How to Change Differential Oil in W140 S-Class

Apart from power steering fluid, this has to be the most neglected fluid change on a car. The intervals are usually long, sometimes in excess of 60.000km, but if you have no history on when this was last changed it is probably a good idea of changing it. It might give you a smoother ride with less rear end noise. At least it gives peace of mind and the job is fairly simple.

Preparation

You will need to get some differential oil from the store. 1.4L to be exact, but in practice that means two bottles of fluid. The differential can either take 75W-90 or 85W-90, you have to decide what is best for you. It should be API GL5 quality at least. I chose to put in 85W-90 since I had good experience with that before. Some bottle comes with a little tube which you can use to fill the oil with. This oil is very thick and is a bit tricky to squeeze into the differential. Consider getting an oil pump which will make this job much easier and faster.

As for special tools you will need a 14mm Hex Socket for the drain plugs.

14mm hex socket
14mm hex socket for the drain plug

Also prepare some brake cleaner and rags to clean up underneath the diff while you are there.

Procedure

Make sure the differential oil is fairly warm, if it is summer it will drain ok without driving it first, but if it is a bit cold outside take it for a short spin before draining the oil. The oil will drain out much easier when it is warm.

Start by raising the entire rear end of the car up. Make sure to block the front wheels from rolling since there is no parking brake there. Secure the rear with jack stands so it is safe to work under. It is possible to put the jack stands int he area behind the rear axle, so you can use the jack normally to raise the car.

Raise rear end of car
Raise rear end of car

Inspect for leaks on the differential, they usually are a bit dirty. I hardly ever see a leak free differential, and they seem to seep no matter what, often they stop seeping by themselves too. No hurry in changing seals unless you see a puddle under the car when it is parked for a few days. Yours is probably looking something like in the picture below. Here the oil was very caked on and old, not fresh as far as I could see.

Dirty differential
Dirty differential, clean with brake cleaner and paper/rags
Differential cleaned
Differential cleaned

After the differential is fairly clean. Locate the upper drain plug on the differential. It should be on the left side just in front of the axle. Be sure to loosen this top drain plug first. This trick is to ensure that you can stop the job and still keep driving if you are unable to get the upper or lower drain plug open. If fluid runs out from the top drain plug, the level is topped off. If not, feel it with a finger to estimate how much oil is missing.

Upper differential oil plug
Upper differential oil plug. Located on the left side in front of the axle

When the upper drain plug is loosened. Now it is time to drain the fluid, open the lower plug and keep clear from the flow into the drain pan. Try to hold on to the nut so you do not have to fish for it in stinky oil afterwards. Differential oil is very stinky stuff, and more so when old.

Open drain plug
Open drain plug to let old oil out
Draining differential oil
Stinky and filthy differential oil pouring out

The oil from my car was absolutely stinky and very filthy, it had turn into a totally brown goo. The oil level was not completely full either it seemed. I think the differential oil here was never changed in the car’s lifetime. Good thing I got to it before differential wear started happening. Now it is a good time to check this oil in the drain pan if it has any metal shavings in it. Also stick your finger into the drain hole and see if you can feel any shavings inside. You can also stick in a magnet and check if you find any. Luckily my car had zero metal shavings which I could find.

Inspecting oil pan for metal shavings
Inspecting oil pan for metal shavings. Here there were none

Remember to put back the lower drain plug. No need to torque it, but it should be torqued to snug with a normal sized ratchet, do not over tighten this. Clean the area around so you can spot leaks after.

Now get your fresh oil and squeeze it into the upper drain plug. Either the bottle you bought have a filler tube, or you have a large syringe or a gear oil pump. I use Mobil1 85W-90, but you can choose of course whatever the brand you like, I do not honestly care.

differential oil bottles
Mobil1 85W-90 API GL5

After you have refilled the oil and lowered the car back to the ground. Take it out for a short spin, come back and look under the differential for leaks. Hopefully the ride will be a bit smoother!

Cheers, Robs out!

How to replace the rear Axle Driveshaft on w123

Replacing driveshafts is like changing hips on grandma.

Cracked driveshaft rubber boots? Maybe you have huge slack in the drive line 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 rear 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 change them. They are overbuilt and can take a lot of beating before breaking. The Achilles heel is the flexible rubber boot that covers the spider joints, it 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. This method might be more expensive, but much easier than changing the rubber boots.

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 bell
  • 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 coupĂ© 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, Robs out!

Refurbish of Sub frame Assembly and Differential

Restoring sub frames might be the next Transformer movie

After removing the whole rear sub frame assembly and all it’s components, they needed some love. Under is an example of all the parts (excluding drive shafts) of the sub frame. Have you never worked with these parts you might not have seen it fully before.

I had to remove some surface rust and then repaint all of the parts. It took a while!

rear subframe mounting plates
These rear subframe mounting plates hold the subframe attached to the car at the jack points

Of course there will be new rubber mounts for the sub frame, both front at the mounting plates and at the differential hanger.

differential 280CE before respray
Differential before respray

differential after repaint
Differential got a nice cool color scheme, why not?

Also the subframe needed a good clean up of surface rust, I used a power tool (angle grinder) with a very stiff wire brush to get off the surface rust and old paint.

subframe before refurbish w123
Subframe before refurbish

After an hour or so with the power tool:

subframe cleaned w123
Subframe after rust removal

My hand were smoking due to the heat and hard vibrations when using the power tool, they were sore for a while after as well, tiring.

hands smoking
Glowing hands smoking in the cold air

subframe main part
Subframe main part after repaint