GL550 alternator DIY
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Member
Joined: Jan 2019
Posts: 83
Likes: 36
From: Central NY State
2010 GL550
GL550 alternator DIY
Since I haven't really found an actual write-up, and even though certain steps are more or less talked about elsewhere, here's my step-by-step. I'll add pictures later on and edit.
Tools needed / suggested:
10mm, 13mm, and 17mm sockets, E-12 socket, T27 torx bit (might be a 30 for some). 6" extension, swivel, and flathead screwdriver or pliers to remove the panel clips. Jack and stands might be needed if you don't have room under to work on it.
First, move your passenger seat fully forward and up. You're going to want to disconnect the battery before you unhook the alternator itself from the wiring, but you might want to make sure you're in a good position, or don't need to move it before unhooking. In my case, I raised the suspension as high as I could prior, for clearance later.
Depending on if you've got just yourself, or a 2nd pair of hands, you may or may not want to remove the radiator fan. If you have a helper, you can get away without - there's enough space to get a breaker bar on the tensioner, and there's enough clearance to pull the old unit out behind the passenger headlight. But when re-installing it, if you don't have a 2nd pair of hands to help hold it in place from beneath while you get the bolts started, you'll want the room. So in case you wish it:
Removing the fan:
There are two plastic vertical fins, that have two push-pin clips each. Pop the pins up, pull the fins and set them aside, Next, there are seven 10mm bolts, and a T27 torx bolt. I've heard it referenced as a T30 but it was a 27 for me. There are three bolts on the left, two that hold the center by the hood latch, and two bolts, and the torx, on the right. On top of the metal piece are two clips that mount over the top of the radiator and such. In my case they weren't latched or if they were, not by much, but you may need to squeeze the tabs while you wiggle the panel loose, setting the weatherstrip forward out of the way.
The fan itself has two 10mm bolts, one on each top corner. If you reach down to the cooler lines and just push the rubber aside ever slightly, you can free up the mounting tab on the passenger bottom to clear, and then just wiggle the fan out. Enjoy your new space!
Altenrator Removal:
Using a 17mm socket on the tensioner (it's slightly hidden by the belt from view but it's there), press down to relieve pressure, and slip the belt from the alternator. You might want to keep a diagram handy for routing, just in case. I found it helpful to remove the engine cover and the passenger air intake duct. The alternator itself has 4 bolts - 2 top and bottom. They are E-12 sockets, which are a reverse torx. They aren't torqued down really tight, but instead of trying to just make a regular socket work, you should have invested or should invest in, a set of the sockets. For as many bolts on these that take them, it's a no brainer. The top two were easy to get with a 3/8" ratchet and the socket. The ground strap, and a clamp to hold the wiring are mounted along with the bolts, so when the bolts are out, move them aside and out of the way. The bottom bolts are easier to get with from underneath.
Remove the under tray:
The tray underneath has nine 10mm bolts holding it up. There are four along the back, and the rest in the middle and outside edges. It just drops down from the back and then slides back out of the car.
From under the car - easy enough if you have the lifted suspension but you may need to jack and stand it to get your clearance. I found it easy to reach the bolts with a 6" extension and a swivel on the end with the socket. Once those bolts are out, the alternator is freed up.
Back up top, rotate the alternator in place so that you have access to the 13mm bolt holding the positive wire to the alternator. If you haven't done it, now is the time to disconnect your battery. On mine, there was a plastic cap over the nut, that I popped off with a small flathead screwdriver. Unbolt the wire, and there's a regular push-clip style plug on the other wire. Once those are free, the alternator can be moved back up and with some careful maneuvering, will come out the passenger side without fuss.
Installation:
This is the tricky part. If you are only one person, best of luck to you. It is a bear to try to hold it in place while starting the bolts. If you can get ANY threads to hold on the top bolts, count yourself lucky and get them in place, then go under and start the bottom bolts. If you have a helper, they should be able to hold it up in place from beneath long enough for you to get the bolts started. However, before putting the bolts in, make sure you hook your wiring back up. Orient the alternator pulley-down, hook up your positive and your harness plug, and then move it back into place for the bolts. The plastic cap may or may not fit on the new alternator, depending on the model. Certain models have the wiring in slightly different places and have a different style tabs for the wiring to sit into that might not hold the cap on. If you feel better about it, you can tape over the exposed bolt, if the cap won't work.
WARNING!!! - Because this happened to me. The mounting tabs are off-set VERY slightly on the casing of the alternator. Or at least on the Duralast 11455 model I had. And unless you sit and stare, you don't notice it. So I oriented the unit to go in such a fashion that the harness clip was in relatively the same position as stock. However, this was actually 180 degrees out, and meant the the "thicker" half was being pressed against the engine. The bolts snug up just fine, however if you have it in this orientation, it'll actually draw the casing of the alternator against the side of the engine, and probably crush it into itself which will cause the alternator itself to seize up. You'll find this out when you turn the key and find a squeal and cloud of smoke from your belt. So make sure you're putting your new one in the correct way, or at the very least make sure as your snugging the bolts down, that they all go very smooth. There should be almost no tension until the last turn of the threads, really. So if you're starting to find torque needed with 1/4" to go, stop, and back out and double-check. I didn't, and now I'm waiting two more days for another alternator. It wasn't until I pulled it back off that I saw the cracked casing, and upon further inspection, saw the very slight difference from side to side distances.
Once the alternator is back on, use your 17mm again on the tensioner and put the belt back on. Clear all your tools and reconnect the battery and start. Ideally test for voltage with a meter, since that's probably why you're replacing it anyway. Running without the fan for a minute won't be an issue. Once satisfied, go ahead and turn it off. Wiggle the fan back down into place, careful to line up the alignment tabs on each side and clearing your hoses. Reinstall the 10mm bolts in the top corners. Put the panel back into place, you'll have to tuck it under the hood latch mount and make sure your clips fit over the radiator tabs but then bolt back in place with the seven 10mm and T27 (or 30) torx bit. Install your vertical fins and push the pins back in to secure them. Install the air intake duct if you removed it, as well as the engine cover. Underneath, reinstall the under tray by sliding the front edge up and into the bottom of the bumper side, and reinstall the nine 10mm bolts under there.
All in all, it should take about an hour or so depending on your luck getting the new one held in place to get your bolts started. If you're like me, you tried to skip removing the fan, because you can still release tension off the belt and get the old one out without that step. But then when you waste an hour trying to get it back in place before giving up and taking the time to take the fan out anyway - and then to smoke the new alternator, well.. then it'll take longer.
Tools needed / suggested:
10mm, 13mm, and 17mm sockets, E-12 socket, T27 torx bit (might be a 30 for some). 6" extension, swivel, and flathead screwdriver or pliers to remove the panel clips. Jack and stands might be needed if you don't have room under to work on it.
First, move your passenger seat fully forward and up. You're going to want to disconnect the battery before you unhook the alternator itself from the wiring, but you might want to make sure you're in a good position, or don't need to move it before unhooking. In my case, I raised the suspension as high as I could prior, for clearance later.
Depending on if you've got just yourself, or a 2nd pair of hands, you may or may not want to remove the radiator fan. If you have a helper, you can get away without - there's enough space to get a breaker bar on the tensioner, and there's enough clearance to pull the old unit out behind the passenger headlight. But when re-installing it, if you don't have a 2nd pair of hands to help hold it in place from beneath while you get the bolts started, you'll want the room. So in case you wish it:
Removing the fan:
There are two plastic vertical fins, that have two push-pin clips each. Pop the pins up, pull the fins and set them aside, Next, there are seven 10mm bolts, and a T27 torx bolt. I've heard it referenced as a T30 but it was a 27 for me. There are three bolts on the left, two that hold the center by the hood latch, and two bolts, and the torx, on the right. On top of the metal piece are two clips that mount over the top of the radiator and such. In my case they weren't latched or if they were, not by much, but you may need to squeeze the tabs while you wiggle the panel loose, setting the weatherstrip forward out of the way.
The fan itself has two 10mm bolts, one on each top corner. If you reach down to the cooler lines and just push the rubber aside ever slightly, you can free up the mounting tab on the passenger bottom to clear, and then just wiggle the fan out. Enjoy your new space!
Altenrator Removal:
Using a 17mm socket on the tensioner (it's slightly hidden by the belt from view but it's there), press down to relieve pressure, and slip the belt from the alternator. You might want to keep a diagram handy for routing, just in case. I found it helpful to remove the engine cover and the passenger air intake duct. The alternator itself has 4 bolts - 2 top and bottom. They are E-12 sockets, which are a reverse torx. They aren't torqued down really tight, but instead of trying to just make a regular socket work, you should have invested or should invest in, a set of the sockets. For as many bolts on these that take them, it's a no brainer. The top two were easy to get with a 3/8" ratchet and the socket. The ground strap, and a clamp to hold the wiring are mounted along with the bolts, so when the bolts are out, move them aside and out of the way. The bottom bolts are easier to get with from underneath.
Remove the under tray:
The tray underneath has nine 10mm bolts holding it up. There are four along the back, and the rest in the middle and outside edges. It just drops down from the back and then slides back out of the car.
From under the car - easy enough if you have the lifted suspension but you may need to jack and stand it to get your clearance. I found it easy to reach the bolts with a 6" extension and a swivel on the end with the socket. Once those bolts are out, the alternator is freed up.
Back up top, rotate the alternator in place so that you have access to the 13mm bolt holding the positive wire to the alternator. If you haven't done it, now is the time to disconnect your battery. On mine, there was a plastic cap over the nut, that I popped off with a small flathead screwdriver. Unbolt the wire, and there's a regular push-clip style plug on the other wire. Once those are free, the alternator can be moved back up and with some careful maneuvering, will come out the passenger side without fuss.
Installation:
This is the tricky part. If you are only one person, best of luck to you. It is a bear to try to hold it in place while starting the bolts. If you can get ANY threads to hold on the top bolts, count yourself lucky and get them in place, then go under and start the bottom bolts. If you have a helper, they should be able to hold it up in place from beneath long enough for you to get the bolts started. However, before putting the bolts in, make sure you hook your wiring back up. Orient the alternator pulley-down, hook up your positive and your harness plug, and then move it back into place for the bolts. The plastic cap may or may not fit on the new alternator, depending on the model. Certain models have the wiring in slightly different places and have a different style tabs for the wiring to sit into that might not hold the cap on. If you feel better about it, you can tape over the exposed bolt, if the cap won't work.
WARNING!!! - Because this happened to me. The mounting tabs are off-set VERY slightly on the casing of the alternator. Or at least on the Duralast 11455 model I had. And unless you sit and stare, you don't notice it. So I oriented the unit to go in such a fashion that the harness clip was in relatively the same position as stock. However, this was actually 180 degrees out, and meant the the "thicker" half was being pressed against the engine. The bolts snug up just fine, however if you have it in this orientation, it'll actually draw the casing of the alternator against the side of the engine, and probably crush it into itself which will cause the alternator itself to seize up. You'll find this out when you turn the key and find a squeal and cloud of smoke from your belt. So make sure you're putting your new one in the correct way, or at the very least make sure as your snugging the bolts down, that they all go very smooth. There should be almost no tension until the last turn of the threads, really. So if you're starting to find torque needed with 1/4" to go, stop, and back out and double-check. I didn't, and now I'm waiting two more days for another alternator. It wasn't until I pulled it back off that I saw the cracked casing, and upon further inspection, saw the very slight difference from side to side distances.
Once the alternator is back on, use your 17mm again on the tensioner and put the belt back on. Clear all your tools and reconnect the battery and start. Ideally test for voltage with a meter, since that's probably why you're replacing it anyway. Running without the fan for a minute won't be an issue. Once satisfied, go ahead and turn it off. Wiggle the fan back down into place, careful to line up the alignment tabs on each side and clearing your hoses. Reinstall the 10mm bolts in the top corners. Put the panel back into place, you'll have to tuck it under the hood latch mount and make sure your clips fit over the radiator tabs but then bolt back in place with the seven 10mm and T27 (or 30) torx bit. Install your vertical fins and push the pins back in to secure them. Install the air intake duct if you removed it, as well as the engine cover. Underneath, reinstall the under tray by sliding the front edge up and into the bottom of the bumper side, and reinstall the nine 10mm bolts under there.
All in all, it should take about an hour or so depending on your luck getting the new one held in place to get your bolts started. If you're like me, you tried to skip removing the fan, because you can still release tension off the belt and get the old one out without that step. But then when you waste an hour trying to get it back in place before giving up and taking the time to take the fan out anyway - and then to smoke the new alternator, well.. then it'll take longer.
Super Member
Joined: Jan 2007
Posts: 622
Likes: 202
From: CA
11 ML550, 95 Supra TT, 14 Audi S4
Good writeup, I didn't see this when I replaced mine. I would have preferred using something other than an AutoZone unit like the OP used, but I didn't have time to wait for a Bosch from FCP Euro, and I wasn't spending what the dealer was charging for one on a 200K+ mile vehicle that is one big repair away from end of life so Duralast it was. It was a little difficult to get the bolts started on the new one, but I didn't need to pull the fan, and didn't have the issue of misalignment mentioned in the original post. It was pretty straightforward. So far so good on the $180 Duralast. one year and 12kIsh miles later.
Thread Starter
Member
Joined: Jan 2019
Posts: 83
Likes: 36
From: Central NY State
2010 GL550
Just as a follow-up, I've had no issues with the alternator. But curiously, when I got the replacement for my originally botched job, it came as the same exact part number, but totally different casing. I left it out of the write-up as it wasn't pertinent, but the original I got was a completely different housing design than the OEM one I removed. The 2nd one I received, was identical to OEM, so I'm not sure what happened with the first one I had. So as an addendum to the original, always verify that the replacement is the same as what you're replacing!
