I started working on my doubler box setup - here's the quick rundown of where i'm at so far
did some reading about the klune, blackbox and blackbox-i and Atlas 4
I already have an overhauled Dana300 with stock 2.6 ratio. I picked up a 4:1 NP241 out of an '03 Rubicon that had the case broken pretty bad (unusable) to scavenge out the giant 4:1 planetary assembly.
the solution i was looking for was a klune type but using the 4:1 planetary out of this busted 241, shafts are available from various vendors so that i didn't think would pose a problem.
once i took it apart though there were 2 challenges that i could foresee with this planetary assembly using the pre-made shafts that are common for the doubler boxes
- the pilot bearing is larger, the 231 uses a 1.125 diameter shaft (where it goes in the pilot bearing), the 241 has a larger one (1.25 or larger, can't remember).
- the shift collar is different so the question was if the splines were the same, luckily enough the spline count and diameter is identical between the 231 and the Rubicon 241
so the only thing to consider remained the pilot bearing, i decided that i could sleeve a pilot bearing for the 231 input shaft so that it will be pressed instead of the larger 241 one.
next step was to decide the overall design - the doublers made out of chopped 231s or the klune-v (and i'm not 100% sure on this one) don't seem to have an output bearing, from what i read is not necessary but my common sense tells me it will be better to have support there since the splines are not pressed but slide in with some free play. The other issue that i am seeing is that the mating between the doubler output and the t-case input will add some unnecessary length (about 3 to 4 inches) as compared to an Atlas 4 speed where the doubler output is integrated with the input at the t-case.
Luckily there is such a doubler as in blackbox-i which basically transforms a Dana300 into a 4 speed just like the Atlas, the problem is that they only make a 2.7:1 version, is great if the t-case has 4:1 gears but in my case i have 2.6:1 stock D300 ratio and it really wouldn't be a true 4 speed but more like a 3 speed - so i picked up the phone and called Northwestfab and they were great, answered my questions and provided measurements to help me figure out if i can use their output shaft for my doubler - i ended up ordering one for the D300 that will allow me to use my input gear from it so it will integrate with the t-case and not have to use a connecting shaft as with the 231 doublers or the klune. I also ordered their sealed bearing so i can use it on the output shaft. If you have a 4:1 t-case and want a doubler this is a great option and these guys are really a pleasure to deal with so i highly recommend you give them a call (they have other parts too but my interest at this time was restricted to the crawl box).
I also had to order a wide input bearing for the 241 planetary (it is same OD and ID as the 231 but about 50% thicker at .940 compared to .629'' and i think is either a double row ball bearing or a roller bearing), a new input shaft seal and a pilot bearing to be sleeved and pressed into the planetary input shaft.
next steps are to get all the measuremets, make some blueprints and finalize the design, fab the parts, take the D300 out, remove the input shaft and attach the doubler box (sound like a long project already) - should give me a nice 4 speed Dana300 with a 10.4, 4, 2.6 and 1:1 ratios, long ways to go but if it works i'm pretty much set as far as crawl ratios (i mean would be nice if it can go lower but should be a heck of an improvement over the 2.6:1)
I will need to redo the driveshafts and the dual t-case shifters since this will move the t-case back about 4 or 5 inches
once i make more progress will get some pics and a thread in the member's projects, since it's not sure yet if it will be a success i'll just post some notes in "the mess hall" for now. I welcome ideas or bashing if you thing i took the wrong route (as opposed to a klune for example which would have saved a ton of work and probably not that much more expensive in the end).
