole in the underside of the unit at the front.   Not only was my bulb blown, but it had come out and was floating around in the dash.   The second was plugging in the cigarette lighter properly so I could charge my phone.

560SEC climate control

I had couple of these bulbs in stock, so it was an easy change.   The Ashtray illumination was flickering as well, so I changed that bulb while I was there.   After putting the dash back together, I had a MBCNSW twilight drive to attend.   I had originally planned to take the 250SE, but the weather was rather poor.  Based on this, the 560SEC was the better choice, especially as I could test the Climate Control.

My results were generally positive, but with some more work to be done.  My 560SEC climate control sort of works.   The climate control unit regulated the temperature well, although once or twice it went from cooling to heating.    The new relay worked fine, and I had no problems with the ignition switch.   The three main problems I had were that the A/C just wasn’t all that cold, the centre vents are not working properly, and the electric fan never kicks in for the condenser.  I’m pretty confident that the centre vents will be the vacuum pods under the dash.   That is a job for another time.   As the weather heats up I need to get the electric fan working as the car gets quite hot during prolonged idle.   After coming so far, I also wold like to get the A/C cooler than it is now.

Next step is to take it back to test the freon level, and see if that sealer has worked at all.   I also need to see if the Aux fan will work if plugged into 12v directly.

Citroen DS sphere pressure check

Today I attended a Citroen Car club tech day.   Since most Citroens are equipped with hydropneumatic suspension, the club has equipment to pressure test spheres.   It has been five years since I tested my spheres, so they were well overdue.   The sphere pressure check equipment consists of a hand pump and pressure gauge.   The club is also equipped with re-gassing facilities, although those were not available today for the rebuildable spheres in my DS21.

The tech day did have a hoist available, but my preference is to remove the spheres at home first.   As with last time I removed them, a strap wrench is easiest.   The spheres are different front/rear so it is important to mark where they came from on the car.

SphereThe tech day was held on the central coast, a good opportunity to take the old Pacific Highway in the 560SEC.   The car seems to be performing well after the EHA adjustment.

There was a good mix of Citroens at the tech day, including a DS, CX, and some modern Citroens.   The CX is becoming a rather rare car.   Quite a few spheres were tested, mostly the one piece units on the later models.

Sphere pressure check

My spheres had readings in the low 40s for the front (42 & 45) and 28 in both the rears.   Specification for a DS front sphere is 44-64, with 59 being the ideal pressure.  Rears should be 16-28, with an ideal of 26.   I will not be able to wait another 5 years to do a sphere pressure check.  It would make sense to re-check them in another 6-12 months and potentially have the re-gassed.    I also learned a neat trick today – the plastic take away containers make great transport units for at least the single piece spheres.  I will need to check them for the rebuildable ones.

Sphere pressure tester

As well as doing the sphere pressure check, I also purchased 5 litres of LHM, the hydraulic oil used in the DS and other Citroens.   The Club sell it for around half the price it is available retail.

If only the hydraulic cells used in Mercedes suspension were re-gassable like the Citroen ones are!

KE Jetronic EHA Adjustment

I discovered at the MBCNSW Dyno day that my 560SEC was running dangerously lean.   Lean enough to cause damage to the engine.  While I was in the USA for work, I went to the Mid Florida Auto show.  I met Pierre Hedary there (who runs an independent Mercedes workshop), who suggested that I should start by testing my fuel pressures and that he had a couple of videos on youtube to help.   The first video was on checking KE Jetronic Fuel Pressures.  The second video was on KE Jetronic EHA adjustment.

As I own two KE Jetronic cars and one K Jetronic, It made sense to purchase some fuel pressure gauges.   They were about $100 USD.  The test gauges plug in to the fuel distributor in two places.   The first plug (without the valve) goes into the test port on the side of the fuel distributor.   The second plug goes into the outlet for the cold start valve.     The gauge set comes with the right fittings to rig it up.

KE Jetronic fuel pressure gauges

Immediately I was able to rule out the fuel pumps and fuel pressure regulator as my starting fuel pressure was good.   The test calls for two readings.   the first one is from the test port and the valve closed.    The second is with the valve open to the cold start fitting.   The ideal readings are 6.0 bar with the valve closed and 6.4 bar with the valve open.   What is more important than the actual values is the 0.4 bar difference.

KE Jetronic EHA Adjustment

As can be seen from the picture above, I had an 0.3 bar difference.   This meant the car was too lean – which is what I had observed on the dyno.   Most KE Jetronic cars have an oxygen sensor that controls the operation of the electro-hydraulic actuator (EHA).  The 560 ECE does not have an oxygen sensor.  In this case, the EHA can be adjusted manually.   It is the small back control unit on the right hand side of engine.

KE Jetronic EHA adjustment

Once removed, the slotted screw is removed to allow for adjustment.  A small allen key is then used to adjust the EHA.  In my case, I adjusted it in about one third of a turn.  The EHA is then replaced, carefully to avoid disturbing the o-rings.

With the EHA adjusted and re-fitted, I re-ran the test.  This time, I saw 5.9 bar on the test port with a bit over 6.3 valve open.  Success! I now have the pressures in specification.  I’m happy to leave that bit extra over 6.3 – I would rather be ever so slightly rich than too lean.

560SEC after EHA Adjust

These test were all done at idle.  Next thing was to check the pressures at some higher RPM levels.   I asked a neighbor to hold the car at 1,000, then 2,000 RPM.  The fuel pressures stayed steady at these increased revs.

KE Jetronic EHA adjustmentI also ran another test from a member of BenzWorld.   Holding the revs at 2,000, I pressed on the air flow meter plate.  This tricks the car into adding more fuel.  If the engine is lean, the revs will increase, but if it is not, the car will bog down from getting too much fuel.   In my case, the car bogged down.  This was another sign the pressures were at the right level.

The final test was to check the readings of the potentiometer for the air flow meter.  This is on the other side to the EHA.  Correct spec is 0.7 volts at idle between pins 2-3.   My car was at 0.9, so very close even if not perfect.  The voltage also increased as I pushed down on the air flow meter pressure plate.


After these tests, all evidence points to having fixed the lean running condition of my car.  I don’t have a dyno to test it on, but the car is now adjusted back to the correct specification.    I found the KE Jetronic EHA adjustment to be fairly straightfoward, with the pressure gauges.

Update, 26/11/19:  While the car was in for an A/C regas,  I asked to have it quickly tested on the exhaust gas machine.   Air/Fuel was 14.8, so this adjustment was perfect.  

2019 Mid Florida Auto Show

A couple of weeks ago, while I was in the USA I attended the Mid Florida Auto Show and Lake Mirror Concours.     This posting is a few weeks old, as I didn’t have the cable for my camera to transfer the photos.   I was in Orlando for work, and Lakeland is about an hour or two away.    The Mid Florida Auto show is normally a picturesque event set on the shores of Lake Mirror.   This year, Tropical Storm Nestor hit North Florida.  While Nestor was a fair way away, it was close enough to cause torrential rain in the Central Florida area.     The rain meant the show was moved to a set of multi-story parking lots.   It also drastically reduced turn out.

While I at the show I met Pierre Hedary, who runs a YouTube channel on Classic Mercedes.    If you have not seen his channel, I suggest you check it out.   Pierre runs an independent Mercedes-Benz workshop in the Central Florida area.   He focuses on Classic Mercedes such as the Adenauer,  Fintail Era (110, 111, 112, 113, 108, 109), Compacts (W114/W115), and the cars of the 70s and 80s.  (116, 107, 126, 123, 124 etc).   He is especially known for his expertise on the more esoteric Mercedes designs such as the M189 engine.

Pierre invited me for a tour of his workshop and collection of interesting Mercedes-Benz models.   He also gave me some tips to tune my lean running 560SEC.    At his workshop was a plethora of 111s, 108s, 109s and 113 SLs.  He also had some really interesting models in his own collection such as a W108 280SE 4.5, a W109 300SEL M189 etc.   In some ways his workshop reminded me a bit of MB Spares and Service in Canberra.    Both specialize in similar models and have the same sort of cars at their workshops at any given time.

The highlights of the Mid Florida Auto show was seeing the 300S, which belonged to a local Attorney and Nicolae Ceaușescu’s Rolls Royce Phantom V.   The Phantom and its competitor, the Mercedes-Benz 600 seemed to all too regularly end up as the conveyance of bloodthirsty dictators.     It was also fun to see some Amphicars frolicking in Lake Mirror, as the weather had cleared up by the afternoon.

Despite the weather it was an enjoyable day.   I would like to visit again to see the show as intended.