How to change automatic transmission oil and filter in W123

Reading Time: 7 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!

How to replace the rear Axle Driveshaft on w123

Reading Time: 5 minutes

Cracked driveshaft rubber boots? Maybe you have huge slack in the driveline or leaking fluid from the differential. All these things will lead to either replacing the rear driveshafts or fixing them by changing the rubber boots and gaskets.

Changing the axles is definitely a DIY job. Most times the axles in these cars are overly worn and have lots of slack before people tend to remove them. They are overbuilt and can take a lot of beating before breaking, what is the Achilles heel is the rubber boot in the spider joints which will start leaking when the rubber becomes brittle with age. I will not cover how to replace the spider joint boots, but how to replace the axles completely.

Preparation

Prepare to maybe use half a day or more on this job, you can get away with doing only one axle in a shorter time, but the process of removing one is quite tedious. I encourage to changing both of them since you will also have access to the other axle from within the differential in the process with just using some extra time.

You will need some basic tools:

  • Jack and jack stands
  • Socket tools
  • Torque wrench
  • Pliers

Parts:

  • New axles x2
  • New differential axle gaskets x2
  • Sealant (metal to metal contact) for the differential housing
  • Differential oil 80w-90
  • Locktite bolt glue
Removal Procedure

I’ll cover the procedure here on a station wagon, but the method is almost equal on the coupé and sedan versions, except on those you have to take the rear seats out to access the dampers so in that way it’s a bit easier in the wagon. You should cover the interior before your make dirty spots and oil with your filthy mechanics clothes and hands, you need to access the inside of the car in order to lower the trailing arms fully, it is lowered by removing the upper bolt on the rear dampers. The procedure is the same for cars with and without the hydraulic rear levelling suspension.

rear damper bolt w123
Locate the upper bolt on the rear damper (here it’s the hydraulic strut)

Start by raising the rear of the car and placing it on jack stands. Take off the rear wheels and unbolt the rear calipers and hang them in zip ties without taking off the felxible brake hose. The suspension has to be lowered more than the flexible brake hose can stretch so this is important. place a jack to support the weight of the trailing arms before you go on to loosening the damper bolts.

rear damper placement w123 wagon
Upper hydraulic strut bolt removed

In the wagon, the bolts for the dampers can be accessed behind two black plastic covers behind the back seat rest. When the dampers are loose you can lower the trailing arms fully with the jack.

Then the driveshaft center bolt inside the wheel hub has to be removed. Use two wheel bolts with a bar between them to keep the wheel from rotating while loosening this bolt. Use a puncher to tap the axle carefully out. Usually you can just pull it out with your hands. Unless the suspension is fully lowered there might be difficult to get enough room to fully get the driveshaft out from the hub.

axle bolt w123
Remove the axle bolt by placing a bar between two lug bolts to prevent the hub from spinning. (even I make mistakes sometimes, the caliper should be off before lowering the suspension)

Now is your turn to drain the fluid out of the differential. Drain it in an oil collector and try not to spill all it over. If the oil is warm it will drain faster. It will keep warm after a drive for easily an hour or so.

differential oil change w123
Draining the fluid from the differential

When the differential oil has drained out. You can start removing the the rear differential mount. Use a jack and wooden blocks to support the differential while you remove the top four bolts securing the differential rear rubber hanger to the frame. Use the jack to relieve tension on the bolts while loosening them. Use a long extension for your socket to loosen the four bolts.

differential w123
Support the differential with wooden blocks and a jack.
differential mount w123
Loosen the bolts to the differential mount which are connected to the under body of the car

Then when these bolts are removed. Loosen the two big bolts securing the rubber mount to the differential rear cover. This is so you can access all the differential cover plate bolts after, some are though a bit tricky to reach.  A flexible socket tool joint or similar is nice to have, especially the top two ones. Lower the suspension with the jack to gain more access.

The cover plate for the differential has 8 bolts. Have the oil pan ready so the remaining oil can drain out when the cover is removed.

The only reason anyone bother to remove all these bolts is to access the internals of the differential where there are two small C-clips securing the axle shafts. It is on the outer end of the shaft right in the middle of the cogs. It’s a bit hard to see since all is covers with black oil, but if you have a good light you will see it, if not just turn the shaft 180 degrees around.

inside the w123 differential
Locate the c-clips inside the differential housing

The C-clips have a little tab with a hole in it, so you can drag it out with using a hook or some strong needle nose pliers to drag it out. With the c-clips detached you can remove the axles, just pull it carefully straight outwards. Note the placement of the shims, don’t forget these when putting in the axles again.

leaking old rear axle spider joint
Time to get rid of that old axle which is leaking from the spider joint

The differential axle gaskets also need to be replaced to prevent future leaks. This tends to be quite stuck, so use a crowbar or the back end of a hammer to pry it out.

differential to axle gasket
Prying off the gasket will destroy it

Look in the picture under if you are in doubt whether it is worth to change it. Even if it looks good, the rubber is most likely old and brittle and can start leaking oil at any time later and all this work has been for nothing.

differential gaskets w123
Old vs new differential to axle gaskets

Without the differential gaskets in place it looks like the picture under. Clean the hole before installing new gaskets.

differential w123
Differential with gasket removed and cleaned
Fitting Procedure

Remember to torque all the bolts to the right torque setting when refitting the car back together. Not fun loosing the brakes or entire driveshaft when going down the road.

  • Axle Shaft bolts: 30Nm
  • Differential rear cover bolts to housing: 45Nm
  • Differential rear cover to rubber mount: 119Nm
  • Differential rear rubber mount to under body: 30Nm (with locktight non permanent glue)
  • Brake rear caliper bolts: 89Nm (with locktight (non permanent) bolt glue)

Start by fitting the differential-axle gasket. Also there is a metal spring in the inner sealing ring, apply some thick grease around the metal ring to prevent it from popping off when installing the gasket. Push the new gasket ring by tapping on the edges very carefully until it goes in evenly, the space is very tight.  Or the best way if you have a similar sized tube or tool you can place over the gasket while tapping it in.

axle washer w123
Install the washer after installing the gasket and before installing the driveshaft

Don’t forget to put the washer back in BEFORE you install the new driveshaft!!!! This is easy to forget.. Push the new axle in AFTER you installed the shim, and install the C-clips on the driveshaft ends inside the differential housing.

Install the other drive shaft end in the hub, then put the axle bolt back on. Then you can raise the trailing arms with the jack and install the dampers back on. Wait with the interior until you are completely finished with the other stuff. Then install the brake calipers back on, remember to apply some licktight on the bolts before torquing them.

differential housing cover w123
Cleaned differential housing cover

Time to get that differential housing cover on. Here is where most people have leaking differentials. Use some cloth or paper to clean the excessive oil inside the differential housing and cover. And scrape the mounting surfaces on the cover and the housing, they need to be super clean from oil and dirt and totally flat so there will be no leakage. Clean off all oil deposits with brake cleaner.

anaerobic gasket maker
100x better than silicone

For sealant I used an anaerobic gasket seal. Silicone will deteriorate and small chunks of it will get inside the differential housing. Not recommended. Put some on both the housing and the cover  and glue them together before bolting on the cover.

Refit the lower draining plug. Remove the upper draining plug and fill new 80W-90 gear oil. Try getting a gear oil with a filling tube so you don’t have to mess around with pumps. Fill the differential up with oil until it starts running out of the filling hole, It will hold slightly more than 1L oil (never heard of the imperial system). Remember to put the filler plug back on.

rear axle w123
New rear axle installed

Take your time and you will avoid the mistakes, feel the satisfaction of doing this relatively major repair yourself. Well done!

Cheers!

How to Remove the Propeller Drive shaft + Changing center Bearing

Reading Time: 3 minutes

Propeller drive shaft CPR

Removing the propeller drive shaft (also called the center drive shaft) is necessary when you are removing the engine/transmission, changing the flex disks or removing the differential/ rear subframe.

The procedure is similar to most cars and it is exactly the same for W126 and many Mercedes models. So guide this will work for both. Expect some wrestling and sweat underneath the car since the bolts can be very tightly on.

Theory

I highly recommend to change the center bearing, the center bearing carrier and front and rear flex disks when you remove the drive shaft for whatever reason, simply due to the long time of the job it would be a waste unless you also change these wearing parts with limited life span.

Practice
Removal

Step 1:
Remove the exhaust, check out How to Remove the Exhaust system
Step 2:
Remove the parking brake adjuster cables and springs. You will have to unhook the spring from the adjuster in order to get the cables off. The system is basically an adjusting rod with three cables attached to it and a spring to keep tension on the cable whem the parking brake is released.

Parking brake cable tightener
Remove this assembly to get more access to the drive shaft.

Step 3:
Now on to removing the drive shaft!

Loosen the sleeve nut in the middle of the drive shaft, this is to be able to collapse the drive shaft so it becomes shorter when removing it. Have a helper to apply the brakes so the shaft wont rotate when you try to loosen the sleeve nut. I do not like to apply pressure to the Transmission with the gear in Park due to the possible damage this may cause. Have the car in neutral instead.

sleeve nut drive shaft w123
The Sleeve nut, needs a very large spanner”

Next step is to remove the flex disks, there are one at each side of the drive shaft. The bolts are of a self locking type (the nuts are not completely circular) and they are hard to remove since they are not meant to get loose when you drive. I actually broke my spanner trying to get one stuck bolt off, so here I recommend some long spanners or some form of extension on the spanners to get more torque. Remember simple physics where the torque = force x length, so the longer the better when loosening stuck bolts and nuts. To get the drive shaft off you only have to remove three nuts. The ones that are attached to the drive shaft spider. If you are planning on replacing the flex disk, then you have to remove all 6.

There might be tricky to access a spanner on the side facing the transmission, and you might end up supporting the transmission with a jack and removing the rear transmission mount.

front drive shaft flex disk w123
Front flex disk

Unfortunately you have to remove the three nuts at the differential end as well,  the access here is easier though.

rear flex disk w123
Rear flex disk

Now the drive shaft is hold in place by the center bearing carrier. The center carrier is just hold there by two bolts in the chassis.

drive shaft center bearing carrier
Center bearing carrier

Now you have to collapse the driveshaft by pushing the front side of the shaft in towards the middle to get it loose from the transmission spindle.

The drive shaft can be so corroded onto the flex disk mouting plates that you will not be able to do this easy by hand. I used a long screwdriver to place it between the drive shaft spider and the flex disk and used massive force until it broke loose.

Warning: You might end up damaging the flex disk which i did. It was so corroded that one tab of the flex disk broke off wæstill attached to the spider.

Caution: Be careful when handling the drive shaft so it doesn’t come slamming into the ground or on youself for that matter. The drive shaft needs to be perfectly straight and it is also balanced by the factory to a, so be careful eh?

drive shaft w123
Drive shaft separated
Bearing Replacement

The bearing is most likely stuck in the drive shaft center carrier, always replace this cheap rubber part or your drive shaft will vibrate while driving. Just rip it off or use a knife to cut it so you can access the bearing.

The Bearing is pressed is pressed on the shaft and you need a puller tool like this. Note the placement of the dust caps around the bearing, so you place the the same direction when fitting the new bearing.

puller tool
Bearing puller tool

After pulling out the bearing, insert the new bearing into the new center carrier.

bearing parts w123
Parts distributed, bearing dust caps, center sleeve, new center carrier and bearing, old one to the right.

Remember to insert the inner dust cap before tapping on the  new bearing.

inner bearing dust cap w123
Inner beaing dust cap placement

Use a metal tube to tap on the inner part of the bearing, be careful with the hammering and do this slowly.

tapping on new center bearing driveshaft
Tapping on new center bearing on the drive shaft with a tube
Assembly

Assembly is pretty much the reverse as removal, however you need to spin the drive shaft around a few times after fitting, before tightening the sleeve nut, this is to remove stress on the drive shaft before tightening. The last thing you should do is tightening the sleeve nut!

Always follow the torque specifications on the flex disk bolts!

Cheers, Robs out