Model A & B

Ford Garage

Rear Axle Gear Ratios

The following table shows the various Ford part numbers and gear ratios for the matched ring and pinion gear sets used on 1928 through 1934 Model A (103-1/2" WB) and Model B (106" WB) Ford car and commercial chassis, not trucks.

In some cases both an 'A' and a 'B' prefix part number are shown for a particular gear set. This is because the original Model A part was physically carried over into 1932 and later production usage, but with a new 'B' part number prefix. The actual physical parts were identical and unchanged.

As a matter of Ford process, all Model A parts which were also used on the Model B were renumbered by Ford in 1932 with new prefixes, and starting with no suffix. The 'AB' and 'ABF' prefixes were issued by Ford in very early 1932, and were quickly superseded by the typical 'B' and 'BF' prefixes.

The 'AF', 'ABF', and 'BF' prefix gear set ratios were used with the small bore, small displacement 14.9 HP (R.A.C.) engines produced by Ford Motor Company, Ltd. in England.

Ford
Part Number(s)
Pinion
Teeth*
Ring
Teeth*
Gear
Ratio
Notes
Aftermarket 11 36 3.27 : 1 Produced by Steve Becker @ Bert's.
This is the highest speed gear ratio available.
Best suited for light cars, and/or flat terrain, and/or higher horsepower/torque engines.
Aftermarket 11 39 3.54 : 1 This gear ratio was used in post-1934 Ford production in a V8 straddle-mounted pinion format, but is not found in Ford Parts Price Lists in a Model A or B format produced by Ford.

This ratio has been available aftermarket for many years in a Model A/B format and is considered a "high speed" gear set.
Best suited for light cars, and/or flat terrain, and/or higher horsepower/torque engines.
A-4209 10 37 3.70 : 1 Early 1928 production usage non-threaded pinion and ring set format for use with the early drive shaft that was threaded for the pinion bearing lock nuts.
  • A-4209 Production gears were 3.70:1 ratio.
  • A-4209-AR Service Replacement gears were 3.78:1 ratio.
A-4209-AR 9 34 3.78 : 1 Early 1928 non-threaded pinion and ring set format for Service Replacement use with the early production drive shaft that was threaded for the pinion bearing lock nuts.
A-4209-B
AB-4209-A
B-4209-A
9 34 3.78 : 1 Typical production Model A and B threaded pinion and ring set.
  • Standard Model A ratio.
  • Optional Model B ratio, typically found on light cars.
This gear ratio is often used with the 26% Mitchell Overdrive unit, or the 1984-87 F-150 Tremec RTS 27.6% OD 4-speed transmission conversion.
A-4209-D
(duplicate of
A-4209-B ?)
9 34 3.78 : 1 Part number appears only in the October 1929 US Parts Price List.
Likely a typo. (duplicate of A-4209-B ?)
Aftermarket (?) 11 42 3.82 : 1 This gear ratio exists in early 1928 non-threaded pinion and ring set format for use with the early drive shaft that was threaded for the pinion bearing lock nuts.
It is not found in Ford Parts Price Lists but may have been produced as an aftermarket replacement at some point in history.
A-4209-C
AB-4209-B
B-4209-B
9 37 4.11 : 1 Typical production Model A and B threaded pinion and ring set.
  • Optional Model A ratio, typically found on heavy or commercial cars, such as Pickups, Fordor Sedans, and Station Wagons, or in mountainous terrain.
  • Standard Model B ratio.
For best overall drivability, this gear ratio is recommended for use with: the 26% Mitchell Overdrive unit, or the 1984-87 F-150 TOD Tremec RTS 27.6% OD four-speed transmission conversion.
Aftermarket (?) 9 39 4.33 : 1 This gear ratio was used in post-1934 Ford production in a V8 straddle-mounted pinion format, but is not found in Ford Parts Price Lists in a Model A or B format produced by Ford.
May have been produced aftermarket in Model A/B format at some point in history.
AF-4209-AR 9 41 4.56 : 1 Early 1928 non-threaded pinion and ring set for use with the early drive shaft that was threaded for the pinion bearing lock nuts.
  • Standard ratio used with 14.9 HP (R.A.C.) British Model AF Fords.
AF-4209-B
ABF-4209
BF-4209
9 41 4.56 : 1 Typical Production Model AF and BF threaded pinion and ring set.
  • Standard ratio used with 14.9 HP (R.A.C.) British Model AF and BF Fords.
AF-4209-D
(duplicate of
AF-4209-B ?)
9 41 4.56 : 1 Part number appears in some foreign Ford Parts Price Lists for use with 14.9 HP (R.A.C.) British Model AF Fords.
Likely a typo. (duplicate of AF-4209-B ?)

* Some ratios listed above have pinion or ring gears having the same tooth count as found in other listed gear ratios, however the individual gears themselves are neither the same nor interchangeable between different ratios!

Ring and pinion gears were individually matched and lapped to each other for quiet operation. NOS matched gear set pairs usually had a matching three digit serial number electrically or mechanically engraved freehand somewhere on each gear.

Additionally, NOS gears usually have traces of orange lapping compound on the teeth. The compound was used during the matching/lapping process of the gear tooth contact. The orange lapping compound residue should not be mistaken for surface rust.

In some instances the original ring and pinion tooth count can also be found stamped on the banjo housing web or flange, as show below.


More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model A & B Original 5-Z-1833 and 5-Z-2065 Pinion Nut Wrenches
  3. Model A & B Drive Shaft Differences
  4. Model B Drive Shaft Removal Methods
  5. Model A & B Pinion Gear Race Removal Methods
  6. Model A Mitchell Synchronized Transmission
  7. Model A Ruckstell Dual High Transmission
  8. Model A & B F-150 TOD Transmission Conversion ~ Tremec T170FT RTS

April 2009