Any gear box breather discussion is a WAY over sold mod or of a real concern, even to the point of being ridiculous. Sorry to say Old brits is not always the cats meow on all tech issues. I built a pressure test rig using a super low pressure guage and did a series of pressure tests of the AMC gearbox. This test was demonstrated at one of the national rally tech sessions. While the test included the demonstration of my clutch rod seals ability to restrain oil leakage, I was actually trying to debunk this old wives tail about gearbox breathing/venting deficiency and the need for further breathing mods.
The results were as I expected, and the gearbox is absolutely NOT able to hold pressure.
The main leakage path is the path in the main shaft that my CCRS fixes.
A close 2nd leakage path would be the normal early vent in the access cover or the MKIII style vent.
A minor but variable third leakage path is the between the main shaft and sleeve gear bush.
The fourth path is the clutch cable entrance. This can NOT hold pressure, even if you RTV the cable entrance, the leakage also goes up the cable itself up to the handle bar.
Try as I might to actively pressurize the gearbox after totally sealing leakage paths one and two, there was no ability to view any residual pressure once the ball valve was shut to stop the regulated compressed air. All remaining air vented through the cable or sleeve gear. The very high resolution...low pressure guage went to zero quite quickly.........
The results of the test show that any theoretical air expansion causing a pressurization of the gearbox due to heat from operation is IMO totally bogus and without any merit what so ever.
