It's not too tricky, just don't get in a rush. I just did this a little over a week ago... this is from memory but i think it will get most of it covered.
-Need to get the truck jacked up a good bit... i have my tires on 8" of solid concrete blocks. chock the tires, make sure that puppy aint gonna roll nowhere.
-remove front and rear driveshafts. I had to engage 4wd to break the u-joint strap bolts loose on the front shaft.
-Drain the fluid from the transfer case.
-unplug all electrical connections from transfer case and tranny.
-brackets on the drivers side of the tranny have to come off.
-Clutch hydraulic hose has a "quick disconnect" up in the engine compartment, below the clutch master cylinder. to be honest i can't remember but i think there was a spring that holds this together... cause i remember i dropped it. (thank god i found it though) so be careful. remove that spring, then carefully seperate the hose. little stubborn, i had to work at it a little. but it will come. the hose stays with the transmission.
-break bolts loose on transfer case, but don't take them all the way out yet.
-jack up the transmission just enough to take weight off the tranny crossmember.
-then remove the tranny crossmember from the truck. (don't know if you absolutely have to but it's not hard to do and makes getting the transfer case out much easier.)
-remove the bolts holding transfer case to tranny (think there was 6 of them?)
shouldn't be hard to seperate transfer case/tranny.
-turn or twist transfer case however necessary to slide out between torsion bar and tranny. not too difficult.
-now the hard part - this transmission weighs ~250 lbs. with fluid in it. need to be extremely careful to not let this fall on you.
-before unbolting bellhousing bolts, get in the cab, remove the shifter handle and boot, then take those 4 allen head bolts out of top of tranny and remove that gear selector mechanism. (i tried to remove tranny without doing this, will not work.)
-now just get all the bellhousing bolts out... some are a little tricky but you can get to them all from underneath. may need several long extensions. make sure you get them all out. if you need, i can count bolts and find socket sizes needed this afternoon after i get off work.
-we used two hydraulic jacks and blocks... but i had like 4 people there with hands on the tranny to help get it back enough for the input shaft to clear, then steady it on the way down. ideally, strap the tranny somehow to be safe and control it from falling. (I'd still suggest having an extra buddy or two around for this part). easy does it. once jacks are all the way down, we eased tranny off the jacks onto a piece of cardboard on the ground.
-the ZF-6 is a tall tranny - remember i said to jack up truck a good ways? - this is why... has to be pretty high to get tranny out from under the frame. the 8" i had left just a little clearance from top of tranny to frame, with tranny on a piece of cardboard on the ground (no longer on jacks.)
-with that out of the way, all you have left is the clutch and lastly the flywheel. i had an aftermarket clutch in mine already. i'd suggest having a clutch alignment tool before removing the clutch but don't reckon its necessary if you're getting a new clutch.
-i had to remove 6 bolts to remove for the clutch, took it all out together, carefully. make sure you got a hold of everything when you get those bolts out.
-lastly, the flywheel - 14 MM allen head bolts. (that's a big allen head, just got lucky that i actaully had that size in the toolbox already.) the suckers are tight too.
-we put one of the clutch bolts back in the flywheel, and used a ratchet strap around the frame (drivers side) and that bolt to hold the crank, to keep it from spinning while loosening flywheel bolts. (once all are loosened, remove clutch bolt/ratchet strap) had to put a cheater bar on the allen wrench.
-be careful and make sure flywheel doesn't fall out on you once last bolt is removed... was not the case on mine though... may not be on any duramax. better safe than sorry though.
-we had to carefully pry/seperate flywheel from crank. kind of like a pressed on design... i couldn't budge it by hand. be careful also not to break the aluminum rear-engine cover... just watch where you pry at and if you see the aluminum flexing, don't pry too much there. what we did was used some sort of pry/wedge and tapped it in (with hammer) between the flywheel and the rear engine cover CAREFULLY. seperate just a little, then i'd spin the flywheel/crank. 1/8-1/4 turn, then do it again. we kept going around til the flywheel came off.
-hold on tight when it comes - it's heavy.
and you're done.
phew... sorry so long.
