|
Most older tractors use spur gears in the transmission. A well designed, high stress, gear train using spur gears will have a contact ratio between gears of a minimum of 1.4, although the ratio can go as high as two. This ratio indicates how many teeth are meshed at once. Because you still have at least .4 of a tooth grabbing (I say at least because often, the root of the broken tooth remains)and the gears are rotating at a relatively low speed, the gear will not lock up or begin shearing gear teeth quite yet. However, there will be a noticeable clunk and whenever a large load is placed on the transmission, the remaining tooth will need to carry at least twice the load it was designed for. Under constant heavy load, it will weaken the remaining tooth every revolution, until it fails. That being said, many antique tractors are being used more for parade duty and light tasks that don't involve heavy drawbar pull. Because the gears were so over-engineered to begin with, they can last a long time before failure. I wouldn't try this with a car transmission, though, as it will be gone in a matter of a weeks due to higher speeds, closer tolerances, smaller factor of safeties, and helical cut gears. That is just my take on it, I am sure others will have other opinions. . .
|
