99 Alternator question and observation

The alternator on my 99 (4.0) has packed up. It's almost certainly the brushes. It has 248 thousand miles, and recently started dropping the voltmeter at random times, recovering if I revved the engine. Finally it dropped and stayed down, but when I hit the alternator it came back up. Classic brush/slipring behavior. So....

My question is first, whether the 95 alternator will fit a 99, or did they change something important, like the mounting or the connectors. Capacity doesn't matter to me. Of course I could go out and look and try it, it's easy enough, but my shop isn't cleared out tonight, and it's cold, so I'm getting lazy and asking.

Second question: does anyone know how easy it is to get a new brush set for this alternator?

My observation is that I first suspected the gauge cluster, because what happened was that the gauge dropped to 0 and the "check gauges" light came on. I'd stop and restart, and all would be well again. Finally this weekend, I noticed that the voltage would first drop, and when it went below 12.6 or so, after about 20 seconds it would drop and set the check gauge light, and not come back up until reset by a restart. I just thought that an interesting thing, because it actually prevented timely diagnosis of the problem. I ended up driving several hundred miles with an iffy alternator, and did the last 40 or so on battery alone.

Not sure on your first question. Had the same thing happen on my 99 though. I'd be driving, and suddenly the volt meter dropped to 0. shut it off and turn it back on, was good for a while. Took it to a rebuilder, he slapped new brushes in it for like 15 bucks, and said everything checked out. Still had the same prob. Took it back to him, he tested it, and it was good. Grabbed one from schucks, and no problems since. I couldnt find any brushes to replace them myself...however the rebuilder would have sold them to me. Check ebay for brushes.

Looking at the RockAuto catalog, none of the units that are recommended for a 95 will also fit a 99 and vice versa.

I know the internally regulated design was switched to a PCM-regulated design when OBD I came out replacing RENIX, so I don't really see what should keep you from doing it... if you don't mind switching the alternator bracket as well I am pretty sure it will fit, though it might fit without switching anything. Or you can get it rebuilt at a local shop or pick up a 136A from the junkyard (with a warranty, the extra 5 bucks insurance is worth it) for less money than a new/rebuilt.

kastein said:

Looking at the RockAuto catalog, none of the units that are recommended for a 95 will also fit a 99 and vice versa.

Click to expand...

that could be based on amps my 99 came with a 124 amp alternator i believe 95 was a 90-95 amp.

the only way to tell is have both side by side and compare mounts.

thanks all for the quick replies. I've looked a bit in the service manuals, and my initial impression is that the connectors are different. Given that it looks also as if I should be able to find brushes, I think I'll probably try that first, especially since I don't really want to rob the 95 of its new alternator.

Any direct experience of interchanging would still be welcome, though.

Not really direct experience, but..... When I was looking for brushes and brush kits for my old boat motor starter, the best things I fouund were on ebay. Quite a few choices were available. Turned out I had armature issues anyway, so I got a new chinese one for $100.

Anyway, point of story. For parts like brush kits, ebay had the most.

I probably should have waited a while after returning home, instead of sitting right down at the computer. A bit of googling came up with this link:

http://www.jeepforum.com/forum/f11/rebuilding-nippon-denso-alternator-00-01-56041822aa-835511/

A nice thorough writeup, which confirms that the earlier alternator is a physical fit with different connectors. That's a good thing to know, since if there's a delay in getting brushes I won't feel too bad about robbing the brand new Grand Cherokee alternator out of my 95, which gets little use in this season because it has no heat.

Update and local business plug

I went to the junkyard, but they didn't have an alternator in stock, despite having about 20 XJ's on the yard from the clunker program, and they wanted $75 for what they could get tomorrow, so I went to a nearby auto electric place in search of brushes, and they GAVE me a set. This is not the first time this place has treated me nicely, and while I was there, a fellow came in with a honking big truck alternator, and the prices they quoted for new and rebuilt replacements were surprisingly reasonable. So....my plug:

If you're ever in the Rutland, Vermont vicinity, and need auto electrical work, starter, alternator, winch motor, etc. I recommend B&B Auto Electrical on Grainger St. in Rutland. Nice guys!

I opened up my alternator, and of course found that one of the slip rings is deeply grooved, but I'll put it back together anyway, figuring it will last a few months. I also opened up the old alternator from my 95, which had been working well but seized up from rust, and found that it had a bad slip ring too. But in the process I also found that the two alternators are physically identical except for the connectors, and the connectors can be interchanged without any issues. That may be a handy thing to know, especially since the 95 style is also used by many Grand Cherokees, with a higher rating than the XJ.

I may swap out the brand new GC alternator I put in my 95 this fall, if it's a true Nippondenso, and swap the connectors.