1997 S600 Bosch Alternator Bearing Replacement

 

An article written and kindly provided by Brett Allison

This article describes replacement of the alternator bearings in my 1997 S600 sedan.  Keep in mind that different model years may be different.  My alternator had been making quite a racket for some time.  Electrically it was fine, so I figured it was just the bearings that were bad.  If it was just bearings, I wasn’t inclined to pay for a completely new (or rebuilt) one.  I was right.  With the new bearings, the alternator runs quiet and smooth, now.  This Range Rover web site covers bearing replacement in the Range Rover Bosch alternator.

http://www.rangerovers.net/repairdetails/electrical/boschaltrepair.htm

I found my W140’s alternator was nearly identical with the exception of a larger front bearing.

Special tools for the job:

We ground down the triple square bit a little and drilled out the socket so that the bit would fit through the socket.  See the part about pulley removal to see a pic.  Alternatively, an air impact wrench may work to remove and install the pulley nut without messing with special tools.

Removal of the alternator is not simple.  It seems nothing is in the V12’s engine compartment.  You must remove the front anti-roll bar, and you must drain the coolant and then remove the lower coolant hose.

1.  I put the front wheels on ramps to remove the anti-roll bar.  It seemed there was a little tension on the anti-roll bar when the wheels were allowed to hang.  Getting the bar off the end links (and reinstalling on the end links) was easier with the suspension compressed with the wheels on ramps.  Do not work under your car without the car properly supported (lift, jack stands, or ramps)!

2.  Disconnect the ground (negative) terminal on the battery.  You will need your radio code to reactivate the radio, and you will have to reprogram the express function of the windows when you’re done.

3.  Remove the ADS sensor attached to the right side of the bar.  Of course, if you don’t have ADS, you won’t have this.  Disconnect the electrical connector and remove the U-bolt and the two nuts holding the bracket to the studs.  (Everything is so clean because I took these pics during reassembly.)  Note the flat on the bar that locates the sensor arm.

4.  Remove the 2 nuts attaching the sway bar links at the end of the bar.  These are ball joints, and you will likely have to counterhold the stud with a 6 mm Allen while turning the nut.  I used a crowfoot on the nut and let the counterholding bar lever itself against something solid.  These nuts are self-locking and should be replaced with brand new ones.  They get 80 Nm of torque.

5.  Remove the 4 nuts (2 on each bracket) that attach the bar to the frame, and remove the bar.  These nuts are also self-locking and should be replaced with new ones.  These nuts get 20 Nm.

6.  Disconnect the 2 wires on the backside of the alternator.  You have to crawl all the way underneath and look toward the front of the car above the cross member to see the back of the alternator.  I used a long extension to reach forward to the alternator.

7.  Remove the lower coolant hose.  Here’s why you need to remove it.  It blocks removal of the bolts.  In fact, there is a nub molded into the hose to keep the alternator mounting bolt from rubbing through the hose.

You can simply separate the hose from the radiator and let it drain, or you can drain from the radiator stopcock on the left side of the radiator and then remove the hose.  About 2.5 gallons will drain out.  Have a big enough container and make sure it is clean if you will reuse the coolant..  To drain from the stopcock, pop out the panel on the left side of the bumper (where the outside temperature probe is mounted).  You will find the stopcock right behind the panel.  Put a clean hose on the nipple, and open the stopcock with a screwdriver.

Drain completely, and then remove the hose clamps on the hose and remove the hose from the radiator and the water pump.

8.  Slacken the belt and remove it from the alternator pulley.  No picture here since I really couldn’t get a good one.  It’s a tight squeeze.  Working from underneath on the left side of the engine, put a 15 mm socket with a breaker bar on the nut in the middle of the tensioner pulley, which is just to the left side of the crankshaft pulley.  I had to push the fan shroud around a bit to work the socket onto the bolt.  Rotate the tensioner to release tension, and remove the belt from one of the pulleys.  Then work the belt off the alternator.

9.  Remove the 2 alternator mounting bolts and remove the alternator.  The bolts are 15 mm.

10.  Remove the 22 mm pulley nut.  With the alternator out of the car, try your impact wrench on the pulley nut.  If you don’t have one, get your special tools out.  You may need to get creative with bracing one wrench and turning the other.  The nut is spun on there pretty tight.  I don’t know what the recommended torque is.

11. Remove the plastic backing.  Remove three small screws and one large screw.  Then release three clips around the perimeter, and simply pry the cover off.

12.  Remove the voltage regulator.  Here are the numbers on my alternator’s regulator.

The regulator is held in by 2 Phillips screws.  Remove them and remove the regulator.  The brushes are spring loaded.  Note how much length is left.  If they are almost worn completely down, you should try to replace the regulator.  I’m not sure if you can buy these regulators easily.  You may have to see if a rebuilding shop will sell you just the regulator.

13.  Split the case.  Mark the case halves so that you can put it back together correctly.  Remove the 4 bolts around the perimeter, and pry the case halves apart.  The front half will come out with the rotor attached.

14.  Recover the rear bearing cup.  The rear bearing has a plastic cup on it.  It may have stuck in the rear case half.  Find it, clean it, and don’t lose it.

15.  Pull the rear bearing off the shaft.  Do not use pressing force on the plastic end of the shaft.  What looks like the end of the shaft is actually a plastic sleeve formed over the shaft, that holds the electric contacts (the copper slip rings) for the voltage regulator brushes.  Guide the tip of the puller into the center of the hole so that it contacts the metal shaft directly.

Note the bearing markings.  The rear bearing is a standard size 6203 bearing (40 mm outer diameter x 17 mm inner diameter x 12 mm width).  You can find this bearing online at many bearing sellers.  Make sure to buy the 6203 2RS (2 rubber seal) bearing.  You can go with the inexpensive Chinese or Japanese import bearing, which costs about $6, or you can go with a name brand one for 7-8 times more (SKF or FAG).  I decided to try the cheap Chinese made bearing.  If the bearing goes bad in short order, I will consider getting the more expensive bearing next time.

16.  Remove the rotor from the front housing.  First remove the 4 screws in the face of the alternator.  These can be corroded and stuck pretty good.  I used a hand impact screwdriver to remove my screws.  I replaced them with new stainless steel screws and used a little anti-seize paste when reassembling.  I then used a hammer to drive the rotor with the front bearing attached out of the housing.

17.  Pull the front bearing and thrust washer off the shaft.  Note the orientation of the thrust washer.  It has a shoulder on the side that faces the bearing.  The front bearing is a big bearing that is apparently an oddball size (52 mm outer diameter x 17 mm inner diameter x 17 mm width).  I looked and looked and could not find this bearing from any online bearing sellers.  I called Nachi, the maker of the bearing that came out of the alternator, and the response was that was not a bearing that they import to the US.  I then called a local alternator rebuilder who said he had the proper size bearing and would sell me one for $45.  Here’s the bearing:

Update 3/23/07...I have located this bearing online. If you Goggle "alternator bearing" you will find sellers of this bearing. Apparently, it is a bearing specific to automotive alternator applications. I have seen the bearing listed under these part numbers: B17-99 (the number on the bearing in the pic above) and also B3043-2RDA. I bought one from this site, http://bearingsdirect.com/products/index.php? action=category&id=56 .

18.  Reassemble the alternator.  Putting it back together is straightforward.  Install the rear bearing on the shaft.  I used a deep well socket as a drift and drove it on lightly with a hammer.  Press the new front bearing into the front case.  I used a block of wood and a hammer with a squirt of WD-40 for lubrication to seat the bearing.  With a little more WD-40 on the shaft, the shaft slid right onto the front bearing.  Don’t forget the bearing retainer plate, which has to go on the shaft before the front bearing.  Install the 4 bearing retainer screws in the front of the case.  Replace the plastic rear bearing cup in the rear case, and mate the case halves with the 4 bolts.  Reinstall the voltage regulator, and replace the rear plastic cover.  Finally, slip the thrust washer back on the front of the shaft (shoulder toward the bearing), and reinstall the pulley using the tools.

19.  Reinstall the alternator in reverse order.  Replace the coolant hose and anti-roll bar.  Reconnect your battery.  Refill your coolant reservoir.  Start it up, and top off the coolant as necessary with 1:1 distilled water to MB coolant.

My total cost was around $70 (bearings + new screws and nuts).  If that front bearing were readily available, it would have been much cheaper.

Thanks go to Brett for this fine write up!

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