Truck transmission jack

A truck transmission jack includes a wheeled base to allow the jack to be moved in position below a transmission, gear box, or the like. A cradle is supported upon the wheeled base for engaging and supporting the underside of a transmission or gear box. The cradle is supported by three support arms, each being pivotally coupled to the wheeled base at one end of each support arm and pivotally coupled to the cradle at the opposing end of each support arm. All of the support arms are parallel to one another for maintaining the cradle in a relatively horizontal position as the support arms pivot. Two of the support arms are elevating arms having coaxial pivot points and extend from opposing sides of the wheeled base. A hydraulic jack rests upon the wheeled base between the elevating arms and includes a piston rod extendable upwardly for raising a yoke that is pivotally coupled to the elevating arms in order to raise the cradle. Adjustable support bars are provided at each end of the cradle to match the contour of the transmission being supported. A sliding support bar and associated collar are releasably clamped to a side of the cradle to position a locator bolt at a desired location.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to apparatus for lifting and 
supporting truck transmissions, gear boxes, and differentials during 
servicing and repairs, and more particularly, to a truck transmission jack 
with improved safety and maneuverability. 
2. Description of the Relevant Art 
Truck transmissions, gear boxes, and differential gear assemblies routinely 
require servicing. In most cases, such servicing is most efficiently 
performed by removing the transmission, gear box, or the like, from the 
truck. Such components typically weigh from 350 to 800 pounds on large 
trucks, and service personnel require the assistance of a jack to support, 
lower, and raise, such components in order to remove such components from 
the truck, and to reinstall such components upon the truck. 
Some transmission jacks that are already available are incapable of 
assuming a low profile near the ground even when collapsed. Such jacks are 
sometimes difficult to use because they are not easily positioned below 
the truck, particularly for trucks having low ground clearance. In such 
cases, the mechanic may actually need to elevate the truck in order to 
create sufficient ground clearance to insert the jack in position below 
the truck. 
Other transmission jacks that are known may be configured in a relatively 
compact profile when collapsed, but are incapable of being raised very far 
off the ground. Such jacks may not have sufficient height to reach the 
transmission, gear box, or other component to be removed, at least not 
without inserting wood blocks or other spacers atop the jack and below the 
component to be removed. However, the need to insert such spacers poses an 
inconvenience, as well as a safety risk if such spacers shift out of 
position. 
Moreover, many transmission jacks which have been made commercially 
available, and which have sufficient range of elevation, often become 
unbalanced and/or unstable when the load is supported at an elevated 
position. In particular, the load may be supported too close to one end of 
the jack and tip the jack over or, alternatively, the load may twist or 
rotate while in an elevated position, potentially causing physical injury 
to the repairman and further damage to the removed component. 
Other transmission jacks which are known to the present applicant typically 
include hydraulic lifting mechanisms which are built into the transmission 
jack, often extending horizontally in order to lower the profile of the 
apparatus. If the hydraulic lifting mechanism fails and can not be 
repaired, the user must go to the expense of replacing the entire truck 
transmission jack. Moreover, positioning the hydraulic cylinder 
horizontally accelerates leakage of hydraulic fluid out of the hydraulic 
lifting mechanism. 
Yet another problem with existing truck transmission jacks is that truck 
transmissions and gear boxes come in a wide variety of shapes and sizes, 
yet many existing truck transmission jacks are not easily adjusted to 
properly support the load in accordance with the particular contour of a 
specific truck transmission. 
Various forms of mobile lifting jacks have been described in previously 
issued patents. For example, in U.S. Pat. No. 2,621,891 to Marsh, a mobile 
jack unit is described including a wheeled base, a scissors jack 
controlled by a threaded draw screw, and a platform for raising and 
lowering a rear axle differential housing or other load. 
U.S. Pat. No. 2,838,278 to Johnsen discloses a transmission jack and a 
clamping assembly for use therewith in order to adjust for different sizes 
and makes of transmission housings. 
In U.S. Pat. No. 2,940,611 to Burch, an automobile transmission dolly is 
described for handling truck transmissions. The dolly includes a wheeled 
base, a pair of lifting arms, a vertical lifting jack for raising the 
lifting arms, a cradle support, and a cradle for receiving a transmission; 
a further jacking device is provided for moving the cradle upon the cradle 
support. The upper end of the vertical jack is coupled to a bridge which 
is, in turn, coupled to the lifting arms for transmitting a lifting force 
thereto. 
U.S. Pat. No. 2,938,635 to Dyer discloses a wheeled floor jack for removing 
engines from vehicles. The jack is raised and lowered by operating a 
handwheel for turning a rotatable screw. 
In U.S. Pat. No. 3,109,626 to Arnes et al., a truck transmission jack is 
described including a tubular base supported by casters. A lifting 
platform is carried by a pair of lifting beams and a pair of parallel 
links. A lifting screw is mounted to the base and passes through a nut 
carried by the lifting beams. A handwheel is operated by the user to turn 
the lifting screw in order to raise and lower the lifting platform. The 
lack of hydraulics, and the necessity for turning a handwheel mounted well 
above the ground make operation of such a device difficult. 
U.S. Pat. No. 3,136,526 to Wolf discloses one example of a prior art 
hydraulic jack mechanism for use under a vehicle to remove transmissions 
and the like. The Wolf apparatus uses two pairs of support arms which 
generally extend parallel to one another. However, the apparatus disclosed 
by Wolf positions the hydraulic piston horizontally; while helping to 
minimize the profile of the jack when collapsed, the horizontally 
extending piston and cylinder promote hydraulic fluid leakage. In 
addition, the Wolf hydraulic ram must be attached at both of its ends to 
the lifting assembly, making replacement of the hydraulic ram 
inconvenient. While a handle is provided at one end of the jack assembly, 
the handle obstructs access to the pump lever of the hydraulic ram. 
Moreover, the relatively flat, planar platform provided by Wolf to support 
the transmission is not easily adjusted to support a wide variety of 
transmissions and other components. 
In U.S. Pat. No. 3,559,981 issued to Abshear, an apparatus is shown for 
removing differentials from vehicles. The apparatus is supported upon a 
conventional wheeled floor jack. 
U.S. Pat. No. 3,958,793 to Garate also discloses a transmission jack for 
raising and lowering transmissions and the like. A ratchet mechanism 
prevents the jack from lowering completely to the ground in the event of 
an inadvertent release of hydraulic pressure. The hydraulic ram is again 
mounted horizontally, accelerating leakage of hydraulic fluid. In 
addition, the hydraulic ram requires a mounting block and mounting bolts 
for being secured horizontally within the apparatus, making replacement of 
the hydraulic ram more difficult. Like the Wolf jack assembly, the Garate 
device is provided with a handle at one end of the jack assembly which 
generally obstructs access to the pump lever of the hydraulic ram. 
Further, the Garate device uses a pair of chains below the transmission to 
form a cradle, and a chain which extends over and around the top of the 
transmission in order to support the transmission, rather than providing 
rigid supports for positively supporting the underside of the 
transmission. 
U.S. Pat. No. 4,269,394 issued to Gray also discloses a truck transmission 
jack assembly. Once again, the hydraulic cylinder disclosed by Gray 
extends horizontally, rather than vertically, and the hydraulic cylinder 
must be attached to the lifting linkage. No handles are provided as would 
assist the user in properly positioning the jack assembly below the truck. 
In U.S. Pat. No. 4,570,905 to Gerstner, a floor jack assembly for removing 
auto differentials is disclosed wherein a conventional wheeled floor jack 
is provided with a platform for supporting differentials. The platform 
includes a flange which supports a pair of arms each provided with a post 
adapted to be inserted through a bolt-receiving opening of a differential 
housing. 
U.S. Pat. No. 4,899,985 to Good discloses a castered low profile lift 
device incorporating a hydraulic bottle jack for raising and lowering a 
lift head. However, the lift head is raised and lowered by a single lift 
arm which is subject to lateral sway, as well as tilting at higher 
elevations. 
While many of the jacking devices described above employ pivoting 
parallelogram structures to maintain the lifting cradle relatively 
horizontal, the parallel arms which form the parallelogram are typically 
positioned closely adjacent to one another. Indeed, in many cases, both of 
the arms forming the parallelogram are pivotally secured to the base at 
pivot points that are closely adjacent to one end of the base. As the load 
is raised, the center of gravity of the combined jack and load comes 
dangerously close to one end of the base. The present applicant has found 
that greater stability is achieved when the arms forming the pivoting 
parallelogram are spaced further apart from one another. 
Accordingly, it is an object of the present invention to provide a truck 
transmission jack which is capable of assuming a relatively low profile 
near the ground when collapsed while being capable of being elevated to an 
extended height without becoming unbalanced or unstable. 
It is another object of the present invention to provide such a truck 
transmission jack which allows a user to safely and easily support truck 
transmissions, gear boxes, and the like, without fear that the supported 
component will twist, rotate, and/or fall off of the jack and injure the 
user. 
It is yet another object of the present invention to provide such a truck 
transmission jack that is adapted to use a lifting mechanism for raising 
and lowering the supporting cradle of the jack, wherein the lifting 
mechanism is easily replaceable at relatively little cost in the event 
that the hydraulic lifting mechanism should fail. 
Still another object of the present invention is to provide such a truck 
transmission jack which is easily adjusted to fit and safely support the 
contour of a wide variety truck transmissions, gear boxes, and the like. 
A further object of the present invention is to provide such a transmission 
jack which is capable of supporting and maintaining the load in an 
elevated position for servicing without maintaining pressure upon the 
hydraulic lifting system of the jack. 
A yet further object of the present invention is to provide such a 
transmission jack wherein the supporting arms that support the lifting 
cradle are spaced sufficiently far apart from one another to evenly 
distribute the weight of the load across the base and to provide a stable 
support for the lifting cradle. 
A still further object of the present invention is to provide such a truck 
transmission jack which is strong, sturdy, safe, easily operated, and 
inexpensive to manufacture. 
These and other objects of the present invention will become more apparent 
to those of skill in the art as the description of the present invention 
proceeds. 
SUMMARY OF THE INVENTION 
Briefly described, and in accordance with a preferred embodiment thereof, 
the present invention relates to a lifting device for supporting 
transmissions, gear boxes, differentials, and the like, and including a 
wheeled base for allowing the lifting device to be moved into a desired 
position under a vehicle. The device includes a cradle supported by the 
wheeled base and adapted to be raised and lowered for engaging and 
supporting the underside of a transmission, gear box, or the like. First 
and second support arms extend parallel to each other along opposing sides 
of the base and are pivotally coupled at their first ends to the base 
along a first pivot axis. The opposing second ends of the first and second 
support arms are pivotally coupled to the cradle along a second pivot 
axis. 
A hydraulic jack is supported in an upright, vertical position upon the 
base, and includes a piston rod selectively extendable upwardly therefrom. 
A lifting member, which may be in the form of a yoke, is engaged by the 
piston rod for being raised and lowered thereby. The lifting member is 
pivotally coupled to both the first and second support arms along a third 
pivot axis located generally between the first pivot axis and the second 
pivot axis. 
A third support arm is provided to help transfer and distribute the weight 
supported by the cradle, and to help maintain the cradle in a generally 
horizontal position. The third support arm extends generally parallel to, 
but spaced apart from, the first and second support arms. A first end of 
the third support arm is pivotally coupled to the base along a fourth 
pivot axis, and the opposing second end of the third support arm is 
pivotally coupled to the cradle along a fifth pivot axis. To enhance the 
stability of the lifting device, the fourth pivot axis of the third 
support arm is spaced apart from the first pivot axis of the first and 
second support arms. Moreover, the first and fourth pivot axes are 
positioned on opposite sides of the third pivot axis, where the lifting 
force is applied, to more evenly distribute the weight born by the cradle 
across the wheeled base. Preferably, the third support arm pivots through 
a vertical plane that is centered between the first and second support 
arms. 
Within the preferred embodiment of the present invention, the hydraulic 
jack is a conventional, inexpensive, manually-operated bottle jack. The 
lifting member is preferably in the form of a yoke that includes an upper 
horizontal member for being engaged by the piston rod, and including two 
opposing downwardly depending side members extending along opposing sides 
of the bottle jack. The lower ends of the downwardly depending side 
members are pivotally coupled to the first and second support arms along 
the third pivotal axis. The bottle jack is removably placed between the 
wheeled base and the upper horizontal member of the yoke, and is easily 
removed for service or replacement. 
The lifting device of the present invention allows the first, second, and 
third support arms to fall under the force of gravity to a substantially 
horizontal position when the hydraulic jack piston rod is retracted in 
order to permit the lifting device to assume a low profile when collapsed. 
In order to safely support a wide variety of transmissions, gear boxes and 
the like, the cradle of the lifting device includes a generally 
rectangular frame having first and second opposing side members and first 
and second opposing end members. The aforementioned first and second 
support arms are pivotally coupled to the first and second opposing side 
members, respectively, along the second pivotal axis. The cradle 
preferably includes a first support bar secured above the first end member 
and a second support bar secured above the second end member; each of the 
first and second support bars are adjustable in height relative to their 
respective end members in order to adapt to transmissions or gear boxes of 
different shapes and sizes. At least one of the support bars may 
advantageously include holes formed therein for receiving locating pins 
used to help support a transmission or gear box. 
Apart from the support provided by the first and second support bars, the 
central portion of the load can also be supported by including an 
additional support bar that is slidingly supported from one of the side 
members of the cradle. The sliding support bar may be used to support a 
locator bolt for assisting in the support of a transmission or gear box. 
The sliding support bar preferably includes a plurality of spaced holes 
formed therein for supporting the locator bolt at a number of different 
positions along the sliding support bar. In order to facilitate sliding 
movement of the sliding support bar along the side member of the cradle, a 
collar extends about and is slidingly engaged with a side member of the 
cradle. The collar may include a clamp bolt for selectively locking the 
collar against further sliding movement along the side member of the 
cradle. 
The cradle is easily adapted to support rear end differentials by securing 
one or more fastening arms to the cradle. Each fastening arm has a hole 
formed therein for receiving a bolt used to releasably secure a 
differential casing, or other truck component, to the cradle. 
The preferred embodiment of the present invention includes handles secured 
to opposing ends of the wheeled base for allowing a user to easily 
position the lifting device at a desired location below the truck and/or 
to pull the lifting device away from the vehicle after the component to be 
serviced has been removed. As indicated above, the hydraulic jack is 
preferably a conventional bottle jack, which includes a pump lever 
extending from a peripheral portion of the wheeled base for allowing a 
user to pump hydraulic fluid in order to extend the piston rod for raising 
the cradle. While a handle is preferably secured to the wheeled base 
proximate the hydraulic jack, such handle is spaced apart from the pump 
lever of the hydraulic jack to avoid interference with the operation of 
the pump lever by the user.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring collectively to FIGS. 1-3, a lifting device in the form of a 
truck transmission jack is designated generally by reference numeral 20. 
Jack 20 is adapted to be used for supporting transmissions and gear boxes 
of trucks and other vehicles, including removal and installation of 
transmissions, rearends, and gearboxes for large, eighteen-wheel trucks. 
Jack 20 includes a wheeled base 22 for allowing jack 20 to be moved into a 
desired position under a vehicle (not shown). Wheeled base 22 includes a 
generally rectangular frame 24 formed of two-inch square by 1/4-inch thick 
steel tubing welded at the corners for structural strength. In the 
preferred embodiment, frame 24 measures approximately 14 inches wide by 42 
inches long. Frame 24 is supported only one or two inches off the ground 
to permit clearance over hoses and tools while minimizing the collapsed 
height of jack 20. The wheeled base 22 also includes four ball bearing 
caster wheels 26, 28, 30 and 32 having neoprene tires supported in steel 
frames. Each of wheels 26-32 is capable of swivelling 360 degrees, thereby 
permitting mobility in any direction. Each of wheels 26-32 is preferably 
rated at 600 pounds capacity in order to support heavy loads. Moreover, 
because such wheels have neoprene tires, rather than conventional steel 
caster wheels, jack 20 can more easily be maneuvered over debris, hoses, 
or irregularities in the surface on which jack 20 is supported, even when 
under load. 
Wheels 26-32 are preferably arranged to provide a 27-inch wide wheel track, 
and a 33-inch long wheel base, in order to provide a highly stable, yet 
easily maneuverable transmission jack. It will be noted that caster wheels 
30 and 32 are spaced a short distance from the end of frame 24, which 
explains why the wheel base is slightly shorter than the length of frame 
24. Each caster wheel is secured by four carriage bolts to an overlying 
inverted U-shaped steel channel member, such as channel member 34 to which 
caster wheel 28 is attached. In turn, each channel member is welded to the 
upper end of a one-half inch thick vertical plate, the lower end of which 
is welded to rectangular frame 24; for example, channel member 34 is 
welded to the upper end of vertical plate 36. This form of construction 
provides a strong attachment of caster wheels 26-32 to frame 24 while 
maintaining frame 24 relatively close to the ground to minimize the 
profile thereof. 
Jack 20 also includes a cradle 38 for engaging and supporting the underside 
of a transmission or gear box. Cradle 38 includes a generally rectangular 
frame 40 formed of two-inch square by 1/4-inch thick steel tubing welded 
at the corners to provide a strong support for heavy loads. In the 
preferred embodiment, frame 40 measures approximately 19 inches wide by 24 
inches long. Frame 40 includes a pair of opposing side members 39 and 41, 
as well as opposing end members 43 and 45. Cradle 38 includes additional 
components secured to frame 40, the nature of which will be described in 
greater detail below. Still referring to FIGS. 1-3, jack 20 includes first 
and second support arms 42 and 44 which generally extend parallel to each 
other generally along opposing sides of frame 24. Each of support arms 42 
and 44 is formed primarily of two-inch square by 1/4-inch thick steel 
tubing. Each of support arms 42 and 44 has a lower end that is formed by 
two opposing parallel diamond-shaped vertical plates welded to opposing 
faces of the lower end of the aforementioned square tubing. For example, 
referring to FIG. 3, support arm 44 includes a pair of opposing diamond 
shaped steel plates 46 and 48 welded to opposing faces of the lower end of 
square steel tube 50. Support arm 44 is pivotally coupled to wheeled base 
22 along a first pivot axis coincident with attachment bolt 52 visible in 
FIG. 3. 
More specifically, bolt 52 pivotally couples vertical plates 46 and 48 to a 
section of square tubing 54 extending upright from, and welded to, a rear 
corner of frame 24. Likewise, vertical plates 56 and 58 welded to opposing 
faces of support arm 42 are pivotally coupled by bolt 60 to a section of 
square tubing 62 extending vertically from the opposing rear corner of 
frame 24. Pivot bolts 52 and 60 extend along a common pivot axis. 
The upper end of support arm 42 includes a vertically-directed plate 64 
(see FIG. 2) welded to the upper end thereof. Likewise, the upper end of 
support arm 44 includes a vertically-directed plate 66 (see FIG. 3) welded 
to the upper end of square tube 50. A bolt and nut assembly 68 extends 
through aligned holes formed in plate 64 and side member 41 of frame 40 to 
pivotally couple the upper end of support arm 42 to one side of cradle 38. 
Likewise, bolt and nut assembly 70 pivotally couples the upper end of 
support arm 44 to the opposing side member 39 of cradle 38. Bolt 
assemblies 68 and 70 extend along a common pivot axis. 
Jack 20 includes a third support arm 72, which may also be formed of square 
steel tubing. The lower end of third support arm 72 is pivotally coupled 
to wheeled base 22. More 8 specifically, the lower end of third support 
arm 72 has a hole extending through both opposing side walls thereof; a 
cross bar 74 formed of square steel tubing is welded to the sides of frame 
24, and a pair of spaced vertical plates 77 and 79 are welded to cross bar 
74 to form a hinge with the lower end of third support arm 72 centered 
between the sides of frame 24. A pivot bolt and nut assembly 76 extends 
horizontally through holes formed in hinge plates 77 and 79 aligned with 
the holes formed in the lower end of support arm 72 to form a pivotal 
connection along a pivot axis coincident with bolt and nut assembly 76. It 
should be noted that this pivot axis is generally centrally located along 
the length of frame 24, whereas the pivot axis for support arms 42 and 44, 
corresponding to pivot bolts 52 and 60, is located at one end of frame 24. 
It will also be appreciated that third support arm 72 rotates through a 
plane that is substantially centered between first and second support arms 
42 and 44. 
The upper end of third support arm 72 is pivotally coupled to cradle 38. 
More specifically, frame 40 includes a vertically extending, U-shaped 
channel member 80 welded at its upper end to the forwardmost end of frame 
40, and wherein channel member 80 opens toward the rear. Bolt and nut 
assembly 82 extends horizontally through aligned holes formed in the upper 
end of third support arm 72 and through the sides of channel member 80 to 
form a pivotal connection between the upper end of support arm 72 and 
cradle 38, and having a pivot axis coincident with bolt and nut assembly 
82. 
Those skilled in the art will appreciate that third support arm 72 extends 
substantially parallel to first and second support arms 42 and 44 even 
when cradle 38 is raised or lowered. Accordingly, support arms 42, 44 and 
72 form a parallelogram structure which maintains cradle 38 essentially 
horizontal irrespective of the elevation of cradle 38. It will also be 
appreciated that the pivot axis for support arm 72 is spaced apart by a 
significant distance from the pivot axes for support arms 42 and 44, 
thereby providing a more even distribution of weight born by cradle 38 
across wheeled base 22. 
Jack 20 also includes a mechanism for raising and lowering cradle 38. To 
this end, a standard automotive hydraulic bottle jack 84 is supported upon 
wheeled base 22. Bottle jack 84 is preferably a ten-inch, twelve-ton 
capacity hydraulic jack of the type commercially available from Heim 
Warner. A support base for bottle jack 84 is provided by welding two 
sections 86 and 88 of two-inch angle iron between the sides of frame 24, 
the vertical flanges of such angle iron sections 86 and 88 being spaced 
apart from one another by approximately four inches, and the horizontal 
flanges of such angle iron sections extending toward one another in a 
common plane coincident with the lower face of frame 24. In this manner, a 
platform is provided for supporting bottle jack 84, such platform being 
located only one or two inches above the ground. 
Hydraulic bottle jack 84 includes a piston rod 90 which can be 
hydraulically extended vertically from the base of bottle jack 84 when 
lever arm 92 (see FIG. 3) is pumped. Lever arm 92 extends from a 
peripheral portion of wheeled base 22 proximate the rear end thereof for 
allowing a user to pump hydraulic fluid, and thereby extend piston rod 90. 
In order to transfer the upward lifting force of piston rod 90 to cradle 
38, a lifting tower 94 is provided. As shown best in FIG. 3, lifting tower 
94 is in the form of a yoke that includes an upper member 96 for being 
engaged by the piston rod, and that includes two opposing downwardly 
depending side members 100 and 102 extending along opposing sides of 
hydraulic bottle jack 84 and pivotally coupled to the first and second 
support arms 42 and 44. Upper member 96 is preferably a central, 
horizontally-extending, steel channel section having an inverted-U shape. 
Welded to, and extending downwardly from, channel section 96 is a short 
stub 98 of one and 1/2-inch square tube opening downwardly and forming a 
pocket for receiving the uppermost load-bearing flange of piston rod 90. 
Side members 100 and 102 of lifting tower 94 are preferably formed of first 
and second steel bars which extend downwardly from channel section 96 on 
opposing sides of bottle jack 84. As shown best in FIG. 1, a pivot bolt 
and nut assembly 104 extends through aligned holes formed in vertical bar 
100 and plates 46 and 48 of support arm 44 to form a pivotal connection 
therebetween along a lifting pivot axis defined by bolt 104. Likewise, 
referring to FIGS. 1 and 2, a pivot bolt and nut assembly 106 pivotally 
couples vertical bar 102 to plates 56 and 58 at the lower end of support 
arm 42 along a lifting pivot axis coincident with bolt 106. Bolts 104 and 
106 lie along a common lifting pivot axis; this common lifting pivot axis 
lies generally between the pivot axis for the lower end of support arms 42 
and 44 (i.e., bolts 52 and 60) and the pivot axis at the upper ends of 
support arms 42 and 44 (i.e., bolts 68 and 70). Moreover, it should be 
noted that the pivot axis for the lower end of support arms 42 and 44 
(i.e., bolts 52 and 60) and the pivot axis for the lower end of third 
support arm 72 (i.e., bolt 76) are spaced apart from one another and lie 
on opposite sides of the common lifting pivot axis (i.e., bolts 104 and 
106) to more evenly distribute weight born by the cradle across the 
wheeled base 22. 
As hydraulic bottle jack 84 is manually pumped by lever 92 to raise piston 
rod 90, lifting tower 94 is elevated, which in turn raises vertical bars 
100 and 102. This lifting force is transferred by pivot bolts 104 and 106 
to support arms 42 and 44, causing such support arms 42 and 44 to pivot 
about pivot bolts 52 and 60, and thereby raising cradle 38. Third support 
arm 72 follows the angular elevation of support arms 42 and 44 as cradle 
38 is raised, thereby maintaining cradle 38 in a horizontal position. 
Alternatively, when the release valve (not shown) of hydraulic bottle jack 
84 is opened, piston rod 90 retracts back into jack 84 under the weight of 
cradle 38 and any load supported thereby, while support arms 42, 44, and 
72 drop from an elevated to a lowered position. 
As seen best in FIG. 2, the common lifting pivot axis (i.e., bolts 104 and 
106) is preferably located at a lower elevation than the pivot axis for 
the lower end of support arms 42 and 44 (i.e., bolts 52 and 60), in order 
to help maintain a low profile when jack 20 is collapsed. In addition, the 
above-described method of pivotally securing support arms 42, 44 and 72 to 
wheeled base 22 allows such support arms to extend substantially 
horizontally when piston rod 90 of hydraulic bottle jack 84 is retracted 
in order to permit jack 20 to assume a low profile when collapsed. 
Hydraulic bottle jack 84 is easily replaced or removed for servicing. The 
user need only raise cradle 38 by hand when cradle 38 is not under load, 
thereby causing lifting tower 94 to rise above piston rod 90. Bottle jack 
84 may then be simply lifted from wheeled base 22 for servicing or 
replacement. 
Wheeled base 22 preferably includes a horizontally disposed handle 108 
extending from the front end of frame 24 of wheeled base 22 to aid in 
maneuvering jack 20. In addition, wheeled base 22 includes a pair of 
vertically extending handles 110 (see FIG. 2) and 112 (see FIG. 3) secured 
to vertical tubing sections 62 and 54, respectively. By providing handles 
at both the front and rear ends of jack 20, a user can more easily 
position jack 20 below a vehicle in a desired position. In addition, while 
vertical handles 110 and 112 are disposed generally near hydraulic jack 
84, handles 110 and 112 are spaced sufficiently far from bottle jack lever 
92 (see FIG. 3) that they do not interfere with the up and down pumping 
motion of lever 92 when cradle 38 is being raised. Nonetheless, handles 
110 and 112 extend outwardly as far as pump lever 92, and thereby help to 
protect pump lever 92 against damage which might otherwise result were 
jack 20 to be wheeled against a wall or other obstacle. Moreover, handles 
108, 110 and 112 are sufficiently spaced above the floor and from the 
caster wheels to avoid pinching the mechanic's fingers during operation. 
As indicated above, in those instances when the transmission or other load 
is to be supported upon jack 20 for extended periods of time, it is 
desirable from a safety standpoint to relieve the hydraulic pressure on 
bottle jack 84. Accordingly, a so-called "stiff leg", or safety bar, may 
be provided to lock cradle 38 at various elevations even when hydraulic 
pressure is relieved from bottle jack 84. Referring to FIG. 1, stiff leg 
113 is provided in the form of a steel tube having a first end pivotally 
connected to support arm 42. The opposing second end of stiff leg 113 
includes a telescoping detent member 115 which can be retracted or 
slightly extended via a clamp knob 117. A series of holes 121 are formed 
in rectangular frame 24 along the side member thereof proximate support 
arm 42. Cradle 38 may easily be locked at an elevated position by pivoting 
stiff leg 113 downwardly toward frame 24 and engaging detent member 115 
with one of the holes 121 formed in frame 24. Stiff leg 113 provides an 
added safety feature against inadvertent collapse of jack 20 should bottle 
jack 84 fail. When not in use, stiff leg 113 can be retained in a stored 
position by engaging detent member 115 with a retaining pocket 123 welded 
to the underside of support arm 42. 
Cradle 38 provides features which permit it to safely and securely support 
a wide variety of transmissions, gearboxes, differentials, and other truck 
components. Support bar 114 is secured to the front end of cradle 38, and 
support bar 116 is secured to the opposing rear end of cradle 38. Support 
bar 114 is a section of square steel tubing; upwardly protruding lips 118 
and 120 are welded to each end of support bar 114 to prevent a load from 
sliding off of support bar 114. Likewise, lips 122 and 124 are welded to 
support bar 116. 
The elevation of support bar 114 relative to cradle 38 can be adjusted. A 
pair of threaded bolts 126 and 128 extend upwardly through end member 43 
of rectangular frame 40 and are threadedly engaged therewith. The extreme 
ends of bolts 126 and 128 are not threaded, but are smooth, and extend 
within receiving holes drilled within the underside of support bar 114. 
The heads of bolts 126 and 128 are accessible below end member 43 and can 
be rotated with a wrench to raise or lower support bar 114. Similar bolts 
130 and 132 are used to adjustably determine the height of support bar 116 
above end member 45 of frame 40. Thus, bolts 126, 128, 130, and 132 allow 
support bars 114 and 116 of cradle 38 to be adjusted to various elevations 
to adapt to transmissions or gear boxes of different shapes and sizes 
without requiring wood spacers, shim blocks, or other less safe devices 
for making such adjustments. 
To further adapt cradle 38 to different loads, support bar 114 has a series 
of holes 134 and 136 formed therein upon the upper face thereof. Likewise, 
support bar 116 has a series of holes 138 and 140 formed therein upon the 
upper face thereof. As shown in FIG. 1, one or more locating pins 142 can 
be inserted into holes 134, 136, 138, and 140 to engage various supporting 
surfaces of the transmission or gearbox. 
Apart from end support bars 114 and 116, one or more central support bars 
may also be provided upon cradle 38 to adapt to loads of different 
configurations. A first central support bar 144 is shown in FIGS. 1 and 5, 
and includes a square tubular collar 146 having inner dimensions 
commensurate with the outer dimensions of side member 39 of cradle frame 
40. Collar 146 is slidingly engaged with side member 39 for allowing 
support bar 144 to be slidingly supported thereby. A clamp bolt 148 is 
threadedly engaged with a threaded hole formed in the lower face of collar 
146. Clamp bolt 148 serves as a locking mechanism for selectively locking 
collar 146 against further sliding movement along side member 39 once 
collar 146 is positioned in a desired location. 
As indicated in FIGS. 1 and 5, a series of holes, such as hole 150, are 
formed in the upper and lower faces of support bar 144. A locating bolt 
152, made of hardened steel, may be inserted into and threadedly engaged 
with any one of such holes 150 in order to support locating bolt 152 at a 
plurality of positions along support bar 144 to aid in supporting the 
transmission or other load. The height of locating bolt 152 can be 
adjusted by rotating the head of the bolt with a wrench. As indicated in 
FIG. 5, the threaded engagement between the hole 150 and locating bolt 152 
can be made via a threaded nut 154 disposed within support bar 144. A 
similar central support bar 156 is provided with a collar 158 engaged with 
the opposing side member 41 of cradle frame 40. Collar 158 can be locked 
via clamp bolt 160, and support bar 156 can be used in conjunction with a 
similar locating bolt 162 which can be adjusted as to longitudinal 
position, lateral position, and height, in accordance with the 
transmission or other load to be supported. 
Cradle 38 is easily configured to support differentials, or rear ends. As 
shown in FIGS. 1, 3, and 4, cradle 38 includes a pair of arms 164 and 166 
secured to the forward end member 43 or cradle frame 40. Arm 164 has a 
slot 168 formed therein, and attachment bolt 170 extends through slot 168 
and secures arm 164 to frame 40. When not in use, arm 164 can be pivoted 
to extend horizontally, as shown in FIG. 1. However, when jack 20 is to be 
used to support a differential assembly, arm 164 is pivoted to extend 
upwardly. Bolt 170 can be loosened to permit arm 164 to be raised or 
lowered via slot 168 before retightening bolt 170. The end of arm 164 
opposite attachment bolt 170 has a hole 172 formed therein; arm 166 has a 
similar hole 174. As shown in FIG. 4, a bolt 176 is extended through hole 
174 of arm 166 and into the casing 178 of the differential in order to 
help releasably secure the differential upon cradle 38 of jack 20. 
Those skilled in the art will now appreciate that a simple and inexpensive 
truck transmission jack has been described which is adapted to maintain a 
low profile when collapsed, but which is capable of being extended to a 
significant elevation without becoming unsafe or unstable; using the 
dimensions specified herein, the present inventor has constructed such a 
jack which can position the cradle at an elevation anywhere between 9 
inches and 36 inches above the ground without becoming unstable under 
load. The transmission jack is capable of using a standard vertical 
hydraulic bottle jack that is easily removable for servicing or 
replacement. The support arms are spaced sufficiently apart from one 
another to evenly and safely distribute weight born by the cradle to the 
underlying wheeled base. The handles allow easy maneuverability of the 
transmission jack without interfering with the operation of the bottle 
jack pump lever. Finally, the cradle is easily adjustable to match the 
contour of a wide variety of transmissions, gear boxes, differentials, 
without requiring chains to secure the load to the cradle. 
While the present invention has been described with respect to the 
preferred embodiment thereof, such description is for illustrative 
purposes only, and is not to be construed as limiting the scope of the 
invention. Various modifications and changes may be made to the described 
embodiment by those skilled in the art without departing from the true 
spirit and scope of the invention as defined by the appended claims.