Hi,

First off, I want to commend everyone involved with the Mudinmyblood site for providing this venue for such a great community to come together! Wow!! I am so impressed with all the help I have seen members giving each other. Great work.

First my machine: 2009 Brute Force 750

A while back my 4WD stopped working. I eventually discovered that the problem was the front left-side axle. The very tip of the splined end that goes into the front gear case had sheared off, right where the little c-clip is (as seen in the one pic, where I am holding the sheared off tip near the newer axle's mangled spline-tip). So, I replaced the shaft, and after 1 minute, literally 1 minute, the 4WD stopped working again. Thinking that perhaps I had done something wrong during the re/re, I pulled the new shaft out, and, as you can see in the pics, again the very tip of the new shaft was wrecked. This time the little splines are just mangled, not sheared off; however, the result is the same...no 4WD because the front left wheel is not receiving proper input.

So...has anyone ever seen anything like this before? I am suspecting that something is not working correctly in my front gear case; however, it makes no weird sounds or grinding etc, and the oil in it is brand new and clean. The oil before I replaced the first axle was pretty grey/milky, so maybe the dirty oil had something to do with the first failure, but as I changed the oil before installing the new axle, which also failed, I doubt it.

I look forward to hearing what you all might have to say.

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Welcome. That is a strange situation. You should know that the ends of the axles past the clip are not supposed to touch or connect to anything. The fact that this one has something interfering with it says there is a real problem. I would say either with the diff-loc cage or more likely with the carrier and/or spider gears or their shaft, Either way....it needs to come out and be pulled down to see. I personally have never seen anything take out the end of an axle before so when you do take it apart...take lots of photos and post them.

Never seen that before. Did u purchase the quad used ? It looks like the axle shaft was not fully installed into the diff. Is there a lift on this quad ?

Yes, the whole thing is very strange.

NMKawierider, I can see inside and there are no signs of damage to the spider gear shaft; however, it is quite a ways inside. I suppose it could be the spider gears themselves, but they are not easily viewed from the outside. Same goes for the dif lock mechanism.

I bought the quad new in 2010. No lift kit. Oversized tires, but nothing insane. It is chipped, clutched, and has a muzzy system, but the geometry has not really been modded.

dman66, actually it seems that the problem is that the shaft got installed too far into the diff, rather than not far enough. As NMKawierider pointed out, the very tip of the axle shaft, after the C-clip, should not be touching anything at all. The fact that it is the part suffering damage suggests that it is either going to far inside the gearbox, or something in within the gearbox - spider gear perhaps - is free to move in and grind against the tip.

Because there seems to be no debris inside, and the gears rotate smoothly - no griding noises etc - it seems unlikely that the problem is related to the inner workings of the gearbox. Maybe I hit the wheel from the side really hard, and pushed the original axle inwards. But I would think that the bearings and oil seal located within the axle receiver would prevent that from happening. Strange.

I have attached a screen snip showing the tolerances for the front left cover of the diff. When I measure the dimension "C" on mine, I read 6.44mm (digital calipers), which would mean that if the axle was pushing in, it would only be by <1mm.

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And this is just the lefty axle. Is there any noticeable or excessive in and out movement after installing the axle?

Yes, just the left. There is always a bit of movement, so it is hard to say if it "seems" excessive or not.

I have a question: Why is the tip of the shaft separated; what is the point of the little notch, the C-clip, and the separation??

The clip expands back out after it gets to the other side of the carrier to hold the axle in against the seal. It takes a "Pop"ing action to get the clip to squeeze back down to pull the axle back out. Some have trouble with this..where others don't install the axles all the way in enough to get that clip to the other side. Once there you won't feel almost any movement because the clip is doing it's job. There are some videos on YT about this.


About the 8-minute mark on this one:

Thank you!