Water PumpTeardown Water Pump Bearings

The grease you'll find inside may still look good but it also may the dried up mess on the picture.

Simply put the shaft in the vise, adjusted tight enough to support the bearing without binding on the shaft and drive the shaft out with a hammer, brass preferred, or soft drift.

Readjust the vise and flip the shaft around, the smaller bearing comes off in the same fashion.

Clean up the shaft, inspect it for possible wear, remove any burrs and press the new bearings back on in reverse order, of course.

Clean up the inside of the pump housing of any old grease and dirt. Apply a generous coat of fresh grease to the pump housing and shaft/ bearing. No need to fill it.

Slide the shaft back into the housing, careful to not damage the small seal, and gently tap the impeller onto the shaft to get started. The press will do the rest. Re-install the grease seal flange and press the pulley flange onto the shaft as well.

A couple of things to know and remember: When you press the impeller back onto the shaft, the back machined edge of the impeller should be flush with the housing surface; the overall height of housing and pulley flange is 145.5 +/- 0.5 mm. The bearing numbers are 6203 2RS and 6206 2RS. "RS" stands for rubber seal, "2" obviously means both sides. You can remove the seals and actually fill the bearing with better grease than what's in it. Should cost around $10. A new pump is usually around $300-400, often exchange.

Mercedes really wants your old pump back so they can fix it for $50 themselves and hopefully you need a replacement soon and charge you again. NOTE: This is a repair for the "wabbly pulley syndrome", not for a leaky water pump; by then it is too late. If you are able to remove the plug in the housing and can find a 10mm (1/8 NPT will also work) grease fitting to replace it, you might even be able to save your pump overall.

There are gasket kits and impeller kits available for the complete rebuild. I find the more expensive impeller kit a waste of money since the it supplies the same open bearings that went out in the first place and impeller and shaft rarely give out; but you will have to inspect that base your decision on your findings

We actually did a little comparison test between the open and the closed bearings. Mainly to see whether I added too much grease to the new sealed bearing, I used my drill press and spun the bigger bearing for about 30 minutes. Temperatures reached about 120 degrees and just a slight amount of greased squeezed past the seal.

With the open bearings (stock Mercedes) the grease built up on top of the inner race, which in a horizontal position would mean eventually it's going to drip down and the bearing will run dry.