Vent Tubing: Hub, Differential, Transmission and Transfer Case

Our project vehicle had been stripped of most of the vent lines, and some it appears may never have been correctly installed.  (See: missing fitting and hose on front differential vent caused water infiltration).

Accordingly, we had to source and locate replacement or substitute hose and tubing for installation. All of the hoses and tubing are indicated in the parts manual as either P/N CPR104420-1 or P/N RB1450-1-4IDX1-20D. 

Upon visual inspection, CPR104420-1 was identifiable as air brake tubing used on semi-trucks. One of the brand names for this is an Eaton product called Synflex®.

Synflex┬« used to vent rear differential and hubs and transfer along frame. 

Upon further research, it was determined that CPR104420-1 is 1/4″ diameter tubing. (note this tubing is measured by O.D., not I.D.) Whereas CPR104420-2 is 3/8″ diameter. (CPR104420-2 is used as the main tube running parallel to the frame to vent the fuel tank).

We were able to identify RB1450-1-4IDX1-20D as being manufactured by Armstrong, and carries an NSN for bulk lengths as 4720-00-684-4033 [4720006844033].  This essentially is a durable 1/4″ I.D. hose, which has the appearance of 1/4″ fuel hose or similar.

There is a number of vendors that make a suitable replacement, although we noted the caveat of not using fuel line because it may not remain flexible enough over time for use on the front hubs. (they will constantly be flexing as the vehicle is steered).

It was suggested to us to consider use of silicone vacuum or vent hose.  Silicone hose was simply not readily available at the time of manufacture and design of the HMMWV. Vendors cautioned against using silicone hose for oil or fuel carrying. The primary reason for not using silicone for fuel is that it simply isn’t rated for pressurized fuel. We determined that 1/4″ silicone hose would be appropriate for venting purposes, and noting its widespread use in commercial and agricultural applications gave us a level of comfort of its reliability.


Front RH vent line from hub attached to tee fitting on frame. Note use of original style clamp 4730-00-954-1251 [4730009541251]


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