Alternative Alternator Amperage?

So my 2007 Jeep Compass 2.4L needs an alternator (I think). It turns out you can either get a 115 amp or 140 amp alternator. Is there a way to know which one i need without first taking everything apart to look at it (just so I can put it all back together, drive to the store and back, and take it all apart again)? Are they interchangeable (they’re the same price, so why not go for the bigger one if it fits)? I don’t have the shop manual and Haynes hasn’t made one yet. Autozone just got around to doing a repair guide for the Compass recently, and it’s still a bit thin. I don’t have access to AllData. Thanks.

An alternator is a pricy part to be replacing on a guess.
Why do you think the alternator is bad?

There are several things which are not directly related to the alternator and which can cause it not to charge.

Ah, it’s a long story:

  1. Growling/howling sound has been getting worse for months. It’s definitely a bearing somewhere along the accessory belt.
  2. I asked my mechanic to pinpoint which accessory, and he couldn’t. Said various pulleys might have felt a bit loose, but nothing seemed really bad. You couldn’t tell where the sound was using a stethescope (he showed me, the vibration got transmitted everywhere, strongest at both the water pump at the back, and the alternator at the front, and a bit weaker at the power steering pump at front top). He wanted to get a non-AC drive belt to see if it was the compressor.
  3. I changed the belt myself. It wasn’t the compressor. The tensioner pulley and lower idler pulley seemed a bit loose, so off to the parts store again. None of the pulleys felt rough while spinning by hand.
  4. During this time, I found out one of my condo neighbors used to be a mechanic (he has his own vinyard now - nice!) In talking to him, he confirmed that if those pulleys felt a bit loose, they were probably the culprit. He also pointed out the rust dust on the front of the alternator could be indicative of a failing bearing.
  5. The new tensioner and idler pulleys made no difference.

Any suggestions to narrow it down further? How about 115 vs 140 amp? Thanks.

Remove the under engine splash shield and look to see if you can read the label on the alternator.

140 amp, 4801477AA
120 amp, 4801323AC

If you message to me the last 8 digits of your VIN I can check the option codes.

I’m no Jeep expert but I think this model uses a clutch pulley on the alternator like some Chryslers. It’s quite possible that clutch pulley is the problem.

As to whether the alternators interchange I do not know but if they do, going to the higher rated alternator will not hurt anything.

Thanks Nevada. The last 8 numbers are 7D371754. Hopefully you can save me from one unnecessary trip under the car.

ok4450: Would a clutch pulley also be called a decoupler pulley?

Should be.

Build code BANS = 120 Amp Alternator

Thanks guys. RockAuto seems to sell the pulleys. Would I need any special tools to pull a clutch pulley off of the alternator?

Say, Nevada, would that VIN tell you whether I have a Sport or Limited model? I bought this thing used, and I really don’t know which one it is.

OK4450 is correct about the clutch inside the pulley, that is probably where the rust is coming from. When you turn the engine off you may hear a growl from that pulley for a few seconds after the engine stops. You can also feel if the clutch is smooth by removing the belt, grab the pulley, quickly twist it clockwise then hold the pulley from turning.

You know, I’ve always noticed a funny sound on shutdown, sort of 3 or 4 chirps like something is trying to keep spinning for a second. I wonder if that was it. So what do you know, I learned something new today. What’s the purpose - smooth out the belt force or something? I thought the harmonic balancer did that.

I just found the special tool needed online. 75 bucks, wow! (plus shipping, tax, exchange rate, plus whatever the government wants for import). Between that and the part, I might as well get a whole new alternator.

The thing is, would a bad clutch pulley make a steady growling noise? The sound is always there when running, and varies in pitch with engine speed. It does vary from trip to trip, as if the slack in the worn bearing seats itself differently every time the engine is stopped.

The pulley can make a steady noise. While idling switch on the headlights and rear window defroster, see if adding a load to the alternator changes the pitch of the noise.

It looks like a base model, it doesn’t show Sport or Limited. This is a Thrifty Canada inc. vehicle so think “economy”.

At this point, I’m convinced it’s the alternator pulley. I’ll need to pull out the alternator and change the pulley on the bench. Unlike a lot of these overrunning alternator pulleys, this one doesn’t need a really fancy tool, just a 17mm hex. You rely on an impact gun to loosen and tighten it before the alternator shaft spins up. YouTube to the rescue (the important bit is around the 8:10 mark):

The guy in the video used an air gun. The instructions say use full torque at 90psi to get it tightened down enough. I’m hoping to use a corded electric impact gun. I have no experience with impacts whatsoever. Would an electric do well enough in this situation? I assume I can’t just lock the alternator shaft with a screwdriver in the fan at the back without breaking it. Thanks.

Well, in the end, I had to replace the whole alternator. First I tried doing the job myself. I borrowed a friend’s compressor and impact, got myself a big 17mm hex driver, and spent hours on the floor of my parkade trying to get the alternator out. The AC and alternator bolts are all hard to get at. But after all that, I couldn’t figure out how to disconnect a two-piece plug for the field wire, and I couldn’t even fandangle the alternator out of the front of the car. So I gave up, put it all back together, and managed to go to bed at 4am. Somehow that led to a stomach flu and strep throat. :slight_smile:

Got my mechanic to do it today. I had to supply him the part, because he was told you can’t get it on its own. My own research, based on the above, told me otherwise. He got the alternator out, got the old pulley off (it fell apart right away and the bearings were rough as all hell), but couldn’t put the new one on. Only a couple of threads engaged before the pulley butted against the stop on the shaft. Somehow the right part number was the wrong part number. At that point I gave up and said give me a new alternator, with the pulley already on it. I think I’m out $70 for the part that got ruined though. Plus the over $600 in parts and labour that the new alternator cost me (I’m in Vancouver, BC).

What’s everybody’s opinion of these fancy pulleys? Worth it just to save some wear and tear on the tensioner?