I needed lower gearing for the buggy and wasn't going to drop the coin for an Atlas or Stak. I didn't like the weight, cost and gearing options of a 203/205 so I settled on using ~1/3 of the housing from an NP241 and its 2.72:1 planetary gearset as a reduction box which transfers power to an NP205 transfer case.
The idea is to use part of the front half of a 241, just enough to support and shift the planetary gearset inside. The NP241 gearset is VERY strong and is used in many other applications; the 4 speed Atlas, Klune V and NWF Black Box all use the 241 gearset.
I like this idea because its light (40 lbs., a 203 range box and doubler adapter is ~110), has good gearing selection (1:1, 2:1, 2.72:1 or 5.44:1) and its cheap.
Here are the hard parts I started with, an SM465 (32 spline) bolted to a 465/(208/241) adapter bolted to a passenger drop NP241 (also 32 spline). I'm also using a round pattern NP205.
I had to buy a blank clocking ring and drill/tap the holes myself to clock the transfer case upside down. You need the larger part of the case on the opposite side of the t-case drop i.e. with a passenger drop transfer case you need the bigger side of the reduction box on the driver's side.
T-case w/clocking ring:
Now cut the front output part of the housing off, its not needed:
And the piece that's removed:
I decided to build my own adapter because Duffy (D&D machine) wanted $270 for it. I spent $50 on plate and about 4 hours to make mine. Duffy has stopped making 241/205 kits but he does make 231/205 kits and they are similar (pics/explanation at the end)
So I put the 241 half onto a piece of .500" aluminum plate, traced the pattern of the case and cut it out with a 4.5" angle grinder.
Then I eyeballed where the mainshaft would pass through the rear of the case (you can see the sharpie marks I made) and cut a hole with the biggest hole saw I had (2.5")
Here's most of the cost of this project, the intermediate shaft that couples the 241 to the 205. I got it from D&D machine for $250, its chromoly and its 31 spline (I'm using the 31 spline input from a Ford 205 that I cannabilized for its 32 spline front output).
I removed more aluminum from the plate using a hole saw:
so that I could do this:
I put a new seal in the seal retainer and slid it over the input shaft I'm using. I supported the input gear to center it the best I could and using this as a template, I spray painted over the seal retainer to get a pattern that I could cut into the aluminum
The hole that is cut in the plate has to serve as a pilot for the seal retainer, it basically insures that everything lines up correctly. The hole in the plate has to be just a few thousands of an inch larger than the seal retainer.
Here's the plate with the hole cut in it (not too bad considering I ground it out with an angle grinder)
I didn't take great pics of this part but the rod that supports the shift mechanism has to be cut down to fit inside the case half. I drilled and tapped it (1/4") and drilled a hole in the aluminum plate so that the rod could be supported on both sides.
I bolted the plate to the 241 box and bolted it to the 465. Then I put the input gear and seal retainer onto the 205 case, slid it onto the 241 output shaft and clocked the 205 flat. A few of the six holes that mount the 205 are drilled all the way through the case, so I marked them on the aluminum plate from the inside of the 205 case. Then I used my clocking ring to drill the rest of the holes. You can see the fill and drain plugs (not tapped yet) and the little hole for the support for the shift rod.
Here's the whole thing put together:
40 lbs. all together, a 203 range box and doubler adapter is ~110 lbs.
Bolted to the adapter
To bolt it together you have to bolt the plate to the 205 case first
And done
I still need to cut and weld a couple pieces of aluminum plate to fill the holes where the front output was cut off and of course make new crossmembers and a skid plate. Because the 241 box is upside down, I'll need to weld up the hole where the vent used to be and drill a new one in the top. Everything will be shifted via cables.
One of the shift rails on the 205 interferes with the 241 box, you can either notch the 241 for clearance (like NWF chose to do, look here) or you can shift the 205 from the rear like this guy did.
You might think that the aluminum case is a weak point but its not if the t-case is supported correctly. That case is ridiculously strong in torsion, but its not hard to break stuff with a heavy 205 hanging off the back (same reason there are so many 465/205 adapter failures and so many auto transmission case failures).
Total cost was about $300, $250 for the shaft and $50 for the aluminum plate. I got everything else for free, but they're not too hard to find for relatively cheap.
The idea is to use part of the front half of a 241, just enough to support and shift the planetary gearset inside. The NP241 gearset is VERY strong and is used in many other applications; the 4 speed Atlas, Klune V and NWF Black Box all use the 241 gearset.
I like this idea because its light (40 lbs., a 203 range box and doubler adapter is ~110), has good gearing selection (1:1, 2:1, 2.72:1 or 5.44:1) and its cheap.
Here are the hard parts I started with, an SM465 (32 spline) bolted to a 465/(208/241) adapter bolted to a passenger drop NP241 (also 32 spline). I'm also using a round pattern NP205.
I had to buy a blank clocking ring and drill/tap the holes myself to clock the transfer case upside down. You need the larger part of the case on the opposite side of the t-case drop i.e. with a passenger drop transfer case you need the bigger side of the reduction box on the driver's side.
T-case w/clocking ring:
Now cut the front output part of the housing off, its not needed:
And the piece that's removed:
I decided to build my own adapter because Duffy (D&D machine) wanted $270 for it. I spent $50 on plate and about 4 hours to make mine. Duffy has stopped making 241/205 kits but he does make 231/205 kits and they are similar (pics/explanation at the end)
So I put the 241 half onto a piece of .500" aluminum plate, traced the pattern of the case and cut it out with a 4.5" angle grinder.
Then I eyeballed where the mainshaft would pass through the rear of the case (you can see the sharpie marks I made) and cut a hole with the biggest hole saw I had (2.5")
Here's most of the cost of this project, the intermediate shaft that couples the 241 to the 205. I got it from D&D machine for $250, its chromoly and its 31 spline (I'm using the 31 spline input from a Ford 205 that I cannabilized for its 32 spline front output).
I removed more aluminum from the plate using a hole saw:
so that I could do this:
I put a new seal in the seal retainer and slid it over the input shaft I'm using. I supported the input gear to center it the best I could and using this as a template, I spray painted over the seal retainer to get a pattern that I could cut into the aluminum
The hole that is cut in the plate has to serve as a pilot for the seal retainer, it basically insures that everything lines up correctly. The hole in the plate has to be just a few thousands of an inch larger than the seal retainer.
Here's the plate with the hole cut in it (not too bad considering I ground it out with an angle grinder)
I didn't take great pics of this part but the rod that supports the shift mechanism has to be cut down to fit inside the case half. I drilled and tapped it (1/4") and drilled a hole in the aluminum plate so that the rod could be supported on both sides.
I bolted the plate to the 241 box and bolted it to the 465. Then I put the input gear and seal retainer onto the 205 case, slid it onto the 241 output shaft and clocked the 205 flat. A few of the six holes that mount the 205 are drilled all the way through the case, so I marked them on the aluminum plate from the inside of the 205 case. Then I used my clocking ring to drill the rest of the holes. You can see the fill and drain plugs (not tapped yet) and the little hole for the support for the shift rod.
Here's the whole thing put together:
40 lbs. all together, a 203 range box and doubler adapter is ~110 lbs.
Bolted to the adapter
To bolt it together you have to bolt the plate to the 205 case first
And done
I still need to cut and weld a couple pieces of aluminum plate to fill the holes where the front output was cut off and of course make new crossmembers and a skid plate. Because the 241 box is upside down, I'll need to weld up the hole where the vent used to be and drill a new one in the top. Everything will be shifted via cables.
One of the shift rails on the 205 interferes with the 241 box, you can either notch the 241 for clearance (like NWF chose to do, look here) or you can shift the 205 from the rear like this guy did.
You might think that the aluminum case is a weak point but its not if the t-case is supported correctly. That case is ridiculously strong in torsion, but its not hard to break stuff with a heavy 205 hanging off the back (same reason there are so many 465/205 adapter failures and so many auto transmission case failures).
Total cost was about $300, $250 for the shaft and $50 for the aluminum plate. I got everything else for free, but they're not too hard to find for relatively cheap.
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Assuming they are obtainable.
