NP 242 Transfer Case & 4L80e Transmission Temperature Sensor Installation

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You should find a casting 'bung' on your tcase located between the fill and drain plugs. Note: some older tcase's don't have the bung. If this is the case you will have to install the sensor in a tapped out hole in the drain plug. I opted to place the sensor in the bung because the sensor is able to stick into the case in the 'flow' of the oil. If you have to locate the sensor in the drain hole the sensor can't stick into the case because there are internal parts in the way. Since the case was made to have a hole tapped there that's what I did. Additionally, the sensor could get damaged located in the drain plug.

Drill a 45/64's hole in the bung and thread it with a 1/2-14 npt tap. Screw in a 1/2 x 1/4 bushing and the 1/4 tcase sensor using teflon paste, not tape. A piece of teflon tape could break off and plug up the oil pump in the tcase. Note that tapping the hole takes a considerable amount of torque.

There are two ways to do this. The most conservative way is to remove the front plate of the transfer case. We did this truck this way because it was in for the cooling loop recall where the case cover had to be removed anyway.

The other way is to drill and tap the cover while it's still on the truck. This is how I did my truck. If you do it this way first drain the oil. Screw the drain plug back in. Then blow compressed air into the fill hole while you drill the hole using cutting oil and a very slow speed. You don't want to seal the air hose to the case. Just use a blow gun into the hole. If you pressurize the case you may blow out the seals. As the hole breaks through, the air will be forced out blowing the chips with it. We also held a shop vac near the hole to catch the chips. Tap the hole the same way. When you're done rinse the case with a quart of Dexron through the fill hole and the sender hole.

Solder the weatherproof connector to the temperature sender and tape up the wires. I like to use heat shrink tubing and liquid electrical tape. Use locktite RED when you screw the sensor into the bushing. Install the bushing into the tcase using liquid teflon pipe paste.

Transmission Sensor Installation

Original TThis is the Original 'T' assembly I removed from the truck.

Transmission sensorSolder the weatherproof connector to the temp sensor and tape up the wires.

Screw the temperature sender into the T using locktite RED.

Move the 3 hose clamps down and pull out the existing T and hoses that join the transmission output, check valve and the steel line which leads to the trans cooler. This is not as easy as it looks. I used a regular slip joint pliers and a channel lock pliers. You will loose a little transmission fluid so remember to check the level when you are done and top it off.

With the old T as a guide cut and measure 3 new hoses with your new T so the final lengths end up in the same location as the stock setup. Then install the new T.

Note: older model trucks do not have a check valve.