Why Does My ATV Move in Reverse Without Giving It Gas?

Why does my ATV move in reverse without giving it gas? That’s what one reader wants to know after fishing his Yamaha Grizzly out of a bad situation.

Here is exactly what reader Dylan asked the ATV AnswerMan, followed by his answer:

My 2011 Yamaha Grizzly 700 was recently sunk. After changing oil and differential fluids several times I went to put it in Reverse and the 4 wheeler started moving without giving it gas or anything, just starts going all by itself. It doesn’t do this when you switch to high or low gear, just when you put it in reverse. Opened the clutch panel to look at it and besides seeing a little grease slung around It looks fine. Would you know what the problem is?

Sometimes the most difficult machine woes are the ones that tend to end up being the simplest, but I would be lying if I said I had an absolute answer on this. I do have something to get you in the right direction. I see that you have listed the pre-curser to the actual issue, but I really need to know a few other details. Does the engine idle higher than normal at any point? How much does it actually move? Does it creep or lope along with idle or is it on a swift mission to exit from your general location?

I ask these questions because it is so peculiar that it will only move like this when placed in reverse. The drive line direction or crank rotation does not change at any point during the engine’s run cycle, so the issue should in theory be isolated to the gearing in the transmission. Even the wet clutch still spins in the same general direction and if the one-way bearing in that clutch was going bad it should creep in all gears.

I know that some 700 engines have experienced a bushing failure that causes the reverse gear to move off of its intended placement by gradually working the external snap ring to push out of its groove, but that is a more sudden occurrence in most cases. Is it possible that this is happening and the gearing is catching a ride on another gear set that is rotating at idle? Its possible and in my experience with expecting the unexpected, I rule nothing out.

You say you had been sunk deep enough to introduce dirty water into the oil or differentials, then possibly during your master plan to extricate the Grizzly you could have sped up the transmission issue I spoke of above by shifting from forward to reverse in haste – essentially causing this problem. I’m not saying you are at fault, as I see this many times in machines that are babied, but that is a possibility.

Did you notice any foreign material in the oil? Were there any small bits of metallic glitter or even solid nuggets of internal parts? My final suggestion would be to pull the CVT cover and simply watch how the clutch works when shifted from Low gear to reverse or even from high gear to reverse. See if the clutch acts any differently when doing so and maybe your eyes will catch a clue there. Good Luck, my friend.