500 Section

500 Section

When Do Parts Wear Out?

When Do Parts Wear Out?

I recently spoke with a section member who wanted to know when parts should be expected wear out on his 95 E320, and the thought occurred to me that others might be interested about their own cars too. Bear in mind these are general estimates based on information exchanged with other Mercedes nuts throughout the country and world for that matter.

Flex disks- Expect the front ones to last about 80-100K miles and the backs to last at least 150K miles. First symptom is clunking sound while coasting to a stop. Center bearing supports can wear out, causing droning vibrations at cruising speeds.

Climate Controls- Most climate control systems (ACC) on MBs do not seem to be as long-lived as the counterpart American systems. Don't know why, but since most Mercedes systems are automatic, an extra layer of complexity has been added to the mix. ACC systems seem to need service at least every 50K miles. A/C parts that tend to wear out are: Evaporators, Compressors, Pushbutton Control Units and Klima Relays. In most cases, just a coolant recharge is all that is needed. Many of the flaps controlling venting are activated by vacuum elements that tend to develop leaks at about 100K miles.

Blower motors typically last about 120K miles. The brushes wear out and the first symptom is intermittent operation. Squealing is caused by the bearings wearing out. Sometimes lubing helps.

Shocks/Struts- They tend to be more robust and last much longer than people expect, which may lead to unnecessary replacements. Expect to get at least 125K miles out of a set of shocks and struts.

Gas Engines- Expect to replace the valve seals at 125-150K miles on gas engines. First symptom is increased oil use. Head jobs are typical at 180-200K miles. Bottom ends should last at least 250K miles as long as oil is changed regularly. Expect oil leak problems on the 190E 2.6/300E/E320 engine at the head gasket, front timing cover and valve cover gasket. Timing chains and tensioners (and maybe rails) should be replaced at 100K miles. Owners of 91 or older 4.2 liter V-8s should especially heed this advice or your engine could be trashed. Big $$$$

Diesels: Most of the Mercedes diesels are very robust and do not require much internal service for 250K miles. Timing chain "stretch" should be monitored and changed if beyond 4 degrees retarded. Chains generally are shorter and last longer in diesels. Expect a set of injectors to last at least 100K miles and glow plugs typically last 75K miles. Older diesels (in 123s) require valve adjustments every 15K miles. Vacuum pumps last 125-150K miles. Failures in certain 123 vacuum pumps can result in oil being sucked into ALL the vacuum lines. $$$$ to clean and replace all the lines.

Exhaust Systems- Tend to be more robust (and heavy!). Expect 100K miles at least. Keep the engine in tune and get longer life from the cat and the muffler. Rust is usually the culprit for failures.

Bushings- 150K miles is a good estimate. The rubber just gets hard or shrinks, resulting in excessive vibrations, squeaks, and harshness. This is one of the most neglected service items and yet it plays such a pivotal role in ride comfort.

Cruise Control (CC)- Is there anyone who has owned a Mercedes at least 5 years who has NOT had CC problems? Typically it is the amplifier under the dash that causes the most problems. The servo and the stalk switch can also cause problems. The amplifier tends to have solder joint cracks that cause intermittent operation, the typical first symptom of trouble. Make sure all linkages at the engine are cleaned and lubed with transmission fluid. There are testers that can quickly diagnose CC problems.

Motor Mounts- Typically last about 100K miles. First symptom is excessive vibration at idle. Mounts for diesels typically last less than their gas counterparts.

Hydraulic Suspensions- Nitrogen cells last about 75-100K miles. First symptom is very bouncy ride because hydraulic fluid leaks into the nitrogen cells. Most other parts are robust, but make sure fluid is drained and filled at recommended intervals. Use only MB fluid. Older vacuum systems have characteristic sag as a first symptom and can be very expensive to maintain. 2000 S-Class? Too early to tell.

Airbags- There may be a sticker on your car that says to replace the airbag after 10 years. The change interval has been extended. Check with Dealer if unsure. NOT a DIY item.

Transmissions- B2 piston failure causes no forward gears but reverse works. Overhaul is usually not required in this case. Most trannys last 150K miles or more. Some diesels will go 250-300K miles without problems, assuming regular fluid/filter changes. 400E/E420/- 500E trannys can have a jolt when cold in first. The fix is to replace the B2 piston and band. Flairing/hard shifts can be a misadjusted Bowden cable, vacuum modulator leakage or modulator out of adjustment. Long delays in engaging reverse usually signal an overhaul is due.

Turbos- Can last the life of the car with proper care. Diesels with Trap Oxidizers can have catastrophic turbo failures. Check dealer for campaign to replace Traps and inspect /replace turbos for free.

Fuel Pumps/Fuel Pump Relays- The relays typically last about 75K miles. Carry a spare. Easy to replace. Fuel Pumps often last the life of the car. Fairly expensive but not hard to replace.

Injection Pumps- Typically last the life of the car. Expensive to have rebuilt or replaced.

Wheel Bearings- Not unusual to get 150K miles out of a set. Make sure grease levels are strictly maintained and runout is within specs. Don't mix greases.

Brakes- Pad wear is too dependent on driving style. Fronts can last from 10K-60K miles.

Backs can last 30-70K miles. Front rotors last about 50K miles. Backs last longer. Do not have them turned; Replace them. Original equipment is highly recommended. ABS systems are fairly robust, with exception of the sensors/wires at the hubs. First symptom is ABS activating when wheels aren't sliding.

Cooling Systems- Plastic radiators crack at upper hose mount. Usually last only about 75K miles. All-metal radiators can last 100-150K miles. Fan clutches last about 100K miles. Water pumps last about 100K miles too. Thermostats last about 40-50K miles.

Electrical- Alternators last about 100K miles and once again the cause is usually the brushes. Bearings cause squeal. Regulators can fail but are cheap and easy to replace.

Fuses tend to corrode over time. Clean and or replace all fuses at regular intervals to prevent intermittent operation of electrical devices. Make sure battery posts and grounds are clean and connections are tight.

Hope this helps in providing general guidelines, but as always your mileage may vary as the saying goes. Happy and LONG Benzing to you all.

Steven Rae, Technical Advisor

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