18ACR Alternator Brush Replacement

SydneyRoverP6B

SydneyRoverP6B

Well-Known Member
Staff member
About 10 miles from home today I noticed my ammeter oscillating slightly about zero, my voltmeter too was flickering. I pulled over and switched the engine off suspecting either the carbon brushes or the voltage regulator. Starting the engine the ign light remained on, the ammeter showed a disharge and the voltmeter read 12 Volts. Once engine revs reached 2000 or so, the ign light went out and the ammeter went back to oscillating about zero.

I removed the alternator after lunch.....

P6130174.jpg


then removed the carbon brushes.....

P6130175.jpg


The two brushes reside in the brush box which allows them to make contact with the slip ring below. When new, the brushes measure 13mm in length, these two have seen just short of 30,000 miles (50,000km). The longer of the two is 12.5mm in length and rests on the axis of the slip ring while the shorter one is 7.5mm in length and makes contact close to the slip ring's outer edge. For this reason it receives far more wear for every revolution of the slip ring...which is affixed to the end of the rotor.

This is a new slip ring shown to aid the explanation....

P6130179.jpg


and these are the removed brushes...

P6130176.jpg


The minimum length for a carbon brush is typically 7.5 to 8.0mm, after which time the little spring is unable to exert sufficient pressure to maintain good contact with the slip ring and spurious readings as displayed today are the result.

So with one new brush….

P6130177.jpg


I was ready to refit.

Road testing upon completion showed everything working exactly as it should... :D

Ron
 
Have to add that to your service schedule Ron - one new brush every 30k miles. We'll all want to know the life expectancy of the second too :wink: Can't have failures in service now, can we.

Seriously though, just shows how well organised and resourced you are. That would have taken most of us at least a couple of posts on here!

Chris
 
Hello Chris,

I like to be organised, find it makes things much easier... :wink: The brush that I just replaced actually lasted the shortest distance of the past three, the others being just over 42,000 miles (68,000km) and just over 47,000 miles (76,000km). The other brush by its location lasts much longer and will typically see over 110,000 miles (177,000km) before needing replacement.

Ron.
 
Hello Dave,

I replaced the original slip ring on my alternator in 2008, at that time it had seen just on 215,000 miles (346,000km). Mine was becoming rather worn and a bit groovy, like on an old record. New ones are available, you just need to unsolder the wires to the old one and pop it off. There is a spring clip that retains it, pop on the new one, resolder the wires and you're away... :wink:

Ron.
 
Co-incidentally, I had the same thing today. After putting up with Bruisers intermittently glowing ignition light for a fair while, I bought a regulator, rectifier & brushes and on opening the 17ACR alternator up found this:

DSC03997.jpg


So I replaced the one brush & all seemed fine on test & on the journey home. But when I got home & switched off I again co-incidentally, got Kokken's recent fault of the ignition light being illuminated when I switched off. It must be the alternator in my case I would've thought, something I've done wrong probably. :roll:
 
I am glad that you found my post helpful The RM.

Can't say I have ever had the "ign light on when switching off", so can't really offer help on that one.

Ron.
 
Harvey informs me it will be the rectifier at fault. One (or more?) of the diodes having gone u/s & allowing current to flow back to the light when the ignition is switched off. So I'll be taking the unit back off in a while to replace it with the new rectifier I bought.
Oh well, Sod enforces his law once again when I try to be frugal. :roll: :mrgreen:
 
The Rovering Member wrote,...
Harvey informs me it will be the rectifier at fault. One (or more?) of the diodes having gone u/s & allowing current to flow back to the light when the ignition is switched off. So I'll be taking the unit back off in a while to replace it with the new rectifier I bought.
Oh well, Sod enforces his law once again when I try to be frugal.
Click to expand...

Hello RM,

When one or more diodes fail, the ign warning light will typically also glow while the engine is idling and then as you gradually increase the revs it will slowly fade out, not go out immediately.

Once you have changed the rectifier, please write back with the outcome.

Ron.
 
Well, the ignition light has been glowing a lot of the time recently as I stated, though showed no sign of this on replacing the brush. But regardless of that, the outcome is; on going to the car to do the job, the ignition light was performing as it should. Namely, going out when the engine is started & when the ignition is switched off. :roll:
So I have left things as they are until such time as the fault re-appears or not.....as the case may be.
I also found that I already had a new regulator & rectifier in stock. I really need to make a list of the parts I have on the shelf.
 
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