Tech Q&A

Richard Simonds

Transmission-shifting Issue

Q

My 2012 ML350 now has 74,000 miles showing and has developed a transmission-shifting problem. This only happens at low speeds and in the lower gears: The transmission hesitates on both up  and down shifts before banging into gear. Sometimes it simply doesn’t kick down and it feels like it’s lugging – in a similar manner to when you lug the engine because you didn't down shift an old manual transmission. The ML’s transmission has been flushed, and a new filter has been installed. No fault codes come up on the computer to indicate there are any issues. At highway speeds and kicking down to pass, it works just fine. My technician at the independent service garage where I have had all my Mercedes-Benz vehicles serviced for many years has tried everything he knows, including repeated flushing; the problem persists. Some folks have suggested this occurs if the transmission is set in “S” (Sport) mode, but not in “C” (Comfort) mode. I am not aware of any S or C settings in my ML350. Any advice you might offer would certainly be appreciated.

A

 All Mercedes-Benz models from the past 20 or more years have a console switch to select transmission modes. On your 2012, it should be a small rocker switch to the left of the shift lever. Comfort mode (C) starts in second gear and shifts gears at lower engine speeds to improve both fuel economy and smoothness. When the transmission is set in Sport (S) mode, this allows for sportier performance by starting in first gear and shifting at higher engine speed than occurs in Comfort mode. In Sport mode, the transmission usually waits until the car is fully stopped before downshifting to first gear; your transmission apparently continues to downshift into first gear while still in motion; this causes the mechanical banging.

Based on your written description of the problem, there are three key components that your service technician should check.

1. Be sure to confirm that the transmission valve body is clean and that all passages are clear; to do so, remove the cover plate and inspect the valve body.

2. Check to ensure that the system’s conductor plate is accepting the correct instruction codes.

3. Next, have the transmission software re-programmed by either your authorized Mercedes-Benz dealership or by a trusted independent Mercedes-Benz shop that has access to the complete Mercedes-Benz Star

Diagnostic System.

Grades of gasoline

Q

 According to my owner’s manuals, my 1986 and 2000 Mercedes-Benz vehicles require the use of premium gasoline. My problem is that none of the fuel stations in my community seem to be selling gasoline labeled “premium.” Have you heard of anyone who has this problem and what was his or her solution?

A

 Fuel may not always be labeled as premium; however, premium unleaded gasoline is simply fuel that has a 91-95 octane rating. That rating is what you need to look for: I suspect that’s what you’ll find available on at least one of the fuel pumps on each service island at your gas station. There is no reason you can’t occasionally use regular unleaded with an octane rating of 87. The car’s engine- management system will automatically retard engine timing to avoid damage, with the result that you will have lower gas mileage and performance. However, you should use a station selling higher-octane gasoline as often as possible. In addition, MBUSA and Daimler AG recommend using “Top Tier” gasoline that has detergents and other additives to reduce deposits on valves and the combustion chamber. Examples of Top Tier brands are Shell, Chevron, Esso, 76, Exxon, Conoco, or any fuel that is labeled “Top Tier” at the pump. Also, many states require that ethanol be added to gasoline for cleaner emissions. Be sure that the gasoline you use does not exceed 10 percent ethanol; any fuel exceeding that percentage of ethanol will void your Mercedes-Benz warranty. See page 76 of this issue for an article on operating fluids for your Mercedes-Benz.

Paint cards for classic cars

Q

 How do I go about finding a set of the correct Mercedes-Benz factory-authorized paint-color cards for the 1970 models?

A

 Your best option would be to do a web search for “Mercedes-Benz Literature.” There are several commercial businesses that specialize in providing manuals, sales literature, and paint -code cards – for a price. Depending upon the model you have, there are also online clubs that offer resources by the chassis number (e.g., W111, W113, W108, W109, W114), and these can be found by doing a web search. Also, some books offer color codes and text descriptions, but without the color chips that make identification possible.

Shock absorber replacement

Q

 My 2015 GLK 350 developed a loud rear rattle at 36,000 miles. I went to my dealer; the technician replaced the right-rear strut under warranty, resolving the issue. I asked the technician if the struts needed to be replaced in pairs; the answer was that with only 36,000 miles on the car, it wasn’t necessary. What is your opinion?

A

Years ago, shock absorbers had to be replaced after 30,000-50,000 miles of use, and it was deemed necessary to always replace them in pairs. Today, 100,000 miles or more of use is the norm, so I would accept your technician’s explanation.

Windshield wipers

Q

 The windshield wipers on my 2013 ML350 chatter and skip. I replaced them with new factory wipers without resolving the issue. I had read that cleaning the glass with vinegar helps, so I did that. I also read that applying Rain-X helps; I did that. The problem only got worse. Then I read that Rain-X actually causes wiper chatter and skipping, so I cleaned the windshield with vinegar again. The problem persists. What is the secret of wipers that operate smoothly without chatter and skip? 

A

 At some point, all of my own newer Mercedes-Benz vehicles have had problems with wiper "chatter." I found the solution for my older cars (1995, 2000, 2006) was to use an adjustable wrench to grip the wiper arm and make a slight twist to the arm – depending on whether wipers chattered on the up stroke or the down stroke – to align it parallel to the windshield. On my 2015 model, I had the dealer replace the wiper blades after three years. I have not yet had to replace the blades on my 2017 model; the new long-life blades are fussy to install and the dealer seems to have exactly the right technique to insert replacement blades so that they align properly. Owners who want to do their own maintenance can sometimes be "penny wise and pound foolish" when it comes to working with highly sensitive newer cars. It’s sad that even replacing wiper blades now seems to be too complex a task for an owner to carry out.

Even a lightly pitted windshield can cause wipers to chatter and streak. If fitting new blades or adjusting the wiper arms doesn’t resolve the issue, a new windshield may need to be installed – a job that is often covered by the comprehensive-coverage clause in auto insurance policies.