1987 325 Bat/Alt/Reg Issue

Hi, I have a 1987 325 with 277K on it and today the car stalled out at a light. Before that the anti-lock brake light came on then the oil light.
It wouldn't turn over when I tried to restart. So I got a jump and after 5 minutes charging, it started right up. After about ten minutes of driving, the indicator lights started coming back on and it died again. Finally got it home and immediately changed the battery (it was over 5 years old and needed repalcing anyway). Now it seesm fine (after 45 minutes of driving), but every now and then the brake light, and charge light blink on when I slow down hard. Also we checked the voltage across the battery when idling and at 2000 RPM. It was steady at 12.4 volts which seems low. I think its the alternator or the regulator, but not sure which. Any suggestions?
Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Greg Kirk wrote:

Greg,
I think it is the alternator brushes are worn out. I believe the brushes are in a "pack" that contains the regulator so replacing them will take care of the situation.
As an aside, I recently have had the same condition on my '88 735. I replaced the brushes and it seemed fine but now, less than two weeks later it looks like the problem has re-surfaced.
My guess is the alternator bearing is wobbly which is causing the brush to commutator connection to wear prematurely. My next step is a new alternator unless someone suggests an alternative.
Good luck with yours, Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You have a problem - it should be circa 14 volts.
First thing to check is the actual charge warning light. Is this on with the engine stopped, but the ignition on? On some designs this supplies the field exciting current, and if the bulb blows etc stops the alternator working.
Now check all the connections to the alternator are clean and secure.
Next step involves removal. You need to remove the regulator and check the brushes. If these are free and have plenty life left, it's most likely the regulator which can be bought as a spare. Next possibility is the diode pack which again can be replaced although that needs soldering skills. Least likely is a failed winding.
Alternators are fundamentally so long lived and reliable that the easy way out is an exchange unit - non dealer ones are often very good value and of course should be warranted. It's near impossible to check all the various bits without expensive test equipment so fixing your own is a matter of guesswork and substitution.
--
*The modem is the message *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.