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The fuel filter on an R107 is one of the cheapest parts in the fuel system and one of the most ignored. A clogged filter starves the K-Jetronic system and makes a healthy pump look weak.
Where the filter is
It is under the car, on the right side ahead of the rear axle, in a cradle with the fuel pump and fuel accumulator. On many years it sits in a bracket next to the pump with large banjo fittings at each end. Later cars with a second pump or different layout still keep the filter in this assembly. Raise the car safely on stands to reach it; see jack points.
How often to change it
Mercedes listed it as a periodic item; check your maintenance booklet for the interval for your year. For a car that sits a lot or has had tank rust, I would change it more often than the book says. If you buy a car with no records, change it now.
Which filter to buy
Buy a filter from a known supplier (Bosch, Mann, Mahle or equivalent) listed for your exact model and year. There are different filters for early and late cars, and the direction of flow is marked with an arrow. Buy new sealing washers for the banjo bolts with it.
Step-by-step swap
- Run the car, then pull the fuel pump fuse or relay and crank briefly to drop pressure, or simply let it sit overnight.
- Disconnect the battery.
- Put a drain pan underneath and rags around the fittings.
- Hold the filter body with one wrench while loosening each banjo bolt with another.
- Loosen the bracket clamp, swap the filter, and note the flow arrow (it points toward the engine).
- Fit new washers and torque the banjo bolts to spec; do not over-tighten.
- Reconnect, run the pumps and check every fitting for weeping.
Avoiding leaks and fire risk
Old banjo washers are the usual source of leaks after this job. Use new ones every time. Work outside or with the garage open, keep a fire extinguisher near, and never use a drop light with an exposed bulb under a fuel leak.
Related pump-assembly parts
While you are there, inspect the pump, the accumulator and the rubber hoses in the cradle. Cracked hoses here are a common source of the R107 gas smell. See also R107 fuel pump and fuel accumulator.
Quick answers
- Can a clogged filter cause a no-start? Yes, if it is badly restricted, but more often it causes stumbling under load, loss of power on hills, and weak system pressure on a fuel pressure test.
- Is there a filter in the tank too? Many R107s have a strainer at the tank outlet or on the pump inlet. Check it if you find rust in the main filter.
- Which way does it go? The arrow on the filter points in the direction of flow, toward the engine. Fitting it backward is a common mistake.
- How long does the job take? Usually under an hour with the car safely on stands, most of it spent cleaning up and checking for leaks.
