Isuzu NPR Archives - Transmission Digest
Switch Hitter

When the owner was asked whether this was a problem before the truck came in to have the transmission replaced, he said it wasn’t but that the alternator had been replaced recently. Hmmm, could there be a “connection?” (No pun intended)

Isuzu NPR/GMC Tiltmaster

The Isuzu NPR Commercial Truck and GMC Forward Tiltmasters use an exhaust-brake system that assists in engine braking during downhill coasting while the trucks are carrying heavy loads. This system is used instead of the familiar Jacobs Vehicle System known as the “Jake Brake.” When the exhaust brake is activated, it restricts the flow of exhaust with a flapper valve in the exhaust pipe similar to that of a heat-riser assembly (see Figure 1). When the flapper valve closes, exhaust pressure increases, causing air intake to decrease. This increased backpressure and slower air intake reduce torque transfer to the geartrain, producing the desired on-demand engine braking needed during downhill coasting with a payload.