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901 Series Porsche Transmission


901 Versions and Gearing

Listed below is a chart of the various versions that Porsche produced

Manual Transmissions

Those transmission that came with what is known as the "Simplified" differential are listed with an "S" after the final drive ratio in the charts Below.

Manual

Type, Qty Gears, R&P Ratio, 1st 2nd 3rd 4th 5th Gears, Serial #s, Note

901/0      5    7:31          AA GA O U Y    1964-65 911

901/02    5    7:31          A F M S Z           1966-67 911S

901/03    5    7:31 S       A F M S Z           1968 911T

901/06    4    7:31 S       A HB S Z            7090001 - 7090223     1969-70 911

901/07    5    7:31 S       A F M S Z           7190001 - 7192529

901/10    4    7:31 S       A HB S Z                                                 1968-69 911S, 911T

901/12    4    7:31 S       A HB S Z            7091001 - 7091469

901/13    5    7:31 S       A F M S Z           7193001 - 7198787

901/50    5    7:31          B GA M T Y                           1967 911 Special ratio option

901/51    5    7:31          AA E I M O                            1967 911 Hillclimb ratio option

901/52    5    7:31         AA F J O S                              1967 911 Airport ratio option

901/53    5    7:31         C HA O T Y                            1967 911 Speed ratio option

901/54    5    7:31         B HA M R V                   1967 911 Nurburgring ratio option

901/75    5    7:31 S B GA M T Y  7390001 - 7390002   1968 911 Special ratio option

901/76    5    7:31 S AA E I M O 7391001 - 7391001   1968 911 Hillclimb ratio option

901/77    5    7:31 S AA F J O S    7392002 - 7392010   1968 911 Airport ratio option

901/78    5    7:31 S    C HA O T Y   7393001 - 7393003 1968 911 Speed ratio option

901/79    5    7:31 S    B HA M R V  7394001 - 7394008 1968 911 Nurburgring ratio option

901/80    5    7:31 S    B GA M T Y  7390101 - 7390109 1969 911 Special ratio option

901/81    5    7:31 S    AA E I M O   7391101 - 7391102 1969 911 Hillclimb ratio option

901/82    5    7:31 S    AA F J O S     7392101 - 7392118 1969 911 Airport ratio option

901/83    5    7:31 S    C HA O T Y   7393101 - 7393106 1969 911 Speed ratio option

901/84    5    7:31 S    B HA M R V  7394101 - 7394109 1969 911 Nurburgring ratio option

902/0      4    7:31 S      A H Q X       160001 - 162462 (up to 7/26/1965),   163001 - 165214 (4 cyl engine), 200000 - 200402 (6 cyl engine)                                                                                                                                     

Type, Qty Gears, R&P Ratio, 1st 2nd 3rd 4th 5th Gears, Serial #s, Note                                                                                                          

1965-66 911, 912

902/1    5    7:31 S      A F M S X      220001 - 221721 (up to 7/26/1965)

                                                           234001 - 238942 (4 cyl engine)

                                                           130001 - 131571 (6 cyl engine)

1965-67 911, 912

902/01    4    7:31      S A H Q X        1080001 - 1089999      1968 912 US

902/02    5    7:31      S A F M S X     1280001 - 1289999      1968 912 ROW

902/04    4    7:31      S A H Q X                                              1969 912

902/05    5    7:31 S   A F M S X                                              1969 912

902/06    5    6:29      A GA O U Z                                 1969 late 912 US

902/16    5    6:29      A GA O U Z                                           1969 912

902/50    5    7:31 S   A E I O U     9285001 - 9285999   1969 close ratio option #1

902/55    5    6:29      A E I O U                                        1969 close ratio option #2

902/60    5    7:31 S   A E I O U                                        1969 close ratio option #3


1970-71 911T

911/00    4    7:31 S            A HB S ZA       7000001 - 7000691 (Model Year 1970)

                                                                     7010001 - 7019999 (Model Year 1971)


911/01    5    7:31 S           A GA O V ZA

                                                                     7100001 - 7109999 (Model Year 1970),

                                                                     7700001 - 7702730 (Model Year 1970),

                                                                     7110001 - 7119999 (Model Year 1971)

                                                                     7710001 - 7719000 (Model Year 1971)

Type, Qty Gears, R&P Ratio, 1st 2nd 3rd 4th 5th Gears, Serial #s, Note

1970-71 911E, 911S

911/80    5    7:31 S      B GA M T Y    7319101 - 7319200    1970 911 Special ratio option

911/81    5    7:31 S      AA E I M O     7319201 - 7319300    1970 911 Hillclimb ratio option

911/82    5    7:31 S      AA F J O S      7319301 - 7319400    1970 911 Airport ratio option

911/83    5    7:31 S      C HA O T Y    7319401 - 7319500    1970 911 Speed ratio option

911/84    5    7:31 S      B HA M R  7319501 - 7319600    1970 911 Nurburgring ratio option

914 Models

914/01    5    7:31     A GA O V ZA

                                                              7500001 - 750.... (Model Year 1970),

                                                              7510001 - 751.... (Model Year 1971)

                                                              7520001 - 752.... (Model Year 1972)

1970-72 914/6

914/11    5    7:31        A F N V ZD

                                                              HA 0000001 - HA 0014826 (Model Year 1970),

                                                              HA 0014827 - HA 0030093 (Model Year 1971)

                                                              HA 0030094 - HA 0053072 (Model Year 1972)

1970-72 914/4

914/12    5    7:31       A F N V ZD

                                                             HA 0053072 - HA 0056362 (Model Year 1973)

                                                             HA 01102 - HA 31122 (Model Year 1973)

                                                             HA 01013 - HA 31073 (Model Year 1973)

                                                             HA 01083 - HA 31074 (Model Year 1974)

                                                             HA 05084 - ... (Model Year 1975)

                                                             HA 05085 - ... (Model Year 1976)

Type, Qty Gears, R&P Ratio, 1st 2nd 3rd 4th  Gears, Serial #s, Note

Sportomatic


905/00    4    7:31 S      C  HB  O  U                                         1967-68

905/01    4    7:31 S      C  HB  O  V                                         1967-68

905/13    4    7:27 S      C  HB  V      7290001 - 7291044   1968-69

1970-71 911T, 911E

905/20    4    7:27 S          Q   X       7200001 - 7201023 (Model Year 1970),

                                                               7210001 - 7219999 (Model Year 1971)

1972-73 911T, 911E

905/21    4    7:27 S      C   I   Q   X       7220001 - 742.... (Model Year 1972),

                                                               7230001 - 743....  (Model Year 1973)

914 Sportomatic (only 8 Built)

914/     4    7:27 S     Z    914/4   Sportomatic Prototype

914/05 4    7:27 S    C  I   X              7800001 - 780....    (Model Year 1970),

                                                              7610001 - 7610027 (Model Year 1971)

1970-71 914/6

Those transmission that came with what is known as the "Simplified" differential are listed with an "S" after the final drive ratio in the charts above.

Gearing and Differential

Differential

901 transmissions were either delivered with a standard open differential, or an optional ZF clutch type limited slip unit. Over the life of the transmission there were design changes to the standard open differential. The type 901, 902 and 905 transmissions used a smaller differential carrier while the type 911 and 914 used a larger and strong design.

"Simplified" Differential"

Along with the differential carrier basic size changes, there were also differences in how the differential carrier pin (part of the spider gear assembly) is held in place. Roughly between 1968 and 1970 a design (known as the “simplified" differential as it was simpler and used fewer parts) utilized special pin like extensions (commonly known as the "teats") on the end of the stretch bolts that attach the output flanges to the differential. When in place, these teats hold the carrier pin in place. However the teats wear off the ends of the bolts over time and once they fail, they no longer hold the carrier pin in place. Centrifugal and other forces allow the pin to slide out of position then impacting the interior of the case leading to a catastrophic failure of the transmission. Campaigns by Porsche at that time tried to address the issue via modifications. So some transmissions from the affected era have been fixed. Earlier and later differentials have a different design and do not have this problem.

Final Drive

The final drive consists of a pinion and ring gear. As this is a transaxle design, the pinion gear is on the end of (part of) the output shaft. The ring gear is bolted to the differential. The final drive ratio is the ratio of the teeth count between the pinion and ring gears. For example a typical 901 final drive has a ratio of 7:31 (4.429). This translates to 7 pinion teeth and 31 ring teeth.

Ratio Gear

6:29 (4.833) Pinion and Ring Gear

7:31 (4.429) Pinion and Ring Gear

7:27 (3.857) Pinion and Ring Gear

Serial Numbers

Model and/or serial number/build date are stamped on the bottom of the case. The location and style/decoding scheme of the stamping are depending upon the type of transmission and year of manufacture. Some stampings includes the type designations, while others do not. Some indicate details such as differential type, while others do not. Some list a unique serial number, while others may only list a build date (implying that multiple transmissions will have the same stamping)

901, 902, 905 and 911 types

AAA/AA BB CDE N….

A = Type (i.e. 06 = 901/06)

B = Differential Designation, 12 = ZF LSD, missing = no LSD

C = Application, 5 = 4 cylinder engine, 7 = 6 cylinder engine

D = ?

E = ?

N = Sequential Serial Number (i.e. 0001, 0002, etc.). Some models did not start with serial number "1"

914/01 and 914/05 types

The 914/01 transmission that was only used in the 914/6 car generally have the stamping in a square raised section of the casting directly under the differential, however some early production examples have the stamping on the "keel" instead. This raised section only appears on the 914/01 transmissions. The 914/05 transmission does not have this raised area and has it’s stamping on the keel. It should be noted the actual transmission type "914/01" or "914/05" is part of the stamping

914/AA B CDE N….

A = Type (01 = standard 5 speed, 05 = 4 speed Sportomatic)

B = Differential, 10 = 80% LSD, blank = standard open differential

C = Application, 7 = 6-cyl engine

D = Type, 5 = 5 speed, 6 = 4 speed Sportomatic

E = Model Year, 0 = 1970, 1 = 1971, 2 = 1972

N = Sequential Serial Number (i.e. 0001, 0002, etc.)

914/11 and early 914/12 (up to and including some early 1973 model year 914/4)

All of the 914/11 and some of the early 914/12 transmissions used a different style of stamping as well as a different location for the stamping. The stamping is located directly on the front to rear reinforcement webbing or “keel” that is part of the casting. This keel runs the length of the transmission, but as with the 914/01 and 915/05 transmission, the stamping is located generally under the differential. It should be noted the actual transmission type “914/11” (and maybe even 914/12” is part of the stamping.

914/AA B CDN….

A = Type (01 = standard 5 speed, 05 = 4 speed Sportomatic)

B = Differential, 10 = 80% LSD, blank = standard open differential

C = Type, H = Manual

D = Gear/Differential, A = 5 speed, B = 5 speed with LSD

N = Sequential Serial Number (i.e. 0000001, 0000002, etc.)

Late 914/12 (most 1973 and beyond)

Other than the very early 914/12 transmissions mentioned above, the bulk of the 914/12 transmissions used a third style of stamping. It used the same location as the 914/11 and early 914/12, but is decoded differently and there is no transmission type indicated on the transmission. Additionally the new numbering scheme is based upon date of manufacture and not individual transmissions. This means that if multiple transmissions are manufactured on the same day, they should have the same stamping.

ABCDE (No "type" indicator on these, however all of these are type 914/12)

A = Type, H = Manual

B = Gear/Differential, A = 5 speed, B = 5 speed with LSD

C = Day of manufacture

D = Month of manufacture

E = Year of manufacture

Main Gears

Each gear set generally consists of two gears. One for the input shaft and one for the output shaft. There are some slight exceptions. As reverse is part of first gear, it has a matching “reverse idler” gear. So 1st gear consists of the input, output and reverse idler gear. On most 901 series transmissions the input shaft includes 2nd gear. So in these a 2nd gear set would include the input shaft. The gear ratio for a gear set is the ratio of the teeth count between the input and output shaft gears. For example an 901 “A” 1st gear has a ratio of 11:34 (3.091). This translates to 11 teeth on the input gear and 34 teeth on the output gear. While all 901 series gears can be described via their teeth count (and associated ratio), to make it easier to identify specific ratios, Porsche used an A through Z based naming system. With “A” being a low 11:34 1st gear and “ZD” being a high 31:22 5th gear.

In a perfect world, any of these gear sets could be used in any location to provide ultimate flexibility with respect to gearing. However due to the basic design of the transmission (internal case space, shift fork locations, input/output shaft design, etc.), specific gears can typically only be used in specific locations. For example in general a gear designed for 5th gear may also be placed in the 4th gear location (and visa-versa) . The same goes for 2nd and 3rd gear (assuming you have a 904 mainshaft). 1st gear is not designed to be relocated into other gear slots. In addition to using gears in their intended locations, there is a concept known as “flipping” which can for example use a 5th gear in place of 3rd gear. This is accomplished by switching or flipping the gears from the input to output shaft to reverse the ratio.

Code, Ratio, Gear Position

A 11:34 (3.091) 1

AA 12:34 (2.833) 1

B 14:37 (2.643) 1

C- 12:29 (2.417) 1

C 15:36 (2.4) 1

CA 13:29 (2.231) 1

D 16:35 (2.188) 1

E 17:34 (2) 2    904 Mainshaft Required for 2nd

F 18:34 (1.889) 2   Mainshaft & Gearset or 904 Mainshaft

G 18:33 (1.833) 2    904 Mainshaft Required for 2nd

GA 18:32 (1.778) 2    Mainshaft & Gearset or 904 Mainshaft

GB 17:30 (1.765) 2    904 Mainshaft Required for 2nd

H 19:32 (1.684) 2,3   904 Mainshaft Required for 2nd

HB 19:31 (1.632) 2,3   904 Mainshaft Required for 2nd

HA 20:32 (1.6) 2   904 Mainshaft Required for 2nd

I 20:31 (1.55) 2,3   904 Mainshaft Required for 2nd

J 21:31 (1.476) 3

K 21:30 (1.429) 3

KA 22:31 (1.409) 2, 3  Welded to Mainshaft for 2nd

L 22:30 (1.364) 3

M 22:29 (1.318) 3,4,5

N 23:29 (1.261) 3,4,5

O 23:28 (1.217) 3,4,5

P 23:27 (1.174) 3,4,5

Q 24:27 (1.125) 3,4,5

R 25:27 (1.08) 4,5

S 25:26 (1.04) 4,5

T 26:26 (1) 4,5

U 26:25 (0.9615) 4,5

V 27:25 (0.9259) 4,5

W 27:24 (0.8889) 4,5

X 28:24 (0.8571) 4,5

Y 28:23 (0.8214) 4,5

Z 29:23 (0.7931) 4,5

ZA 29:22 (0.7586) 4,5

ZD 31:22 (0.7097) 4,5



Print this 901 Gear chart of all available gears and get out your pencil and ruler!




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Our Site is under construction. I am busy making the same type charts for 915, G-50, and 996. There is only me doing this work with no one to delegate the work to and we turned on this site 1-1-2019.

If you need help with ratios call me and I will be glad to help you. Cog