PeachParts Mercedes ShopForum - View Single Post - 603 vacuum pump failure (How to Diagnose?)

bustedbenz · #7 03-04-2011, 11:21 PM

Interesting story of getting it home. Left Boone with the noise still rattling just as it had been that morning. Decided to chance it, knowing the risks, but having an instinct that it wasn't going to get much worse. Was really figuring that whatever damage was done, had been done within the first revolution.

About 20 miles into the trip, the noise went away completely. Simultaneously, ALL vacuum disappeared. Previously, it had been sort of making "half" its usual vacuum. Once the noise stopped, there was none. Brakes were fully mechanical, and engine shut off didn't occur with the key. Drove it the rest of the way home without incident.

Got home, took the pump off my parts engine so I could see what I was in for. This engine is removed from its car and sitting on a sheet of plywood on concrete blocks, so it was easy to get to. It LOOKS intact, but I have no idea if it's "good" or not. Tomorrow's project is making that determination.

I'm sorry to disagree with whoever all said I could pull it off to inspect it in 15 minutes, but it took a LOT longer than that with two people working on it. Loosened the belt to get it out of the way, but still could barely get to where I needed. The bottom two bolts are TORTURE; i have no idea how on earth we'll get them started again. Can't remove the fan shroud without removing the radiator hoses and losing coolant, and typically the radiator has had to come out too whenever we worked up near the front. So we left that all intact and just worked around it all to remove... but we may still remove the radiator and fan shroud and possibly the fan to reinstall. Or the power steering pump and pulley which was the main obstruction for the right side bolts.

I'll post pictures of what came out tomorrow. The entire "spring" assembly; the main guts of the pump, was completely broken loose from the housing. It came out in pieces, and the metal "bowl" shaped thing that is attached to the block in the hole where the pump came out of, has been gouged in several places where the pump mechanism was driven into it. Will post pics of that too. Going to remove the "bowl" in the morning and hope to see no damage to the gears and such behind it. Assuming it's that simple to replace (we have those parts on the donor engine as well) then we'll be back in business, IF that vac pump is good.

Any good way to test a vac pump on the bench or do you have to just bolt it up and see if it works? Besides looking for visual damage I mean. Is there a way to test the mechanism?

Conclusion: The slapping noise was the pump mechanism halfway broken away but still lined up with the plunger enough to make partial vacuum. When this finally all shook loose after 20 miles of driving, it laid in the bottom of the housing where it fortunately couldn't get turned sideways enough to drop down the hole. At that point, all vacuum production ceased and it was an uneventful trip home.

It may only take 15 minutes if you are really good at removing the fan shroud and all the other associated bits and pieces. But last time we tried to do this, IIRC, the lower rad hose is threaded through the shroud, which means taking THAT loose and then re-bleeding the entire system afterwards, to say nothing of catching the coolant, and then even after you do that you still have to pull the radiator to get enough clearance to put a socket or wrench on the fan, and get something in there to hold the fan still........ there just ain't no way. And there's not enough clearance to do it quick-and-easy without; it's a matter of sticking wrenches and such in and getting one ratchet click or 1/32 of a wrench turn and then repositioning and taking the next 1/32 until it finally comes out one bolt at a time.