Hey everyone, 

 

I currently have the 3rd gear/lockup issue that seems to be common with these trucks. I installed and set up a new TPS  last winter, and cleaned all the grounds which didn't solve the issue.  Eventually I caved and bought a noise filter, which made everything work great for about 4 months. However, I noticed that with the filter hooked up, when I let off the throttle at highway speed, the TC didn't unlock  and bring the RPM's back down to ~1k like before. Instead it held and would engine brake the way a manual trans would, unless I hit the brake pedal, or went below  about 40mph.  But aside from that, things worked fine, no shifting back and forth like before.  

 

Yesterday, the 3rd/Lockup shifting problem came back. I spent a few hours last night reading through the info on the site and did some testing with a good fluke multimeter today after work. My battery voltage is around 14.2 with the truck running, but the alternator is only putting out 10.5v DC.  When I switched the meter to AC it showed 7v.  From some of the other threads I've found, it seems that maybe the meter automatically switches to mv?  If so would this be enough AC voltage to cause a problem? Obviously if it's actually putting out 7v then there is something seriously haywire going on. 

 

 

Appreciate the help, sorry for the long winded post. 

 If your battery  voltage is showing 14.2 v while the engine is running I would have a hard ime believing the alternator is not putting out 14.2v. How are you reading the alt voltage? 

4 minutes ago, dripley said:

 If your battery  voltage is showing 14.2 v while the engine is running I would have a hard ime believing the alternator is not putting out 14.2v. How are you reading the alt voltage? 

 

 

B+ terminal on the alternator to passenger side neg post on the battery, truck warmed up, no grid heaters cycling. 

Here is the down low on the alternator noise issue that makes this problem.

 

Somethings goofy. You would not read 14.2 at the battery while running if the alt is only putting out 10.5v. You might ought to try that again and make sure your lead is making good contact. Before you do that check the battery before you start it and I will bet your around 12.5v not running. Then start and check both again. 

 

And for the sake of getting this right, someone confirm what I am thinking since I am a card carrying member of the electrically challenged club.

Yessir, I read your article and watched your video as well. I tested mine exactly how you tested yours, only my b+ terminal was located slightly higher on the alternator case.  I was confused by it showing only 10.5 volts charging while my batteries are showing good voltage. My meter is a similar vintage to yours and clearly showed ~7.06  on the AC setting. 

 

 

Dripley, I checked it several times because I didn't believe what I was seeing myself

 

 

Edited April 17, 20186 yr by ctxj90

I would pull that alternator and have it bench tested I'm pretty sure the diodes are gone.

I'm fairly certain the post title is a misprint. For future reference you have a 47 series transmission. But if it is in the 1996 truck in your sig. I would think you have a 47RH and not a 47RE. 

23 hours ago, ctxj90 said:

Dripley, I checked it several times because I didn't believe what I was seeing myself

 

I'm with Dripley here.  Truck is running, battery voltage is at 14.2 volts (normal) - that means the voltage at the  alternator output terminal has to be slightly higher to bring the batteries to 14.2 volts.  It is possible that you are getting a poor connection with your test meter at the alternator output terminal.  Something doesn't make sense here.

 

- John

Edited April 17, 20186 yr by Tractorman
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2 hours ago, dave110 said:

I'm fairly certain the post title is a misprint. For future reference you have a 47 series transmission. But if it is in the 1996 truck in your sig. I would think you have a 47RH and not a 47RE.

He would have a 47RE transmission. The 47RH was used up until '95. '96 is the first year of the RE (my '96 was one of the early models to get the RE).

Far as your alternator, it would be physically impossible for it to be putting out 10.5 volts and have the batteries at 14.2 volts. If you are getting 7v AC you really need to fix your alternator.

Dripley- You were correct, I'm pretty sure I was probing the wrong post on the alternator. 

 

This bothered me all day yesterday at work and didn't make sense to me, so I retested everything when I got home before I went to the parts store. 14.3 DC at the alternator with .028 v AC

 

Also yes, it's a 47RE. I'm really batting 1000 here....

Some days are better than others.

Something you can try is to unplug the field wires and go for a drive. That will take the alternator out of the loop. If everything works like it should then you know for certain.