Technical Q&A

Letters to the Technical Editor:
If you have a technical questions related to a Mercedes-Benz send it to Peter Vandeveer our Technical Editor for a response here.

Q: I have a bump, thump, bump noise coming from the front end while driving. Any idea what it could be? Steering is not affected so I don't think the front end is out of line. What do you think?

A: It sounds like a front wheel is out of round, perhaps you hit a pothole and bent the rim a bit. This is easy to diagnose and repair by a qualified technician.

Q: My car has a high pitched squeak or squeal sound, mostly first thing in the morning, when I apply the brakes. Is this unsafe? Also sometimes during day the same sound will occur, mostly during around town driving. How should I view this? I know my brakes have recently checked out O.K.?

A: This somewhat familiar sound is usually pretty harmless if it does not progress toward happening more and more of the time. Small amounts of brake dust and overnight oxidation will wipe away when you hit the brakes first thing and sometimes after stop-and-go city driving. High pitched noises almost always are produced by harmless high frequency vibration of the brake pads.

Millions are spent by auto manufacturers to tryand eliminate brake squeal. Top secret brake pad formulas are developed to ensure fade resistant good braking AND cut down on brake dust resulting in squealing!! Caution would be advised against using ‘dust free' brake pads like ceramic pads. You may not like the dust on your wheels or the occasional squeaking. My brakes didn't seem to grab as well when I tried a set of dust free ‘ceramic' brake pads, while other say they are fine. Brake squeal that you do not fully understand or don't feel good about in any way, is a different story. Talk to the person who maintains your car until you become comfortable with the explanations. Sometimes squeaking can be a sign of sticking calipers or other hazards.

Q: Why does my remote open the car locks on my ‘94 SL500 only from the right-hand side and not from the left?

A: There are receivers in both the left and right door handles and the driver’s side isn’t picking up the signal from the remote. New receivers are installed through an access hole near the door handle as needed to effect the repair. This might also be the case for the trunk receiever if the lock won’t open from the rear.

Q: Why have my doors stopped closing automatically on my 1995 S500?

A: The doors will close safely and completely even when the automatic feature isn’t working just close them a little harder than normally. The vacuum pump that pulls the doors completely closed can develop an internal air (vacuum) leak that causes the pump to keep running after the task of door “close-assist” is complete.

A circuit breaker/ timer eventually shuts off the pump and disables the “close-assist” feature. To determine if the pump is not shutting off the right away, go to the fuse panel in the trunk, locate and remove the “close assist” fuse and then reinstall it. This resets the timer so the doors will automatically close again. After closing a door listen for the pump and see if it’s still running well after the door has closed. The pump is located behind the upper left (driver’s side) front corner of the trunk in a 140 chassis.

The pump is the usual culprit; however, other possible leaks include the air (vacuum) lines
to the doors and or the vacuum motors in the doors themselves causing the “closeassist”
vacuum pump to keep running until the timer shuts the system down. Go around and close each door one at a time and check the pump. If one particular door causes the pump to run on - the pump may not be bad. Most often though the pump is leaking and needs to be replaced.

Q: “How do I change the tailight bulb on my 2003 E320 4-MATIC ?”

A: Short answer-- definitely not as simple a task as on the older Benzes!

In or around 1986 the seal beam headlight bulb became obsolete. The new 300E at that time came with a fixed headlight lens. Finally the front of the car would start to become more aerodynamic. The old seal beams had to sit straight up and caused the front of most cars to drag through the wind.

Enough was known about shaping car bodies to slip through the wind, so designing lights to be better performers and more aerodynamic was a different challenge. In this country anything from a stop sign, railroadcrossing sign, school bus reflective tape and ‘markers’ of all types are made to pick up this diffused light. This type of reflection allows the soft, semi-focused light
of a sealed beam to safely alert the driver to what is ahead. Yes, the order of the day is for wedge-shaped sleek bodies to be more efficient against the wind. To make a good diffused yet modern headlight design is a surpassingly complex technological tour de force requiring new types of bulbs everywhere.

When a bulb burns out (yes, they still do) they are generally easy to replace, but beware putting the wrong bulb in the wrong socket. The common blinker/parking light bulb may not fit!
The old bulb has must be closely examined to see if the anchor pins are exactly opposite each other or are they ever so slightly offset? The offset is used to alert people to use a different wattage bulb for instance.

With another small bulb the anchor pins not only offset for one application, but also the ‘depth’ of the pins can be off set creating a double offset for a different application. It is quite easy to force the wrong bulb that almost looks the same into a socket, so please be careful here.

Yes, car lights have changed a lot lately - definitely brighter and most would say prettier than years past. More cars with bulb failure warning systems means those lights are all working too. Mercedes-Benz of course has pioneered many of the lighting and aerodynamic advances - as long as they enhance the safety and security of the people inside.

Q: “Does wanting a Diesel car still make sense?"

A: The diesel (power plant) is making a comeback. According to an advertisement in the London Times - Jaguar’s X type sedan with a 2.0 liter diesel direct injection engine
gets 55 M.P.G. combined city/highway! Why is this not available here? An ML270CDI gets 30 M.P.G. combined.

That’s a 5 cylinder, 20 valve, 370 ft. lbs. of torque at 1600 R.P.M. screamer of a diesel!
A diesel C-class with a top speed of 129 and 58.9 M.P.G. highway weights 500 pounds more (in U.K. trim) than a Toyota Prius hybrid which touts 60 M.P.G. highway. Excuse me, but I’ll take the safety premium of the extra weight. No automobile manufacturer puts that weight to better use than Mercedes-Benz. Yet diesel passenger car popularity finds major stumbling blocks
in the U.S. There is too much sulfur in U.S. diesel fuel. In most of Europe, diesel fuel is additionally processed to remove all but trace amounts of sulfur - the ‘rotten egg’ smell we associate when following a diesel powered vehicle.

The Sierra Club and other environmental groups have (effectively) lobbied to outlaw diesel powered cars. Sulfur also produces acid rain which, of course, kills trees. Political help is on the way. The U.S. has set a timetable (2006) for getting sulfur out of the picture and oil refineries across the country are gearing up for ultra-low-sulfurdiesel (ULSD) production. This legislation
coupled with the new diesel injection technology has oil companies predicting that average Americans who like to buy larger vehicles will buy diesel in the near future.

Q: “What precautions should I take when changing from winter driving to summer ?”

A: Some things to remember about driving as hot summer conditions begin and travel increases. Summer is the time to watch out for the “first rain” after weeks of dry dusty weather. This is when road dust, oil, and rubber make roads very slippery. Summer is a traditional time to have a good evaluation of your summer car, truck, or S.U.V.

A pre-trip inspection should be done at least a week before a long trip. This gives the maintenance and repair work a chance to prove itself before you take to the road. Plan to be stuck in traffic at peak times more than ever as Americans turn to safer ‘’feet on the ground” vacations these days.

Drive those SLs and SLKs, but give the four and five year old cars a good radiator coolant flush - also check hoses and belts. Let’s sit in traffic feeling good about having done this work. Tires and TIRE PRESSURE need checking when the seasons and temperatures change. Don’t rely on a tire pressure reading when the wheel and tire have been in direct sunlight on a hot day.

Bring the car into the shade or check these things early in the morning. Try to walk around the car and become familiar with how your tires look at the proper inflation on flat ground. You can often tell a tire is going soft by a change in the tire profile. On a long journey take a quick look at all four tires when you stop for fuel. Get a fresh wiper blade or blades and an air filter.
An old air filter robs performance and lowers fuel mileage. Have a safe and happy summer!