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Alternator diode replacement

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Old 03-18-2017, 02:53 PM   #1
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Alternator diode replacement

Tried searching to no avail.
'01 2500, 245K, all stock other than Edge EZ, original owner and alternator. No codes.
Having issues on and off for years with light throttle surging, along with occasional tranny being slow to upshift. At low boost with steady pressure on the throttle, the gage will vary between 8 and 10 lbs.
Bothersome as hell. Other throttle positions are fine. More noticable with Edge EZ plugged in.
Did grounds numerous times. Reset and test apps. Pulled the ground wire out of the harness across the radiator, moved away from alternator.
Still doing it.
Tested my alternator AC output yesterday. Standards from other threads were
.020 at idle, .1 at 2500 rpm, max. All accessories on.
DC voltage was beautiful at 13.7 at all battery and alternator connections.
I got .045 and .160 respectively. I'm assuming this means my diodes are bad.
What do you buy to replace the diodes? The rectifier? Best brand and/or source.
What's the replacement procedure?

Thanks in advance
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Old 03-19-2017, 01:33 PM   #2
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Sounds like you're getting some serious AC voltage feedback. You can either have a alternator/starter shop rebuild it or get another one. I'm not sure you'd want to bother with replacing just the diodes as everything else may be needing attention soon too.

That said, you'll want to be careful with picking up a parts store unit because they can generate excessive AC just because of their overall quality. Then you questioning this with the parts guys will not go over very well because they only test pass/fail based on DC voltage levels.

I recently replaced my alternator with a Nations 180 amp unit. Not terribly expensive and works nice.....
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Old 03-19-2017, 01:52 PM   #3
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Several years ago I made the choice to repair my original alternator rather than replace it with a parts store reman, because I believe our trucks were built with some of the longest lasting alternators in the industry. I needed a rectifier at the time, and simply went to a local rebuilder. He matched up the rectifier I had and sold me a new one, which has been working great for several years. Anyway since then, I have found that new rectifiers are available for our Denso alternators at Larryb - Shop online for auto repair, truck repair parts, alternators and starter solenoids from Foster Truck.
A new set of brushes at the same time, and that alternator should be good for another 100k miles.
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Old 03-19-2017, 08:16 PM   #4
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Originally Posted by torquefan View Post
Several years ago I made the choice to repair my original alternator rather than replace it with a parts store reman, because I believe our trucks were built with some of the longest lasting alternators in the industry. I needed a rectifier at the time, and simply went to a local rebuilder. He matched up the rectifier I had and sold me a new one, which has been working great for several years. Anyway since then, I have found that new rectifiers are available for our Denso alternators at Larryb - Shop online for auto repair, truck repair parts, alternators and starter solenoids from Foster Truck.
A new set of brushes at the same time, and that alternator should be good for another 100k miles.
Where did you get the rectifier in Calgary? Thanks!
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Old 03-19-2017, 09:59 PM   #5
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Where did you get the rectifier in Calgary? Thanks!
It was an alternator rebuilder on Ogden Rd. SE called "Lo Cost" or something, I think. Usually I stay away from that kind of name, but he had a good reputation.
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Old 03-19-2017, 10:07 PM   #6
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It was an alternator rebuilder on Ogden Rd. SE called "Lo Cost" or something, I think. Usually I stay away from that kind of name, but he had a good reputation.
Thanks!

I just spoke with someone there; they didn't understand the AC noise at all. New rectifier is 48.00 though.

Last edited by Marine; 03-20-2017 at 09:34 AM. Reason: addition
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Old 03-20-2017, 11:13 AM   #7
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Thanks!

I just spoke with someone there; they didn't understand the AC noise at all. New rectifier is 48.00 though.
Not sure I'd be shopping from an alternator supplier who's clueless about AC noise.
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Old 03-20-2017, 11:14 AM   #8
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Thanks for the responses, guys.
I have a Bosch alternator, not a Denso.
LarryB's stuff is all for the Denso.
I too feel that our OEM stuff is built to last and would prefer to install new parts as opposed to buying a whole new unit.
Any more ideas?
Is this amount of AC voltage likely to cause the problems I described?

Katoom, where in norcal are you? I'm in the Placerville area and have been riding KTMs since 1984.
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Old 03-20-2017, 11:28 AM   #9
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Yes, AC voltage is bad and harms other sensitive electronics. Not something you want to ignore.

And yes, the Cummins OEM alternators are very good so no problem having it rebuilt as long as the re-builder uses the right quality parts. The only reason I chose to go with a Nations over rebuilding was because technology has improved throughout the years and hairpin windings are superior.

I paid something like $275 for a 180 amp unit, and it would have cost me probably well over $100 to rebuild my OEM 136 amp one.....which still sits on the garage shelf in case I ever need it. Just my personal preference. That said, no need for the crazy high amperage alternators either unless you're running tons of lighting or a massive stereo system.

And I'm up by Redding. Haven't taken my bike out for too long too..... The weather has been great but work and chores keep getting in the way. Plus I no longer have anyone to ride with and solo riding in the hills is kinda dangerous since it may take days for people to find you.
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