superdog405 Posted May 5, 2009 Share Posted May 5, 2009 Hi guys, could someone give me a little advise on transmissions? I have a '90 RW713 with a 7spd. (2070A).It has 5.23 rearend gears.I would like to swap it for something with more gears,but do not want to change rearends. I've never driven a 12spd. and just wondered if top gear would be close to the 7spd.?Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/ Share on other sites More sharing options...
bts-4120 Posted May 6, 2009 Share Posted May 6, 2009 your T-2070 has a .60OD a 12spd has a .78OD you will be loosing alot of road speed, not much you can change to t-2080 8spd would give you a deeper low hole but thats about it Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34801 Share on other sites More sharing options...
superdog405 Posted May 6, 2009 Author Share Posted May 6, 2009 your T-2070 has a .60OD a 12spd has a .78OD you will be loosing alot of road speed, not much you can change to t-2080 8spd would give you a deeper low hole but thats about itThanks for the reply,how much do you think I would lose? 5 to 10? Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34803 Share on other sites More sharing options...
David Posted May 6, 2009 Share Posted May 6, 2009 If you divide .78 by .6 you get 1.30. So at any given speed your engine will need to run 30% faster. If your turning 1600 rpm at 60 mph now, With the 12sp. you will be turning 2080. Change the rears or keep the 7 sp. and add an auxiliary. Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34804 Share on other sites More sharing options...
GearheadGrrrl Posted May 6, 2009 Share Posted May 6, 2009 Your 7 speed is a wide split Maxitorque designed for your truck's Maxidyne engine, It's a 5 speed with two "low hole" gears. It provides all the gears your Maxidyne engine will probably ever need- the Maxidyne engine is designed for these wide "splits" and even lugged down to it's 1200 or 1000 RPM downshift point it's still putting out over 90% of it's full rated power. The 12 speed is a 5 speed with one low hole and a splitter that can be used to split each of those gears. The 12 speed is designed for engines with narrower operating ranges like the Econodyne. It can be used with a Maxidyne, but doesn't have any clear advantage over the 7 speed. About the only advantages I can think of is the ability to use the closer splits to stay closer to the engines most economical operating speed to pick up the odd tenth of a MPG or so, or to keep the engine wound up to get more engine braking if you have an engine brake. Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34810 Share on other sites More sharing options...
superdog405 Posted May 6, 2009 Author Share Posted May 6, 2009 Your 7 speed is a wide split Maxitorque designed for your truck's Maxidyne engine, It's a 5 speed with two "low hole" gears. It provides all the gears your Maxidyne engine will probably ever need- the Maxidyne engine is designed for these wide "splits" and even lugged down to it's 1200 or 1000 RPM downshift point it's still putting out over 90% of it's full rated power. The 12 speed is a 5 speed with one low hole and a splitter that can be used to split each of those gears. The 12 speed is designed for engines with narrower operating ranges like the Econodyne. It can be used with a Maxidyne, but doesn't have any clear advantage over the 7 speed. About the only advantages I can think of is the ability to use the closer splits to stay closer to the engines most economical operating speed to pick up the odd tenth of a MPG or so, or to keep the engine wound up to get more engine braking if you have an engine brake.Thanks to all of you for the help! Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34818 Share on other sites More sharing options...
MACKTRUCKS4 Posted May 9, 2009 Share Posted May 9, 2009 I changed my transmission in my superliner. I went to a 12 spd. from a 9 spd, the same od that you are talking about. I lost 6 miles per hour, top speed went from 82 down to 76. I went to a 12 spd because I needed different reverse's for what I use the truck for. Quote Live every day like it's your last, because one of these days, it will be. Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34977 Share on other sites More sharing options...
David Posted May 10, 2009 Share Posted May 10, 2009 The 9sp is .71 overdrive. So .78/.71 is 1.10, or 10%. That's a lot different than the 30% change from a 7 sp. Quote Link to comment https://www.bigmacktrucks.com/topic/9290-12-spd-or/#findComment-34985 Share on other sites More sharing options...
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