CK5 Network
Become a member of the largest online community for Chevy K5 Blazer, Suburban and C/K series truck owners!

Alternator Question

500$k5

wallet under gas pedal
Premium Member
GMOTM Winner
Joined
Apr 17, 2007
Posts
371
Reaction score
1,249
Location
Montrose, Colorado
Yes it will work fine, with two "alike" batteries. All gm diesel trucks are wired this way. The alt charges to one battery, and then connects to the other battery with large battery cables. I would definitely suspect the belt slippage. Mark your tensioner at the "at rest" position, then remove the belt, and let the tensioner travel to it's lowest position, and check the marks that you made. The tensioner should travel well past where the marks are. If it doesn't, then the belt may be too long, and under acceleration, it may stretch, and allow slipping. Another problem can be caused by a buildup of belt material in the grooves of the crank pulley. Remove the belt, start the engine, and run a wire brush in the grooves, until clean. BE CAREFUL! You can overheat the engine very quickly, with no water pump turning, or worse yet get your arm ripped off.
 

Fordum

1 ton status
Premium Member
Joined
Jul 31, 2008
Posts
11,351
Reaction score
1,992
Location
Fl
I'm going to chime in with a vote for belt slippage. Other than it being serpentine, the symptoms are classic belt slippage.
The upgraded alt is going to be heavier internally than stock, and the added inertia of the rotor may be causing a marginal belt or tensioner to let it slip.
You might be able to feel of the alt pulley, ENGINE OFF, when its cold. Then crank it and rev it a few times. Then turn the engine off and feel the pulley again.
If its noticably hotter, then its probably slipping.
Even if the tensioner is good, a glazed belt or stretched belt might be the cause. Plus, if you can find a store with the information, you might be able to buy a belt just a tiny amount shorter than stock to add a little more tension.
Look at the tensioner, and some of them have a range marked on the body with an arrow on the moving part. If its not worn or weak, all should be well if the arrow is in the range. So if a shorter belt stays in the range, it should work fine.
 

Justin Fleming

1/2 ton status
Premium Member
Joined
Aug 24, 2005
Posts
886
Reaction score
34
Location
Oxford MI
Here is my follow up thus far, I separated the batteries and mimic-ed a stand alone battery and the issue still exists to identify if a isolator was warranted. I looked up the belt part number and spec on the belt and it is what the vehicle calls for. Effective length 95.47 and outside circumference 96.03 so I believe I have the correct belt on the vehicle as it calls for. Attached are two photos, showing belt hooked up and belt unhooked. The tension-er seems to have a great about of force and the spring does not feel dead. Whats your thoughts on the scale and the distance of travel when belt is unhooked? All components see to spin freely with out and noticeable drag.

belt on.jpg

belt off.jpg
 

rampage

3/4 ton status
Joined
Mar 20, 2001
Posts
5,913
Reaction score
4,821
Location
Humboldt, CA
At this point it does sound like the belt is slipping. Have you taken it off and inspected it for cracks and what not? If you can’t remember the last time you changed it then it’s likely due. I hate to just throw parts at a problem, but how much do they go for these days, like $40?
 

Justin Fleming

1/2 ton status
Premium Member
Joined
Aug 24, 2005
Posts
886
Reaction score
34
Location
Oxford MI
So I did just throw some parts at it for good measure do to the rust and pitting on the idler and tensioner pulleys. I put two new pulleys on, cleaned groves of all other pulleys and a shorter gates belt that provide even more tension on the belt with the same issue. You can see from the black mark and tensioner position in this photo that the shorter belt made a difference.

new shorter belt.jpg
 

rampage

3/4 ton status
Joined
Mar 20, 2001
Posts
5,913
Reaction score
4,821
Location
Humboldt, CA
So I did just throw some parts at it for good measure do to the rust and pitting on the idler and tensioner pulleys. I put two new pulleys on, cleaned groves of all other pulleys and a shorter gates belt that provide even more tension on the belt with the same issue. You can see from the black mark and tensioner position in this photo that the shorter belt made a difference.

View attachment 397138
Actually no, I can’t see, but I’ll take your word for it. :rotfl:
 

6872xtc

make mine modified
Premium Member
GMOTM Winner
Joined
Sep 16, 2008
Posts
7,956
Reaction score
8,247
Location
Palisade,Colorado
Looks like a decent difference. The direct drive fan puts extra load on the belt as well, so maybe you have found the solution.
:dunno:
 

70jimmy

3/4 ton status
Premium Member
GMOTM Winner
Joined
Mar 3, 2000
Posts
7,290
Reaction score
2,266
Location
Released from Pueblo, told I belong in Southpark
disregard below info, I went and looked at mine and its the same.:whistle:

Does your pulley that is connected to the fan have grooves in it?

All the pictures seem to show the grooved side of the belt facing up as the belt passes over that pulley. If it does have grooves for the belt then I would look at the belts routing. I can't see in the pics if the pulley is grooved or not.
 
Last edited:

Justin Fleming

1/2 ton status
Premium Member
Joined
Aug 24, 2005
Posts
886
Reaction score
34
Location
Oxford MI
Correct me if I am wrong but maybe I should take a step back, the two wire connector to the alternator. Can someone explain the function of those two wires. I believe I should have "key on position" power on one to ground and I am not sure what to check on the other one. Maybe I need to start back at ground zero and make sure I have consistent power on this wire? Also anyone in the know if this is a symptom of a faulty regulator. Maybe for the 35 bucks I should swap out the regulator. I really prefer to prove the problem before throwing money at it but at the moment I am at my last thoughts. The other thought is I might dig through some old parts bins and see if I have a standard alternator and swap it in place and see how it acts.
 

Justin Fleming

1/2 ton status
Premium Member
Joined
Aug 24, 2005
Posts
886
Reaction score
34
Location
Oxford MI
So I went out and probed both wires. This is factory wiring/factory connectors. The two wire which are the two center pins on the factory 4 pin housing/connector both have 12+v key on and when running.

If my understanding is correct, this should excite the alternator/regulator and call for charge.

Also I can add I did a diode test on the alternator and that seems to check out fine while in a static position
 
Last edited:

Justin Fleming

1/2 ton status
Premium Member
Joined
Aug 24, 2005
Posts
886
Reaction score
34
Location
Oxford MI
Well first I start off with kicking myself in the ass for not taking pictures to share with the k5 community (sorry for that) but the end result is that I didn't give up today. I decided that if the alt was acting bad already I had nothing to loose on tearing it apart. So I took it apart and as I mentioned previously the truck might get drive 1k miles a year. That being said lets just say that old mother nature took its tool on some of the internals. I cleaned up the stator contact points and the rotor, cleaned up the armature where the brushes ride and put the unit back together and Voilà it appears that the gauge is right where it should be and holding. I would like to get some drive time before I celebrate to much but thus far looks like success!!
 

rampage

3/4 ton status
Joined
Mar 20, 2001
Posts
5,913
Reaction score
4,821
Location
Humboldt, CA
Maybe I missed this, but out of curiosity, why do you have dual batteries? Do you have a high amp device like electric radiator fans?
 
Top Bottom