There is a strange whine coming from the engine on the truck in my signature. It is most noticeable between 1,400 & 2,000 rpm. After about 30 minutes of driving the noise diminishes but is still noticeable. It sounds a bit like the alternator when the grid heaters are cycling.

Have installed another (used) belt tensioner pulley, installed a new bearing in the idler and changed the water pump and belt.

Cannot isolate where the sound is coming from. Neither can a mechanic friend who listened to it. Could a bad alternator diode cause this? The noise is not getting any louder as I put more miles on the truck.

Anybody have any suggestions?

 

Stan I had the alter nator in the wife's Chry sler do this, it finally gave up the ghost and I replaced it. Don't know if that is your issue but sounds similar....

 

I have suspected the alternator from the start, but as it is still charging properly, have not considered changing it. Have a set of bearings and brushes (from Genos) ready to go in when the time comes.

Does anyone know if just the diodes are available and how hard is it to change them? Or should I just go to some place like NAPA or Autozone and get a replacement alternator? Does this rebuilt stuff last?

Not going to do this now as all my driving is local and no big deal if the alternator fails. However, if I go on another long trip, then I would be worried.

 

An alternator with failing bearings may charge fine, but make noise. Might be good to pull the belt and turn everything by hand, to confirm.

Also in 2003 the stock alternator mount bracket was formed from sheet metal. There was a TSB about it cracking, causing slight misalignment and noise. The new bracket is cast. http://dodgeram.info/tsb/2003/08-007-03.htm

 

I did take the belt off and the alternator spins freely and with no noise.

Thanks for the info re the bracket. This TSB was done many years ago when it first came out. I remember being irritated by this because it came bare and immediately started to rust. I pulled it off, painted it and reinstalled it.

 

The whine is gone! I cannot explain this, but maybe some electrical guru can come up with an explanation.

In all the years that I have owned this truck there has been no corrosion around the batteries, except at one place. Every now and then, have seen and cleaned off some corrosion on the LH battery terminal where the RH battery cable connects. For some reason this is the only place that corrosion keeps on returning. Not much, but it is there. Yesterday I noticed that the corrosion had returned, so dismantled all that I could at the positive terminal of the LH battery, cleaned everything up with baking soda and a wire brush and reassembled it. No big deal. This morning I took the truck out and the first thing I noticed was that the whine had vanished.

I know that these trucks are very sensitive to bad grounds and sundry other electrical connections, but even tho I know a bit about electrical stuff, this baffles me. I never touched the alternator and only cleaned up the terminals. Not sure, but the voltmeter in the truck may now be reading about half a needle lower. A check at the battery posts showed just over 14 volts for both batteries with the engine at idle. How can cleaning the terminal make the whine go away?

 

Interesting, and glad you got it fixed.

As I understand it, the two batteries are paralleled together, with the alternator output cable running to one side. The alternator is externally regulated type, controlled by the ECM, and the ECM reads battery voltage from the other side. If the parallel cables or any connection is weak, one battery gets over charged as the other battery's voltage drops and causes the ECM to run the alternator at continual full output.

I wonder if the coils could make noise at full output?