How to replace tie rods, center drag link and steering damper on W123

Reading Time: 4 minutes

When your car steering starts to feel floaty and maybe the car is starting to drift to one side so you constantly have to correct when going down a straight road, consider changing the steering linkage components and do a wheel alignment.

I will describe how you replace the tie rods, the center drag link and the steering damper only. I will not describe how to do a wheel alignment, because professional wheel alignment equipment is needed.

Changing the idler arm bushing is also possible if you experience a knocking sound going over bumps, but this procedure will be described later in a separate article.

 Theory

Get the parts needed for this job, they are quite cheap since they are normal wear items on a car.
Parts you should get:

  • Right and left side tie rods
  • Center drag link
  • Steering damper
  • Idler arm bushing (job not described in this article)

You will need a special tool for removing the tie rod ends, this can be picked up quite cheap. Either a tie rod fork or a tie rod press tool will do, the latter will not render the tie rod bushing seal useless, but if you are only changing the parts then this does not matter. Additionally you will need a hammer, a torque wrench, some hex tools and some spanners.

 Practice

Start by raising the front of the car on to jack stands, make sure you block the rear wheels. You will have to be able to remove the front wheels to gain access to the tie rods and also be able to turn the wheels.

Because you are working around the brake rotor, it is important that you wear a dust mask and get a bucket of soapy water and start cleaning the brake rotor and the area around to get rid of all the harmful brake dust before you do any other further work. Think of your health!

When you have cleaned the brake dust, turn the steering wheel all the way left if you are working on the right side, and vica versa.

tie rod tool
Use of tie rod press tool to pop the ends off

Get a small pick and clean road grime from the top of the tie rod so you can get a hex tool inserted in to the top. You will loose the bolt with a spanner, but because the whole tie rod end will rotate you have to counter it with the hex tool. When he bolt is off you will notice the tie rod is still extremely stuck. Hit the side hard a couple of times with a hammer to knock the rusted component loose, this might help to loosen it. Insert the tie rod press remove tool and start tightening until the tie rod pops off, this can sometimes be violent. Be careful and don’t lie under it when this happens, because it can happen quite suddenly and the tool and parts might fall on top of you, ouch!

You have to repeat the process twice on each tie rod for both of the car’s sides.

When you have gotten both off, measure the length by counting the turns the tie rod end can rotate before it comes off, it is important that this is exactly the same for the new tie rod. The new and old tie rod should have exactly the same end so your car will have the same handling properties, so it will not be too much “toe in” or “toe out”. The workshop will do the last alignment with reference to the manufacturer specifications after you take the car there. Tighten the tie rod adjustment screw so it will not rotate when the lengths are right.

w123 steering damper
New vs old steering damper. Old one was leaking and in bad condition

Time to take the steering damper off. This is the easiest procedure, it is held in place with two bolts only.

w123 steering damper bolt
Steering damper bolt on the frame side.

One end is attached to the frame of the car while the other one is attached to the center drag link.

Now it is time to get the center drag link off, the procedure is the same here as with the tie rods. Except you don’t have to adjust anything.

W123 center drag link nut
Unbolting the center drag link nut

The fitting is pretty much straight forward, but remember to use the right torque settings for the tie rod mounting nuts. You should tighten them down only to 41Nm, the tie rods will be stuck in the steering arm and the nuts have plastic inserts in them. Remember throw out the old tie rod ends nuts since thee plastic self tightening mechanism is word. The new tie rods and drag link comes with new nuts and be sure to use these. Loosing control of the car because of some old nuts would be as stupid as driving off a cliff.

Safety warning:
You absolutely have to take the car to a workshop where they will do a new wheel alignment. This must always be done right after changing the lower suspension parts!

Cheers, Robs out 

 

How to change fuel injectors in the M110 engine

Reading Time: 5 minutes

Ever felt that the engine is not making as much power as it used to? And that the fuel economy has been slowly decreasing? The first thing you should check is the condition of your injectors. Unless you have a pressure tester for the injectors, you would have to guess out from the age of the injectors. If they are more than 10 years old I would suggest to change them, that said if the injectors are relatively cheap since they vary a lot in price between the models. They are still relatively cheap for the M110 engine. E.g. If you have the rarer M100 engine, it will cost you nearly a new house to buy new injectors!

I will describe how you change the injectors with new ones. Refurbishing the old ones is a bit more cumbersome and it needs a pressure tester which you can clean them with and test for release pressure and spray pattern.

 Theory

Changing the fuel injectors is not difficult and you don’t need much preparation except acquiring new injectors, gaskets and o-rings. There are two gaskets per injector you will have to change or you will end up leaking fuel which is expensive. You can change the injectors easily in an afternoon. I also recommend to change the fuel filter at the same time to not clog up your new injectors.

Practice

 Removal

Start with opening your hood and disconnecting the battery. Sparks can make explosions from gasoline vapor when you are working with the fuel system, and we don’t want that to happen.

mercedes m110 engine without air filter housing
Remove air filter housing to gain access

Remove the air filter housing to get access to the fuel delivery system.

The four front injectors you can now access without removing more stuff, but to gain access for the last two, you have to remove throttle linkages, fuel hard lines and a fuel regulator. We’ll come to that later.

Two and two injectors are held in place by a single metal plate, to remove the metal plate loosen the injector hard lines first. The injector hard lines should not sit on very hard unless they corroded over time or they have been over tightened. Use two spanners, one 14mm to loose the line nut and one 12mm on the injector itself to to keep it from rotating.

fuel injector removal
Loosen fuel injector hard lines with two spanners.

When two hard lines are loosened you can bend them a little to the side to get more access and then remove the injector hold-down plate.

injector removal
Loosen the injector hold down plate

After the plate is removed you can pull out the injectors with you fingers, they sit loose in there. The injector housing will be left, This plastic housing you can just pull out straight too, but be warned, do not use excessive force and pull only the housing straight out with you fingers, don’t use tools or you might damage it. It most likely have become quite brittle by heat over the years. If they are in such a bad condition they are cracked, you have to replace them.

Most likely some of the injector housing gaskets do not come out with the housing, but is still sitting in the injector hole, use a small flat screwdriver and pry it carefully out.

After removing the first four injectors, the two back injectors are left, now the big job starts. See in the picture below that these things blocks access to the fuel injectors.

fuel injector access
Throttle linkage, hard lines, fuel stuff blocking access to the injectors.

Start with removing the throttle linkage. Remove the pin and the c-clip along the ball joint. I use a wide flat screwdriver to pry the ball joints off. Remove some more linkages and then you are ready to remove the regulator.

throttle link removal
Remove the throttle linkage.

Warning:
Get a small collecting can of some sorts and tilt it towards the injector line shown in the picture below. Loosen it and fuel with shoot out with high pressure. Wait until the fuel stops flowing, then loosen the second fuel line connected to the regulator.

fuel line disassembly
Fuel will shoot out when you loosen this line so be prepared with a can of some sort.

Also loosen the vacuum lines before removing the fuel regulator, it is fastened to a bracket with two small bolts.

removing fuel regulator m110
Unbolt the fuel regulator.

Now you should have clear access to the last two injectors.

fuel injector removal M110
Clear access for the last two injectors.
Inspection

Now is the time to inspect the old injectors and look at those old brittle gaskets. It is a reason why your car was using excessive fuel…

injector o-rings
New vs. old, looks can deceive.

My old gaskets were super hard, especially the round outer ones. No wonder why there was a lot of dirt around the injector area by the engine, they have probably been leaking a while. This job should have been done years ago. I didn’t notice it when the engine performance still was very good, but obviously not optimal when looking at this leaking issue. The old injectors I don’t even bother testing, I will just throw the old ones and put in new ones.

brittle old injector o-ring
Just look how brittle the old injector o-rings were. They must have given little sealing when they are hard as rock!
Assembly

This is how you should assemble the injector with the gaskets:

  1. Pop on the big rubber gasket on the injector itself.
  2. Pop on the little rubber ring on the injector plastic holder.
  3. Pop the injector holder into the engine block until you hear and feel a nice pop.
  4. Slide all the injectors into the holders. Put the hold-down plates over them and tighten.
injector assembly M110 engine
Injector assembly

The injectors will now have a good seal and no fuel will leak. It is also a good idea to clean up the area around the injector holes in the engine before assembly. Also try to be super clean with the new injectors, keeping the plastic cups on as long as possible before fitting them.

No you also have the perfect opportunity to lubricate all the throttle linkages, such as the pivot points and ball joints, I know they have been neglected for years and we are all guilty as charged. However now is the perfect opportunity for redemption. Remove all the linkages and pivot plates, clean them and apply new synthetic grease that will last a while and hold up to water and heat from the engine.

When everything is bolted back together, there is no such thing as dreadful bleeding like in a diesel. Just crank the engine over a few times and the engine should start, it will run rough for a little while until the pressure have settled, and you might experience hard start the first couple of times before the first drive. This is the time when you realize if the electric fuel pump needs replacement or not, mine is some years old and still going strong, although it have been replaced a couple of times the last 15 years.

Cheers, Robs out! 

How to remove the M110 engine from W126/W123

Reading Time: 10 minutes

If you did enough work with cars you end up some day with the need of removing the engine, the very heart of any car. Think of it as heart surgery, but not entirely so complicated. Actually quite easy compared to many other car related tasks, but it’s a long job if you venture down this road.

So how do you take out the M110 engine from a Benz? I’ll teach you the dark arts of car surgery so stay with me in this dreadfully long post.

Always leave the transmission on the engine when pulling it out..

Theory

If you have either w123 or w126 the procedure is almost the exact same. The complication will be if you have an AC or not and small difference in wiring and placement around in the engine bay. Usually the bigger the engine the more difficult it is to get out since the space gets really tight and hard to get to places when removing stuff.

If you are doing major engine overhaul or need to do something with the transmission, it is best to just take out the engine with the transmission. Always leave the transmission on the engine when pulling it out even if just doing engine work.

Preparation

Preparation is key like most things in life. Don’t plan to use your car in the next few days, or a week if you are new to car fixing. Taking out the engine can be done in under a day and putting it just takes a bit more time. This is definitely a job where more people can be helpful, so go get your buddies and offer them some beers.

You need to acquire an engine lifter also called an elephant jack, and some good quality lifting chain and shackles that are rated for some hundred kgs (I think the M110 is not heavier than 300kg, but you have to cross check that since I don’t have the exact numbers). A very nice tool to have is an engine tilter which you can hang from the lifter. It will make your life easier since the engine needs to get out of the engine bay beam at a very tilted angle, but it is doable without. I made it without, but it required some wrestling and tryouts with different chain lengths.

Other than that you basically need some jack stands and a basic socket tool set, and of course patience which is found at the bottom of the beer glass.

SAFETY WARNING:

NEVER crawl under or have any body parts like your arm, or place your friends under the hanging engine and crane while lifting the engine. Then you won’t come at harm if the lifting mechanism should fail and the entire engine come smashing down. The engine will be needed to be lifted quite high to get over the front support beam in the engine bay and you must take lifting heavy objects very seriously. Also try to minimize the time of the actual lift, not leaving the engine hanging, but setting it down as fast as you have it outside the engine bay. This will minimize the time of potential hazards hanging from the crane.

Practice

Procedure

The first thing you will do is to remove the battery and start to drain engine fluids. You will be removing oil and coolant hoses connected to the engine. Start with the engine coolant, open the heater switches to full heating then drain fluid via the radiator drain and the engine block drain. Check out How to do a coolant change on the M110 engine. Remember to put the caps back in in order to not loose them and to prevent dirt from entering the system.

Then drain the oil sump. When it has drained disconnect the hoses to the oil cooler next to the radiator, lots of oil will come dripping out of here as well so watch out.

It is not necessary to drain out all the automatic transmission fluid if you do not plan to do any transmission related job.

The third liquid to drain is the power steering fluid. Open the power steering reservoir cap and suck out the oil with a oil sucking pump. When empty disconnect the hoses to the power steering reservoir and be ready for more of this oil to come leaking out of both the reservoir and the steering box. Sometimes the hoses can be tricky to get off while the engine is still in the car. I could only get one off and had to connect the second hose when the engine was lifted slightly up.

power fluid reservoir w123
Suck out the power steering fluid

If your car has an automatic transmission, the fluid is also cooled via the lower radiator and connected with two flexible hoses. It is not necessary to drain out all the automatic transmission fluid if you do not plan to do any transmission related job. Instead, when the car is standing level, disconnect the two flexible hoses from the hard lines which transports the fluid to the radiator. Some fluid will come dripping out, mostly from the radiator. Carefully clean the tips of both hard lines, then cover them securely with duct tape sealing the holes to prevent more fluid to leak out and preventing dirt to enter. This way you are not needed to drain the automatic transmission fluid which takes forever.

transmission cooler lines w126
Disconnect the transmission cooler lines.

After the fluids are drained, start by removing the engine two coolant hoses connected to the radiator and all heater hoses connected to the chassis.

removal of lower radiator hose w126
Remove the lower radiator hose.
radiator hose M110
Disconnect the radiator hoses and and it should look like this when the top ine is removed.

After the hoses are disconnected, the exhaust is needed to be removed. I really dislike this part since it involves heavy and big parts. Now you need to raise the car up on jack stands for access. I personally use ramps for the front wheel so I can just drive the front up, and then raise the back end up on stands. For me this is much quicker. If you have a car lift, then bless you sir.

disconnecting heater hoses W126
Disconnect every heater hose you can see that is attached to the engine.

With car up on jack stands, the exhaust needs to be loosened at the manifolds. You only need to loosen four bolts when you have the twin pipes, but they can be a pain in the butt since they always are rusty due to the heat.

exhaust pipe removal w126
Disconnect the exhaust pipes from the manifolds.

When the manifold bolts are loosed, support the front end of the exhaust from under the car before you loosen the exhaust support that is on the transmission. Now the exhaust is only hanging by the rubber donuts at the back and sitting on the support at the front. One last thing to loosen before you remove the exhaust, is to completely is to remove the starter motor ground cable, which the exhaust pipe can get stuck at when you try to drag it out from the back of the car.

starter motor ground cable M110
Loosen the starter motor ground cable.

When the starter motor ground cable is loosened, lower the exhaust to the ground with removing your front support and removing/ cutting the rubber hangers. Be careful so it doesn’t fall on you since the exhaust system is very heavy. You should have some help when removing the exhaust system. Finish by dragging the exhaust out from the rear of the car while rotating it sideways so the front pipes don’t get stuck.

Also make sure the automatic transmission is set to neutral to prevent stresses internally if the transmission is set to park (the flex-disc bushing bolts are usually set to very high torque..

Now with the exhaust removed the fun part starts. The drive shaft has to be disconnected from the rear of the transmission output. First remove all the aluminum heat covers under the car. Block the back wheels from turning, by handbrake or the pedal brake or whatever, this to prevent the shaft from turning when you loosen the bolts. Also make sure the automatic transmission is set to neutral to prevent stresses internally if the transmission is set to park (the flex-disc bushing bolts are usually set to very high torque + corrosion). Loosen the drive shaft collapsing bolt first, which is located just in front of the center rubber bearing. This way you are able to collapse the drive shaft and remove the front part from the transmission later. Before removing the flex disk nuts, it’s a good idea to remove the transmission back support plate to get greater access with spanners, just remember to support support the weight of the transmission with a jack, slightly raising it so it won’t fall down when you remove the plate along with the rubber mounting to the transmission. Then finish by loosen the 3 flex-disc nuts that are connected to the drive shaft. The other three nuts you can leave in and the flex-disc will stay on the transmission while pulling out the engine. Check out How to Remove the Propeller Drive shaft.

Hopefully you managed to loosen the front drive shaft without too much effort and being strong like some 80s hero. While you’re already under the car, it is a good time to disconnect the three control wires that are connected to the transmissions along with the shifter rod. Place them out of the way of the transmission so they will not get caught or stuck later.

automatic transmission cable w126
No tools needed for this on, just pull it out.
automatic transmission cable w126
The cable is secured with one bolt.
automatic transmission cable w126 w126
The cable has a plastic locking system which you have to turn first and then pull to get it out.
Mercedes w126 transmission shifter bushing
Disconnect the shifter rod from the transmission. Here the bushing is so worn and dried up that I would never reuse, replace at any circumstance when this worn. Since the car actually disengage the park gear when the car is parked!

When you’re done with the transmission cables, it’s the time to remove the radiator and the oil cooler. They are held only with clamps and are easy to remove. However the fan needs to be loosened before the radiator can be pulled out. Take care of the sharp fins on the radiator to not cut yourself or to ruin it if you want to reuse the radiator.

Radiator fan M110
Loosen the radiator fan to get more access.

When you think you have removed all the hoses and wires that are connected to the engine, then check again, and then recheck the recheck.

Radiator removed from Mercedes W126 280CE
Radiator and oil cooler removed.

There are many wires around the top of the engine, like grounding wires and other various wires and hard vacuum lines. Before you start removing all the cables and vacuum lines, and there is a lot of them, use a camera or write down which one goes where in order for you to remember, then the reassembly will be much less frustrating! You can for instance write on a piece of tape what the wire is connected to and tape it around the wire. Make sure all the wires and vacuum lines that are connected to the chassis are disconnected before removing the engine, otherwise they will be ripped out and broken easily. I will not show all the images of every wire  here, but will show some example pictures.

Various electrical wires
Fuel hard lines
Hidden vacuum lines
Coil and ignition wires

When you think you have removed all the hoses and wires that are connected to the engine, then check again, and then recheck the recheck. It might be a good idea to have an extra pair of eyes. Do not rush it.

Ok, so are you ready to remove the engine? No!! You have to unbolt the engine mounts to free the engine from the chassis first! Do not worry, the engine will not move or fall off while you do this. I do not have the picture here, but you need to unbolt from the underside of the car. There are one hex bolt on each side up inside some holes, use a torch to see them, and an extender for your hexagon bits. The are sitting there quite hard, so make sure you have the hex tool fully inside the bolt before applying force. If you round off these bolts you will have a huge problem! Once they both are removed, the engine is free from it’s base. Lower the car unto the floor again down from the jack stands.

Now and the engine can be pulled out. Move the front bonnet in the vertical upright position, in that way there is no need to remove the hood of the car. The bonnet mechanism is an ingenious design by Benz.

Move your elephant jack in position and use shackles to fasten the engine to the chain, the chain thick enough to withstand at least 300 kg. There are two “ears” which you can fasten to the engine at the rear, and one “ear” at the front of the engine. Take care to not damage any of the injector hard lines that are very close at the right side of the engine, if needed bend them a little to make more room for the shackles. The best would be to use an engine tilter to secure the chains in, but I didn’t have this tool, but it went fine without it, then you just more rely on a helping hand. Since I did not have the engine tilter, I adjusted the chain to be shorter at the front than at the rear ones, so the engine will tilt upwards at the front, in order to get the front part of the engine above the front chassis, and also lower the transmission under the firewall.

M110 engine removal w126
Engine shackled up! Ready to go!

Slowly start lifting the engine with the jack, also making sure the transmission do not hit the ground or it gets stuck at the underside of the car. Make sure all wires are out of the way and they don’t get caught on something. Basically continue until the engine is high enough so it clears the front chassis frame, you might also need to shift the car a little back and forth by pushing it, obviously having the park brake off since you need to move the car often.

M110 Engine removal w126
Engine in mid air, slightly dangerous and time should not be wasted at this point.

Never ever move the engine lifter while the engine is hanging high up. Just push the car backwards when the engine is high enough and immediately lower the engine so it sits just inches above the ground. Then you can start moving the engine it a bit around, but put it down somewhere safe as fast as possible.

M110 engine removed w126
Engine completely removed.

I hope you liked the procedure, now go out and actually do it, cheers!

Robs out! 

M110 engine mercedes benmz

 Back ground story of this engine pull out

Over the summer back in 2015 I had one goal with dealing with cars and that was to pull a M110 engine and transmission out of the rusty 280SE that had been standing still and taking up space for some years already. The car was destined to be scrapped due to rust, but the condition of the engine and transmission is surprisingly good after over 300.000 kilometers. So I got to it and pulled the engine with the transmission out and then the rest of the car got scrapped. Good riddance, it’s a huge car taking up space for nothing. 

How to change automatic transmission oil and filter in W123

Reading Time: 8 minutes

Now to the post you all have been waiting for. Time to defy old myths and the car companies themselves! Mercedes usually warns about changing the transmission oil yourself and in newer models they are so called sealed where you cannot even measure the fluid level without buying an accessory dipstick. I do not agree on this level of manufacturer control and you can totally do this yourself even on a Mercedes. Sometimes I really think that car companies have a bad attitude towards their customers. Just take for example the VW diesel scandal which they tried to cheat everyone…

Thoughts

Fluid changes are the number one maintenance priority of making your car perform optimally and mitigating excessive wear and damage. Fluid changes of the transmission oil should always be your concern. Some idiot say that changing automatic transmission oil in an old car will cause it to slip and thus you should not change oil. This is only true if the transmission is already very worn/broken and the only thing keeping the transmission from slipping is the high friction of metal particles and the old smudgy oil which is totally broken down and provides little friction and cooling. Then of course it might starting slipping when fresh oil is added which sole purpose is to give less friction and cool the internals. However not changing the oil will only delay the inevitable of total transmission failure.

A good transmission will always benefit from an oil change since this reduces friction and wear!

Mercedes does not recommend this job and it should be left to the “professionals”, all my respect to the mechanics, but they work on a hectic schedule and the quality of the oil change might not be perfect 100% of the time. Not saying they usually make mistakes, because they usually don’t when talking about good workshops. Anyway I think changing automatic transmission fluid is something you can easily do yourself on a Mercedes as any other car. It is not as easy as changing the engine oil, but not very difficult either. There are some fall pits so just be prepared IN ADVANCE.

I cover here the procedure for the M110 engine with the 722.xxx transmission. The procedure is basically the same for all older Mercs. Changing the automatic oil will give you a good indication about the condition of your transmission unit so you can take preventative measures or just continue like usual.

Preparation

You will need to get some new stuff

  • 6.6L ATF Dex3 on earlier models
  • 6.1L ATF Dex3 on later models (usually 81-85)
  • New filter and oil pan seal (get the right one from Mercedes)
  • Narrow Funnel
  • Brake cleaner
  • Shop towels (lint free)
  • Jack stands and jack
  • Dripping pan
  • Tools – sockets and hex bit
  • Torque wrench
Draining

Unless it is a very warm summer day, go for a drive (recommended is 24km to really warm up the transmission to operating temperature, but sure you can go less if it’s highway speeds) , it will drain easier and faster when warm. Try planning to do this work when coming back from work or after a trip to the store to avoid unnecessary driving.

There are two choices when draining the fluid. Either just from the oil pan or both from the oil pan and the torque converter. I highly recommend to drain from both so you can get rid of as much of the old oil as possible.

Torque converter mercedes 280ce
Torque converter, but no drain plug in sight. The engine has to be turned.

Get the car up on jack stands, at least in the front. Block the wheels and apply the parking brake. Put the Transmission in Neutral (N). Start by locating the torque converter at the front of the transmission. In 99% of the cases you will have to turn the engine so the torque converter drain plug is pointing straight down so you can access it. In order to turn the torque converter you will have to have the car in Neutral! Use a socket wrench to turn the crankshaft pulley bolt in front of the engine and rotate the engine CLOCKWISE. If you have a helper he or she can tell you when the torque converter drain plug is coming into sight. Otherwise you have to crank the engine a bit at a time.

Torque converter drain plug mercedes 280ce
Torque converter drain plug in position for draining.

When you turned the engine so you can see the drain plug, don’t drain the torque converter before you have started draining the oil pan.

Open the oil pan drain plug with a hex socket, be careful to avoid burning yourself on the warm oil suddenly coming out very fast! Do the last unscrewing by hand to catch the bolt so it doesn’t fall into the drain pan.

automatic transmission oil
Draining the transmission oil pan

When no more oil is coming out reinstall the drain plug so you won’t loose it. Now you can remove the torque converter bolt with the same procedure as with the pan. Reinstall when no oil is coming out of the torque converter.

Now it is time to remove the oil pan completely for installing the new filter. The pan is secured with 6 bolts. be careful to hold it horizontally when loosing the last bolts because the pan contains a lot of oil still. After the pan is removed, let the fluid drip for a while from the valve body before removing the filter. Cleanliness at this point is of importance, do not wipe off the oil coming out of the valve body or you might get dirt on the valve body which is quite bad. It is pretty hard to clean the valve body since oil is constantly coming slowly out of it underneath for days.

The filter is held by three Phillips screws, be careful to not loose these screws! Also be careful of even more fluid coming fast at you when removing the filter from the valve body.

With the filter gone, the transmission will keep on dripping slowly, I mean for days if left like this. So have the drain pan under at all times.

The quantity in the drain pain will determine how much oil you need to add later. Overfilling the automatic transmission is not good due to overpressure which may lead to excessive fluid leaks and foaming of the oil.

Inspection

Now it is time to inspect the oil pan for metal particles, and fluid quality. If there are no visible particles and the fluid has a fresh red color (slightly darker than new oil is normal) and there are no oil sludge at the bottom of your pan, your transmission is just fine and you have changed the fluid in time. Also use your smell, the fluid should have a sweet smell and not smell like excessive burnt oil. If  you find a very tiny amount of metal particles and no sludge in the pan, your transmission is probably fine too, but the mileage of the car is starting to show and you should consider finding a replacement transmission. If there are both particles and the oil is very sludgy and of dark color, then you probably have noticed some shifting problems already. Also the fluid change have been long overdue and the clutches are starting to wear out. Decide if you should change or service your transmission!

transmission oil pan w123
Inspection for metal particles and sludge in the oil pan. The oil here had a sweet smell and was only a bit darker red than new oil which is perfectly normal. In the picture it might look that it had some metal particles but it is simply some dirt that fell off from beneath the car and my sloppy handling before I managed to take the picture.

In my car, the pan was empty of particles and sludge, the oil also was very red and clear still after many years as seen in the picture, however I did not drive the car a lot either the last years since it has been in a “project state”. The shifting is super smooth and I have not encountered any shifting problems. These transmissions are usually rock solid and will outlast the car itself, only if however if the fluid have been changed at regular intervals.

Cleanliness

Clean the pan very throughly with some brake cleaner, wipe it completely dry with no fluffs from paper hanging inside it. Use your palm to feel it is super smooth and no dirt traces are left. Now you can also clean the surface of the transmission where it meets the seal, so you can expect a leak free gasket around the pan. Do not clean the valve body though, just leave it wet with fluid.

Cleaned transmission oil pan w123
Cleaned transmission oil pan and new gasket
Installation and Refill

Fit the new filter and apply the new gasket to the pan.

Install the oil pan and do not over tighten the bolts to not crush the gasket, make the rubber do the sealing and not brute force. Use a crisscrossing pattern like tightening the lug bolts to ensure evenly distributed gasket. If you are OCD then you should use a torque wrench.

Now time is due to measure the quantity of oil you extracted. A leak free automatic transmission will not use any oil and this is the quantity you should use. Pour in exactly this amount into the transmission through the filler tube, which also happens to be the fluid level checking tube. You have to use a narrow funnel to avoid spilling oil over your (hot) manifold which will make a lot of smoke and can cause fires.

Filling transmissio oil 280CE
Fill transmission oil through the filler/measurement tube. Use a funnel

Inspect under the transmission to see if there are any leaks. Then it is time to start the engine. Let it go for a few minutes before you start engaging all the gears one by one. Do this gear cycling  3-4 times with a minute in between so the fluid can distribute itself within the transmission.

gear lever mercedes w123 280CE

gear level mercedes w123 280ce
Cycle through the gears 3-4 times with staying in each gear for about a minute
Level measurement

After this is done, check the fluid level again with the car running in idle. It should be some below the maximum mark, also it can also be slightly under the minimum when the transmission is not warm. The level will usually be below minimum when the oil is cold even when the transmission is filled with exact fluid quantity. The transmission oil heats up slower and you need to go for a drive to get the right operating temperature, and the fluid will start expanding reaching to the recommended level. Check under the car again now while car is running to be sure there are no leaks. Then go out for a spin, drive at least 24km at normal cruising speeds. Do not race or do any high RPM of the car. When coming back after your drive the oil should have reached the right operating temperature. Remember to keep the car idling when checking the fluid level again. If the fluid level is still under the minimum mark, fill more ATF slowly and re check until it reaches between min and max level on the dipstick. If it is already this level, then you have filled the right amount and your car has probably not leaked a single drop between oil changes. Normally you have to refill some after this test drive so the level can reach the desired level between minimum and maximum, older cars have a habit of sweating slightly some oil through old gaskets.

If you over fill, so that the level is above maximum, do not panic! Then you have to suck out some fluid from the filler tube with some brake bleeder tool or similar oil extractor hose. It is critical that the level is between the max and the min mark, since little fluid can make gears slip and wear out the clutch material, and too much fluid can make to much pressure and your transmission might start leaking from gaskets and the oil can start foaming.

The only big difference here between engine oil and automatic transmission fluid, is that the transmission fluid has to be warm and the engine has to be running while checking the level. The engine oil can just be checked while parked and also when the engine is cold. If you happen to check your transmission fluid and forgot to turn on the engine, you would swear and rip your hair out since it looks like there is too much oil, then you turn on your engine, and while the fluid is still cold it looks like it is too little.

-> Correct automatic transmission oil measurement is when fluid is warm with engine at idle 🙂

Cheers, Robs out!