GMH Transmissions
Transmission ID Codes (compliance plate)
HK-HT-HG Models
Powerglides for the 253 and 308 were 6cyl units with a bolt on bellhousing. Powerglides on the 307 and 350 had an integral bellhousing.
| Rev | 1st | 2nd | 3rd | 4th | |
| ??? 3spd Crash (No synchro on 1st) | -2.99:1 | 2.99:1 | 1.59:1 | 1.00:1 | |
| M15 Aussie 3spd (HT 253) | -3.59:1 | 2.48:1 | 1.68:1 | 1.00:1 | |
| M15 Aussie 3spd (6cyl, HG-HQ 253) | -3.59:1 | 3.07:1 | 1.68:1 | 1.00:1 | |
| M20 Opel 4spd (All Synchro 4 on the floor) | -3.317:1 | 3.428:1 | 2.156:1 | 1.000:1 | 1.366:1 |
| M21 Saginaw 4spd 2.54:1 1st | -2.54:1 | 2.54:1 | 1.80:1 | 1.00:1 | 1.44:1 |
| M22 Saginaw 4spd 2.85:1 1st HT only | -2.85:1 | 2.85:1 | 1.00:1 | 2.02:1 | 1.35:1 |
| M35 Powerglide (6cyl, 253, 308) | -1.82:1 | 1.82:1 | 1.00:1 | ||
| M35 Powerglide (307/350) | -1.76:1 | 1.76:1 | 1.00:1 |
HQ-WB
| Rev | 1st | 2nd | 3rd | 4th | |
| M15 Aussie 3spd (6cyl, HQ 253) | -3.59:1 | 3.07:1 | 1.68:1 | 1.00:1 | |
| M20 Aussie 4spd Std. ratio (L6) | -3.05:1 | 3.05:1 | 2.19:1 | 1.51:1 | 1.00:1 |
| M21 Aussie 4spd Close ratio (V8) (High Perf.) | -2.54:1 | 2.54:1 | 1.83:1 | 1.38:1 | 1.00:1 |
| M22 Aussie 4spd Wide ratio (L6) One Tonner | -3.72:1 | 3.74:1 | 2.68:1 | 1.68:1 | 1.00:1 |
| MC7 Muncie | -2.59:1 | 2.52:1 | 1.88:1 | 1.46:1 | 1.00:1 |
| M40 TriMatic (L6, 253, 308) | -1.85:1 | 2.31:1 | 1.46:1 | 1.00:1 | |
| M41 TH400 (308, 350) | -2.08:1 | 2.48:1 | 1.48:1 | 1.00:1 |
Trimatic ID Plate Codes:
HG Holden:
| HH | All 6 Cylinder execpt high performance |
| HJ | All 6 Cylinder high performance |
HQ Holden:
| HN | 173 (2.85L) 6 Cyl |
| HT | 202 (3.3L) 6 Cyl |
| HO | 253 (4.2L) V8 |
| HP | 308 (5.0L) V8 |
HJ Holden:
| HN | 173 (2.85L) 6 Cyl |
| HT | 202 (3.3L) 6 Cyl |
| HO | 253 (4.2L) V8 |
* From HJ onwards, the Turbo 400 replaced the Trimatics behind 308 V8's
HX/HZ Holden:
| KJ | 202 (3.3L) 6 Cyl |
| KK | 253 (4.2L) V8 with all diff ratios except 2.6:1 |
| KX | 253 (4.2L) V8 with diff ratio of 2.6:1 |
WB Holden:
| FU | 202 (3.3L) 6 Cyl with all diff ratios except 4.44:1 |
| FV | 202 (3.3L) 6 Cyl with diff ratio of 4.44:1 |
| FX | 253 (4.2L) V8 |
| FW | 202 (3.3) 6 Cyl with 4.44 diff and T-Bar Floor Shift |
Identifying GM Automatic Transmissions
Holden Trimatic
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Trimatic ID Plate. The very large HT letters define this as being from an LH, HQ or HJ Holden. The F Calibration relates to the Band tightening requirement. |
GM 3 and 4 speed Automatic
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Here are the four most popular automatics available from GM. All of these transmissions are fitted with the standard small-/big-block Chevy bellhousing bolt pattern. From left to right they include the TH350, the TH400, the TH200-4R and the TH700-R4. A quick way to differentiate the 350s and 400s from the later boxes is by the vacuum modulator. |
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Sometimes it’s easiest to identify an automatic by its pan shape. Here, from left to right are the pans for the TH700-R4, the TH200-4R, the TH400 and the TH350. |
Dimensions
All dimensions are in millimetres (inches). Length is measured from the bellhousing mounting flange to the end of the extension housing. The transmission mount position is also expressed from the bellhousing flange rearward to the centerline of the mount. The TH400 length and mount dimensions are for the “shorty” tail-housing model. There may be other transmission models in which these lengths may vary, but these are the popular models.
| Transmission | Length | Rear Transmission Mount Position |
| Powerglide | (27) | (19.5) |
| T350 | (27) | (19.5) |
| T400 | (28) | (26.25) |
| TH200-4R | (27) | (26) |
| TH700-R4 | (30) | (21.25) |
Transmission Ratios
| Transmission | First | Second | Third | Fourth |
| TH350 | 2.52 | 1.52 | 1.00 | N/A |
| TH400 | 2.48 | 1.48 | 1.00 | N/A |
| TH200-4R | 2.74 | 1.57 | 1.00 | 0.67 |
| TH700-R4 | 3.06 | 1.63 | 1.00 | 0.70 |