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Bosch Alternator Slip Rings ....

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Old Jun 18th, 2018, 19:36   #1
bob12
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Default Bosch Alternator Slip Rings ....

.... I have made excellent progress on sourcing all the necessary parts at a reasonable price to give my circa 1990 Bosch 80A Alternator Pt No. 0 120 469 788 a complete overhaul.

Taking the thing apart and replacing bearings etc gives me no concern. However, while I vaguely understand how the slip rings are connected I am unsure exactly what it takes to remove and replace them. When I get that far I might even find that they are serviceable!

On the alternator the rings are on a core that fit over the shaft unlike more modern alternators where the slip rings are on a plastic cradle.

I realise that it will be necessary to un-solder and re-solder the connections, but I am wondering exactly what removal and replacement entails. If anybody has done this or can direct me to something on the web that specifically deals with slip rings I would be grateful.

Bob.
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Old Jun 18th, 2018, 22:03   #2
Laird Scooby
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First you need to measure the distance from a fixed point on the rotor assembly to the centre of one or other (preferably both) slip rings Bob.

You need this so you can fit the new slip rings on in the same relative position to the brush box/brushes/voltage regulator.

You'll need a beefy soldering iron, 75W minimum to desolder the rotor wires from the slip rings and a solder-sucker to remove the molten solder.

Once it's electrically "free", you need a bearing puller to get behind it and draw it off the S/R/E of the rotor - Slip Ring End.

Clean the rotor shaft up and prepare some Araldite, smear some on the shaft where the new slip rings will contact it.

Now press the new slip rings on, taking care to ensure the two lugs for the electrical connections are in the right place but only press it down to your previously measured point so the slip rings will line up with the brushes.

Solder the connections and leave the Araldite to set.

Reassemble with new D/E (Drive End) bearing and S/R/E bearing, cleaning the rotor shafts with emery cloth to ensure a good sliding fit, not too tight or loose.

Are you renewing the rectifier as well Bob?
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Old Jun 18th, 2018, 22:11   #3
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PS - any parts you're struggling to find, try this site :

https://woodauto.com/product/ALT10281

That takes you directly to the same alternator that has about 17 different part numbers in addition to the one you've listed! Nearly 120 different applications as well!

Can't remember how to get the parts menu up on that site but i'm sure you'll work it out if you need it!
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Old Jun 18th, 2018, 22:41   #4
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Thanks Dave .... I knew you would come up trumps. Why did you take so long

Basically, along the lines of 'wot I waz thinkin' without actually looking at the animal, but with the finesse in the detail I was looking for.

Of course I was always prepared to get the Dremel out and cut them off!! Let's hope they don't need changing when I get that far. Just a little 'freshen up'.

At the moment I am going to put my spare alternator on and see how that goes, and then 'explore' why the miscreant is misbehaving! I have a gut feeling it might just be very worn down brushes after 145K miles. Naturally, I shall update this thread in due course and, if I remember, with some pics.

Thanks again Dave, Bob.
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Old Jun 18th, 2018, 22:51   #5
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If you have one of those "dentists mirrors" you can pop the brush holder/voltage reg out of the alternator while it's still on the car - takes a bit of care but easily possible - then use the mirror to get an idea of the state of the slip rings.

If you need to test the rectifier pack, you'll need to make a lash-up with a 21W indicator bulb and some wires and a 12v battery - they don't generally show fault on the low current a multimeter provides. Obviously they can only be tested once the rectifier has been desoldered from the stator wiring.
There's also a little "diode trio" pack on the back of the rectifier which is a low current rectifier used by the voltage regulator and charge warning light - these also need testing.

Good luck with it and any queries/questions, give me a shout!
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Old Jun 18th, 2018, 23:02   #6
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Yes, I have one of those little mirrors, and will have a little look-see.

I don't think the cause of my light 'whirring noise' that matches the engine speed is serious at the moment.

As commented on in other threads the alternator appears to be still preforming well electrically voltagewise. However, and additionally, the front bearing is starting grumbling if you listen to it with a stethoscope.
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Old Jun 18th, 2018, 23:11   #7
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The front (drive end) bearing would almost certainly be the source of your "light whirring noise" then Bob.

Strange as it may sound, that will be effecting the output, all down to the magnetic fields in the rotor and stator and will also cause it to get hot.
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Old Jun 19th, 2018, 09:42   #8
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IME, bosch slip rings were relatively hard and had good depth of material. We used to machine them to flat (on a lathe) if they were scored. Occasionally, but not often, replaced them.

Its no problem refitting them - they locate against a step so you can't misalign it
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Old Jun 19th, 2018, 09:47   #9
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Quote:
Originally Posted by aardvarkash10 View Post
Occasionally, but not often, replaced them.

Its no problem refitting them - they locate against a step so you can't misalign it
That leads me to believe we got a different level of quality here Ash - the OE Bosch slip rings did have an excellent service life but certainly the aftermarket pattern ones i fitted had a recess to go over the step so needed careful measuring to line the new rings up with the position the original were worn in.
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