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converting Eaton 9 speed to 13 speed


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As the topic says, what is needed to do this? I have 442 rears and i thought the cheapest option to get better economy and more power through the hills is to get a 13 speed or just add more gears. What is involved in this process and has anyone done this???

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Not sure about the Eaton transmissions, but the Mack 18, 13, and 9 speeds are pretty similarly geared. Want to drive an 18 like a 9? Leave the splitter in the high split and the gear ratios are identical. The 13 is in the low split in the low range...so you'd have SLIGHTLY lower gearing down low...and smaller steps between the gears in the high range...but the top gear would still be the same since the 9 uses the same gear ratios as the high split.

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Glenn thanks for the info, im going to call mack with my vin and see what info they can give me and i am pretty sure i do have an overdrive too. I would like to be able to split the last gear i have and get the rpms down lower when cruising. would this do that?

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I have an RD that was set up that way. Fuller 9 sp od with Mack 4.42 rears. I didn't like it all. I went and found a 13 sp Fuller to put in it. Problem was that the 13 sp I found was a direct, not an overdrive. Now I'm pretty stupid, cuz I didn't relize it until we got it all put together and I had no top speed. Went digginig through all spare parts and found a set of 3.63 gears to put in it. I can cruise 65 MPH at about 1600. The low hole isn't quite what I would want it to be, but I make it work. On a nice highway run, pulling a flatbed I can usually pull 6-6.5 MPG's. Not bad for an ol' Mack with a million miles on it.

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wow thanks for the good info storkmack i would hate to have made that mistake. so basically i just need to find a 13 speed with an overdrive in it and i will be alot happier. my dad just found an eaton manual with all the ratios and makes of the trans. how exciting now i can get exactly what i want. what i hate in my trans is that the top right gear in high which is 7 for me goes to 45 or at 1800 rpm and if the speed limit is 40 i have to be in that gear to have any useable power if i go to 8th at 40 its around 1100 rpm which is too low for me so for me to be able to split it to lets say get around 1350 or so would be great. 65-68 mph goes to 1800 so if i can split my last gear to do lets say even 1500 at that speed i would be happier. is this all possible if i keep my same rear end?

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The trans is a RTXF14609 B . the guy on fuller said that i wouldnt be able to increase topspeed at a lower rpm though with a 13 speed which doesnt really make sense to me. so i have to change the rear end and the trans just to get more useable power and fuel economy? is this the only option? how much does this all cost?

Slow and Steady Wins the Race!

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I looked up your transmission online and I see it has a 0.73 overdrive and the next lower gear is direct 1.00 I also looked around online and most the eaton 13 speeds I found ratios for also had a top gear of 0.73 and the next lower gear was 0.86 and then below that 1.00 So that would explain why the guy you talked to said you would need to change your rear end also to get a higher top speed.

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yeah its a .073. what i dont understand is why if i can currently do 65 at 1800 in 9th how come if i get a 13speed with a ratio of .73 it would still do 65 at 1800 but then when i put it into 13 wouldnt it still go that speed but drop down the rpm a little and maybe get a top speed of 70? this is what i dont understand about it. i figured i would be able to get a 13speed that does what my nine does but just split the high gears which should allow me to drop the rpms when i max out a gear to make it more useable and also if i max out 65 at 1800 flip the switch to split that gear and go to maybe 1500 or 1600 at 65 which also would let me do a higher top speed because of splitting it. Or i am just not understanding this correctly. I know that lower rear end would solve the top end more but i cant i squeeze out a tiny bit more with just a 13 speed is all. sorry about the rant. my truck is in the shop and im not working and im bored :)

Slow and Steady Wins the Race!

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Nevermind, i think i understand it now. I cant get more out of my top gear because its maxed out but if i want to split the other gears to drop down the rpm i can. if i max out 7th gear and want to drop the rpms down a lil lower then i can do that but i cant do the same with my final gear because it doesnt have a gear after that to share i guess. im talking about if i had a 13 speed by the way. hope i didnt confuse you all but i think i finally understand all this now lol

Slow and Steady Wins the Race!

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Also realize if you do put a back box on your nine speed to convert to a 13 speed you will have to do some driveline work too. If a nine speed has a .73OD and a 13speed has a .73OD you will run the same speed at any give rpm. You will get better performance out of the 13 speed because the steps(gear ratios)are closer together.

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Also realize if you do put a back box on your nine speed to convert to a 13 speed you will have to do some driveline work too. If a nine speed has a .73OD and a 13speed has a .73OD you will run the same speed at any give rpm. You will get better performance out of the 13 speed because the steps(gear ratios)are closer together.

Food for thought. Make sure you got the motor to turn the 13. I know a guy that took a good running 9 speed and put a 13 speed in. Truck was a slug after that. Just didn't have enough motor and the top gears where supposedley the same.

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Nevermind, i think i understand it now. I cant get more out of my top gear because its maxed out but if i want to split the other gears to drop down the rpm i can. if i max out 7th gear and want to drop the rpms down a lil lower then i can do that but i cant do the same with my final gear because it doesnt have a gear after that to share i guess. im talking about if i had a 13 speed by the way. hope i didnt confuse you all but i think i finally understand all this now lol

I thank you are wanting a trans that will allow you to have more top end. Now i do not know what engine your truck has but with that ratio you could run a 13 double overdrive, which is a 13 speed overdrive that the countershafts have been fliped, which gives you three overdrive postitions, but it also make all thr gear ratios higher in the trans you lo ho is more like frist gear in a 10 speed. My other question is what size rubber are you running on the truck, if you have a low pro or 22.5 you can change to a 11r 24.5 and gain about 5 miles an hour or more. I ran a mack superliner with a 13 double over with 464 ratio, but it had a 400 cat in it and i could run about 70 at 1900 or so and she would top out at about 82 at 2250, now if you are runing a mack engine i have allways liked a 15 speed fuller behind them they also have a good overdrive and give you a deep reduction in the lo lo positon, i hope i have helped you some and the shop book you have will help you also so the 13 double over may be the way to go if you are not loaded heavy all the time.
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The trans is a RTXF14609 B . the guy on fuller said that i wouldnt be able to increase topspeed at a lower rpm though with a 13 speed which doesnt really make sense to me. so i have to change the rear end and the trans just to get more useable power and fuel economy? is this the only option? how much does this all cost?

Come to thank of it that is basicly the same trans as a 8LL without the deep reduction, and yes i do belive you can actually but a 13 speed rear box on that trans and make it a double over because you allready have a overdrive in the main, all you would be doing is addin the overdrive section from a 13 speed on you trans. That is what you split the gears with anyway
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Nevermind, i think i understand it now. I cant get more out of my top gear because its maxed out but if i want to split the other gears to drop down the rpm i can. if i max out 7th gear and want to drop the rpms down a lil lower then i can do that but i cant do the same with my final gear because it doesnt have a gear after that to share i guess. im talking about if i had a 13 speed by the way. hope i didnt confuse you all but i think i finally understand all this now lol

An RTX 9 and an eaton 13spd both have the same top gear ratio, one has .73 in 9th the other has .73 in 13th. I know it can be confusing if you are new to it but it comes with time, the easiest way to get more road speed is taller tires, with an 11R24.5 tire, eaton OD trans(.73OD) and a Mack 4.42 rear you get about 74mph at 1800. I try not to turn my truck that high for extended periods I like the 15 to 1600 rpm range its a lot easier on the engine, I think with your current road speed the best gear ratio for you to try would be 3.86 there are carriers out there with this ratio(I am actually wanting a set now I have 4.64 gears) I know that 4.17 is a good ratio for taller tires like 11r24.5's but sounds like you are running 22.5's with the rpm you are turning. I would ask are you running spoke wheels or budd/disc wheels? if you are running budd wheels a wheel tire swap would be a lot cheaper than a gear swap if you can get a tire shop or other truck owner to give you some money for yours, a set of CRD92/93 chunks with 3.86 gears will be $1500 to $4000 depending on condition. I hope that info helped I have been there before and like I said I want to make a swap now Im just waiting on winter (and more money).

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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Come to thank of it that is basicly the same trans as a 8LL without the deep reduction, and yes i do belive you can actually but a 13 speed rear box on that trans and make it a double over because you allready have a overdrive in the main, all you would be doing is addin the overdrive section from a 13 speed on you trans. That is what you split the gears with anyway

Actually if memory serves me right the eaton transmission rear (OD) box is not there to get an OD trans to run double OD its made to fit a NON OD trans there is something about the gear tooth count that wont work on an OD trans, the same with the LOW gear set box for an 8LL and 18/15L etc. the Low gear set box works with the OD trans the OD box works with the direct trans. I cant rmember what it was but Ill do some looking for my old overhaul manuals.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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An RTX 9 and an eaton 13spd both have the same top gear ratio, one has .73 in 9th the other has .73 in 13th. I know it can be confusing if you are new to it but it comes with time, the easiest way to get more road speed is taller tires, with an 11R24.5 tire, eaton OD trans(.73OD) and a Mack 4.42 rear you get about 74mph at 1800. I try not to turn my truck that high for extended periods I like the 15 to 1600 rpm range its a lot easier on the engine, I think with your current road speed the best gear ratio for you to try would be 3.86 there are carriers out there with this ratio(I am actually wanting a set now I have 4.64 gears) I know that 4.17 is a good ratio for taller tires like 11r24.5's but sounds like you are running 22.5's with the rpm you are turning. I would ask are you running spoke wheels or budd/disc wheels? if you are running budd wheels a wheel tire swap would be a lot cheaper than a gear swap if you can get a tire shop or other truck owner to give you some money for yours, a set of CRD92/93 chunks with 3.86 gears will be $1500 to $4000 depending on condition. I hope that info helped I have been there before and like I said I want to make a swap now Im just waiting on winter (and more money).

I do like the 4.17 gears which is what the truck i run now has but it has a 13 speed maxitouqe trans and it runs 70 at about 1700, but he can put a 13 speed box on his trans and make it a double overdrive and lower his rpms at crusie and split the last four for more proformance, i ran a truck with this trans and 4.64 that pulled quit well.
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Actually if memory serves me right the eaton transmission rear (OD) box is not there to get an OD trans to run double OD its made to fit a NON OD trans there is something about the gear tooth count that wont work on an OD trans, the same with the LOW gear set box for an 8LL and 18/15L etc. the Low gear set box works with the OD trans the OD box works with the direct trans. I cant rmember what it was but Ill do some looking for my old overhaul manuals.

Yes come to thank of it you may be right, but he can get a 13 and have it fliped and make it a doubleover but lo gear is not much in them.
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Yes come to thank of it you may be right, but he can get a 13 and have it fliped and make it a doubleover but lo gear is not much in them.

The doubleover flip is a old school tranny build that you don't see alot of now for some reason, but the rig i ran did work very well, let us know what you find.
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I forgot all about flipping the gears I have never seen it done only heard about it from back in the day, with the overall gearing hes got(short tires 4.42 gears) he might be good with that.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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I forgot all about flipping the gears I have never seen it done only heard about it from back in the day, with the overall gearing hes got(short tires 4.42 gears) he might be good with that.

Seems to me you can gain about 15 ti 20 miles an hour on top end with a fliped box, with 4.64 ratio and tall rubber the old supeliner would top out about 82 and 70 was no sweet for it and if i rember right it was a rt 15613 that was fliped, any good trans shop should be able to do this for him.
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Come to thank of it that is basicly the same trans as a 8LL without the deep reduction, and yes i do belive you can actually but a 13 speed rear box on that trans and make it a double over because you allready have a overdrive in the main, all you would be doing is addin the overdrive section from a 13 speed on you trans. That is what you split the gears with anyway

Might want to check that with Glenn. He is pretty good with what swaps and what doesn't.

The normal gear flip is done to a direct main box 13spd. An underdrive rear would give you about .75 OD and the OD rear box would end up around .62. Top 4 gears would be direct, .83, .75, and .62. Thats from memory but it is in that neighborhood. Glenn would tell you not to make these boxes as the gear shift is a little funny afterwards and you loose the low hole. More or less for a hobby truck only.

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