Purpose of checkballs in AT


Old 03-23-05, 01:11 PM
rav12's Avatar
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Join Date: Oct 2003
Location: California
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Purpose of checkballs in AT

I'm curious to understand the purpose of the checkballs in the valve body of automatic transmissions (mine has 4). I understand one of them is to prevent the torque converter draining back when stopped and so prevent delayed engagement when starting after the car has been sitting for while. I also understand that one of them may be for the oil cooler line (I guess to regulate flow through the cooler). However, there is no clear explanation of why all these checkballs are required and I wondered if anyone could shed any light on this.
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Old 03-23-05, 02:39 PM
Join Date: Jun 2002
Location: Long Island, NY
Posts: 1,531
They are used in some cases to keep fluid in a passage or device so when it needs to work it is “charged up” and ready to go. As you already stated.

They are used in clutch packs for the fluid to drain out so they can release. Pressure from a shift valve seats them and when pressure stops the return springs push on the piston and unseat the check ball and fluid “vents” out of them.

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