by Gary Edwards, Technical Advisor Peachtree Chapter
I bought this needy 2000 ML55 from Rubin Howard, fully knowledgeable of its issues. Rubin’s acquisition story was unusual; he had posted about how great a car the ML55 was and immediately got a contrary response from someone who absolutely hated his ML55. Rubin got in touch with him and eventually bought the car for a very low price. He sent it to DC Motorwerks where they repaired a big oil leak from the oil cooler and many other items. I eventually bought it from him with full disclosure of all known problems, as if I needed another car.
It did appeal to me, though. The ML55 is historically significant in that it was the first high performance SUV. What got into Mercedes to build an AMG version of the ML is a mystery to me, but now most car companies have performance versions of their SUVs (including Cadillac). It was, however, a long path to getting this ML to be a usable vehicle.
The tires had visible sidewall cracking, so I limited the car to local trips only, planning to replace the tires after I had solved the other major drivability and safety issues. One of the frustrations is that the original equipment tire size (285/50-18) is no longer available. This car has 19 inch wheels which are ½ inch narrower that the originals, and the tires are slightly narrower that what came from the factory.
When I picked up the car, it had a misfire, and I could see that the driver’s side window didn’t work. To troubleshoot the misfire, I was able to read fault codes to determine which cylinder was misfiring, so I replaced that cylinder’s coil, spark plugs and plug wires. When troubleshooting this misfire, I learned that the ECU on this car won’t allow revving up in idle above about 3000 rpm, and it sounds like a misfire when you try to rev above that RPM. This was a bit confusing while troubleshooting a misfire, until I figured that out. Fixing the misfire allowed me to drive the car.
The new window regulator is riveted in place. Note the wedge holding the window up
Once on the road, I felt a weird ride motion on rear wheel bumps; the rear would go over a bump, and the car would go from left to right. Very unsettling! I looked under the car and saw that the left rear lower control arm ball joint had no nut securing it into the control arm. It’s important to note that though the original equipment ball joints are pressed in, all replacement ball joints are bolted in – and the securing nut was missing on this ML. I ordered some ball joints, primarily just to get the nut and ordered the special socket that fits the nut. Once they arrived, I jacked up the car and put the nut on the ball joint. Since that corner of the car was off the ground, I also checked the play in the left rear wheel – and got a big surprise – there was a huge amount of play in the wheel bearing. The hub nut wasn’t very tight, and I tightened it as much as I could, but it still had play. This was a problem! I resolved that I needed to replace the left wheel bearing before going beyond the local area.
I ordered some rear wheel bearing and researched the job. I found forum posts about the difficulty in replacing the bearing, requiring removal of the wheel carrier and use of a large hydraulic press. I also set up an eBay search for an ML55 left rear hub. Quite a while later I was able to obtain a used left rear hub off eBay for a reasonable price.
In the meantime, I experienced the odd air conditioning problem that I have previously written about and another misfire issue which I again resolved by changing a coil, spark plugs and connectors. I should also mention that I was getting intermittent BAS/ESP/ETS/ABS lights with some fault codes calling out speed sensors especially the left rear. Shortly before Thanksgiving, I felt the brake pedal go nearly to the floor and found a large puddle of brake fluid under the left rear of the car.
No surprise that these brake lines leaked
In my experience, most older Mercedes run the brake lines under the car with no covering. On the ML, however, the lines run along the edge of the body just outboard of the frame, under plastic panels. The plastic allows the area to trap debris and moisture. I never found the exact location of the leak, but what I did find was two brake lines that were totally covered in rust wherever they were “protected” by the plastic covering. I found a source for a complete set of brake lines, but I didn’t see a way to install them. These brake lines run between the body mount and the frame through a very tight space. I cut the rusted sections out of both brake lines (about six feet long each) and made up new sections, joining them with unions.
The space I had to thread these into was so small that I couldn’t put the nut on or flare the tubing until after working it through this space. This meant I was doing the flaring under the fenders. I have four different flaring tools (I broke one while doing this job) and I haven’t found one yet that I’m happy with – I had a hard time making good flares that wouldn’t leak. This was a time consuming job, but after redoing several of the flares to resolve leaks and finally bleeding the brakes, the car was drivable again.
As Christmas approached, I decided to get the ML55 fully operational. Since I had the LR hub assembly with a good wheel bearing, it was much easier to just replace the hub assembly than to replace the wheel bearing. After doing the CLK55 LR hub recently, I found this one to be easier though with some twists. After the CLK55, I was worried about being able to get the axle shaft out of the hub, but that turned out not to be a problem for this car.
The challenges I found had more to do with the clearances on the back side of the hub. There is very little space above the nut for the lower ball joint, and I couldn’t get any of my ball joint pullers on this ball joint. I was lucky that it broke loose from my efforts to loosen the nut on this lower ball joint. The real challenges came when I was reinstalling the hub. Typically, when bolting up ball joints, the stud tries to turn with the nut and Mercedes typically provides an Allen or Torx wrench fitting in the stud so you can stop it from turning. I was using a Torx socket attached to a ratchet to hold the stud for the upper ball joint as I was tightening the nut. When I got the nut fully tightened, I found that the stud had been pulled in far enough that the ratchet was tight against the control arm and I couldn’t remove it. I had to remove the ball joint again to get the ratchet out and come up with a physically shorter way of holding the stud from turning.
I had a similar problem with the lower ball joint. There was even less clearance above the ball joint stud when it was fully tightened. I did not have a tool short enough to stop it from turning when tightening the nut. I finally took a 6 mm Allen wrench and hacksawed a very short length, holding it with a 6 mm box end wrench while tightening the ball joint nut.
An additional side benefit of the used hub was that it had a speed sensor already installed, so most of my warning lights went away. The car now drove well, but I still had a driver’s door window that was trying to creep down every time I drove. Fortunately, I had a new driver’s window regulator given to me by one of our long term members. This is riveted in, so you must drill out the rivets, and you must maneuver the window out of the regulator and off the rear track and wedge it in the up position. Not a difficult job though the window alignment is a bit tricky.
I also wanted low range to work. I had previously replaced the transfer case shift motor with a used one from eBay which did not solve the problem. I thought perhaps it was bad also, and I took the motor’s gearbox apart – and found an incredible buildup of corrosion products. I cleaned it up, put it back together, tested it with 12V and put it on the car – and it worked!
I now had a reasonably operable ML – I replaced the tires and released it for unrestricted operations. I really enjoy it, it’s a very useful vehicle, but with the resonator removed and the 5.4 L V8, it sounds great too (and is fairly quick for a heavy vehicle). Will probably always have a check engine light though.
The Corrosion in the transfer case shift motor gears