Differential Rear End Restoration Revised 2014
Differential Rear End Restoration Revised 2014
Differential Rear End Restoration Revised 2014
Spring Spreader
1
The Model A Ford Differential:
The rebuilding of the Model A Ford differential, in addition to replacing worn or damaged parts, should
take into consideration three distinct adjustments. First: the carrier bearing pre-load. Second: the
pinion bearing pre-load. Third: the ring & pinion gear backlash. Each of these adjustments is described
in this procedure.
2
Torque tube roller bearing race and seal removal: (Photo P-1)
To remove the seal in the torque tube, the race for the front roller bearing has to come out first. Both are
removed at the same time with a very simple technique. Stand a drive shaft up vertically with the threaded
end resting on a block of wood. Place a 1-1\16 inch, six point, 1/2 drive socket over the spline end of the
drive shaft. Slide the torque tube down over the drive shaft until it seats against the end of the socket. Hold
the torque tube in a vertical position and gently bounce it up and down until the socket pushes the grease
seal and roller bearing race out the end of the torque tube. It is best to hold a rag loosely over the end of the
torque tube during the process to capture the seal, bearing race, and socket as they exit the torque tube.
Photo P-1. Removal of the bearing sleeve and grease seal: The sleeve is at the top
followed by the grease seal, then the socket. All are sitting on top of the drive shaft
spline. A 1&1\16", 1\2" drive, six point socket fits over the splines on the end of the
drive shaft.
Axle keys:
Assuming that the rear brake backing plates have been removed from both sides, check that both axle keys
have been removed from the axles. If they are not removed the axle housings will be prevented from sliding
off the axles. Usually they can be pried out with a small screwdriver. For the more stubborn ones, clamp a
portion of the key with a pair of vice grips. Lock it tightly and tap the vice grips with a hammer.
3
Axle housing removal:
Remove the ten 9/16 hex bolts from the left side of the banjo. The left axle housing can now be removed by
pulling it off over the left axle. For the more stubborn housings, tap the end of the axle housing with a brass
hammer to dislodge it from the banjo. Remove the entire axle shaft assembly by taking hold of the left axle
and pulling the whole assembly out from the banjo and the right axle housing. Set the axle shaft assembly
aside and remove the ten 9/16 hex bolts from the right side of the banjo. Remove the right axle housing
from the banjo in the same manner as the left housing was removed. There should be any number of gaskets
on either side of the banjo between the two axle housings. Set both axle housings aside on some newspapers
to allow the residual oil to drain out.
Photo P-2. Mitchell drive shaft puller tool: This tool can be purchased
from the Mitchell Company. When purchasing an overdrive from
them it can be rented.
4
Photo P-3. Tom Endy drive shaft puller tool:
Photo P-4. Pinion gear puller tool: This tool was originally sold by Sears years ago.
Its intended purpose was for the removal of the flywheel on small lawn mower
engines. The block of steel with the hole was fabricated. A small bearing puller will
also work.
6
Photo P-5. Pinion gear removal: Tension is applied to the puller tool; the end is then
smartly tapped with a hammer. Repeat tightening and tapping with the hammer
until the gear comes off the shaft.
7
Photo P-6. Pinion gear removal: Do not remove the nut when attempting to remove
the gear as it may come off and fly across the room. Once the gear breaks loose from
the taper on the shaft the puller will drop free. Remove the nut then.
8
Photo P-7 Pinion gear removal: Photo 5. Pinion gear removal: Tension is applied to
the puller tool; the end is then tapped smartly with the hammer. Repeat tightening
and tapping until the gear comes off the shaft.
9
Photo P-8. Removal of rear pinion bearing: A shop press is used to press the rear
pinion bearing off the pinion gear sleeve.
10
Photo P-9. K. R. Wilson axle housing race removal tool: The left end of the tool is
placed down into the axle housing and grips the edge of the bearing race. As the nut
is tightened it pulls the race out.
11
Photo P-10. Removal of axle housing bearing race: As the nut is tightened the race is
removed. An impact wrench works very well for this task.
12
Photo P-11. Removal of axle housing bearing race: The axle housing is supported in
the vertical jig for the removal process.
13
Photo P-12. Carrier disassembly: Before beginning the process, center punch both
carrier halves so they can be re-assembled as before. The safety wire is removed and
the nine carrier bolts are removed. When the two carrier halves are separated the
spider gear assembly will drop out and the two axles can be removed. Care should
be taken to not damage the threads on the nine carrier bolts. Do not hammer
aggressively on the threaded ends of the bolts.
14
Photo P-13. The nine carrier bolts have been removed and the two carrier halves
separated and the spider gear assembly drops out: Note the three spider gears are
installed on the three shaft segments of the yoke so that the taper of each gear faces
the center of the yoke. When assembled inside the carrier the three spider gears mesh
with the gear on the end of each axle. When the car is going straight down the road
both axles are turning at the same speed. The spider gear assembly is rotating with it,
but the individual spider gears are stationary. When the car is turned in either
direction one axle speeds up, the other slows down. This is the only time the three
spider gears rotate on their individual shafts.
15
Photo P-14. Carrier bearing removal: A shop press and a bearing removal are used to
press both bearings off. If either or both bearings have spun on the mounting hubs,
the hubs will have to be repaired by knurling or the carrier replaced.
16
Photo P-15. Knurled repair of a carrier bearing hub: Very often the carrier bearing
hubs are found where the bearings have spun on the hubs. Knurling can restore the
carrier half to serviceable use if the material that has been worn away is not severe.
A shim or two may be required to compensate for wear to the bearing stop.
17
Ring & pinion inspection: (Photo P-16)
Check both gears for broken or damaged teeth. Some amount of wear and pitting is not a problem. Legend
has it that the gears were a matched set at the factory. Some speculation is that they are only matched when
they have been run together for some period of time as a set in a car. Often you can find a matching number
on the two gears, but not always. It is prudent to keep them together as a set once removed from the
differential.
Photo P16. Quite often matching numbers are found on an original ring & pinion gear
set where the number is stamped onto the end of the pinion gear and the same number
is found hand written on the back side of the ring gear with an etching tool. This is
found so frequently that I believe this must have been a factory practice when a new
ring and pinion were mated up to go into an assembly.
18
Ring & pinion gear ratios:
There are four different gear ratios available for the Model A Ford differential. The 378:1 ratio is the
standard and is most often found in a differential. The majority of Model A Fords were produced with the
378:1. The 411:1 ratio was used for lower gearing and was generally installed in commercial pick-ups,
station wagons, or other vehicles expected to haul heavy loads or climb steep hills. The 354:1 ratio was an
after market ratio used for higher gearing and became generally available when the nations roads were
greatly improved after the Model A era. The 370:1 ratio was used in the very early 1928 cars that are
generally referred to as an AR car. The physical shape of the 370:1 pinion gear is different than the other
ratios and is not interchangeable. An AR drive shaft is required with the use of the 370:1 ring & pinion gear
set (See appendix D). To determine the ratio of a gear set count the number of teeth on both gears and
divide the smaller number into the larger number.
34 9 3.78:1
37 9 4.11:1
39 11 3.54:1
37 10 3.70:1
Clean up:
Thoroughly clean the inside of the axle housings and banjo. Often there is metal wear particles embedded
inside the axle housings. A wire brush attached to a length of angle iron makes a suitable tool. Pay
particular attention to the area where the grease seal will be installed. Quite often you will find pieces of
metal shims that were used on the tapered axle shaft ends. Remove the grease fittings and clean out the area
where grease is supposed to flow into the wheel bearings from the grease fitting. Clean the torque tube as
well. Clean all the other parts. Bead blasting of the gears, carrier halves, and axles is recommended. If you
do not have a bead blaster in your garage, treat yourself to an evening of wire wheeling.
19
Photo P-17. Original banjo bolts, Quantity 20: Note space between the threads and the
head of the bolt. Lock washers are not used with these bolts. The bolt head has a
unique thickness. The stud at left is one of the alignment studs used to position the
gaskets. The thread size is 3\8-24.
Burr removal:
Run a flat file lightly over the machined surfaces of the axle housing flanges, the three banjo flange
surfaces, and the mating surfaces of the two carrier halves to remove any burrs or high spots.
20
Minimum new parts required:
It is prudent to replace all bearings, seals, and gaskets regardless of the visual condition they appear to be in.
The following parts\price list is taken from Bratton's Antique Auto Parts 2014 catalog.
21
Photo P-18. Vertical assembly jig: The carrier with part of the pre-load tool inside is
inserted into the banjo between the two axle housings. Gaskets are added and
subtracted from only the left side (top) to achieve the correct carrier pre-load. The
other half of the pre-load tool can be seen at the top of the left axle housing.
22
Temporary carrier re-assembly: (Photos P-19, P-20)
Bolt the two carrier halves and ring gear together without the spider gears and without the two axles
installed. Install only the spider yoke, preferably one that has been made into a tool. Torque the nine bolts
and nuts to 35 ft. lbs. Do not safety wire the nuts at this time. Press a new bearing onto each side of the
carrier. Make sure they press tight onto each hub. (See Appendix B and Appendix C)
Photo P-19. Carrier bearing installation; New bearings are pressed onto the hub on
each side of the carrier. They must press on with an interference press fit.
23
Photo P-20. Carrier assembly ready for pre-load setting: Both bearings have been
pressed on. Part of the pre-load tool has been installed in place of the spider gear yoke.
All 9 carrier bolts are torqued to 35 ft. lbs.
24
Photo P-21. Installation of axle housing bearing races: The banjo is used as a platform
to install the bearing races in the axle housing. The banjo is placed on the press rails
and the axle housing is placed down inside.
25
Photo P-22. Installation of axle housing bearing races:
26
Photo P-23. K. R. Wilson axle housing bearing race installation tool: The long shaft is
placed down inside the axle housing with the end fixture at right resting on the
bearing race. The T-handle at left and the shaft guide are installed on the threaded
end of the long shaft. As the T-handle is turned it pulls the race into place. Tapping on
the fixture on top of the race with a hammer will aid in seating the race. Use a dental
mirror to determine that the race is fully seated around the race stop.
27
Photo P-24. Grease seal installation tools: The long tool is used to install the seals in
the both axle housings. The short tool is used to install the seal in the front of the
torque tube. Both tools are made from a length of 1\2" water pipe with the seal tool
threaded onto the end. A seal installation tool can be purchased from most any Model
A supplier.
28
Photo P-25. The grease seal is inserted on the installation tool: Apply a coat of grease
to the seal: The original grease seals were made by a company called Chicago
Rawhide. They will have CR stamped on the side. The actual sealing portion of the
seal was made of leather. New seals are made of neoprene.
29
Photo P-26. Grease seal installed in axle housing: The grease seal is driven into place
with the hammer. When the seal has bottomed out against the stop there will be a
change to the hammer sound as the seal goes in. When it bottoms there will be a
ringing sound. Be certain the seal has bottomed correctly. Run your finger down into
the hub end of the axle housing and feel that the seal is up against the stop.
Temporary re-assembly of the banjo and axle housings: (Photos P-27, P-28, P-29, P-30)
Bolt the right axle housing to the right side of the banjo without any gaskets. Orient the drain hole correctly.
Torque the bolts to 30-35 ft. lbs. Place the assembly in a large wood vise or vertical holding fixture and
orient it so that the assembly is vertical with the left side of the banjo facing up. Lubricate the bearings and
races with 600W oil and place the ring gear and carrier assembly inside the banjo with the ring gear at the
top. Install the left axle housing onto the banjo without any gaskets. Begin tightening the bolts to 35 ft. lbs.
30
Photo P-27. The axle assembly is in the vertical jig for the pre-load setting:
31
Photo P-28. The right axle housing is at the bottom of the jig: The banjo is on top and
properly aligned with the mounting holes in the axle housing flange. It is
recommended that the two axle housings and the banjo be marked for proper
orientation before beginning the process.
32
Photo P-29. Alignment studs are used during carrier pre-load adjustment: The task
is a trial and error effort to determine the total quantity and thickness of banjo
gaskets that will be used on both sides of the banjo during the final assembly.
33
Photo P-30. The left axle housing is on top in the jig with alignment studs installed in
the banjo: The studs will aid in the trial and error process of selecting the quantity
and thickness of banjo gaskets required to set the pre-load.
Carrier pre-load adjustment: (Photos P-31, P-32, P-33, P-34, P-35, P-36, P-37)
Reach in through the pinion opening in the banjo and try to turn the ring gear. It should be locked up tight
before you reach 35 ft. lbs. If it does not, remove the left axle housing and place shims behind either of the
carrier bearings or the axle races. The purpose of the shim is to move the bearings and races closer together
relative to the position of the junction of the banjo and axle housings. If you cannot lockup the ring gear you
will never be able to achieve the desired carrier pre-load. The installation of the shims is a trial and error
effort. After adding shims, bolt the left axle housing on again and check if you are able to lock up the
movement of the ring gear. Once you have achieved this, remove the left axle housing and install a number
of banjo gaskets between the banjo and the left axle housing. A very helpful tool is to obtain a length of 3\8-
24 threaded stock and cut ten 2-inch long studs to be used as guides when installing banjo gaskets. Continue
adding and subtracting gaskets until you can move the ring gear with your finger, or can measure 20-in. lbs.
on a dial indicator using the spider yoke tool (See Appendix B, carrier pre-load tool). This is also trial and
error effort. If you are adjusting by feel, the ring gear should turn with some amount of force from your
finger. If you cannot turn it, it is too tight, if it spins free, it is too loose. The correct pre-load is somewhere
in between. Once you are satisfied with the pre-load, remove the left axle housing and the gaskets and set
the gaskets aside. It is a good idea to write down the number and thickness size of each of the gaskets.
During the final assembly the total quantity of these gaskets will be used on the two sides of the banjo. The
34
determination of how many on each side will be done later when the backlash adjustment is performed.
Remove the carrier and both axle housings from the banjo.
Photo P-31. Carrier pre-load adjustment without axle shafts and spider gears
installed: During the pre-load process you can reach your finger in through the banjo
torque tube flange and turn the ring gear. This will give you a ballpark indication that
you are zeroing in on the pre-load. If the ring gear is locked or difficult to turn more
gaskets will need to be added. With zero gaskets installed the ring gear should lock up.
By adding gaskets the ring gear will become free to turn.
35
Photo P-32. Carrier pre-load adjustment: Add and subtract banjo gaskets on the left
(top) side when the banjo is installed. Note the carrier half markers. These punch
marks were in place when the rear axle assembly was taken apart. Center punch
marks should not be made over the tunnel for any of the 9 carrier bolts as it will make
it difficult to remove the bolt. Add the punch marks below and above the end of any of
the three spider yokes.
36
Photo P-33. The carrier pre-load measuring tool is inserted into carrier spider tool:
The left axle housing has been removed to show that the pre-load tool shaft passes
through the left axle housing and into the carrier where it threads into the modified
spider gear yoke inserted between the two carrier halves. Turning the threaded shaft
will rotate the entire carrier and ring gear assembly. The pre-load on the two bearings
can them be read from a dial indicator torque wrench.
37
Photo P-34. Dial indicator torque wrench measuring carrier bearing pre-load: The
desired measurement is 20 inch pounds.
38
Photo P-35. Dial indicator reading 20 inch pounds of torque:
39
Photo P-36. Carrier bearing pre-load measuring tool: The modified spider gear yoke
is temporarily installed in the carrier to accept the threaded shaft. The shaft turns the
carrier and the torque reading is taken off the hex nut at the right end of the shaft.
40
Photo P-37. Carrier bearing pre-load measuring tool: The spider gear yoke has been
modified with a threaded hole that will accept the end of the threaded shaft.
41
Photo P-38. Installation of the banjo double bearing pinion race: The inside of the
banjo where the race stop is located should be supported when pressing in the new
double race. Placing the bottom of the banjo on the press platform will cause the
banjo to become deformed.
42
Photo P-39. Installation of banjo double bearing pinion race: Note the inside of the
banjo is being supported at the back side of the race stop with a discarded banjo race
with a small block of steel on top of it (not visible).
43
Photo P-40. Installation of pinion gear rear bearing: The bottom (rear) bearing is
pressed on with an interference fit. The pinion sleeve should have (an original does)
two different dimensions on the sleeve of the gear. The dimension for the front bearing
is slightly smaller to allow the bearing to be able to be snugly maneuvered during
preload adjustment. The rear bearing should slide over the area of the first bearing
before it encounters the second dimension where it will press on with an interference
fit. Many reproduction pinion gears do not have the two dimensions on the sleeve and
this will make it very difficult to achieve proper pinion bearing preload.
Reproductions with only one dimension should have the area for the front bearing
turned down slightly before installation is attempted. The difference in the two
dimensions is .0015".
44
Photo P-41. Two large Ford factory pinion nut wrenches:
45
Photo P-42. Adjustment of pinion bearing pre-load: The inboard nut is held with the
wrench on the left locked against the workbench. The nut on the right is used to
tighten the outboard nut up against the inboard nut to lock it in place. A pipe wrench
is also used to hold the drive shaft from turning. This can be accomplished by one
person. The pre-load setting can increase as the nuts are tightened. For this reason the
pre-load should be set lower than 20 inch pounds initially before tightening the
outboard nut. This is a trial and error effort and it can be frustrating. This is the
reason there should be two dimensions on the pinion gear sleeve so that the front
(outboard) bearing can snugly slide back and forth as required to set the pre-load..
46
Photo P-43. Adjustment of pinion bearing pre-load: The adjustment of this pinion
pre-load is being done with a Mitchell stub shaft installed. In this case duct tape was
applied to the spline on the end of the shaft and a 36mm socket was pushed on over
the end of the shaft. A 1&1\16" six-point socket is used over the end of a standard
Model A drive shaft to set the pre-load.
Backlash adjustment:
The backlash adjustment is best done before the axles are installed in the carrier. Reassemble the banjo and
axle housings as before with the carrier inside. Place all of the banjo gaskets previously selected on the two
sides of the banjo temporarily with an educated guess. This will also be a trial and error effort. The backlash
adjustment is made by shifting the number of banjo gaskets between the right side of the banjo and the left
side of the banjo. These are the quantity and thickness of gaskets that were previously determined to be
required to set the pre-load on the carrier bearings. The more gaskets installed on the right side of the banjo,
the less backlash there will be. The more gaskets installed on the left side of the banjo, the more backlash
there will be. The gaskets are essentially moving the ring gear laterally in relationship to the fixed position
of the pinion gear. Use only the gaskets previously determined during the carrier pre-load adjustment. Do
not add or subtract any gaskets. Some books say that backlash can be as great as .020, other say that .010 is
the max. The desired backlash is sometimes difficult to achieve since you are working with a fixed number
of gaskets as determined by the carrier pre-load adjustment. You also do not want to end up with no gaskets
at one side of the banjo or you will have an oil leak. Generally you may end up with more backlash than
you want. This is usually due to the wear in a used ring & pinion gear set, and it cannot be avoided. You
47
also do not want to end up with no backlash. When that is the case the gears are bottoming out and are
binding. Always provide at least some amount of backlash in the gears. You can also experiment by moving
any shims you placed under the bearings or races from side to side. The backlash adjustment is the least
critical of all the adjustments but it can be very tedious and time consuming, as you will be taking the
assembly apart numerous times. The end result should be some amount of play as you rotate the drive shaft
back and forth slightly by hand to feel the amount of space between the gears. This is called backlash. Once
the backlash has been achieved disassemble the banjo and axle housings and make a note of the number and
quantity of banjo gaskets that will be placed on the two sides of the banjo during the final assembly.
Photo P-44, The two carrier halves are re-assembled with both axles and the spider
gears installed.
48
Photo P-45. Final assembly of carrier: The axle shafts and spider gears are installed:
The 9 bolts are torqued to 35 ft. lbs. and safety wired. Rotate both axles by hand in
opposite directions to ensure there is no binding. Note: Some reproduction axles will
bind inside the carrier because they are made incorrectly.
49
Photo P-46. The nine carrier bolts are torqued to 35 ft. lbs. and safety wired.
50
Photo P-47. Indian head gasket Shellac compound is recommended for use on the
banjo gaskets. Coat each side of all gaskets used during final assembly.
Photo P-48. Installation of torque tube roller bearing race: Squeeze the sleeve slightly
in the vice to bring the split together. Wrap safety wire around it. Put a chalk mark on
the top edge right above the dimple. Note dimple on the lower right side of the sleeve.
52
Photo P-49. The K. R. Wilson tool is used to remove and install the bearing race sleeve
in the torque tube: This is an alternate option if the tool is available.
53
Photo P-50, Safety wire the torque tube: There are a number of safety wire
techniques. It is unknown to me how Henry did it. Most I have seen were a sloppy
zigzag technique. My method is to form a perfect circle that looks very neat. This
requires that the wire holes in the head of the bolt be lined up correctly. To achieve
this I have a sufficient quantity of original torque tube bolts that are installed on a
trial and error basis to line the bolt holes up properly and have the bolts tight.
54
Painting:
The entire assembly (axle housings, banjo, and torque tube) should be painted gloss black as a unit when it
is completely assembled. This includes painting of the 20 banjo bolts, the 6 torque tube bolts, and the safety
wire installed through the torque tube bolts. I leave the speedometer housing off until the rear axle assembly
is painted.
Remember to put 600W oil in the banjo
It is prudent to hang a tag on the assembly with the following notation: leave the tag in place until the
assembly is installed in the car and is oil serviced.
55
Appendix A
Differential Assembly Fixture
The vertical mounting fixture:
The rebuilding of a Model A Ford differential is better accomplished if it can be mounted in some type
of vertical fixture. The right axle housing is clamped in the fixture. The banjo and the left axle housing
can be installed and removed with little effort. After both pre-loads and the backlash adjustments have
been accomplished the differential is completely assembled in the fixture minus the torque tube. Directly
above the fixture is a small electric hoist used to lift the differential out of the fixture and set down into
the differential cradle tool. The differential shown in the photo has the carrier pre-load tool inserted in
the top of the left axle housing.
56
Appendix B
Carrier Bearing Preload Tool
How to make the tool:
A carrier pre-load adjustment tool can be made from a discarded spider yoke, part number A4211. Drill a
hole through the center with it mounted on a lathe. It is important to have the hole perfectly perpendicular to
the three gear shafts on the spider yoke. Tap the hole was for a 3/8-16 thread. Obtain a three-foot length of
threaded stock from a local hardware store; make certain it is perfectly straight. Also purchased three hex
nuts. Make an aluminum insert plug on a lathe with a flange on it that will fit snugly into the opening of the
axle housing where the axle protrudes out. Drill a hole in the center of the plug to allow the threaded stock
to slide through smoothly. Cut the threaded stock to a length of 31". Chamfer one end and run a hex nut on
about one inch from the end and tack weld in place. Slide the threaded stock through the insert flange and
Install the other two hex nuts on the opposite end of the threaded stock and lock them together.
Carrier yoke (A4211) tool Insert and threaded shaft The complete tool
57
Appendix C
Differential Carrier (Early & Late)
Description:
The differential carrier is the device the ring gear is bolted to and it is located inside the rear axle
assembly. There are two halves to the carrier assembly. Inside the two halves is located the three spider
gears and the gear end of each rear axle. There are nine carrier bolts and nuts that hold the two halves
together. There is an early version and a late version. Either can be interchanged as a complete
assembly.
Early Carriers:
The early carriers used at the beginning of production are identical halves. Each half is the same part
number A-4205. The ring gear can be installed on either half. Where the two halves join together the mating
surfaces are not notched. They join together flush with one another. The nine bolts have a half round domed
head. The head of the bolts go on the carrier half on the opposite side from the ring gear. The flat side of the
domed bolt head fits up against the machined surface where the ring gear would install if this half were used
for the ring gear side. This prevents the bolts from rotating when the nuts are tightened. The nine nuts
mount flush against the ring gear surface. Early carrier halves are not interchangeable with the later halves.
Later Carriers:
The later carriers were introduced some time after production began. The two halves are not identical
and each half has a separate part number. The ring gear side is part number A-4205B and is the only side
the ring gear will fit on. The opposite side is part number A-4206. The ring gear will not fit on this side.
The surface where the two carrier halves join together is notched so that they lock together when joined.
The nine mounting bolts have a flat rectangular head. The bolt head goes on the ring gear side with the
bolt head flush against the ring gear surface. The nine nuts go on the A-4206 carrier. The nine bolts are
able to rotate when tightening so it is necessary to hold the bolt head in place while tightening the nuts to
line up the safety wire holes.
The Early Carrier A4205 The Late Carrier A4205-B and A4206
58
Appendix D
Early Ring & Pinion
The early cars, from the beginning of production until mid 1928 used a very different style ring & pinion
gear combination than is found in the later cars.
The early ring gear looks the same as the later; however, the pinion gear is very
much different. Note the pinion gear sleeve does not have threads on it for the two
large nuts used to set the pre-load. The early pinion nuts are smaller than the later,
as is the tab washer. The pinion gear is installed on the drive shaft with a woodruff
key instead of a locking key.
59
The early drive shaft is threaded to accommodate the two pre-load nuts. The nuts
and tab washer must first be installed on the drive shaft before the pinion gear and
bearing assembly are installed. Note the drive shaft is machined for a woodruff key
instead of a locking key.
60
The later pinion gear has a longer sleeve and has the threads the two pre-load nuts
and the tab washer install on. The later pinion gear also uses a thrust washer
inserted between the front bearing and the first nut. Note the later nuts and washers
are much larger than the early. The later drive shaft does not have threads on it and
is machined for a locking key.
61
Drive shaft used with the later style pinion gear.
Comparison of early and late pinion gears: Early on the left, late on the right.
62
At the beginning of production the ring & pinion gear ratio was 370:1 (10-37). When the change was
made to the later style ring & pinion the ratio was changed to 378:1 (9-34).
A service bulletin was issued in March 1929 to accommodate replacement parts for the early cars. The
gear ratio of the early pinion gear was changed from 370 to 378 (from 10 teeth to 9 teeth) so it could be
mated up to the later style 34-tooth ring gear. I have personally encountered both 370 and 378 ring &
pinion ratios of the early style. The photos in this article are of the early style replacement 378 ratio ring
& pinion gear set.
Note that Ford retained the same part number even though they significantly changed the part.
Mitchell overdrive:
The Mitchell overdrive stub shaft is not compatible with the early pinion gear. When encountering one
of these early cars it becomes necessary to replace the ring & pinion with that of the later configuration
in order to install the overdrive.
63
Ford factory wrenches used to set the pre-load on the later pinion gear assemblies
that use the larger pinion nuts.
64
Though the late and early pinion pre-load nuts differed in size, they had one thing in common. Most
seem to have been molested with a chisel over the years by people attempting to set the pre-load without
using the proper wrenches.
65