Holy cow Randy. I will start typing
On all my cubs I have built I have done the following with great results and no broken parts. My cubs have been in the 25-30hp range. With a 26 inch tire.
1)Completely dissasemble the tranaxle. Keep the main shaft gears and spacers in order along with the counter shaft gears and spacers.
clean it out with the power washer.
2)reinstall the diff, and axle housings with axles.
with the diff clean of all oil use the trusty arc welder and weld the diff gears at all 8 meeting places. This makes it a posi. If you don't do this you will blow the diff up. This is my personal thing to do. Some guys don't like welded carriers. I won't run one without it. You can buy a after market one for big money but unless your making 50hp you don't need it.
3)with the diff out of the way you can choose your gears, a three speed setup will give you 3 pulling gears in a close ratio. 4 speed setup will give you 4 and no reverse. I have always just ran a 2 gear setup. It leaves 1st and rev stock and gives you 2nd and 3rd for pulling. Close ratio. At my tracks pulling at the 800lb-1000lb range I have ran 23-25 gears sets and won my points championship with my cub. A 2 gear setup is the least amount of money.
4) you can run a stock top shaft and pinion bearing support. I have never broke any parts in the transaxles with that setup. 2 gear setup and a welded diff, everything else stock.
5)when you get into the a real hard bitting track that sucks up hp and you have to run a lower gear set thats when you should think about a good topshaft and pinion bearing support.
6)Our open v-twin has ate up a stock welded diff, a top shaft and a stock 12 tooth pinion gear. It make 50hp, 7000rpm with a set of VM07's and we pull on very loose tracks with a 25-26 tooth gear at 1050lbs.
7) BRian miller web sight has a ton of trans axle photos for assembly as well. He also goes over alot that I just typed.
on the clutch setup. I have ran a set of aftermarket pressure plates and a replacement kevlar disk from Vogel with a 800lb spring. This was behind my open rpm opposed twin and I never had a problem with it. I could slip it out of the hole and it would hold great at the end of the track. This is a cheap alternative to a 3 puck setup. If you buy a complete unit Midwest has a good deal on the 3 puck setups. It will take most anything a S/A 16 will dish out. On our open v-twin we have a 4 puck setup from super cub. Just remember on the clutch you want to be able to slip it 25-30 feet taking off to keep the engine rpm up in the power band.
9)when pulling you pick one gear and it stays there until pull is over. That is why gear choice is crucial. After you pull a little and get some time in you will be able to pick a gear set for what ever your building and have good luck with it.
10)Stock class stuff can get away with stock clutch parts and a good spring with a kevlar disk. Resurface the pressure plates, 4140 steel drive shaft and your good to go.
11)I make my own forks as well. You use the stock stuff in 2 and 3 gear setups. You just have to modify them a little depending on the gear size you choose. I use as much stock stuff as I can because if it aint broke it doesn't need fixed.
12) If you have questions and your looking at things to by feel free to im me or call Randy. I will help in any way you need. It does'nt bother me so don't be afraid to ask.
13)if your under 30hp or say running a S/A engine your build is cheaper. If your in the vtwin class or the 48-50.5 classes thats when you want some good drive line parts because if not you will break the stock stuff.