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Building a Chain Drop Box

32K views 20 replies 12 participants last post by  willwiebe 
#1 ·
I use my truck for mostly trail driving and mud pits, and never shift out of low range, so I'm installing a chain drop box.

I know the concept of building them, and most of the parts. But trying to convey that to the guy behind the counter is a challenge.

Have any of you built one.? Or can anyone tell me what I'd need to ask for in regards to 2 standard cut gears, one larger than the other. I need them to be able to install on a shaft, with a pillowblock on either side to hold them inplace.

These two gears then have a Double 40, or Double 80 chain driving your axles..??

I know there's machinists out there, and I need the proper terms to ask for..


Thanks..
 
#5 ·
Goof said:
Take a stock t-case, put into 4lo, and torch off the shifter. Really though...I don't really see a benifit over a normal transfer case. Am I missing something?

Also...what vehicle is this for?

the only benefit is for mud bogging man, less moving parts= less crap that can break and their very simple to design and build beefy.
 
#6 ·
Why not use gears and not a chain/sprocket?

Line up 3 gears in a row?

Id go a bout finding the sprockets first, then the chain, then the shaft then the bearings.

If you cant find the chain then you'd have to ditch the sprockets, so this order makes sense. You would definately not have a problem finding a shaft (can machine) or bearings (thousands of em!)

Make sure you get materials that can handle the torque of your rig. You have to consider shock and impact as well. Multiply the torque coming out of your yokes by ten. That should be a good safety factor to start at, and if you find something stronger, good!
 
#7 ·
Gears would work, but there to tempremental, if I strip the teeth off one, it's expensive and problematic to fix.

With the Chain Drop, you can change ratio's in about 20min, and replace parts if need be cheaply.

I'm looking to push roughly 700 ft/lbs torque, and need something beefier than a 205.

I know combines use the chain drive for there pickup's, what kind would a guy need to handle the torque.?
 
#8 ·
you say you use it for mostly trail driving and mud bogging? so what else are you doing with it? you do NOT want to drive that thing on pavement with a chain and sprocket setup, not even a little bit. also its a very simple design but the building of one isn`t so simple, if your still hellbent on a chain box link me to a canadian industrial parts supplier online and i`ll show ya everything you need.
 
#10 ·
So you're looking for a monster truck type transfer case, so you can run serious amounts of lift and have good driveshaft angles.

I dont know where to find them, but they're made by SCS Machine and ProFab Machine.

The reason for the chain drive instead of three gears is so the driveshafts will run in the right direction. Otherwise you have to put the engine and transmission in backwards :)
 
#15 ·
Goof said:


It'd be kinda funny to watch...it'd be a pretty loud snap when the front and rear axle try to go opposite directions :D
Actually the axles would both run the same direction, since the box we're talking about here drives both the front and rear axles off the bottom gear, but you'd have one forward gear, and three or more reverse gears :p
 
#16 ·
Around here, (central alberta) chain drives like what you describe are quite common on large equipment for winches etc. Try places like BC Bearing for the gears and chain or possibly try a truck rig up shop like Danco supply or maybe a shop that works with PTO equipment like Pat's Driveline. A little yellow page reading should give you a few alternate choices.
Your idea is sound for what you want to do and will act just like a divorced t-case.
Doing it this way would allow you to use a engine/trans out of any 2wd rig.
 
#17 ·
Well this is what I've come up with.

Double 60 sprocket, 48 teeth,
weld on hubs
Pillough blocks, and bearings.
And run the setup on a 3/4" keyed shaft
for the 2nd sprocket us on with 24 teeth.

Do you guys think 3/4" shaft will be strong enough.?
 
#18 · (Edited)
No I don't, and I don't think double 60 will be enough either, but what do I know?;)
I know mud boggers use it, and I know that some rail buggies use chain to drive the axle shafts, so it works obviously.

Now what I do know. You'll be better with two, three, or whatever, single strand chains than using multi-strand chain. The separate chains will handle misalignment of both shaft and sprockets better. Multi-strand chains are very alignment sensitive.
While you're at Western Equipment ask them for some handout literature, they should have some stuff from Reynold, or one of the other chain manufacturers, that will have chain drive design suggestions and guidelines. There will also be charts for HP capacity, torque handling, etc.
Basically you want the biggest drive sprocket you can manage while still getting the ratio you want in the space available. Chain and sprocket power handling capacity and life span goes down a lot when it's run on a small sprocket. Power handling capacity also goes down as speed decreases, and down at high speeds as well. I don't think you'll have a problem with high speeds though.
The main question in my mind is whether it can handle the shock loads it's going to get on the trail. In mud once the tires are spinning there isn't a bunch of shock load, on the trail, well...
I think I'd try at least 1 1/4" shafting, the stronger the better, 4130 or better I'd say, and keep the distances between the bearings as close as possible. The chain will side load the shafts, so they need to be able to handle the radial loads, as well as torsional loading. The larger shaft and hubs will also allow bigger keyways and keys, and bigger bearings.
The power and torque you'll be putting through there will exceed the manufacturers recommendations at least 10 fold, but like I said, works for the mudboggers, so give her a try. I'd be interested to know how it works.
Oh, here's a link that might help with planning.

http://www.ustsubaki.com/chainguide.html
 
#19 ·
#21 ·
jeepFREAK said:


You want your key to break before the shaft.
haha to true, i dont know what hp or torque you r running, ive seen these on big mud trucks. they are easily serviced. id go with 3/4" to 7/8" thick shaft.
 
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