Sheridan Sheridan blue streak pumping issues

Just got a blue streak that’s having an issue pumping. It is holding air but has a whining noise and occasionally after 2-3 pumps the pump arm almost seems to feel stuck in the open position and have to force it closed. It seems to be shooting quite well but don’t want to damage any further. Assuming it’s something with the pump assembly and hoping someone can point me in the right direction to fix it.
 
If the pump arm is making noise and it sounds like it might be whining air, it's likely the check valve not holding. You can easily test the check by pumping it up maybe 4 pumps and leaving the pump arm partially open, maybe half-way, then leave it sit for a few hours with the rifle laying on the barrel so that there is no interference with the pump arm allowing it to move. If the check is leaking, it will push the pump arm to the fully open position.
The leak pushes against the pump plunger forcing it open.

Mike
 
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I don't own one but I've never heard of a pump gun that retains air AFTER firing.
When you exceed the the max pressure the hammer can't open the exhaust valve leaving residual air. Back in the day kids would get them locked and have to send them to Sheridan to let the air out.
 
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The lockup or stiff point, is about how from closed?

Just an idea that maybe its an adjustable throw which is unlikley if its stock and not modified.
If so, maybe it's out of adjustment?, but that is a stretch.

I am thinking that you have an obstruction of some kind on the pump wall. Crusted dirt and oil etc.
Another ldea am thinking is that someone oiled it and you can't compress oil. For either of those problems you can flush it with cleaner degreaser.
I use a foaming spray and a tiny glue tip to get it into the air hole. Then just shoot and repeat it till its clean.

If that doesn't do it, the next thing would be to drive out the front block pins2, Remove the block, slide the pump out, then align the last pin in the pump lever with pump arm pivot hole, remove that pin then the pump will come out. Then you can have a look in the chamber and give it a good cleaning, and maybe replace the pump plumger while you have in apart.
 
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Tried some pellgun oil but didn’t seem to help. The noise it makes when pumping is kind of a creeking or whine noise but does not leak out air. It doesn’t need to be forced close every time but when it does it feels like it’s damaging something. I see they have new piston assembly I can try but don’t want to get unneeded parts.
Is that noise coming from the pump chamber or pump linkages?

I have another post in this thread, that talks about one of these. That is an adjustable pump, from a 1955 Bluestreak. The newer ones aren't adjustable, unless a gun has been modified for higher pressure.
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