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Note 1:
Advance Adapters Saturn overdrive. This
unit fits on the Model 18 ‘45-71 transfer case,
though Advance Adapters is working on a version to
fit the WWII military transfer cases. It‘s a 25 percent
overdrive (0.75 ratio), meaning it drops rpm by 25
percent. It‘s capable of handling up to 300 lb-ft of
torque, according to the manufacturer.
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Note 2:
TeraLow builds a replacement gear set for
the Model 18 with a 3.15:1 low range. The conversion
works only on a ‘66-and-later Model 18 cases,
‘63-79 Wagoneer cases, or ‘72-9 Model 20 cases.
The Model 20 case can be used with the offset output
of the Model 18.
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Note 3:
O‘Brien‘s 4-Wheel West makes four
replacement gear sets called the JP Rock Eaters for
the Model 18 in 3.0:1, 3.6:1 4.10:1 and 4.86:1.
The 4.10 and 4.86 kits require significant case modifications.
The detailed instructions outline the necessary
mods to be performed by competent machinists
and certified welders, but O‘Brien‘s can supply
modified cases or complete kits.
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Note 4:
Hicks 4x4 Specialists offers a kit to drop
the Model 20 low ranger from 2.03:1 to 2.46:1.
Installation involves only very minor clearance
grinding of the case and parts that are stronger
than stock.
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Note 5:
O‘Brien‘s 4-Wheel West makes a tapered
roller bearing kit to replace the roller bearings and
thrust washers of the original setup. this is an
option to the company‘s Model 18 and Model 20
Rock Eater kit, and it significantly quiets the Model
18 unit. O‘Brien claims a 300-325 percent over design
compared to the stock setup.
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Note 6:
O‘Brien‘s 4-Wheel West offers two replacement
gear sets for the Jeep Model 20 in 3.0 and
3.6:1 ratios. No welding is required, and only minor
mods are necessary to the case and shift rail.
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Note 7:
TeraLow offers a 3.15:1 low-range gear set
for the Jeep model 20 in a kit that contains everything
needed to do the swap. It requires only
minor clearance grinding of the case for the larger
gears.
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Note 8:
TeraLow‘s Dana 300 kit offers a whopping
4.0:1 low-range option. These quality gears are said
to be very quite. Normally, clearance grinding isn‘t
necessary for installation, but a tiny bit of grinding
in one strategic spot will make assembly easier.
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Note 9:
MileMarker‘s part-time conversion for the
BW-1339 Quadra-Trac eliminates the fuel-sapping
full-time system, annoying clutch chatter, and need
for special oil. It includes a new chain and locking
front hubs.
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Note 10:
Currie Enterprises Twin-Stick shifter for
the Dana 300 evolved as an answer to automatic
lockers up front. It allows the front axle to be
uncoupled from the transfer case while in low-range.
This is easier than climbing out and unlocking
a hub to make a tight turn or shifting out of
4WD and low range at the same time.
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Note 11:
The Atlas II transfer case is manufactured by
Advance Adapters and can replace nearly
any transfer case in nearly any Jeep. It‘s an
aluminum cased, gear driven design that‘s based on the
best features of the bulletproof NP205 and Dana
300 transfer cases. It‘s available with 3.77 or
4.33:1 low-range gearing.
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Note 12:
Short-tailshaft kits for NP231s, and
NP242s have appeared from a variety of manufacturers
to answer the needs of lifted rigs with drive shaft angle
problems. They‘re all variations on the
same theme: conversion of the sliding rear output
shaft to a fixed yoke and the loss of about 4 inches
of drive line length. In the case of the JB
Conversions kit, the replacement rear-output shaft
is at least 50 percent stronger than the stock one.
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Note 13:
TeraLow‘s 4:1 low range kit for the
NP231 includes a new heavy-duty rear case as well
as a six gear planetary gear set that offers a 4.0:1
low range gearing.
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Note 14:
If you combing an NP-231 and an automatic
front locker, you may experience the need for
a 2WD low position on the transfer case to make
trail maneuvering easier. Both TeraLow and JB
Conversions supply suck a kit to add and extra position
to this popular New Process case. Shown are the
TeraLow pieces.
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