Driver's side engine mount failure - GLS 550
05-23-2023, 08:34 PM
#1
Member
Thread Starter
Driver's side engine mount failure - GLS 550
I just did the mounts on our 2017 GLS 550 with 44k miles. The driver's side was absolutely toast, ready to completely fall apart. If you are feeling a "thud" in the car when you accelerate from a stop, this is the culprit. The engine torque pulls up on it and eventually makes it fail, faster than I've ever seen on any car, and I've been wrenching on many cars over the past 30 years. It's like the mount just isn't stout enough for this type of engine.
The passenger side was in like-new condition still, but that one is very, very difficult to remove. There's really not enough space to get it out, it took some use of a pry bar to move the engine to the side while it's on the jack and it took every millimeter of room to let me pry it out. The driver's side was a breeze in comparison. Came right out and the new one went back in pretty easily. I think next time, probably in another 40k miles, I'll just do the driver's side. Just have to remove the exhaust downpipe and O2 sensors, two heat shield bolts, and then it's ready to come out.
Couple notes:
The mounts can be bolted in two ways, you can spin it 180 degrees and bolt it in either way, but they have a little tab on top where the engine mount bracket would sit on them, and they tell you which way to orient the mount. They have to be pointing out towards the outside of the car, otherwise the engine bracket won't be allowed to sit fully on the mount, and then you can't get the large bolt through the mount and the mount bracket.
Tools I used:
3/8" e-torx bits sizes 10, 12 and 18. 10 for the downpipe to exhaust manifold and heat shield bolts. 12 for the downpipe to center exhaust clamps and lower engine mount bolts. 18 for the engine mount bolts. btw, the motor mount bolts are indeed VERY tight, it took me having to use a pipe on my 1/2" ratcheting socket wrench (along with some extensions, a reducer and a swivel) to break them loose. It calls for 85 nm when you re-torque them which is a lot when you don't have optimal room to work on them.
Ratcheting e-torx wrench with a 10 on one end and 12 on the other end for some of the heat shield bolts which are really close to the frame of the car (no room for a socket and socket wrench). I found it on Amazon and was here in a day.
22mm open end wrench for the O2 sensors.
16mm socket for the chassis brace bolts.
3 of the 10" long 3/8" extensions, and a swivel.
Floor jack with a few blocks of 2x4 pieces of wood to fit on the lower oil pan.
8mm socket on my cordless driver to zip off all of the plastic splash shield bolts.
On the driver's side, it is impossible to remove the 3rd and final bolt for the heat shield that covers the engine mount and mount bolt. It's way up around and behind the mount, it'd only be accessible when the engine is completely out. All I did was bend the heat shield up and away enough to where I could get the bolt out and back in. Just bent it back in place with my fingers and got the other two bolts back in no problem.
I jacked up the engine as far as I could to where the back side of the engine is just touching the firewall. I was getting up and checking to see if the engine still wiggled when I pushed it around to make sure it was still free. As soon as I made contact, I stopped. Then back below, I used a crow bar to help rock the engine over to the driver's side to allow JUST enough room for me to pry the passenger side mount out and to get the new one back in.
I'm really surprised how bad the driver's side mount was. It's like they used a mount from a smaller engine car because I really don't think it should be that bad after only 44k miles. I'm so glad I was able to tackle this one myself, the Mercedes procedure starts with "remove the engine and transmission" as step 1; it sounds like it's a $3k job, minimum.
Quick Youtube vid showing how bad the mount was and a few other things -
The passenger side was in like-new condition still, but that one is very, very difficult to remove. There's really not enough space to get it out, it took some use of a pry bar to move the engine to the side while it's on the jack and it took every millimeter of room to let me pry it out. The driver's side was a breeze in comparison. Came right out and the new one went back in pretty easily. I think next time, probably in another 40k miles, I'll just do the driver's side. Just have to remove the exhaust downpipe and O2 sensors, two heat shield bolts, and then it's ready to come out.
Couple notes:
The mounts can be bolted in two ways, you can spin it 180 degrees and bolt it in either way, but they have a little tab on top where the engine mount bracket would sit on them, and they tell you which way to orient the mount. They have to be pointing out towards the outside of the car, otherwise the engine bracket won't be allowed to sit fully on the mount, and then you can't get the large bolt through the mount and the mount bracket.
Tools I used:
3/8" e-torx bits sizes 10, 12 and 18. 10 for the downpipe to exhaust manifold and heat shield bolts. 12 for the downpipe to center exhaust clamps and lower engine mount bolts. 18 for the engine mount bolts. btw, the motor mount bolts are indeed VERY tight, it took me having to use a pipe on my 1/2" ratcheting socket wrench (along with some extensions, a reducer and a swivel) to break them loose. It calls for 85 nm when you re-torque them which is a lot when you don't have optimal room to work on them.
Ratcheting e-torx wrench with a 10 on one end and 12 on the other end for some of the heat shield bolts which are really close to the frame of the car (no room for a socket and socket wrench). I found it on Amazon and was here in a day.
22mm open end wrench for the O2 sensors.
16mm socket for the chassis brace bolts.
3 of the 10" long 3/8" extensions, and a swivel.
Floor jack with a few blocks of 2x4 pieces of wood to fit on the lower oil pan.
8mm socket on my cordless driver to zip off all of the plastic splash shield bolts.
On the driver's side, it is impossible to remove the 3rd and final bolt for the heat shield that covers the engine mount and mount bolt. It's way up around and behind the mount, it'd only be accessible when the engine is completely out. All I did was bend the heat shield up and away enough to where I could get the bolt out and back in. Just bent it back in place with my fingers and got the other two bolts back in no problem.
I jacked up the engine as far as I could to where the back side of the engine is just touching the firewall. I was getting up and checking to see if the engine still wiggled when I pushed it around to make sure it was still free. As soon as I made contact, I stopped. Then back below, I used a crow bar to help rock the engine over to the driver's side to allow JUST enough room for me to pry the passenger side mount out and to get the new one back in.
I'm really surprised how bad the driver's side mount was. It's like they used a mount from a smaller engine car because I really don't think it should be that bad after only 44k miles. I'm so glad I was able to tackle this one myself, the Mercedes procedure starts with "remove the engine and transmission" as step 1; it sounds like it's a $3k job, minimum.
Quick Youtube vid showing how bad the mount was and a few other things -
Last edited by FWP!; 05-24-2023 at 12:54 PM.
The following users liked this post:
Mort (05-23-2023)
05-24-2023, 11:37 AM
#2
Super Member
Thanks for sharing your experience and install notes. I've replaced several engine mounts on my Mercedes over the years and I believe they build them to maximize absorption of engine vibrations over longevity. My old E55 AMG (1999) ate through motor mounts. I'll save your DIY info for future reference. When I purchased by 2017 GLS450 the dealer I bought from said the motor mounts were shot as you could see the motor moving when revving engine (while in Drive) from the top of the engine bay. My long-time Mercedes indy mechanic said the motor mounts were fine. I do occasionally notice a light thud from a stop, so you have me thinking maybe one of my mounts are shot, but at the moment not enough to make me address the issue. The vehicle idles smooth and is smooth at speed.
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chassis (05-24-2023)
05-24-2023, 01:23 PM
#3
Member
Thread Starter
Thanks for sharing your experience and install notes. I've replaced several engine mounts on my Mercedes over the years and I believe they build them to maximize absorption of engine vibrations over longevity. My old E55 AMG (1999) ate through motor mounts. I'll save your DIY info for future reference. When I purchased by 2017 GLS450 the dealer I bought from said the motor mounts were shot as you could see the motor moving when revving engine (while in Drive) from the top of the engine bay. My long-time Mercedes indy mechanic said the motor mounts were fine. I do occasionally notice a light thud from a stop, so you have me thinking maybe one of my mounts are shot, but at the moment not enough to make me address the issue. The vehicle idles smooth and is smooth at speed.
05-25-2023, 12:13 PM
#5
Member
Thread Starter
No problem, I think it's a big issue that people should know about. If it gets left like this, I could see how it could cause other damage to things like wiring harnesses, connectors, hoses, etc.
