Technical Q&A
Richard Simonds
Transmission Issues
Q
I thought that sealed transmissions never needed fluid replacements. Do they actually need servicing?
A
The myth of the sealed transmission is that it never needs servicing. However, it is advisable to service a transmission every 60,000 miles (change automatic transmission (AT) fluid and filter, check the clutches and bands). Although the transmission is “sealed,” the basic structure and operation have not significantly changed over the years. Dealerships can do this servicing. The cost is far less than rebuilding a transmission ($400-$500 vs. $5,000-$7,000). Without servicing, automatic transmissions begin to fail around 125,000 miles though some can last up to 150,000 miles or more, depending upon driving conditions (city stop-and-go vs. open-highway miles).
Q
I have been having problems with shift flare (engine “overrun” during 2-3 upshifts) on my W123 300CD and have had no success with changing AT fluid, checking vacuum modulator for leaks, and adjusting the vacuum modulator and the control cable. What else can be done? (From the MBCA Forum as posted by normajean).
A
Check the K1 automatic transmission accumulator spring and plunger assembly, which is designed to help with smooth upshifts. It can sometimes fail, causing the symptoms you describe.
The owner adds: “I bought the K1 spring kit and it has changed both my and my car's life. The new spring is noticeably more robust than the old. Shifting across the range is now smooth and sure, probably as good as new for this primitive 4-speed. I had a very competent independent shop do the installation. It is only about a one-hour job. Well worth it to not have to lie on my back with transmission fluid running across my chest.”
Fuel Filling Issues
Q
I bought a 2011 S550 as a CPO (certified pre-owned) just over a year ago, and from Day 1, it has been difficult to fill the tank without shut offs from the pump. Can someone point me to a quick fix – parts and location? Thanks! (From the MBCA Forum as posted by jehardy).
A
One technique is to pull back the sealing boot on the nozzle and to push the nozzle firmly into the fuel-filler tube. This should allow the nozzle to push open the back-flow valve in the fuel-filler tube and allow the tank to fill without shutting off. If this simple fix doesn’t work, another option, (as posted by nishboo): “The problem may be the Charcoal canister/filter. You can remove it from the passenger rear wheel well, and either blow it out with compressed air and let it heat in the sun (no guarantee it will work – but worth a shot), or you can purchase a new one. While you are removing and cleaning it, also clean the shutoff valve attached to the top of the canister.”
Radio Issues
Q
The volume does not adjust on my radio in my 1997 SL500. I have heard that there is a shop that will repair the controls so that the radio will once again operate as designed. I believe that I read it in here but cannot find it right now. Can someone help? (From the MBCA Forum as posted by johnobo).
A
Contact Becker AutoSound in Saddle Brook, New Jersey – 201.773.0976 or beckerautosound.com. The company repairs a variety of Mercedes-Benz radios from vintage and classics to young-timers including the two most common brands, Becker and Alpine. A representative will refer you to another source if Becker doesn’t work on your particular model of radio.
Q
Suddenley, the radio in my 1993 500SL stopped working. The dealer said all was hopeless and a new radio (over $800) was the only answer. (From the MBCA Forum as posted by oxbow).
A
As reported by the owner: “I did some research and discovered that SLs have Alpine radios while most other models have Becker radios. I instructed the dealer to send my radio to an Alpine repair shop. Radio was back in a week and works perfectly. Total cost (including shipping) was less than $100. Moral of the story is to insist that the dealer do more diagnosis instead of always just replacing parts.”
Richard Simonds adds: When a radio doesn’t work, the shop technician should, of course, first make sure that the problem doesn’t originate in the vehicle (e.g. an issue in the electrical system) but once that’s been confirmed, then the radio itself should be checked by an audio specialist such as Becker, as mentioned above. You can also contact the Alpine service center for information on out-of-warranty OEM products at [email protected] or 800.421.2284.
Steering Noises
Q
My 1976 450 has developed a strange knocking sound when turning to the right only. This occurred after I had new tires mounted and balanced. I don’t remember hearing this before. Any suggestions? (From the MBCA Forum as posted by United Pilot).
A
As reported by the owner, it turns out the dealership used regular lead wheel weights that attach to the rim of the wheel when the tires were replaced last month – the old wheels use clips to attach the weights, but there weren’t any available; one of the regular lead weights on the left-rear wheel was coming into contact with the axle assembly when he turned to the right. “The tech is going to try to adjust the balance of the wheel weights. My hometown dealer, Mercedes-Benz of Beaumont, Texas, diagnosed the problem.” Be sure that the tire shop uses the correct style of weights for your model when balancing the wheels. Typically, this mean using the same type of wheel weights that are already being used.
Tire Pressure Monitor Systems
Rather than submitting a question to “Tech Q&A” I have a follow-up comment regarding the problem that the club member was having with the tire-pressure monitoring system in a 2005 CL65 Coupe (Nov.-Dec. 2016 issue of The Star). Most cars in Canada are delivered with the passive pressure monitoring system that uses wheel speed sensors to detect a soft tire (which will run faster than the others). Accordingly, it was a change for me to get a 2013 C63 AMG, which has individual TPM sensors that communicate individually with a control module in the center stack.
When I needed to swap to winter tires, I also didn’t think I needed the sensors – or their expense. However, when I asked Mercedes-Benz Canada how to shut this system off, I was unhappy to find that it technically isn’t possible; I would have to get the individual sensors with my new winter wheels and tires.
I purchased aftermarket sensors that cost about $60 (U.S.) each as part of a package from one of the online tire sites; they work fine. There are a number of online sources for good quality sensors for installation by a local shop as opposed to the more expensive replacement parts from Mercedes-Benz. If you’re having a problem with your system, I suggest you try these before checking the head-unit TPMS control module as a source of the problem.
Alex Currie
Vancouver Island Section