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Automatic Transmission Sprag Clutches Defined..

Talking about transmissions in detail can leave a lot of blank spots for people, meaning when I use the term Sprag and other specialized transmission terms as in my article on early 700R4 transmissions. I know when I read something and don’t understand even one critical word, I may not get this jist of what is being said.

With that being said we are going to define these terms and transmission jargon as we go along so you eventually will understand how an automatic transmission functions, or better yet, understand what the transmission shop owner or transmission supplier is dazzling you with. When you come to a term you don’t understand go to the Transmission Anatomy & Theory category for the definition in terms you understand. I will add terms as I go, if I don’t have a particular term listed, please ask me for a description.

What is a Sprag Clutch? A sprag is a one way metal roller clutch. Picture going to an event such as a concert, fair, basketball or football game, where you pass through a turngate, when you give the usher your ticket, notice that the turngate does not go backwards? This is a sprag at work.

one way bearing roller clutch detail_700

one way bearing roller clutch detail_700

Sprags are used in many industrial products other than automatic transmissions. Essentially, the inner race is locked in place by a shaft that it attaches to, the yellow/ metal thing in the middle is the actual roller clutch element and the race on the outside will only turn one way, because of the internal configuration of the element and race. Thus it locks in one direction and spins free in the other direction. Transmissions make wide useage of sprag assembly’s. Most automatic transmissions such as a 700R4 have 2 sprags or more depending on how many speeds it has. The only transmission I know of without sprag elements is the Chrysler TF 604 front wheel drive automatic overdrive transmission.

In most cases a failed or broken sprag requires that the transmission be replaced. I have seen mechanics put a sprag in backwards, the second that sprag comes into use, Kapow, the transmission becomes junk. Like a carpenter, check it twice, fix it once! If you are a transmission rebuilder, that is. Generally speaking a sprag fails due to mileage and lack of slippery new automatic transmission fluid, which should be maintained regularly. Abuse is another reason for sprag failure, either intentional abuse or over working your vehicle can cause a sprag to break.

If the unfortunate happens and a sprag breaks, it means it is time to call to talk with an expert and develop a strategy for a replacement transmission. Whether it be a good used one, a remanufactured unit or a brand new one. Their number is 866-320-1182.

For more free information on transmissions see our Blog. It may be helpfull one day in making a good educated choice if a transmission is in your future.

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