12 Spd. Or ?

[superdog405]

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.

[bts-4120]

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

[superdog405]

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

Thanks for the reply,how much do you think I would lose? 5 to 10?

[David]

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.

[GearheadGrrrl]

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.

[superdog405]

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!

[MACKTRUCKS4]

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.

[David]

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.