On the way home I used more RPM than usual. (in a rush to see the wife?)Noticed the battery light luminate as I was approaching 5,000 RPM. As the revs dropped the light went out. I thought nothing more of it. This morning the eng. was slow to turn over, also the battery worning light is gently flickering. I put a volt tester on the battery with the eng off the volts are only 12.1. Think they should be 13. something. Is there anyone out there who can advise. the truck is a F150 1997 4.6 v8

 

What is the voltage across the battery with the engine running? Intermittent charging, especially at high RPMs is usually due to worn out brushes in the alternator. Running at 5000 RPMs should not hurt the alternator...

 

Thanks for your reply. The volts with the eng running is 13.3. Is there a test I can do to tell if I need new brushes or do I need to take it apart.
Mike.

 

You can take it to autzone and see if it fails on their machine.

 

Thanks for your interest in my electrical problem. Latest update! With the eng at high idle RPM the volts drop to under 12. With the eng off, the volts are above 12. I live in the uk so we dont have an autozone that I know of. I have bidded on a second hand Alternator which has only ran for 11,000 miles on ebay. Can anyone tell me if my truck needs a 95 amp or a 130 amp. My truck is a 4.6 v8 F150 1997 Vin Details are 1FTDX0766VKA36164 Date 02/96

 

More than likely your brushes are worn down and no you do not have to take it apart to put them in. There are some screws around a square plastic thing. Here is a photo of it.
http://fordfuelinjection.com/public/alternator/3Galternator05.jpg
Take the screws out and the brush holder comes out the back. I would say you have a 95 Amp one unless there were something special about your truck for high Amp use. A brush set only cost about $12.00 U.S. and you would be good to go for another round. The valves in the alternator do not go bad unless you cabled up with another bloke to start him and the cables were backwards. I have a herd of Ford’s that I have been driving for 45 years and I have yet to buy an alternator. I just replace brushes.

PS, In the USA we do not rush home to see the wife, a shelia maybe.

 

Your truck could have had either a 95 or a 130 amp alt. I saw a reference to the size of the alternator cases. They said the 95 was 5 1/8 " diameter while the 130 amp was 5 5/8" diameter.

 

Hi Franklin2, took the alt. out and measured the caseing. The measurement was 5.2". I can guess it is a 95 amp. The truck has nothing extra, or special about it which would need 130 amp. so I'm going for the 95 amp. Thanks for your help. Mike

 

Hi subford, Thanks for taking time out to help. Your experience with that herd of fords has proved good for my 'alt'. Took the square plastic block out and the brush holder as you described. The lower brush looks brand new approx 1/2" long, just under. But the top brush is down to the spring. Looks like I might be saving some £££££ cheers.
Ps. In UK shelia are expensive. ££ best spent on brush kits.

 

Make sure you examine the slip rings (this is what the brushes contact) to make sure they are smooth. If they are rough, try to smooth them out with emory cloth before installing the new brushes.

 

Thanks bob. Top ring looks burnt and rough, will try to clean up. Mike.

 

To everyone who has taken time to replied to my 'alt' bleatings. Being a member of this comunity is realy great. Cleaned up the slip rings, sanded down some replacement brushes to fit the smaller brush block, soldered them in, put it all back together, ran it and got 14 volts, job done. Cheers everyone.

 

You might want to keep an eye on the alternator brushes for awhile. It might still be wearing the one you changed due to a badly machined brush contact ring.