Hi i have an 1985 toyota 4runner. I know it has a W-56 and a top shift t-case. I also know i need to get a 21 spline input but what output spline do i get. I am getting the line up from marlin crawler.

here is the link-

http://www.marlincrawler.com/transfe...ar-drive-tcase

 

Your current case is 21 spline input, matches the transmission 21 spline output. The new reduction box would likely fit in between those two (obvious answer to your question), unless you want to change it and your current box to a 23 spline output/input.

 

I know the 23 spline is stronger but how much stroger? Am i likely to break a 21 spline? What is involved in changing it to a 23? What do i have to buy?

 

Unless you plan on beating the hell out of your truck, the 21 spline will be just fine.

 

Sounds like you need to do the research yourself, before you undertake this project. Will save you the unadvertised additional cost of a dual setup.

 

The way i look at it it isn't very much more to get the crawl box already built. The adapter is 370 from marlin lets say i get a stock T-case for 150 bucks. That's $520 just for the parts then i still have to put it together. I know i have the capability to do it myself but for $80 bucks ill have it done by marlin. I have searched for a while, and was almost positive i needed 21 spline output i just wanted to double check. I already have made a square drive line for my RUF should i put trail creeper U joints in it? I only see upgraded one's on trail gear, are those the best ones to get if needed?

 

Shoot you know it all, seems like experience is the best teacher. Have fun.

 

I've been wheeling hard on the standard marlin MC07 21 spline all season with no breakage. I started on tires that were way too big (40s) but now I am running a more sensible 34x10.50 with 5.29 gears. It's important to re gear your axles to relieve stress on the t-case output shaft. Just cause you have duals doesn't mean that you can keep 4.10s.

 

so how low do it has to go in the diff

 

I think you need to do some more research on dual cases. If you don't know anything about gearing in the axles or what is involved in a dual case set up, you most likely would be fine without either.

What is your intended use for your truck? Search dual cases on this forum, or toyota dual cases on google and you'll learn alot real quick. As for which setup you need, you should probably call them if you have no idea. They were very helpful when I ordered my dual case stuff.