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Transmission TECH/TALK

GM 4L70E Leaking out of Vent


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After overhaul, a 4L70E has a complaint of transmission fluid leaking from the transmission vent. There were no cooler restrictions or filter problems and there was no evidence of cavitation.

Figure 1


The input speed sensor passage and the vent passage in the pump can be connected as shown in figure 1. The rebuild technician either did not install an O-ring seal on the input speed sensor, or the ISS retaining bolt was left out causing the speed sensor to work its way out of the passage and resulting in fluid getting to the case vent, refer to figure 2. A P0717 trouble code would be set.

Figure 2


The installation of an O-ring seal onto the input speed sensor and /or the retaining bolt stopped the transmission fluid from leaking out of the transmission vent, refer to figure 3.

Figure 3

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