You should be sure to have a certified pump curve from each OEM manufacturer and know your system curves for what you are trying to obtain. I would look in the Cameron Hydraulic Data Handbook at the end of chapter 1 for what typical curves look like. You need to know the terms the pump industry...
Agree with JJPellin more information is necessary. Is it a split case or end suction or vertical in-line centrifugal. About 14 years ago I worked at Crane Pumps which manufacturers the Weinman pump brand.
Post some photos of the pump and I along with the other people with access to this site...
FYI - just a different thought you may wish to look at a sleeve bearing.
Link - (look down the list of bearings)
Just a thought, however it depends on your overall arrangement.
Good luck
There is a lot to read in this post, but from 38 years experience in industrial situations, this type of problem happens when there is no discharge check valve installed or it is leaking back through the check valve and you have been fortunate the shaft has not broken or the impeller has not...
