901 transmission
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Introduction
The type 901 transmission was a four or five speed transmission designed and manufactured by Porsche between 1964 and 1976. The transmission was used primarily in the 911 product line but variations were also used in the 904, 906, 912 and 914.
History
As part of the creation of the type 911 (901) car, Porsche created an all new transmission which became the 901 transmission. The initial version utilized a cast aluminum housing with later models having a cast magnesium housing. The basic design consists of a main segment that houses the gears, differential and bellhousing. However the two shafts and gear sets themselves are attached to an intermediate plate that is sandwhiched between the larger casting and the end plate. The transmission was designed as a 5-speed however 4-speed versions were offered. The shift pattern is considered to be odd with reverse at the top left and first on the bottom left. This makes for a more difficult 1st to 2nd upshift.
The transmission was used frequently in Porsche racing cars partially due to the wide selection of gears that were available. Variations include the type 911 used in later 911 cars, the type 914 used in the 914 car and the type 902 used in the 912 car. A feature of the mainshaft on a 901 was that 2nd gear was machined as part of the shaft. A special main shaft that was used on the 904 car (commonly known as the 904 mainshaft) does not include 2nd gear on the mainshaft. This allows you to change the ratio for 2nd gear. Reproduction 904 mainshafts are available. The 901 transmission was eventually replaced by the type 915 transmission.
Versions
Listed below are the various versions of the 901 that Porsche produced as well as the stock gear sets...
Manual
| Version | Gears | R&P | 1st | 2nd | 3rd | 4th | 5th | Serial Number | 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 | |
| 901/03 | 5 | 7:31 | A | F | M | S | Z | 1967-68 | |
| 901/06 | 4 | 7:31 | A | HB | S | Z | 709 0001 - 709 0223 | ||
| 901/07 | 5 | 7:31 | A | F | M | U | ZD | ||
| 901/10 | 4 | 7:31 | A | HB | S | Z | 1968-69 | ||
| 901/12 | 4 | 7:31 | A | HB | S | Z | |||
| 901/13 | 5 | 7:31 | A | F | M | S | Z | ||
| 901/75 | 5 | 7:31 | B | GA | M | T | Y | ||
| 901/76 | 5 | 7:31 | AA | E | I | M | O | ||
| 901/77 | 5 | 7:31 | AA | F | J | O | S | ||
| 901/78 | 5 | 7:31 | C | HA | O | T | Y | ||
| 901/79 | 5 | 7:31 | B | HA | M | R | V | ||
| 901/80 | 5 | 7:31 | B | GA | M | T | Y | ||
| 901/81 | 5 | 7:31 | AA | E | I | M | O | ||
| 901/82 | 5 | 7:31 | AA | F | J | O | S | ||
| 901/83 | 5 | 7:31 | C | HA | O | T | Y | ||
| 901/84 | 5 | 7:31 | B | HA | M | R | V | ||
| 902/0 | 4 | 7:31 | 1965-66; 911, 912 | ||||||
| 902/1 | 5 | 7:31 | 1965-66; 911, 912 | ||||||
| 902/01 | 4 | 7:31 | 1967-68; 912 | ||||||
| 902/02 | 5 | 7:31 | 1967-68; 912 | ||||||
| 911/00 | 4 | 7:31 | A | HB | S | ZA | 1969-70, 911T | ||
| 911/01 | 5 | 7:31 | A | GA | O | V | ZA | 1969-70, 911E | |
| 911/80 | 5 | 7:31 | B | GA | M | T | Y | ||
| 911/81 | 5 | 7:31 | AA | E | I | M | O | ||
| 911/82 | 5 | 7:31 | AA | F | J | O | S | ||
| 911/83 | 5 | 7:31 | C | HA | O | T | Y | ||
| 911/84 | 5 | 7:31 | B | HA | M | R | V | ||
| 914/01 | 5 | 7:31 | 750 0001 - 750 ????, 751 0001 - 751 ????, | 1970-72; 914/6 | |||||
| 914/11 | 5 | 7:31 | A | F | N | V | ZD | HAO 000 001 - HAO 014 826, HAO 014 827 - HAO 030 093, | 1970-72; 914 |
| 914/12 | 5 | 7:31 | A | F | N | V | ZD | HAO 053 072 - HAO 056 362, HA 01 10 2 - HA 31 12 2, | 1973-76; 914 |
Sportomatic
| Version | Gears | R&P | 1st | 2nd | 3rd | 4th | 5th | Serial Number | Note |
|---|---|---|---|---|---|---|---|---|---|
| 905/00 | 4 | 1967-68 | |||||||
| 905/01 | 4 | 1967-68 | |||||||
| 905/13 | 4 | 1968-69 | |||||||
| 905/20 | 4 | 72 00001 - 72 0????, 72 10001 - 72 1???? | 1969-71 911T, 911E | ||||||
| 905/21 | 4 | 72 20001 - 74 2????, 72 30001 - 74 3???? | 1971-73 911T, 911E | ||||||
| 914/?? | 4 | 7:27 | C | J | S | Z | ? | 914/4 Sportomatic Prototype | |
| 914/05 | 4 | 7:27 | C | I | Q4 | X | 760 0001 - ?, 761 0001 - ? | 1970-71 914/6 |
Gear Sets
| Code | Ratio | Gear |
|---|---|---|
| 7:31 (4.429) | Ring and Pinion | |
| 8:31 (3.875) | Ring and Pinion | |
| 7:27 (3.857) | Ring and Pinion | |
| 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 | ?:? (2.31) | 1 |
| D | 16:35 (2.188) | 1 |
| E | 17:34 (2) | 2 |
| F | 18:34 (1.889) | 2 |
| G | 18:33 (1.833) | 2 |
| GA | 18:32 (1.778) | 2 |
| GB | 16:30 (1.765) | 2 |
| H | 19:32 (1.684) | 2,3 |
| HB | 19:31 (1.632) | 2,3 |
| HA | 20:32 (1.6) | 2 |
| I | 20:31 (1.55) | 2,3 |
| J | 21:31 (1.476) | 3 |
| K | 21:30 (1.429) | 3 |
| L | 22:30 (1.364) | 3 |
| M | 22:29 (1.318) | 3,4,5 |
| N | 23:29 (1.261) | 3,4,5 |
| O/O3 | 23:28 (1.217) | 3,4,5 |
| P | 23:27 (1.174) | 3,4,5 |
| Q/Q4 | 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 |
Serial Number
Model and Serial Number are stamped on the bottom of the case.
Style used on 901, 902, 905 and 911 types
901/AA BB CDE NNNN 911/AA BB CDE NNNN
- 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"
Style used on 914 types
Up to and including 1973 model year
914/AA B C NNNNNNN
- A = Type (i.e. 06 = 914/11)
- B = Type, H = manual?
- C = Differential Designation, A = no LSD, B = LSD
- N = Sequential Serial Number (i.e. 0000001, 0000002, etc.).
1974 model year and beyond
914/AA B C DD EE F
- A = Type (i.e. 06 = 914/11)
- B = Type, H = ?
- C = Differential Designation, A = no LSD, B = LSD
- D = Day of manufacture
- E = Month of manufacture
- F = Year of manufacture
Production Changes
- 1964 - Start of production; First appears in the Type 904 racing car.
- 1968 - Last of the cast aluminum models (aka. "chill cast aluminum" cases).
- 1969 - Start of the cast magnesium versions. This also includes a slightly different differential, and possibly side bearings, thicker intermediate plate, same Ring and Pinion gears, larger threads on the aft end of the mainshaft, and slightly different synchro internals.
- 1976 - End of production?
914 Relevance
The 914/11 and 914/12 are the stock transmissions used in the 914 car. It is believed that Porsche set 138 lb/ft (sand cast aluminum) and 148.5 lb/ft (die cast aluminum) maximum torque values for the 901. However this value most likely represents a torque level that maximized longevity and that while the 901 can handle higher torque values, they would be expected to impact the lifespan of the transmission. In high torque situations, first gear is known to be a weak link in the transmission as it is canteleaverd out from the intermediate plate and can be twisted off the shaft.
The two largest factors in dealing with a 915 upgrade is that of the higher cost of the transmission itself and that the shift linkage attaches to the tail end of the transmission. This requires a non-stock shift linkage to be purchased or fabricated.
