maybe a bad alternator?
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Junior User
Joined: Aug 2008
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Hello, update after about a week.
It turns out cleaning the terminals has not made any difference however I think I have pinpointed exactly when the problem occurs. At high rpms right before when I usually upshift, I'll guess about 3 - 3.5k, the headlights and instrument panel go dim. Then as soon as I engage in the next gear and the rpms fall, the lights immediately return to normal. Or, if I wind up the engine but let it slow down, staying the the same gear, the lights return to normal right when the engine slows past a certain point. And this is predictable and happens every time.
Searching google shows that people are solving this by replacing the bushes in the alternator and replacing the voltage regulator. My question is, is it necessary to replace the volt regulator? Also, would it be better just to replace to whole alternator as opposed to trying to rebuild it?
Thanks.
It turns out cleaning the terminals has not made any difference however I think I have pinpointed exactly when the problem occurs. At high rpms right before when I usually upshift, I'll guess about 3 - 3.5k, the headlights and instrument panel go dim. Then as soon as I engage in the next gear and the rpms fall, the lights immediately return to normal. Or, if I wind up the engine but let it slow down, staying the the same gear, the lights return to normal right when the engine slows past a certain point. And this is predictable and happens every time.
Searching google shows that people are solving this by replacing the bushes in the alternator and replacing the voltage regulator. My question is, is it necessary to replace the volt regulator? Also, would it be better just to replace to whole alternator as opposed to trying to rebuild it?
Thanks.
Elder User
Joined: Jun 2009
Posts: 560
Likes: 3
From: 92592
Hello, update after about a week.
It turns out cleaning the terminals has not made any difference however I think I have pinpointed exactly when the problem occurs. At high rpms right before when I usually upshift, I'll guess about 3 - 3.5k, the headlights and instrument panel go dim. Then as soon as I engage in the next gear and the rpms fall, the lights immediately return to normal. Or, if I wind up the engine but let it slow down, staying the the same gear, the lights return to normal right when the engine slows past a certain point. And this is predictable and happens every time.
Searching google shows that people are solving this by replacing the bushes in the alternator and replacing the voltage regulator. My question is, is it necessary to replace the volt regulator? Also, would it be better just to replace to whole alternator as opposed to trying to rebuild it?
Thanks.
It turns out cleaning the terminals has not made any difference however I think I have pinpointed exactly when the problem occurs. At high rpms right before when I usually upshift, I'll guess about 3 - 3.5k, the headlights and instrument panel go dim. Then as soon as I engage in the next gear and the rpms fall, the lights immediately return to normal. Or, if I wind up the engine but let it slow down, staying the the same gear, the lights return to normal right when the engine slows past a certain point. And this is predictable and happens every time.
Searching google shows that people are solving this by replacing the bushes in the alternator and replacing the voltage regulator. My question is, is it necessary to replace the volt regulator? Also, would it be better just to replace to whole alternator as opposed to trying to rebuild it?
Thanks.
If it were mine, I'd replace the alternator (and regulator if its separate); the way my lucks runs I'd spend a half a day replacing the brushes then a day later the bearings would fail.
Check the belt and belt tension too.
Cargo Master
Joined: May 2004
Posts: 3,007
Likes: 5
start with brushes, should be about three dollars, at least that's what it was the last time I replaced the brushes on my cadillac. Mercedes brushes were about 30, and very simple to replace.
I would suspect the regulator more tho since it acts up only at high rpm.
I would suspect the regulator more tho since it acts up only at high rpm.
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Junior User
Joined: Aug 2008
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Maybe it would just be best to spend the $120 or so on a rebuilt alt and call it a day but since I'm short on funds I might just try replacing the brushes and see if it works.
I couldn't locate any brushes at any of the major parts stores in the area, but I found this Alternator Brush Assembly on Napa's website at this link: Store Locator | NAPA Online
Apparently for $12 and taking off two screws at the volt regulator you just drop this in as a direct replacement. However the only one listed is for the 4.0L engine and there is nothing for the 2.5L engine. Does anyone know if the alternators used with the 4.0 trucks are any different than those from the 2.5L trucks?
I couldn't locate any brushes at any of the major parts stores in the area, but I found this Alternator Brush Assembly on Napa's website at this link: Store Locator | NAPA Online
Apparently for $12 and taking off two screws at the volt regulator you just drop this in as a direct replacement. However the only one listed is for the 4.0L engine and there is nothing for the 2.5L engine. Does anyone know if the alternators used with the 4.0 trucks are any different than those from the 2.5L trucks?
Cargo Master
Joined: Feb 2002
Posts: 2,414
Likes: 22
From: Tucson USA
I would recommend if $$ are the issue you go to either a alternator rebuilder or to a local junk yard. Brushed and stuff may not be all thats bad, diodes and other items may be involved. A junk yard may allow you to have it tested before purchase if that is a concern, but actually the $120 may be a better investment once time parts and add on become involved. Many modern parts are just not designed for partial rebuild or repair. These are not like old generators and stuff where you could clean and add new brushes and bushings.
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Junior User
Joined: Aug 2008
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I went ahead and just replaced with a new (reman.) unit this afternoon. The location getting to the alternator is kind of a pain with the 2.5L engines - I wonder if its any better for the others. Its definately a two-man job to lift out the old one and place in the new one unless you take out some hoses. I spent the most time out of anything trying to unplug the small electrical connector (not the wiring harness, the small one next to it.) After more than a half hour of wiggling around with a screwdriver and needle nose pliers it finally came out.
So far so good after a half hour drive however I'm hearing a faint high pitched "wheeeeew" sound when revving the engine when parked. I tried to be careful to center the belt on all the pulleys when putting it back on, the belt was my first thought about what it could be. But its not very noticeable and after a test drive the sound seems to be going away.
So far so good after a half hour drive however I'm hearing a faint high pitched "wheeeeew" sound when revving the engine when parked. I tried to be careful to center the belt on all the pulleys when putting it back on, the belt was my first thought about what it could be. But its not very noticeable and after a test drive the sound seems to be going away.
