The arrow in the photo above indicates the position where the vent hose leading from the fuel tank vent line filter 2910-01-210-5872 [2910012105872] (behind the surge tank) is to be placed for clearance when the hood is closed. Note a Corbin style clamp 4730-00-954-1251 [4730009541251] needs to be placed on the hose ends both where the hose attaches to the tube and to the filter.
The callout for this hose is for an 11″ length of CPR104420-2 (replaceable with 3/8″ air brake tubing, such as Eaton Synflex®). We instead replaced this with 1/4″ SAE J30R9 hose (which we consider a modern and equal substitute for RB1450-1-4IDX1-20D).
Our reasoning for using hose instead of tubing is based on a couple factors: First, it is called out as RB1450-1-4IDx1-20D (or equivalent) to connect the fuel tank vent line to the fuel vent line filter (See Figure 18, Item 6). We are of the opinion the hose leaving the vent line filter should be the same as the hose entering the filter, and that indication of tubing may be an error in the TM. Second, use of air brake tubing essentially requires a heat gun to soften the tubing enough to slide over the tube on the stack and bead on the filter itself. Although this can be accomplished, should field repairs be necessary, it essentially requires cutting the tubing, where the hose can be easily removed by loosening the Corbin clamps.
We note the installation instructions for the DWF kit also indicates the CPR104420-2. See http://www.hummerknowledgebase.com/driving/dwf.html (at Image 3), where is specifically calls out an 11″ length. (We do, however, note this document is extremely dated, as it calls out for use of Dexron II at Image 5). Dexron II was long ago deprecated: In 1993, GM released new Dexron-III fluid (GM Spec GM6417M and later GMN10055). As noted above, we believe the J30R9 hose is made from material superior to what was available during original engineering of the HMMWV. and stand by our recommendation to instead use J30R9 hose.
Although we have no way of knowing at this time, there may have been a UV (sun) resistance issue where the engineers preferred the air brake tubing over the hose for that reason. It may well be that the CPR104420-2 tubing has a greater resistance to breakdown that the RB1450-1-4IDx1-20D hose. However, we are around 30-some years since the original design, and materials have changed. We will monitor the J30R9 hose to determine if it exhibits any undesirable weathering characteristics.