09 yz450 drive axle oil leak has me stumped!

I am repairing an oil leak on a 2009 yz450 that was bought as a left over model in fall of 2010.

It started leaking from behind the sprocket. Simple fix, right? Yep, so I replace the oil seal, collar, and oring. It held for about one 20 minute practice session. The next time I started it up I noticed it was pouring out, not just dripping.

I thought maybe I had made a mistake and replaced the seal and oring again. This time it leaked instantly with the new parts.

I figured maybe there was something wrong on the inside. I removed the engine, split the cases, inspected everything. A few of the bearing were questionable so I replaced them all as well as every oil seal, o ring, gaskets and other little questionable parts. I assembled everythng and for more security I put a small amount of yamabond around the outter edge of the drive axle seal. It did not leak for 30 minutes of ride time. Then I noticed it was starting to seep under the sprocket again. Now I am getting frustrated.

I inspected everything as best as I can from the outside. The shaft does not appear to be bent with running the bike. The oil is coming out between the collar and the seal lip, I was able to watch it slowly come out at about the 10 or 11 o clock area and run down and start to drip.

I noticed the bearing covers about 1/3 of the oil hole in the shaft when installed. Could this "blockage" be causing the seal the not hold. The bearing was fully bottomed.

I decided to split the cases again and look at everything again even more closely. I am not finding any definite causes.

What could this possibly be? If it was some type of defect in the shaft or the case I would think the problem would have happend much sooner. If I had unlimited income, I would replace the cases and the shaft but that just is not logical.

Any help is greatly appreciated. I have pictures but cannot figure out how to upload them.

Thank You!

A common mistake is to install the seal too deeply, and/or to install it out of square. It needs to be no farther than flush with the outer end of the seal bore, preferably about one millimeter proud of it. If it runs in too far, the lip can overhang the notches on the inner end of the collar, allowing oil to bypass.

The other common cause is a groove worn in the collar from the old seal, but you replaced that.

I made sure to not install the seal too deep and also made sure it was square the 3 times it was replaced.

I noticed on the parts diagrams online that it shows the collar/spacer having square cutouts on the side that goes in for oil to pass through to the shaft. The one that was originally in the bike and the ones that I ordered have small C-shaped cutouts? Could this be an issue not allowing enough oil to pass through?

This one has got me stumped..

Also, How to I upload pictures on here? Maybe a visual of what I'm talking about will help.

Edited by ben782

To post pictures, they need to be hosted at a web site, then linked using the "image" button in the post toolbar (bottom row, near middle) or by enclosing the URL of the image in img tags, which would be {img} at the start, and {/img} at the end, but substituting [ and ] for { and } style brackets.

The best solution is a free hosting site like Photobucket.

Oil is fed from the oil filter well on the right side through a passage behind the cylinder, to the bore for the clutch release arm. From that point, it branches to both transmission shaft bearing pockets, where it flows through the hollow shafts to the trans gears and the clutch. Since the end of the output shaft extends beyond the seal, oil has to be fed into the space between the bearing and the seal, then through oil holes into the shaft and across its length. But in order for an abnormal amount of pressure to overwhelm the seal like that, it seems to me that BOTH shafts would have to have some unusual obstruction to flow.

Check the crankcase vent hose for a kink or blockage. Had this happen to me once on a little XR50...it kept blowing the seal out from too much pressure.

I have also been looking at the lubrication diagrams and I see what you are talking about. The clutch pushrod goes through the "main axle" and the splines on there help push oil through the clutch release arm area into the "drive axle" I am going to go through and clean all of the oil passage ways (actually, clean everything) and make sure there is no blockage anywhere.

The oil flows to the two trans shafts in parallel, not series. The branch point of the Y is at the clutch release arm. I repeat that because it wasn't clear to me that you understood that. If you did, my apologies.

If you take the oil filter cover off, the trans feed passage is next to the bolt hole at 10:00 o'clock. If you remove the clutch cover and the pressure plate, you should be able to take some sort of squirt bottle like a mustard or gear oil bottle and force oil into the passage way at the filter cover flange and have it come out the center of the main shaft. I think it should be obvious that there is no problem with oil getting as far as the left end of the output shaft. That passage also feeds the top end, so while you're checking, you can pull the oil pressure check bolt out of the head and see what happens if you feel inclined to.

I understand what your talking about and that the oil runs in parallel. Thanks though, for restating in case I wasn't sure. I cleaned and went through every oil passage and also made sure the oil holes on the shafts were open under the gears.

My next question is about the bearing on the left side of the main axle. (part number


Is this supposed to be the half sealed bearing? (seal side obviously facing out, away from the inside of the case). The parts diagrams do not show it as a sealed bearing but it was a sealed type originally in the bike. Perhaps this should be a non sealed bearing?

That one is a half sealed bearing using a steel "seal" in most cases. Without the seal, oil would escape past the bearing without running the length of the shaft and oiling the main shaft gears and clutch.

You make a good point. That's true, in this case it uses a rubber seal, but still serves the same purpose. I only brought it up because I've rebuilt several other engines that have a half sealed bearing on the right side of the case as well. Just trying to think of every possibility.

Any other suggestions or possibilities that you can think of? Otherwise I guess Ill just put everything back together once I get the parts in and hope for the best this time around.

I can't think of anything else off the top of my head, no.

I know someone else touched on this, have you checked for excessive crankcase pressure?

Crankcase pressure takes a while to build, even if the breather is totally blocked off, so it couldn't account for an immediate leak. Besides, that would ordinarily push out one of the half moon seals at the cam cover. There is full lube system oil pressure behind the drive shaft seal.

Thanks for your advice and help, when I get this figured out I will be sure to post the results.

Thanks again,


sorry to bring this thread alive again. but was this the problem, just the seals? i have the exact same problem on my bike.

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