R170 Manual Transmission Mount Confusion
I thought I would share my recent confusing (for me anyway) experience replacing the "transmission mount" on my 2000 SLK 230 Kompressor with 5 speed manual transmission. I used the "quotation" marks for the part name because it is actually referred to by a number of different names depending upon where you see it referenced. Using VIN number look-up, as well as year/make/model/trim/engine, the part is variously labeled "transmission mount", "engine mount", "rear engine transmission mount", and "rubber mount'. All under the same part number ( 212-240-04-18) and in identical diagrams. This should have been a red flag, but of course I blundered ahead despite that. Hopefully, this DIY may save you from doing the same.
I noticed a rattling noise beneath the car over rougher roads and bumps, and a vibration that almost felt like a misfire at higher RPMs under load, while shifting gears. A look underneath, and some leverage on a pry bar at the mount and bracket revealed the bad mount. No codes were recorded, no other faults found, and all the other usual culprits (shelf, trunk lid, catalytic converter, exhaust, engine function, etc.) were eliminated as possible sources. The rubber in the mount had split and deteriorated causing the transmission to bounce and vibrate on the bracket.
So, I did some research and found the part (as numbered above) at several different suppliers and several price points, from sources such as "genuine Mercedes Benz", Corteco (OEM), Lemforder, Uro, and a couple others of unknown origin. All the photos and sketches looked the same, with the exception of the Lemforder which had 3 mounting holes on one side, and a single hole on the other side opposite the center hole. The Pelican DIY said to line-up the center hole(s) with the holes on the mounting bracket. The Lemforder seemed to me the best quality at the best price, so that is the one I bought. All the different listings were for automatic transmissions, but when manual transmission was searched, the same mounts showed-up in all the listings. All the mounts had an "ear" on each side through which it is bolted to the rear of the transmission. Then it is attached to the mounting bracket through the mounting holes, and the bracket is bolted to the chassis. I did not find an exhaust bracket in the way of one of the bracket bolts as described by Pelican.
I ordered the mount, and while awaiting its arrival, I removed the defective one. The new one arrived. It looked exactly like the photos and diagrams. It did not look at all like the broken one I removed. The "ears" did not line-up with the transmission mounting points (too far apart), and the holes on the mount did not line-up with the bracket holes (too narrow a spread). After re-checking all the diagrams, photos, part numbers, and listings, I was stumped, and concluded that the part had been improperly manufactured. But because the exact same looking part was shown on all listings, I kept looking. I cleaned-up the broken part, and with a magnifying glass and a bright light I managed to decipher a different part number: 210-240-03-18. Yeah - I know. Shoulda done that to begin with. I have only re-learned this lesson a dozen times or more, so it has yet to actually sink in. Since all the listings looked the same, I had no clue there might be a different version. This is my best excuse, and I am sticking with it! When I plugged-in the newly discovered part number, it was not found on the first 4 sites I searched. Then - BINGO! I found it, included in a diagram which showed only one transmission, one bracket, and BOTH mounts. The parts listing also included both mounts, with the original/wrong mount described as an "engine transmission mount", and the correct part listed as a "rubber mount". Neither part was designated for automatic or manual transmission, and no hint of an explanation of why 2 different mounts were shown in the same diagram.
I will post photos (I hope.) that help illuminate this issue. The darker mount on top of the bracket is the old/correct part. You will see that it aligns properly with the bracket holes for it. The lighter/shiny mount is the wrong mount that was listed everywhere I looked. You will see that it is too narrow to align with the bracket holes. The photo that shows the mounts together illustrates that the "ears" used to attach it to the transmission are further apart on the wrong(shiny) part than on the old part.
It turns out that you can actually see the old mount itself without disassembling anything. Who knew? Not me, that's for sure. So you can check this BEFORE you order the part, as most intelligent people would! I am working on a book: "How To Make Easy Repairs Incredibly Difficult". Advance orders can be pre-paid by credit card, check, or Monopoly Money.