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Rear Wheel Bearings


250 SL, 280 SL


This component is part of the Rear Axle.

Most of the information in this page has been taken from http://www.sl113.org/forums/index.php?topic=4487.0

Definition

A bearing is a part on which a shaft, journal or pivot turns. These bearings are part of the assembly that attaches the rear wheels to the drive shaft.

These are the bearing diagrams for the different cars. Note that the 230SL has drum brakes, and we have no photographs of the assembly. The 250SL and the 280SL have disc brakes. The bearings are similar except for the brakes, and so are the maintenance procedures.

This swing axle differential has two oil seals on each axle. The inner seals isolate the differential 90W oil from the wheel bearings which are packed in bearing grease. The outer seals keep the bearing grease from getting into the brakes.

The right side of the swing axle must be able to hinge with the suspension and the right side wheel bearing is a special barrel shaped "roller bearing" which can actually hinge with the axle.


230 SL


This right side wheel bearing is three or four times more expensive than the left side "ball bearing". Fortunately since "roller bearings" are designed to handle higher loads than a standard "ball bearing", this expensive right side "roller bearing" seldom fails. (Note that an axle sourced from a V8 M-B may also have the "roller bearing" on left side as well.) View the photo below;


Bearing types


Since the rear wheel bearings are isolated from the differential oil, running the car with a low oil level in the differential will not normally cause these bearings to fail. Long term storage, dried out bearing grease, and normal usage may eventually cause a bearing failure. If left in use the bad bearing may seize and may begin to spin inside its seat in the axle housing, wearing the casting itself.

Maintenance

When the bearing fails, you may notice a low pitch groaning noise coming from the rear axle area. It can be further diagnosed by driving the car down the road and swerving from side to side. As the car leans to the side with the bad bearing the noise will increase. As the car leans to the other side the noise may disappear or become less.

In order to fix this, the bearings will need to be replaced.

Despite the difference in brakes between the 250SL or 280SL and the 230SL, the basic procedure is the same except for the brakes. 230SL specific information is added in places, and there are some additional 230SL photos at the end of this document.

Parts needed

  • 1 right side axle wheel bearing "roller cylindrical bearing" #000 981 05 06, or
  • 1 left side rear wheel bearing "ball bearing" #008 981 42 25
  • 1 seal and gasket kit # 111 586 0035 which includes the following parts or can be ordered separately:
    • 1 inner oil seal # 001 997 3446
    • 1 outer oil seal # 001 997 4746
    • 1 paper gasket # 110 423 0079
    • 1 lock plate # 183 353 0373
    • 1 special grooved nut (optional, but comes in the kit) #153 357 0026
  • 2.5 quarts (or 2,5 ltr) of 90w or equivalent gear oil
  • bearing grease (synthetic best)

Special Tools

  • a 14mm drain plug tool or equivalent (a 9/16" allen wrench will work or use a 14mm bolt head in vice grips)

The BBB advises use of a special puller and a special "grooved nut tool". However these items are expensive and not needed. Depending on how tight the bearing is on the axle shaft after removal you may need to take the axle to your local NAPA store or automotive machine shop to have the wheel bearing pressed off. However there is also a simple method which you can use which will work most of the time. To install the new bearing, no special tools will be required.

Others note: I used a regular two arm bearing puller to pull the bearing off the axle. What I had to do though was to take four long flat pieces of steel to fabricate "new" links for the puller claws. If you look at a conventional puller, you will notice how the claws are attached to the screw section with four bolts and four small links. It was a simple matter to just make the longer links to provide the additional reach needed to pull the bearing in the manner they show in the BBB.

To perform the work you will need two jack stands, an oil drain pan and a jack.

Procedure



Rear Wheel

The first step is to place the rear of the car on jack stands and support the rear axle so it is as level as possible.



Drain oil

A 14mm drain plug tool is used to remove the drain plug at the bottom of the differential casting, allowing the 2.5 quarts of gear oil to drain.



Retainer

The rear wheel is removed and the brake caliper can be unbolted and hung out of the way without opening any brake lines. The brake disc can now be removed. In the case of a 230SL the rear drum is removed. The 230SL drums have three threaded holes on the flat side of the drum. Winding three M6 bolts into these threaded holes magically removes the drums.

Unfortunately on the 230SL drum brakes the wheel cylinder must be disconnected to remove the backing plate.

Disc brake cars have a complex emergency brake arrangement, while drum brake cars have the usual complexity of springs and shoes. Pay special attention to the arrangement in either case.


Axle

Disc brake cars have two large holes in the axle wheel hub so the spring retainers holding the emergency brake shoes in place can be removed. Needle nose pliers or small needle nose vice grips can be used through these openings. An old screwdriver can be modified to work as a simple removal tool also. In any case the axle must be stripped of its brake and emergency brake assemblies.

The brake backing plate or bearing retainer is held on by six 13mm nuts around the axle. These can be removed using a socket through the holes in the axle hub.


Axle removal

Drum brake cars will also have to have the two 10mm nuts holding the emergency brake pulley assembly (#20 on the 230SL diagram above). An additional 14mm bolt (#2 on the 230SL diagram) also must be removed behind the brake backing plate on the drum brake cars.

The axle should be ready for removal at this point. In place of the expensive special axle puller, bolt a piece of angle iron or uni strut to the axle and tap it out with a hammer (see above).

Tom Kizer provided an alternative method to remove a rear axle with drum brakes.



Axle out



Vice test


Remove the axle assembly with bearing. Confirm the diagnosis by slightly pinching the bearing in the jaws of a bench vice and turn the axle. The slight pressure of the vice on the bearing will simulate normal load on the axle. You will feel a definite flat spot on the defective bearing as the axle is turned.



Axle

A special "grooved nut" holds the bearing in place. The grooved nut is locked in place by a lock plate which is bent up into the grooves of the nut. Grind a punch so as to fit the groove and straighten the lock plate enough to release the grooved nut.


Grooved nut

The grooved nut can be loosened by use of a special tool, or a spanner wrench, flat drift or even a pipe wrench.



Bearing removal

The axle bearing must be removed next. The BBB shows a very special and expensive puller, your local NAPA or automotive machine shop can press it off. I use another simple trick. Place a block of aluminum or hardwood on the floor. Strike the axle assembly splined end down firmly on the block. With one or two blows the bearing should pop off, (see photo). This method has worked many times for me. Do not use anything harder than aluminum or wood or you may distort the end of the axle.



Inner seal

The old axle seals can easily be removed next. The inner seal located in the axle tube can be tapped with the drift by hitting it inward in one spot so it will twist so it can be pulled out.



Seal installation

The next photo shows the installation of a new seal using a large socket to drive it in place. I coated the outer surface of the seal with gasket shellac to insure a good leak proof seal against the axle housing.



Outer seal

The outer seal located in the backing plate can be tapped out on the workbench.

Find a correct size socket or pipe to drive the new seals in place. Also coat the outer seal surface with gasket shellac to insure a good leakproof seal against the housing. Coat the soft seal lip with some grease so you do not have a "dry" start up. Starting the new seal in straight is the challenge here.



Housing

The bad bearing can vibrate or actually spin in the housing, wearing away its seat. A highly polished suface in the housing can be a sign of bearing rotation in the housing. You can tap a series of punch marks arount the circumference of the housing and also use "Locktite Stud and Bearing Mount" or equivalent to insure a good snug fit for the new bearing.



Housing


230SL photos


Pulling the cover plate off was easy - a tap from the rear and it falls forward. We used Joe's puller design to get the axles out.

We checked the bearings using a vice (with protective plates of lead on the jaws to avoid marking the bearing) as Joe suggested. The bearings were fine. Note that if the bearing needs changing, you will need a new locking plate. Actually locking the nut in is challenging. In the end, and to avoid damaging the bearing, I tightened the nut fully, marked the two places on the locking plate, removed it and then pre-cut the locking plate with a hack saw. It made the job far easier.

After a thorough clean and re-pack, we reassembled the axels. It was a little tricky to get them to slot in, and we had to resist the temptation to 'use a bigger hammer.' They went it after about 10 mins of faffing around. Note that the early 230's don't have the circlip on the axles that the later cars have, and so the need to jack the axle tubes fully in order to get the circlips to lock in is not necessary, though it's probably good practice to get them properly seated. It is, though, unnecessary to remove the springs and stops for the earlier cars.

To reassemble, one needs a paper gasket. We also used Hylomar sealant to bond it properly. We did not have the correct gasket when doing this work so used a suitable card. Here's a photo of making the gasket using a hammer to 'punch' it out of the car to ensure the dimensions are correct:


We then refilled the diff with Castrol SAE 90 (diff) oil and put the drums with new shoes back together. (We then discovered that a brake cylinder had an old broken nipple so now we need to wait for SLS to send a new cylinder - hence the importance of inspecting things properly as you take them apart, not when you're trying to put them together!)

When putting the brakes together, it is very helpful to compress the main spring upon which the shoes pivot (item 50 in the 230SL exploded view, above). This is easily done using two thin cable ties and a mole grip. When fully compressing the spring it is possible to assemble the shoes and bolt them in with all the washers when working single handed. At the end of the process simply cut the cable ties and remove in order to allow the spring to operate properly. Note also that the last step in the process of re-fitting the rear shoes is to put on the top lateral spring (item 13 , above). If it's done earlier, it makes putting everything else together far more difficult. Once that is done, the brake drum can be placed on.

Since we have to wait for some parts, we'll change the brake lines also.

Anyway, again, Joe's instructions are top. It took us about a day of work, but we made life difficult for ourselves at times with the brakes. It could be done more quickly perhaps but it isn't a job to rush. It is far easier than it sounds, although putting the drum brakes back together was a serious chore. Thankfully I had an expert helping hand!


We already had the drums off to change the brake shoes, but here's a few photos of the brake assembly when assembled (taken at the end of the process):





Footnote from Colin Ferns Ltd: I have noticed that the spherical roller bearings now supplied by MB (they are a FAG bearing) have excessive end float. I tried to source another bearing from a bearing supplier but ended up with exactly the same bearing. Pay attention to end float when purchasing these bearings as I have had to switch to a double-roller self aligning bearing in order to eliminate end-float.


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