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I have a 2012 C250 that I purchased on December 2019 with 45K. I've been a bit disappointed in the car, as it seemed to suffer from turbo lag or so I thought. When accelerating into traffic, the car would be sluggish, when the power did kick in, it could be abrupt. I changed the coils and plugs, but it was still the same result. Just kind of lived with it and thought it was a quirk of the model. About a year ago, my cam phasers went out and I had the phasers and timing chain replaced. I also had the transmission flushed. I was hoping all these fixes would help the car, but it still didn't fix the sluggishness when accelerating. Over the last 4 months, the car was getting louder and I had that exhaust growl that suggested the transmission mount needed to be changed. In addition, I started getting poor gas mileage, got a P2805 and a P0705 error and the RPMs would suddenly shoot up 1-2K when accelerating.
I was about to take the car into the shop but decided to change the transmission mount myself before taking it in. The transmission was a lot lower, I think I had to raise it up a half inch to get everything installed. On the test drive, it was like night and day. The car was quiet, it was smooth, the power was responsive, the lag was gone and the errors were gone. This was the car that I was expecting when I bought it.
Could a transmission mount cause that many problems in the car? Been driving for a week now and am amazed at the difference.
Last edited by RS250_Chester; Jan 18, 2023 at 06:32 PM.
I was thinking it could have been the high pressure fuel pump until I read that the problems were fixed. quite surprised too. glad its fixed thou!
Last summer, I did get a high-pressure fuel pump error when I accelerated into traffic on a freeway, the car couldn't put the power down, RPMs jumped and then a CEL appeared. I cleared the CEL and high-pressure fuel pump error never again appeared.
I'm just wondering if the transmission was so low it wasn't outputting the engine power properly and caused a whole set of issues.
I updated my post to reflect that I actually bought the car in December 2019, not 2012 as originally posted.
Ive heard of rough idling and hard shifting when the transmission mounts are bad, but could have never expected the plethora of other seemingly unrelated problems that associated with it
How was the job to replace the transmission mount? Any pics of the work in progress, or the good vs bad mounts?
The job itself is simple, if I had to do it again, it probably take 15-20 minutes, It's basically lift the front of the car, support the transmission with another jack, remove 6 bolts from the cross mount, remove 3 bolts in the middle of cross mount that are attached to transmission mount. Then remove 2 bolts that attach the mount to the transmission. Install is the reverse, but the transmission will need to be lifted a bit with the jack.
Here is a pic of the old one that came out. The inner support bracket is much lower than the new one. Also some of the rubber at the bottom seems to be missing.
Pelican parts has a write-up on this and there are a couple of good videos available on youtube
You will need a low profile jack and 2 jack stands.
Last edited by RS250_Chester; Jan 18, 2023 at 10:23 PM.
Ive heard of rough idling and hard shifting when the transmission mounts are bad, but could have never expected the plethora of other seemingly unrelated problems that associated with it
I've been waiting for the other shoe to drop for the last week, but so far all the issues I've had are gone (knock on wood). I spoke to 3 indie shops about the P0705/P2805 error; one said the shifter assembly needed to be replaced, another pointed to the transmission conductor plate, and another said I needed to go to a dealership. While also looking to replace the high-pressure fuel pump because Mercedes would not cover my vehicle for the extended warranty repair.
All I know is the car is responsive, smooth, and quiet and power is on demand. The car has never felt like this in 3 years of ownership. Hopefully I've saved a few thousand dollars in repairs, but like I said, I've been waiting for the other shoe to drop.
I've been waiting for the other shoe to drop for the last week, but so far all the issues I've had are gone (knock on wood). I spoke to 3 indie shops about the P0705/P2805 error; one said the shifter assembly needed to be replaced, another pointed to the transmission conductor plate, and another said I needed to go to a dealership. While also looking to replace the high-pressure fuel pump because Mercedes would not cover my vehicle for the extended warranty repair.
All I know is the car is responsive, smooth, and quiet and power is on demand. The car has never felt like this in 3 years of ownership. Hopefully I've saved a few thousand dollars in repairs, but like I said, I've been waiting for the other shoe to drop.
Thats great! and thank you for your post, I think itll help out others experiencing the same thing to first perhaps replace the transmission mount before tackling on the other more expensive fixes.
Hopefully nothing else goes wrong!
So it's been around 35k miles and 2 years later since I originally started this thread. The last month the car has been sluggish, with lots of road noise. A week ago the same CEL codes appeared.
Again, I just changed the transmission mount. As with the original post, car is driving and shifting smooth and road noise is gone. The last transmission mount was a Corteco brand, this time I used a Bilstein.
I guess these transmission mounts don't last very long and it needs to be part of your maintenance. Going to change my parents C300 and see it helps their car too
So it's been around 35k miles and 2 years later since I originally started this thread. The last month the car has been sluggish, with lots of road noise. A week ago the same CEL codes appeared.
Again, I just changed the transmission mount. As with the original post, car is driving and shifting smooth and road noise is gone. The last transmission mount was a Corteco brand, this time I used a Bilstein.
I guess these transmission mounts don't last very long and it needs to be part of your maintenance. Going to change my parents C300 and see it helps their car too
I can't help but think there's something else going on with your car. There are plenty of these cars on the road, and I've never seen anyone else reporting this sort of issue on any of the forums or FB groups.
With that said, maybe you could upgrade to a more durable transmission mount? Creative Steel makes a poly one - https://creative-steel.com/shop/merc...mission-mount/. I've used their mounts & bushings on my CTS-V for years, everything has worked great and they're good people. (It's a small, family-owned business, as far as I know.)
I can't help but think there's something else going on with your car. There are plenty of these cars on the road, and I've never seen anyone else reporting this sort of issue on any of the forums or FB groups.
With that said, maybe you could upgrade to a more durable transmission mount? Creative Steel makes a poly one - https://creative-steel.com/shop/merc...mission-mount/. I've used their mounts & bushings on my CTS-V for years, everything has worked great and they're good people. (It's a small, family-owned business, as far as I know.)
Thanks for the link of the durable mount. I will look into it.
Like I mentioned previously, I've been waiting for the other shoe to drop, but the times the car has thrown this code, a new transmission mount seems to work for me. When I tried clearing the codes prior to a new mount, the codes would clear but would inevitably come back in a few days. But once a new mount goes in, codes don't reappear until a the mount is again worn.
The mount that I just removed, all the edge bushings were gone, just the middle bushings remained, which were cracked. I have never seen anything like this before on other cars I've owned and I am in a bit of disbelief. But my butt dyno and the feel of the car is night and day whenever a new mount goes in
Thanks for the link of the durable mount. I will look into it.
Like I mentioned previously, I've been waiting for the other shoe to drop, but the times the car has thrown this code, a new transmission mount seems to work for me. When I tried clearing the codes prior to a new mount, the codes would clear but would inevitably come back in a few days. But once a new mount goes in, codes don't reappear until a the mount is again worn.
The mount that I just removed, all the edge bushings were gone, just the middle bushings remained, which were cracked. I have never seen anything like this before on other cars I've owned and I am in a bit of disbelief. But my butt dyno and the feel of the car is night and day whenever a new mount goes in
Interesting, I didn't know failing mounts can trigger a fault code, I got curious, what is that code exactly?
I have not changed the engine mounts, just transmission mount
Any issues with the engine mounts? was going to replacement my transmission mount at my last transmission fluid change by read somewhere that you should replace with engine mounts other wise it puts more stress on new transmission mounts, not sure if that is true or not.
Any issues with the engine mounts? was going to replacement my transmission mount at my last transmission fluid change by read somewhere that you should replace with engine mounts other wise it puts more stress on new transmission mounts, not sure if that is true or not.
I've always tried to change all mounts at once. In this case it didn't happen because I had other pending issues to deal with and I could DIY this for cheap before it went to the shop for my codes. Didn't think my codes with disappear when I changed it
I will change the 2 engine mounts soon, will see if it makes the transmission mount last past 30k
I've always tried to change all mounts at once. In this case it didn't happen because I had other pending issues to deal with and I could DIY this for cheap before it went to the shop for my codes. Didn't think my codes with disappear when I changed it
I will change the 2 engine mounts soon, will see if it makes the transmission mount last past 30k
Good idea, however, if you have 4matic it is such a pain to change the engine mounts, labour is also 8 to 12 hours easily depending on the shop's experience.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
From the diagram @TimC300 provided, a collapsed tranny mount could definitely shift the lever arm further than it is intended to be. And a ½" drop would seem significant.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Here is a picture of the tranny mount I just replaced on my SL. It has about 54,000 miles on it. I'm not sure it needed to be replaced, but I did so anyway. The is no load on it and it does not seem worn -- no cracks in the rubber, etc. But in an unloaded view, there is space above and below the rubber. I replaced it without removing the cross member.
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