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FOR '89-'93 for Dodge TURBO DIESEL 4X4s,
REPLACING THE GETRAG FIVE-SPEED WITH A
NV4500HD
Since 1996, Quad 4x4 has been retrofitting
1989-'93 Dodge Turbo Diesel pickups originally equipped with
the Getrag five-speed transmission with the newer NV4500HD
five-speed transmission that is original equipment in 1994 and
newer trucks.
Complete 4x4 NV4500HD
Conversion Kit features a brand new, current production
transmission and all required parts to replace the original
Getrag G360. |
When off-warranty 1989-'93 Dodge trucks with blown Getrags
started coming in our shop in 1996, it was obvious a simple
rebuild wasn't going to be the solution. These trucks came
with a 7 year-70,000 mile warranty which must have caused Dodge
a fortune in transmission warranty claims because nearly 75% of
these trucks we have seen had one to four transmissions replaced
under warranty. With that kind of track record, you know the
factory part just isn't up to the job. In addition, many of the
parts required were not available and those that were had a
gold-plated price tag.
Our inspection of failed Getrags revealed
that excessive heat and insufficient lubrication were causing
the transmissions to literally self destruct from bearing
failure. At that point, I started doing research on the Getrag design and service procedures, looking for possible ways
to modify it for better lubrication and cooler operation.
My research showed the basic problem of premature failure with
the gearbox was probably a combination of premature pilot bearing
failure, use, bearing preload, basic design, type of lubricant
and the power of the Turbo Diesel. We considered
installing an external oil cooler and using synthetic lubricant.
Our conclusion: while an oil cooler might prolong transmission
life, we would still see bearing failures due to the modest size
of the preloaded bearings; the use of a single tapered roller
bearing on the front of the main shaft to handle radial, lateral
and thrust loads; and drivers who would power up hills with
heavy loads in fifth gear.
The only contributing factor to Getrag
failures that is easy to remedy is the clutch pilot bushing. Why
Dodge used a pilot bushing in the first place is a mystery, but
a simple flywheel modification that any competent machine shop
can perform permits the installation of a heavy duty, sealed
ball pilot bearing.
 Broken
stock clutch pilot bushing on left only lasted 44,000 miles. It
is strongly recommended you replace the stock bushing (a new one
is shown on the right) with the heavy duty, thick wall
QU51010 sealed
ball pilot bearing (center). Flywheel modification is required. |
Our first thought was to install an older style four-speed with
an auxiliary overdrive or installing a medium duty truck
five-speed with adapters. These options may be viable
alternatives, but high cost and supply problems made us decide
to try the update to the NV4500 gearbox. Our first
conversion took a week and utilized an adapter plate between the
transmission and original bellhousing. Currently we are
buying brand new, semi-finished bellhousings to adapt the NV4500
transmission to the Cummins engine.
The NV4500HD is a reliable and heavy duty
transmission that is more than capable of handling the power of
the Cummins engine. Early models had problems with retaining the
fifth gear, but that has been taken care of by new mainshaft and
nut designs. It is still a current production transmission, which
means brand new units are available and affordable, plus service
parts will be readily available for years to come.
The combined length of a new 4x4 NV4500HD and bellhousing is
only 1/8" longer than a Getrag, so no driveline or crossmember
modifications are required on 4x4 trucks. There is minor
welding involved to reinforce the original transmission support
plate and to modify the transfer case shifter to bolt to the new
transmission. The weld-on pieces are included with the
conversion kit.
The 4x2 conversion is a bit more involved.
Cross member and propeller shaft modifications are necessary. We
supply steel to weld to the crossmember as part of the kit. The
4x2 conversion also comes with a new transmission mount and rear
output yoke for the transmission. Some 4x2 trucks will also need
the speedometer driven gear replaced for proper speedometer
calibration.
4x2 NV4500HD with modified crossmember installed in a 1993 W250 |
Included in all 4x4 conversions is a brand new, modified,
current production NV4500HD transmission, new bellhousing with
slave cylinder studs and pivot ball, clutch pilot bearing,
clutch release bearing, transfer case input seal, transfer case
adapter gaskets, adjustable transfer case linkage, Syntorq 75w85
synthetic gear lube for the transmission, transmission shifter,
new floor plate, heavy duty transmission mount, made in the USA
grade 8 hardware, 100 minute installation video, miscellaneous
small parts, shop supplies, etc.. The primary components of the
4x2 kit are the same except of course the transmission is a 4x2
unit.
(left) Getrag G360. (right)
NV4500HD. Larger case of NV4500HD requires a new bellhousing to
retrofit first generation Dodge trucks. |
The actual time required for an amateur
mechanic to install the new NV4500, is probably around 15 hours. The conversion starts with the removal of seat and
shifters. The new shift tower is farther back, so once the
carpet is removed, a hole is cut in the floor to provide
clearance for the new shift tower. Next, remove the drive
shafts, disconnect the wiring, remove the transfer case, crossmember, transmission, bellhousing, and clutch components.
The clutch assembly is a long-lasting (but somewhat "grabby" on
take-ff) 13" Sachs/Borg and Beck unit which can almost always be
reused, unless it has been subject to abuse or high (200,000)
mileage. If required, a brand new Sachs/Borg and Beck
assembly is available as are a number of 12.4" and 13"
South Bend performance clutches. The modified flywheel
and ball clutch pilot bearing are installed after checking the
rear crankshaft seal for leakage. Next is clutch assembly
installation, then the new bellhousing and transmission.
The original 4x4 crossmember is reused with the addition of a
new heavy duty transmission mount. After the new transfer
case input seal is installed, the transfer case is bolted to the
transmission. One of our two styles of transfer case
linkages is then installed, depending upon the year of the
truck. With our kit, drive shaft modifications are not
required, so finishing the underbody portion of the conversion
requires simply replacing the remaining components and pumping
the lubricants. The truck is then lowered for finishing
the interior portion of the conversion which requires installing
the new floor plate and shifter, relocating the transmission
shifter boot, replacing the carpet, seat, and transfer case
boot."
First generation 1989-1993 Dodge turbo-diesel trucks have steel
shell rear crankshaft seal pressed into an aluminum seal
housing. Over time, the different expansion and contraction
rates of the two metals will compress the seal shell. When this
happens, engine oil starts to seep between the seal and
seal housing. Replace this original seal before installing
the NV4500HD. The
QK6000 crankshaft seal
kit includes the new design, Teflon lip seal with rubber sealing
rings, installation tool, and video guide. |
The forward gear ratios of the current NV4500HD are
slightly wider than the original Getrag. Reverse gear is slightly
faster. (Gear Ratio Chart). Given
the relatively narrow rpm band of the Cummins engine, does the
wider ratio adversely affect performance? That was one of
my main concerns when we started doing these conversions, but
every customer that has commented on the gear splits tells me
that they have a better spacing than the original Getrag.
Everyone seems to like the lower first gear and the higher
overdrive too. As a rule, NV4500's shift a lot nicer than
the old Getrags.
The bottom line on retrofitting the NV4500
into '89-'93 models is that for about the same price as most
Getrags can be pulled and rebuilt, the customer gets a stronger,
more reliable, and easier shifting transmission. |
