Applications: BMW, Mercedes, Porsche, Saab, Volvo and other European and Domestic cars with Bosch internal fan alternators. Note, this article applies to those models with 7mm shaft which was used on many cars made during the 90's and early 2xxx models.

The original slip ring material is quite thin, only about 1mm thick so if the brushes have worn very far into the material it’s time to replace the slip rings. The job is not so difficult as it is a bit tricky. You will need a small bearing puller, a good soldering iron and an ohm meter along with the skills to use them.

Note the picture. These slip rings were removed from a Volvo 960 alternator.

1. To remove the slip rings you will need to dismantle the alternator and remove the rear bearing. With the ohm meter check the reading across the two slip rings and write it down. When finished with the job the reading should be the same.

2. Unsolder the wires from the tabs at the base of the slip ring assembly. If you don’t have a suitable puller for the slip rings they can be hack sawed most of the way through and split so they will come off. It’s VERY IMPORTANT that all of the slip ring material is removed. If even a chip is left of the insulation material from the old slip ring the new one won’t seat properly.
3. NOTE: The new slip ring must be installed so the little knob on the slip ring goes into the notch that you can see in the fan that is spot welded to the rotor. Study the picture.
(If the slip rings were installed backwards the current would be flowing backwards through the rotor windings. Not good)



5. You will need a tool to press the slip ring on. Note the picture shows a tool made from ¾” plastic pipe with a cap glued to it. Cut a piece of the plastic pipe about 40.75mm. Use a cap that is flat across on the inside and cement it on.

Make sure this tool drives the end of the slip ring assembly as well as the base of the slip ring so the plastic slip ring assembly doesn’t break. Spend a few minute be sure you have it right.

It won’t take much to press the new slip ring assembly in place. BE SURE the copper tips of the wires aren’t under the new slip ring assembly. When properly installed the outer end of the slip ring assembly will be about 4.50mm past the end of the rotor shaft.



6. Use good solder to solder the wires. Note the replacement slip ring assembly has small holes in the tab so you can insert the wires and then solder them for an excellent job.

7. Press the new rear bearing in place and reassemble the alternator.

Click here to purchase Bosch internal fan slip ring and parts

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Below are the Bosch alternator numbers that use the above slip rings:

0120335006  0120335007  0120335008  0120335010  0120335011  0120335012  0120465003  0120465004  0120465006  0120465007  0120465008  0120465009  0120465010  0120465011  0120465012  0120465013  0120465014  0120465015  0120465016  0120465017  0120465018  0120465020  0120465021  0120465023  0120465026  0120465027  0120465028  0120465029  0120465031  0120485005  0120485006  0120485007  0120485008  0120485011  0120485012  0120485015  0120485017  0120485018  0120485020  0120485022  0120485023  0120485024  0120485025  0120485026  0120485028  0120485029  0120485030  0120485032  0120485034  0120485036  0120485038  0120485039  0120485041  0120485043  0120485044  0120485046  0120485047  0120485048  0120485050  0123100001  0123100002  0123100003  0123105001  0123105002  0123110004  0123110005  0123110006  0123110007  0123110008  0123114005  0123115009  0123115010  0123115011  0123115012  0123115013  0123115014  0123120001  0123212001  0123213005  0123213006  0123213007  0123214002  0123215001  0123310001  0123310002  0123310003  0123310004  0123310005  0123310006  0123310007  0123310008  0123310010  0123310011  0123310012  0123310013  0123310014  0123310015  0123310016  0123310017  0123310018  0123310019  0123310020  0123310022  0123310023  0123310024  0123310025  0123310026  0123310027  0123310028  0123310029  0123310030  0123310031  0123310032  0123310033  0123310034  0123310035  0123310037  0123310038  0123310039  0123310040  0123310041  0123310042  0123310043  0123310044  0123310046  0123310047  0123315001  0123315002  0123315003  0123315004  0123315005  0123315006  0123315007  0123315008  0123315013  0123315015  0123315016  0123315017  0123315018  0123315019  0123315020  0123315021  0123315022  0123315500  0123315501  0123315502  0123315503  0123320001  0123320002  0123320003  0123320004  0123320005  0123320006  0123320007  0123320008  0123320009  0123320010  0123320011  0123320012  0123320014  0123320016  0123320017  0123320018  0123320019  0123320020  0123320021  0123320022  0123320023  0123320024  0123320025  0123320026  0123320027  0123320028  0123320029  0123320030  0123320031  0123320032  0123320033  0123320034  0123320035  0123320036  0123320037  0123320038  0123320039  0123320040  0123320041  0123320042  0123320043  0123320044  0123320045  0123320046  0123320047  0123320048  0123320049  0123320050  0123320051  0123320052  0123320053  0123320054  0123320055  0123320057  0123320058  0123320059  0123320060  0123320061  0123320062  0123325002  0123325003  0123325004  0123325005  0123325006  0123325007  0123325008  0123325010  0123325011  0123325012  0123325013  0123335001  0123335002  0123335003  0123335004  0123335005  0123335006  0123335008  0123340001  0123340002  0123340003  0123340005  0123340006  0123340007  0123345004  0123500001  0123500002  0123500004  0123500005  0123500006  0123500007  0123500008  0123500009  0123505001  0123505002  0123505003  0123505004  0123505005  0123505007  0123505008  0123505009  0123505010  0123505011  0123505012  0123505013  0123505014  0123505015  0123505016  0123505017  0123505018  0123510001  0123510002  0123510003  0123510004  0123510005  0123510006  0123510007  0123510008  0123510009  0123510010  0123510011  0123510012  0123510013  0123510014  0123510015  0123510016  0123510017  0123510018  0123510020  0123510021  0123510022  0123510023  0123510026  0123510027  0123510028  0123510029  0123510030  0123510031  0123510032  0123510033  0123510034  0123510037  0123510038  0123510039  0123510040  0123510041  0123510042  0123510043  0123510044  0123510045  0123510046  0123510047  0123510048  0123510049  0123510050  0123510051  0123510052  0123510053  0123510054  0123510056  0123510057  0123510058  0123510059  0123510060  0123510061  0123510062  0123510063  0123510064  0123510065  0123510066  0123510067  0123510068  0123510069  0123510070  0123510071  0123510072  0123510073  0123510074  0123510075  0123510079  0123510080  0123510081  0123510082  0123510088  0123510089  0123510091  0123510092  0123510093  0123510094  0123510095  0123510096  0123510099  0123510100  0123510101  0123510102  0123512500  0123512501  0123515002  0123515003  0123515004  0123515007  0123515008  0123515009  0123515010  0123515011  0123515012  0123515013  0123515014  0123515016  0123515017  0123515018  0123515020  0123515021  0123515022  0123515023  0123515024  0123515025  0123515028  0123520002  0123520003  0123520004  0123520005  0123520006  0123520007  0123520008  0123520010  0123520011  0123520012  0123520013  0123520014  0123520017  0123520500  0123525001  0123525500  0123525503  0123540001  0123540002  0123540003  0123540004  0123545001  0123545002  0123545003  0123545004  0124625019