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Old 08-11-2015, 11:04 PM
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YJ Alternator Swap/Importance of Upgrades for the Future

I'd like to let other Jeepers know about my alternator swap (stock 75 or 90 amp YJ alternator to 136 amp WJ alternator). I did this for a few reasons:
My old alternator was bad (at least I thought, it ended up being a bad connection that drained the battery).
I knew I would need more amperage, which is why I went ahead and replaced it rather than testing before fixing.

I had read about this swap on Wrangler Board, here. I thought that my alternator at the time was a 90 amp, but it turned out to be a 75 amp after taking a look at my build sheet. Chrysler wiring is very cheap, as they tend to use the minimal strength required. At that time I had a power inverter running along with a phone charger, that would drain my battery. Since then I have added offroad lights, but I also see a winch in the future.

Now, the reason I didn't just put in another YJ alternator was that I knew I would have to replace it down the road to handle my electrical crap.

For anybody on the fence about this swap, do it. It is just like putting in the stock alternator.

After reading the Wrangler Board write-up, I was a little concerned with the fit. The two issues that THE_TOOLMAN mentioned were the different angle insulator and the wrong pulley size. The insulator worked for me, but I did need to impact the pulley off. The new pulley went right on with a low torque setting on the impact. However, the new alternator was a little too wide. A couple of careful taps with a hammer on the bracket did the job, I didn't even use my BFH.

I wish I took photos to document this swap, but it was done in sort of an emergency. Just keep in mind these tips:
Remove the old alternator first, and take the pulley and insulator off. It won't affect the core. The new alternator was $150 with a $90 core, so I definitely wanted to bring in the old one.
Borrow an impact. The impact made it a lot easier, just to get the sudden torque on a moving part.
Draw an outline of the serpentine belt. Just a rough pencil-on-paper sketch. Keep in mind the crank pulley, alternator pulley, A/C compressor, power steering, or any other pulleys on the belt. I didn't need it, but you might.
Disconnect the battery.
Have two 15mm sockets or wrenches to use.

I'm sure that this swap has been done before, but I'd like to make myself available for any questions regarding this job. If you're wondering whether or not it's worth it, how difficult it is, what tools you'll need, or anything else, ask me for my opinion and hopefully some other members will chime in so you all can get some more information. I'd like to spread the wealth that I found on Wrangler Board, as we're all friends here.

*I've heard this will work, with a little more effort, in an XJ Cherokee as well, they're very similar to YJ Wranglers.

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Old 08-12-2015, 12:08 AM   #2
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Originally Posted by Chrysler_is_JK_I_hope... View Post
I'd like to let other Jeepers know about my alternator swap (stock 75 or 90 amp YJ alternator to 136 amp WJ alternator). I did this for a few reasons:
My old alternator was bad (at least I thought, it ended up being a bad connection that drained the battery).
I knew I would need more amperage, which is why I went ahead and replaced it rather than testing before fixing.

I had read about this swap on Wrangler Board, here. I thought that my alternator at the time was a 90 amp, but it turned out to be a 75 amp after taking a look at my build sheet. Chrysler wiring is very cheap, as they tend to use the minimal strength required. At that time I had a power inverter running along with a phone charger, that would drain my battery. Since then I have added offroad lights, but I also see a winch in the future.

Now, the reason I didn't just put in another YJ alternator was that I knew I would have to replace it down the road to handle my electrical crap.

For anybody on the fence about this swap, do it. It is just like putting in the stock alternator.

After reading the Wrangler Board write-up, I was a little concerned with the fit. The two issues that THE_TOOLMAN mentioned were the different angle insulator and the wrong pulley size. The insulator worked for me, but I did need to impact the pulley off. The new pulley went right on with a low torque setting on the impact. However, the new alternator was a little too wide. A couple of careful taps with a hammer on the bracket did the job, I didn't even use my BFH.

I wish I took photos to document this swap, but it was done in sort of an emergency. Just keep in mind these tips:
Remove the old alternator first, and take the pulley and insulator off. It won't affect the core. The new alternator was $150 with a $90 core, so I definitely wanted to bring in the old one.
Borrow an impact. The impact made it a lot easier, just to get the sudden torque on a moving part.
Draw an outline of the serpentine belt. Just a rough pencil-on-paper sketch. Keep in mind the crank pulley, alternator pulley, A/C compressor, power steering, or any other pulleys on the belt. I didn't need it, but you might.
Disconnect the battery.
Have two 15mm sockets or wrenches to use.

I'm sure that this swap has been done before, but I'd like to make myself available for any questions regarding this job. If you're wondering whether or not it's worth it, how difficult it is, what tools you'll need, or anything else, ask me for my opinion and hopefully some other members will chime in so you all can get some more information. I'd like to spread the wealth that I found on Wrangler Board, as we're all friends here.

*I've heard this will work, with a little more effort, in an XJ Cherokee as well, they're very similar to YJ Wranglers.
Good to know for the future? Thanks! Wow, that's almost double the amps!?

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Old 08-12-2015, 05:19 AM   #3
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I found a 160 amp one for mine off eBay that works great without any fit issues but I also added 0/1 gauge wiring for the big 3 and an inline fuse to the battery 175 amp iirc now when I use my winch the battery charges back up to 14.5 in very very little time
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Old 08-12-2015, 09:46 AM
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Originally Posted by xjrjrx View Post
I found a 160 amp one for mine off eBay that works great without any fit issues but I also added 0/1 gauge wiring for the big 3 and an inline fuse to the battery 175 amp iirc now when I use my winch the battery charges back up to 14.5 in very very little time
I second using larger wire. I didn't do that, because wire is cheap and easy to do so I will when I put on a winch. Now the current gauge is fine.
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Old 08-12-2015, 10:50 AM
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Good to know for the future? Thanks! Wow, that's almost double the amps!?
I was concerned about the big jump in amperage. However, car batteries are not meant to be completely discharged (I confirmed by reading this). They are meant to keep a full charge, and normally don't drop below 80%. When running a heavy electrical load, the alternator will need to keep up. If your car battery doesn't charge back up enough before the car shuts off (like when turning off your Jeep to check your line), the battery will not go through the cycle it was made for.
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Build thread for OJ, my YJ. 1993 Wrangler S 2.5L/AX-5/NP231 with SYE, Spartan locked Dana 30/Aussie locked Ford 8.8 @ 4.88, SOA lift with 2.5" OME HD springs and front Bilstein/rear Rancho shocks, Barricade 9500 winch, custom front and rear bumpers, 136 amp alternator, 35" Super Swamper LTBs.
1999 Ford F-250 Super Duty 7.3L Powerstroke, single turbo, 6 speed manual.
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Old 08-13-2015, 12:53 AM   #6
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I went a different route. Good to know the WJ is an option. The stock YJ alternator really is pathetic.
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Old 08-14-2015, 11:13 PM
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I went a different route. Good to know the WJ is an option. The stock YJ alternator really is pathetic.
What other "route" did you go? The WJ is a popular swap but I'd like to hear some more options.
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Old 08-15-2015, 08:29 PM   #8
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Found one out of a dodge v8 on eBay for $35, 136 amps vs 90 amps stock. Direct bolt on, works flawlessly.
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Old 08-29-2015, 03:17 AM   #9
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What year was the WJ from?
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Old 08-30-2015, 05:27 AM   #10
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Premier Power Welder system includes an alternator that is significantly more powerful than most stock applications. My alternator is 160 amp hot rated. Most stock alternators are cold rated. When cold the alternator produces maximum power. As it warms up when you drive down the road the alternator produces less power. My Premier Power Welder alternator was rated when brought to full operating temp. Also of note, most alternators are rates at a fast rpm of the engine. Meaning alternators produce less power when vehicle is at idle. Normally this means little. However, add a winch and offroad rock lights this becomes very important.
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Old 08-30-2015, 09:09 AM   #11
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One weird thing to look out for...the motor mount bolt on that side is a very LONG bolt. After I did my alternator swap, I needed to replace the motor mounts. The bolt ran from front to back, and pulling it out, it butted up against the alternator with quite a bit of bolt to go. I had to actually take the belt off and unbolt the alternator to remove it.

The long term solution is pretty low tech; when I or the motor mount back in, I ran the bolt from back to front since there's plenty of room behind the motor mount.

I thought to myself at the time, that if I'd known, I would have spent an extra 10 minutes while I was doing the alternator and just stuck a jack under the engine and switched the bolt at that time.
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Old 08-30-2015, 11:44 PM   #12
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One weird thing to look out for...the motor mount bolt on that side is a very LONG bolt. After I did my alternator swap, I needed to replace the motor mounts. The bolt ran from front to back, and pulling it out, it butted up against the alternator with quite a bit of bolt to go. I had to actually take the belt off and unbolt the alternator to remove it.

The long term solution is pretty low tech; when I or the motor mount back in, I ran the bolt from back to front since there's plenty of room behind the motor mount.

I thought to myself at the time, that if I'd known, I would have spent an extra 10 minutes while I was doing the alternator and just stuck a jack under the engine and switched the bolt at that time.
Yeah, haha that kinda sucks.

I may do the alternator swap if my alternator ever goes. So I'll just do motormounts too.
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Old 08-31-2015, 08:17 AM
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What year was the WJ from?
I used one for a '98 Grand Cherokee 9 Limited. The part number is 13742A.
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Build thread for OJ, my YJ. 1993 Wrangler S 2.5L/AX-5/NP231 with SYE, Spartan locked Dana 30/Aussie locked Ford 8.8 @ 4.88, SOA lift with 2.5" OME HD springs and front Bilstein/rear Rancho shocks, Barricade 9500 winch, custom front and rear bumpers, 136 amp alternator, 35" Super Swamper LTBs.
1999 Ford F-250 Super Duty 7.3L Powerstroke, single turbo, 6 speed manual.
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Old 08-31-2015, 08:21 AM
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Originally Posted by entropy319 View Post
One weird thing to look out for...the motor mount bolt on that side is a very LONG bolt. After I did my alternator swap, I needed to replace the motor mounts. The bolt ran from front to back, and pulling it out, it butted up against the alternator with quite a bit of bolt to go. I had to actually take the belt off and unbolt the alternator to remove it.

The long term solution is pretty low tech; when I or the motor mount back in, I ran the bolt from back to front since there's plenty of room behind the motor mount.

I thought to myself at the time, that if I'd known, I would have spent an extra 10 minutes while I was doing the alternator and just stuck a jack under the engine and switched the bolt at that time.
I didn't have any trouble with the motor mounts being in the way. However, the previous owner put in new motor mounts so it may be because these are just aftermarket and don't get in the way. I did notice that the nut was nearly coming off the bolt (not sure if it's related or not), and it was a b**** to tighten. I did manage to get an open wrench in by the alternator and an impact on the other side from underneath the Jeep. I don't think that the alternator I used turned out to be much bigger than stock.
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Build thread for OJ, my YJ. 1993 Wrangler S 2.5L/AX-5/NP231 with SYE, Spartan locked Dana 30/Aussie locked Ford 8.8 @ 4.88, SOA lift with 2.5" OME HD springs and front Bilstein/rear Rancho shocks, Barricade 9500 winch, custom front and rear bumpers, 136 amp alternator, 35" Super Swamper LTBs.
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Old 08-31-2015, 08:28 AM
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Premier Power Welder system includes an alternator that is significantly more powerful than most stock applications. My alternator is 160 amp hot rated. Most stock alternators are cold rated. When cold the alternator produces maximum power. As it warms up when you drive down the road the alternator produces less power. My Premier Power Welder alternator was rated when brought to full operating temp. Also of note, most alternators are rates at a fast rpm of the engine. Meaning alternators produce less power when vehicle is at idle. Normally this means little. However, add a winch and offroad rock lights this becomes very important.
I personally think that the serpentine belt is the best thing since sliced bread. It uses the engine that's already turning over to generate power, which produces minimal load on the engine and really only wastes heat energy.

The changing engine RPMs is essentially the only downfall that I see. I notice the difference when my dad's SUV is at a stop light, and the air conditioning fan gets quiet all of a sudden. Other than that, the serpentine belt is a very efficient system.

When you think of when you'll be using all of those things, your vehicle is going to be idling a lot. You won't be driving your Jeep when you're winching, and you probably won't shut off all your lights when you hop out to look at your line.
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Old 08-31-2015, 09:45 AM   #16
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Originally Posted by MudMagnetYJ View Post

When you think of when you'll be using all of those things, your vehicle is going to be idling a lot. You won't be driving your Jeep when you're winching, and you probably won't shut off all your lights when you hop out to look at your line.
Which is why having a hand throttle is so handy. Whether I'm giving someone a jump, running my winch from outside the cab, or just slow speed crawling over rough ground it a $30 add on that has made my wheeling easier.
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Old 09-07-2015, 09:31 PM
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Which is why having a hand throttle is so handy. Whether I'm giving someone a jump, running my winch from outside the cab, or just slow speed crawling over rough ground it a $30 add on that has made my wheeling easier.
That's a great idea. I'll have to get one when I get a winch. With a stock alternator, I'm sure that a hand throttle will be necessary. Especially when you're night wheeling, blasting music, and winching somebody.

One odd thing:
I installed some fog lights that go above my tail lights. They're wired into my purple reverse light wire. I can turn on my front fog lights, front truck lights, and headlights/running lights. There is negligible voltage drop (according to the gauge on my dash).
When I put my shifter into reverse, it drops about a full volt. Not sure why this happens, but my point is that all my front lights really don't draw that much power.
I even had them on for a full hour with the Jeep off. I was working on my friend's Jeep and wanted lights, but he could jump me if my battery died.

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Build thread for OJ, my YJ. 1993 Wrangler S 2.5L/AX-5/NP231 with SYE, Spartan locked Dana 30/Aussie locked Ford 8.8 @ 4.88, SOA lift with 2.5" OME HD springs and front Bilstein/rear Rancho shocks, Barricade 9500 winch, custom front and rear bumpers, 136 amp alternator, 35" Super Swamper LTBs.
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