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Followup To
Question -
Hi John,
No, there are no noticeable problems with any readouts, nor is there any degradation of handling.
I suppose it's possible there are two independent problems, but since the symptoms all appeared at the same time (near as I can tell), and the tone coming out of the speakers sounds exactly like the noise coming from the engine compartment, I tend to believe they have a common cause.
For every phenomenon there is a theory that's simple, elegant, and completely wrong.
My theory was that I had a dry bearing that was setting up a resonance. The resonance was being transmitted along the serpentine belt to the alternator and mechanically modulating the alternator's electrical output. It sounded quite reasonable to me, until I removed the belt and spun all the pulleys. They all spin smoothly and easily, with no sign of roughness or excessive friction. The alternator bearings are particularly slick. So much for my theory. Of course, the only thing I couldn't do is to introduce more than a small amount of side thrust to the pulleys. Even so, they felt really smooth.
I agree with you that the alternator is the most likely culprit, but it's not easy to prove without just replacing it. Each time I try to listen to the engine to locate the noise, it seems to fade away and elude me. I plan to monitor the situation till it gets bad enough so I can more easily locate the source. Maybe I'll wait till the smoke comes out, then I'll be able to see where it's coming from.
I like your idea of shaping the brushes. I could rig something up with the Dremel. I would mean skimming the slip rings too, since they are contoured to the brushes now.
Anyway, I won't trouble you further with this. It may take a while to get to the bottom of it. Many thanks for your time. I appreciate your suggestions.
Happy Rovering,
Paul
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Followup To
Question -
Hello John,
After sending the question below, I tested the condenser - looks good. Also checked the Alternator brushes - 3/4" carbon remaining. Next trick is to make up a stethoscope and listen around the engine. Maybe I can get it to cough.
Thanks for your thoughts on this.
Paul
Hi John,
My 95 Disco developed a problem a few days ago, at 103k miles, and I'm hoping you may be able to offer some insight into the root cause.
At idle, stationary, in gear, there is a low, continuous moaning noise emanating from the engine compartment (sounds like a cow with constipation). If I raise the revs by even a small amount (say by shifting into neutral) the noise stops or reduces dramatically. I replaced the IAC, but that didn't fix it. Then I discovered the noise is also present on the radio for the first second or so after it's switched on (till the filter caps pump up). This is a new development. The radio has always emitted a noise burst after power-up, but now it's a coherent frequency burst. It's the same frequency as the engine moaning. The difference is that the noise is still present on the radio even if I can't hear it coming from the engine compartment. Put another way, if I'm at freeway speed and turn on the radio, the noise comes out of the speakers for about a second following power-up, but at a higher frequency than at idle.
So, I looked at the DC bus ripple with a scope and found 200mVpp, somewhat sinusoidal. Doesn't seem excessive to me, but it's about double what I see on my wife's Corolla, where it's just incoherent noise.
There are no other symptoms I can discover. The tach works fine. The DC voltage rises from 13V to 14.4V on engine start.
Any thoughts on what may be causing this?
Thanks and regards,
Paul
Answer -
Hi Paul,
it could be your alternator or maybe its a condensor. Usually, when a condensor or alternator begins to fail, it can make all sorts of noises. What's confusing is that you have a 14.4V on startup. Somewhere its discharging and your your radio is picking up the static. Its also possible that an ignition module could cause such problems too. What is the state of your spark plug wires? How is your coil? Can you test these? Is there a short within these items?
This is beyond my limited skills. Electrical problems are a continuing mystery to me.
Best of luck,
JohnMc
Answer -
Hi Paul,
do you think the radio interference is being caused by what is causing the noise? Could this be two separate problems?
Could the noise be pulley related? Brush length is good. I had mine 'shaped' with a fine sandpaper drill press that I rigged up. This ensured that they were spaced perfectly. I did have difficulty in finding replacement brushes. LR does not sell them. I went to a auto electric shop.
How were the bearings on the alt?
I guess the stethoscope idea may verify if it is bearings in one of the pulleys. I'd start with the alt. You don't notice any change in how the Disco performs? Steering is ok? Temperature looks normal?
Best of luck,
JohnMc
Answer*************************** Follow-Up ************
Hi Paul,
I wish you luck in locating this problem. I hope you get some warning from your Disco BEFORE the problem gets too serious.
I had a power steering problem that, at first, seemed like a strange noise. Not long after, it started to leak thru the pulley shaft and within minutes I lost all my fluid. I purchased a replacement from a salvage yard for around $85. Don't overlook salvage yards for parts. I keep an extra water pump and brake parts...just in case. Always seems like something else breaks down, though. Funny how things work out.
Dremel is good if its mounted in a fixed position. I used a drill press and could carefully move the brushes in and out. I've gotta get me a dremel kit/package one day...they look so handy.
If I ever need help on electronic problems, can I write to you? You seem more at ease with Lucas electronics than I am. I tend to walk carefully when it comes to electrics and my Disco. Besides, I'm always looking for good sources for myself and other Disco owners. Send me an email if you are interested.
Bye for now,
JohnMc
jmcinnis64@hotmail.com
