Help With Leaking Gearbox

Joined
Apr 17, 2007
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#1
I own a 1999 YZ125. I just changed the gearbox oil for the first time since I bought it. I drained it and filled it up to the check bolt until it started seeping out and tightened it. I went on a ride and when I got back I noticed oil up under my fender and on my swingarm. I checked to see where it came from and it was coming out of the transmission breather tube. I let a little oil out and went on another ride and it did the same thing. It does it everytime I go riding. The oil level seems to go down. What do I do?
 

IndyMX

Crash Test Dummy
Joined
Jul 18, 2006
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#2
I'd check the crank seals... Could be you are building pressure in there that's causing the oil to leak out..

I could be totally wrong, but it seems logical to me.
 
Joined
Nov 18, 2003
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#4
...normally leaking crank seals manifest by white-colored exhaust, but he is right that a simple leak-down test will tell u. See this site for how to do it, or Eric Gorr's excellent $18 book...u will need a ~Craftsman SCREW-in compression gauge and a few rubber expansion-plugs from Lowe's to do the test..."normally" it is the ignition-side seal. Often it can be replaced w/o splitting the cases. Extract it with two long thin sheet metal screws, screwing them into the seal oppostie each other and drawing them out.
Put your new one in your wife's freezer for a couple hours, or spray it with freon, to greatly ease installation. Coaqt it with a light coat of silicon grease will help some too.
Used to have an RM350 (to race the open class with) that literally ate those things...like most RM's it was a joy to ride as long as u didnt mind it aging much quicker than other bikes do...