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HT4100 vacuum pump

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I have a 1983 Fleetwood brougham. I changed my valve cover gaskets. I got everything back together and fired her up there was a loud knocking noise like a woodpecker. I narrowed it done to the vacuum pump by taking the belt off, but could not figure out why it started making this noise. To be clear this is the pulley-driven vacuum pump near the front of the engine on the drivers side. I pulled it off and took it apart and couldn't see anything out of order. Shaft bearing seemed OK, cam lobe housing was filled with oil, diaphragm button felt good. Bought another pump and pulley at the junkyard, tried it, same noise. When you pull off the outlet hose of the pump the noise softens a little until the hose is reattached. I would appreciate any help. thank you

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It could be that the pump off the junkyard car was bad too. It is possible you can't feel the bearing is bad when the belt is not installed but when the belt is installed and tensioned, it loads the bearing enough to make the noise.

I had a vacuum pump go bad on an '85 Brougham (same car as the '83) but replaced it with a new pump.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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