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Vacuum pump rebuild kit or whole new pump

3161 Views 1 Reply 2 Participants Last post by  p100
So I took my car into an MB dealership to have my window switches replaced. One was broken by a friend and I needed to get it fix in a hurry since the window was down.

MB performed a 27 point inspection and said my brakes were hard and I needed to replace the vacuum pump. Which is costly.

My power locks all work fine (doors, gas door, etc.) I do notice my brake pedal is a bit hard but not anything crazy.

I was wondering if anyone has rebuilt their vacuum pump using the kit on diesel giant. If so, was it an easy job?

What should I be checking (e.g. what lines and connectors) before I make the decision to rebuild or replace the pump?

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There is an easy way to check your vacuum pump operation. You need to get a vacuum test pump with a gauge, like the MityVac. Your car most likely has the new style piston vacuum pump. Unplug one of the branch vacuum ones off the main vacuum line that is connected to the power brake booster. Connect the hand vacuum pump to it and start the engine. You should see about 21-22 inches of vacuum build up in a few seconds and remain at that level.

The engine vacuum pump also has a check valve at the outlet, which is not included in the rebuilt kit. It is sold separately for about $ 35. You can test this check valve for correct operation by removing it and blowing into it. It should let the air through in only one direction. If the check valve is the problem, rebuilding the vacuum pump will not do any good.

With the hand vacuum pump still connected, shut off the engine. The vacuum should remain steady. If you loose vacuum rapidly at this point, you could have a leaky brake booster or some other leak in the system, or even a leaky vacuum pump check valve.

Rebuilding the pump is not difficult, but do these tests to make sure that the vacuum pump is in fact in need of rebuilding.
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