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The pump (Dura Hydro-Lectric)on my car came with deep cup on pump. my buddy whos older than me and Moses, tells me a small cup pump will work don't have to be deep cup. I think the small cup pumps are for power window cars and the deep cup pump is for power windows and top. comments please.

Believe the cup length is going to depend on the length of the pickup tube on the pump. If the tubes extend down X inches the cup will have to be a slight bit longer. Conversely if a short tube pump has a long cup there will be a lot of fluid in the cup that is not really needed.

The only fluid the cup has to hold is the amount the windows and seat cylinders hold plus a slight bit for contingency. Generally there will be that amount in the cup and then some space left over for expansion and a slight amount extra from the top cylinders. The top cylinders displace almost the same amount back to the cup as is needed to move the piston. What is on one side of the piston returns to the cup as more is added to the other side to move the piston. The portion above the piston will hold slightly less fluid because of the space taken up by the rod so when the top is down the cup has to hold an extra few ounces.

Howard
thanks
Ken