YZ 400 wide ratio questions

So after looking through the FAQ and doing searches I have yet to find the answer I am looking for... so I am sorry if I missed it. I have a 99 YZ 400 that I am looking at putting a the wide ratio WR trans into it. I already have the cases split and need to replace a couple of gears so I thought this would be a great time to do it. What I want to know what gears to replace, and what year WR do I need to get the gears (and shafts if needed) from? I hope there are still a few 400 experts around here that know a thing or two about these old beasts.

I would poke through the parts catalog and identify those parts that are the same, and those that differ between the two gear sets, and order what you need. I'm pretty sure it will all fit.

Find the part numbers you need here:


(no need to sign up for anything, just click the "proceed to catalog" link.)

Then go here for the parts:


You'll save about 30% or more. You may want to call to verify they can get the stuff, but it would surprise me if they can't.

It wasn't clear to me after looking at the diagrams and part numbers. I will keep doing some research. Thanks.

Probably, only the output shaft (sometimes they call it the drive axle) and the shift forks will be the same. The main shaft has the low gear pinion cut directly on it, so you'll need that. All nine other gears are probably also different, too. Figure to spend $500 or so with a discount to convert it with new parts.

The way it looks you are correct. One of the threads I was looking at said that third gear was the same but it seems to be different. I will keep digging.

If the ratios are close enough, you might be able to reuse the YZ 3rd gears, if the gears that they engage against fit up to them properly.

Look closely at the sides of the gears which are commonly referred to as the dogs. certain ones have to fit together. This is why there is the 3rd/4th gear issue with mixing YZ and WR ratios the dogs are not compatible. Not sure what you are trying to accomplish but a nice mix which I use on my motard/street 426 is 1st and 2nd from a 99 400 and 3rd ,4th and 5th from a2002 WR. This gives a nice medium ratio gearbox very similar to the 03 to 05 4 speed with a added 5th gear. Also consider upgrading to the 2002 shift drum as they really removed a lot of weight from that part from earlier versions. So net you could use 5th only from the WR or if you want a WR 4th then you have to use WR 3rd too. Using 1st and 2nd from a 400 gives slightly wider ratios than 426 1st and 2nd.

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