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Valve body testing

S.T.S. Transmissions -Your Local Sarasota Transmission Rebuild Expert



A worn valve or valve body bore can result in incorrect pressures in the transmission, which may lead to poor performance or failure of the transmission.


With proper equipment, vacuum testing is an effective way to determine if a valve or valve body bore is worn and can also be used after repairing the bore or valve that the repair has been performed correctly. Using this tool will give you peace of mind that the valve body is a serviceable item.

Why Vacuum Testing for Leakage?

Wear occurs as valves repeatedly stroke in a pump or valve body casting. Eventually, this wear creates increased clearance beyond what is necessary to maintain a proper hydraulic seal. Once that occurs, the valve does not function properly and transmission failure results.

How does it work?

Essentially we are isolating or sealing a circuit, and attempting to pull air between the valve spool and the bore. As air flow is intentionally restricted by tight clearances, we can create, hold and read vacuum. Since we are rating a vacuum, the measurement will be in negative pressure. In order to maintain a hydraulic seal, there is very little design clearance between the critical valve spool and mating bore. A swear occurs, this clearance increases. A perfect vacuum (no leakage points) will measure29.9" of negative pressure. As wear occurs and leakage points are introduced, vacuum reading levels will decrease. So in checking valve clearance, the vacuum loss is directly proportional to the amount of wear.

Vacuum Testing - Start a Rebuild Right | Sonnax