PeachParts Mercedes-Benz Forum - View Single Post

skybound · #50 03-17-2008, 06:40 AM

Wow, I am so amazed at all the controversy as whether to change the fluid on the "sealed for life" transmission. I came to this thread in curiosity about "when" to change the transmission fluid in my 1999 SL500.

I know this is a Mercedes forum, but I must let you know my experiences with my 1998 Ford Ranger. I have religiously had the transmission fluid flushed at 30 to 40K based on the recommendations from a good friend who is an ASE mechanic for more than 20 years. I once did not flush the fluid for almost 60K and noticed that when starting and shifting into gear the transmission would not engage and then suddenly with a "thunk" engage. This scared me a bit and I had the fluid flushed soon after and the problem no longer occured. According to my mechanic friend the transmission on a Ford Ranger will fail at around 100K without proper service, thus far I have 211K on my original transmission without any more problems at all.

Taking all this into account, I cannot believe that any transmission is "sealed for life". Parts do wear and contaminants can pass through filters, and if the contaminants do not pass through the filter, the filter will begin to slow the flow of fluid. In addition to this fluids (oils) begin to break down with heat, and if you say their is not much heat in a transmission, then why is there a transmission cooler?

Then there is the argument why Mercedes had the "sealed for life" transmission in the first place. As far as we know it very well could have been a marketing feature to tout how great their cars are and how great their transmissions and fluids are. I do not claim to be and expert by any means, just my own personal observations and knowledge of any device that has moving parts; where there is friction there is wear and contaminants will be introduced into the lubricants and even small contaminants will begin to cause increased wear. A previous post stated how even small contaminants can pass though a filter once they are small enough and this I agree. With this in mind, how better to rid the system of contaminants than by changing the fluid that holds these contaminants in supsension. So, if I spend $200 to $300 having a fluid and filter change will this really do any harm? I do not think so, in any case whether or not this may extend the life of my transmission I will take my chances that it will most likely will. In comparison a fluid and filter change is nothing in comparison to the cost of complete replacement of the transmission. I guess the other thing that scares me is not having any way of checking the actual fluid level in my transmission and with a fluid change, even for a small time, I can be assured that the fluid level is correct. Yes any transmission will eventually fail no matter what, sooner or later it will fail. But maintenance is the the best prevention for failure.

BTW why does Mercedes recommend changing the fluid in the soft top system on the SL500? Hmmm, maybe because of contaminants in the fluid? I am not sure wheter this system has a filter, in any case this is an interesting thought. Just my 2 cents for all it is worth, I guess in the end this topic is like that of the chicken and the egg, I guess we all have to make up our own minds.