41chevy Posted April 11, 2016 Share Posted April 11, 2016 In the early 1950's GM used the experience gleaned from making their Hydra-Matic's for use in tanks( late WWII and pre Korea) to develop a practical automatic for heavy trucks up to and including class 8. . Three ranges, seven forward gears and reverse gave it 16 gear changes. Pretty interesting. Page 112 was 1/2 paragraph on warnigs about granny gear usage. Paul Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment https://www.bigmacktrucks.com/topic/44772-gms-twin-hydra-matic-1954/ Share on other sites More sharing options...
HeavyGunner Posted April 11, 2016 Share Posted April 11, 2016 What am I missing? Wouldn't 7 forward gearsX3 ranges=21 plus the 3 ranges in reverse for a total of 24 gear changes not 16? Just curious if it was a typo or for example creeper range couldn't be used with gears 5, 6 and 7? Good read at any rate. Quote The problems we face today exist because the people who work for a living are outnumbered by the people who vote for a living.The government can only "give" someone what they first take from another. Link to comment https://www.bigmacktrucks.com/topic/44772-gms-twin-hydra-matic-1954/#findComment-330131 Share on other sites More sharing options...
kscarbel2 Posted April 11, 2016 Share Posted April 11, 2016 Correct me if I'm wrong, but I believe the 8-speed Hydramatic was first developed for the M135 (single rear tire) and M211 (dual rear tire) two and a half ton 6x6s. And after being tortured and proven at Aberdeen, it was then offered to the civilian market. (There were also M215 tipper and M221 tractor variants). I think the M5 (Stuart) and M24 (Chaffee) tanks had 4-speed Hydramatics. Quote Link to comment https://www.bigmacktrucks.com/topic/44772-gms-twin-hydra-matic-1954/#findComment-330135 Share on other sites More sharing options...
j_martell Posted April 12, 2016 Share Posted April 12, 2016 2 hours ago, HeavyGunner said: What am I missing? Wouldn't 7 forward gearsX3 ranges=21 plus the 3 ranges in reverse for a total of 24 gear changes not 16? Just curious if it was a typo or for example creeper range couldn't be used with gears 5, 6 and 7? Good read at any rate. The article said that it would equal 21, but in practice there are some overlapping of ratios between ranges. Leaving a distinct 13 speed Quote Lack of planning on your part does not constitute an emergency on my part.... Link to comment https://www.bigmacktrucks.com/topic/44772-gms-twin-hydra-matic-1954/#findComment-330142 Share on other sites More sharing options...
HeavyGunner Posted April 12, 2016 Share Posted April 12, 2016 Ok that makes sense, I figured there was something I was missing. Quote The problems we face today exist because the people who work for a living are outnumbered by the people who vote for a living.The government can only "give" someone what they first take from another. Link to comment https://www.bigmacktrucks.com/topic/44772-gms-twin-hydra-matic-1954/#findComment-330152 Share on other sites More sharing options...
41chevy Posted April 12, 2016 Author Share Posted April 12, 2016 (edited) 3 hours ago, kscarbel2 said: Correct me if I'm wrong, but I believe the 8-speed Hydramatic was first developed for the M135 (single rear tire) and M211 (dual rear tire) two and a half ton 6x6s. And after being tortured and proven at Aberdeen, it was then offered to the civilian market. (There were also M215 tipper and M221 tractor variants). I think the M5 (Stuart) and M24 (Chaffee) tanks had 4-speed Hydramatics. M-5 and M-24 both had twin Cadillac 44T24 V-8 engines of about 110 h.p. each and a 4 speed Hydra-Matic model T-250 with a fluid coupling, driving through a manual shift 2 speed transfer case, giving it 8 speed forward and 2 reverse. M-18 and M-26 both used the Detroit Transmission's Torqmatic (built across the street from the Hydra-Matic plant) with used a Torque Converter, mainly for the heavier vehicle weight and 400 to 500 horse power engines engines . You are correct on the G-749 family of trucks (M135, M211,M221 and M222) All ran the Dual Range Hydra-Matic , with 4 speeds in two different ranges. All the driver needed to do was select the range he wanted. Single speed transfer case with Neutral. The Twin Hydra-Matic was a pair linked together. One in low range, one in high range with a 3 speed reduction box on the rear that gave it the split gears for a potential of in reality 21 speeds with about 3 or 4 of the gear ratios over lapping. It was originally intended for post WWII heavy Tanks but the M-46 to M-60 Tanks went to Allison Automatics in stead of the Hydra-Matics. Paul. Edited April 12, 2016 by 41chevy Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment https://www.bigmacktrucks.com/topic/44772-gms-twin-hydra-matic-1954/#findComment-330161 Share on other sites More sharing options...
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