Transmission Vent line Modification

Proceed at your own risk: see explanation below.



July 2009


The standard transmission vent line looks something like this. Why do we need a 1/2" hose for the transmission vent? Beats me!


added content:

An old friend of mine, Jim D., emailed me about this vent line thing. The reason the stock vent line is so big is to prevent water from being sucked into the transmission if the bike should be dropped into deep water. (like, if you crash into a big puddle, or loose it during a water crossing) When the motor is suddenly submerged the transmission will be suddenly cooled, and this will create a small amount of suction. With a small hose (like I have on my bike) the water will be sucked in like it was going through a straw. If you have the gigantic hose on the bike, the suction will probably not be able to move enough water for it to get into the transmission. KTM is king of off-road, they certainly know what they are doing, so I do not advise this mod to anyone who does water crossings or rides near water deep enough to be a problem. Many thanks to Jim for explaining this to me!


So, working with the air bags for my rear suspension on my truck, I noticed that a stainless instant fitting screws into the vent line fitting for the KTM transmission. I shortened the KTM fitting and gently tightened the instant fitting in its place. Weighing the two will show you an increase in weight, as stainless is a lot heavier than plastic. But wait! If you measure that ridiculous 1/2 hose along with the fitting, and the 1/4" plastic tubing that fits the instant fitting, it turns out you save 2 ounces! From 2.5 ounces for the plastic fitting and big hose, to 1/2 ounce for the new modified fitting and the plastic tubing. Excellent!


And to top it off, it ends up looking like this!