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Hummer Knowledge Base

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Cooling the Transfer Case Separately:

If you really want to "vampire-proof" your truck, you must provide separate cooling for the transfer case. There are several ways to approach this problem.

All of the below scenarios require some type of pump and a cooler (radiator). In addition, you need some way to control the operation of the pump (e.g. a thermostat).

  • The simplest modification is to hook the pump and cooler to the old inter-cooler inside the t-case. This does not circulate the t-case fluid, and would not allow filtering. If the intercooler leaks, the pump circuit would leak into the t-case, but the transmission would not be affected. Running the t-case over-full is not instantly fatal to the t-case, although it may cause overheating and other problems.

Each of the following scenarios circulate the fluid from the t-case itself. It is possible, therefore, to add a filter to the circuit to help keep the t-case fluid cleaner. Such a filter would also help to protect the pump. It is possible that such a system may have a drain-back problem. Specifically, if there is nothing to prevent the air inside the t-case entering the cooling circuit and/or to prevent the fluid from the cooling circuit from draining into the t-case, incorrect fluid levels may occur whenever the pump is not actually running. At one time, AMG policy re warranty on transfer case cooling circuits included: fluid must be within 1" (+ or -) of the correct level at all times. There are various methods available to address the drainback issue.

  • The next-simplest method is to drill out the fill and drain plugs and connect a pickup and return hose from the new pump. The main attraction of this method is that it is not necessary to open the transfer case to install it. One possible problem is that the drain plug (pickup location for new circuit) is quite near the internal t-case pump pickup. It is possible that reduced oil flow internally may result. (It is worth noting, however, that no one who is using this method has reported any problems related to the internal pump.) The early-model Hummers had fill and drain plugs that look like a bolt, rather than the late-model version that is a plug with a hex recess for an Allen-key. The bolt-type must be used so that it can be removed/replaced after the center is drilled out.

  • Next, you might try to arrange some type of pickup located farther from the internal pickup.

  • Finally, you might try to make the return line spray the (newly cooled) fluid all over the inside of the t-case to further improve cooling and lubrication.

Dave B.

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