Hello!

I am dealing with an alternator problem in my 1984 SIII xj6.

Symptoms: Ocassionally needs to be jump-started. While running, the dashboard volt indicator never gets to the middle. It will slowly drop down into the red. After idling for 30 minutes or so, starts to run roughly. There is about 3/4 inch deflection on the alternator belt, which I believe is too much, however the alternator is spinning and there's no squealing or anything.

I charged the battery for a few hours and started it up, I get these voltages at idle:
battery + to -: max 12.48V, drops slowly over time.
alternator voltage drop on - side: 0.01V
alternator voltage drop on + side: 0.07V


Battery is 4 months old. Negative battery cable is 12 months old (was loose on the battery post). Previous owner modded the alternator + cable to have a ring terminal. That connection feels solid. The alternator is still on the engine.

I am unsure which alternator the engine has (I believe it is either from lucas or motorola?) but I didn't find a name plate on the alternator. It is still on the car as it is a giant pain in the *** to R&R, I want to be sure before tackling it. Same story for replacing the belt; since it involves taking all the other belts off first I'd rather have all the info I need before doing it.

There are a few other electrical gremlins, but they don't seem worth mentioning until I can be sure the charging system works.

Is there any more information I need to gather to help diagnose this? Is my alternator toast or is there some other culprit to rule out?

What are my next steps?

Thanks in advance.

 

The alt is not hard to remove.
Just unbolt it, remove the anti-roll bar/stabilizer bar end links and swing the bar enough to get the alt out the bottom.
I have done it DOZENS of times in the last 40 years.

 

Thanks for helping with the confidence. Does it sound like the alternator is the issue, in your opinion?

 

For the little bit of labor, I would get the alt to a repair shop for an inspection and 'freshening-up' or maybe a complete rebuild.
A repair shop can test it and recommend the repair.
I never trust decades old alts with an AUTO PARTS STORE replacement.
On these old ones I just take them to a trusted STARTED/GENERATOR shop.

A newer model car might be OK to buy a rebuilt replacement but I deal with a local shop that has been doing this for decades.