Eaton fuller

[theakerstwo]

These two trans have different gears inside so the ratios will not be messed up.If you want to know for sure go to the eaton parts section and pull the gear part nunbers and you will see the gears are not the same even if you do swap them.i have been there and have tried to telll customers the same thing and most say some driver told them to try it.And I say that's the best way to find out.

[doubleclutchinweasel]

I'm not saying that swapping the front gears with the 4th gears is necessarily the same thing as getting a "real" overdrive box.

All I'm saying is that, by swapping those gears, you are speeding up the countershafts, effectively raising every gear ratio about 20%. The steps in-between gears will not change, as they are determined by the ratio of teeth on each gear set. Of course, if any steps ARE affected, it would be one step to either side of "direct"...and that COULD be a real nuisance!

If someone will get me the number of teeth on all the gears in a standard RT-910 or -915, I'll be more than happy to calculate the ACTUAL gear ratios achieved by doing the gear-set swap. Or, would the number of teeth be in the parts book? I'll look and see if I may already have those numbers.

Incidentally, this is fun!

[jdfordhd]

Not that everyone here does not already know this, but there could be others reading all this with a big question mark hanging over their heads..!! Basics: a "direct" drive designated transmission means the engine crankshaft turns over one time, the driveshaft turns over one time when the transmission is in "high". An overdrive transmission is capable of turning the driveshaft faster than the engine crankshaft when in high gear. An RT910 can easily be made into a "homemade" RTO910 by flipping the 4th gear gearset in the main box. The reduction ratio of the gearset in the 4th stick position (I use "stick position" hoping everyone knows what I mean.!) when flipped around (the larger gear becomes the drive not the driven) becomes the overdrive ratio when the stick is in the 4th stick position. The 5th stick position remains "direct" or 1:1. The unsavory "gap" is after you shift thru the first three gears (range selector in high or low doesn't matter), the stick moves over and back to the 5th stick position essentially skipping what used to be the reduction ratio of 4th, then the final move is the stick going forward to the 4th stick position which has now become an overdrive ratio by flipping that one gearset on the shafts.! That was the explanation given to me 30 years ago by a transmission guy. I have never done this but did consider it years ago.

[doubleclutchinweasel]

Not that everyone here does not already know this, but there could be others reading all this with a big question mark hanging over their heads..!! Basics: a "direct" drive designated transmission means the engine crankshaft turns over one time, the driveshaft turns over one time when the transmission is in "high". An overdrive transmission is capable of turning the driveshaft faster than the engine crankshaft when in high gear. An RT910 can easily be made into a "homemade" RTO910 by flipping the 4th gear gearset in the main box. The reduction ratio of the gearset in the 4th stick position (I use "stick position" hoping everyone knows what I mean.!) when flipped around (the larger gear becomes the drive not the driven) becomes the overdrive ratio when the stick is in the 4th stick position. The 5th stick position remains "direct" or 1:1. The unsavory "gap" is after you shift thru the first three gears (range selector in high or low doesn't matter), the stick moves over and back to the 5th stick position essentially skipping what used to be the reduction ratio of 4th, then the final move is the stick going forward to the 4th stick position which has now become an overdrive ratio by flipping that one gearset on the shafts.! That was the explanation given to me 30 years ago by a transmission guy. I have never done this but did consider it years ago.

You're all over it! We're currently trying to figure out exactly what the gear ratios would be after doing that. I hope I can find the tooth count in a direct & see what the resulting ratios would be in the homemade od box.

Incidentally, you are exactly right. We should always assume a new guy is reading this. That's why I'm frequently guilty of providing more than just a short answer.

[doubleclutchinweasel]

I have some part numbers. But, I have no descriptions (i.e.: tooth counts).

Direct Drive (RT-910, -915)

Input Drive Gear - 14486

Countershaft Driven Gear - 14303

Countershaft 4th Gear - 14299

Mainshaft 4th Gear - 14487

Overdrive (RTO-910, -915)

Input Drive Gear - 16601

Countershaft Driven Gear - 16003

Countershaft 4th Gear - 14303

Mainshaft 4th Gear - 16002

If anybody has the tooth counts on these, and knowing what the 1-2-3 ratios are, I think we can accurately chart the effective gear ratios of a home-made RTO.

All the rest of the gears appear to be the same.

Any info?

[jdfordhd]

:)Just because I like math ! If the fourth gear reduction is 1.24:1 like the 15 spd direct quoted above, let's just throw a tooth count out there to play with: 40 teeth driven by 32 teeth is 1.25:1 ratio. Flip those two gears, 32 teeth driven by 40 teeth is 0.8:1 which is pretty durn close to factory OD ratios..!

[doubleclutchinweasel]

:)Just because I like math ! If the fourth gear reduction is 1.24:1 like the 15 spd direct quoted above, let's just throw a tooth count out there to play with: 40 teeth driven by 32 teeth is 1.25:1 ratio. Flip those two gears, 32 teeth driven by 40 teeth is 0.8:1 which is pretty durn close to factory OD ratios..!

Yes! Yes it is!

In fact, there is one gear which is common between the RT and RTO, within the 2 gear sets we are talking about. gear 14303 is the input/driven gear on the RT and it is 4th gear driver on the RTO. Now, what that means is that the mating gears (14486 and 16002, respectively) MUST also have the same tooth count. If they didn't they wouldn't mesh!

Soooooooooo, there are only a few gear part numbers to be identified. And, yes, the input "set" on the RTO and that of the RT could still be different, which could cause a different effective input ratio. This would have an effect on every gear, except the direct, which could cause a different step percentage between 3-4 and 4-5...like we said above. The 1-2 and 2-3 steps would, however, be unaffected.

As soon as we can get some tooth counts, I think we can quantify the effects of making a do-it-yourself RTO. And, I'd really like to know the numbers, since I have been tempted to do mine!

[doubleclutchinweasel]

Found some numbers! Working on it now.

[doubleclutchinweasel]

Okay...

The gear sets in question, for the input set and 4th gear set of the RT/RTO-910/915 are as follows....

RT - Input Set - 28 Driver / 40 Driven

RT - 4th Gear Set - 37 Driver / 32 Driven

RTO - Input Set - 32 Driver / 37 Driven

RTO - 4th Gear Set - 40 Driver / 28 Driven

These are based on the part numbers in the Eaton-Fuller parts manual.

So, these ARE the exact same gear sets (tooth/tooth). They ARE also different part numbers in some cases. Not sure why...maybe hub shapes or something.

If you plug in these numbers, and calculate the remaining variables (remaining gear ratios, low-gear ratio, etc...), and then substitute the known numbers, you get the gear ratios shown below.

Now, this only applies to this particular series! I have no idea what might be in a different model, or a different revision. Use (or not) at your own risk!

[doubleclutchinweasel]

This where you post your message and add pictures

??????

[thomastractorsvc]

I made some slides to help folks up load a files/pictures thought I deleted it

http://www.bigmacktrucks.com/index.php?/topic/1344-how-to-add-photos-to-your-post/

[doubleclutchinweasel]

I made some slides to help folks up load a files/pictures thought I deleted it

http://www.bigmacktrucks.com/index.php?/topic/1344-how-to-add-photos-to-your-post/

So, my picture isn't where it should be?

[thomastractorsvc]

I used this topic for the screen shots, read the slides you should be able to figure out what I did. I thought I had deleted the post but only the picture it is now gone.

Don't worry you should or shouldn't be confused?!

[doubleclutchinweasel]

The only way I have been able to put a screenshot on here is to save it as a .jpg and load it like a picture...like you show.

Wouldn't it be nice if one could cut from elsewhere and paste in here? I can cut & paste from within the forum, but not from outside! Browser mis-match, perhaps?

[jdfordhd]

Ok...my head is hurting.... let's move on to u-joints or compression ratios or the effective ground pressure (in PSI) differences between 425 and 385 floaters when used on a steering axle..!! JUST KIDDING...!!

[6368]

Had a guy when we had dumps that would not touch it for any reason. Think he was scared or tearing up driveline. I do not know why and he is in the fed pen. Damn truck was a beast. Slower then hell but would go everywhere. 270 Cat 8LL with 5.29's in the back

i must have a pretty similar setup on the Brockway 270 cat 8ll ( i think) with 6.44s.

[6368]

Okay...

The gear sets in question, for the input set and 4th gear set of the RT/RTO-910/915 are as follows....

RT - Input Set - 28 Driver / 40 Driven

RT - 4th Gear Set - 37 Driver / 32 Driven

RTO - Input Set - 32 Driver / 37 Driven

RTO - 4th Gear Set - 40 Driver / 28 Driven

These are based on the part numbers in the Eaton-Fuller parts manual.

So, these ARE the exact same gear sets (tooth/tooth). They ARE also different part numbers in some cases. Not sure why...maybe hub shapes or something.

If you plug in these numbers, and calculate the remaining variables (remaining gear ratios, low-gear ratio, etc...), and then substitute the known numbers, you get the gear ratios shown below.

Now, this only applies to this particular series! I have no idea what might be in a different model, or a different revision. Use (or not) at your own risk!

I need help understanding this chart. 5th low doesn't use the countershaft? The gear set ratio for fourth is .86 how does it get to be .70.

[doubleclutchinweasel]

When in 5th gear, the output shaft is connected directly to the input shaft. So, no, 5th gear does not use the countershaft. This is your direct gear.

[theakerstwo]

Well I have been proven wrong again,must be my memory.Try me on something simple next time.

[other dog]

My brain is starting to hurt too. I'm gonna go post pictures of the week that require no thinking. With brief descriptions, because everybody has seen a girl in a car before.

[doubleclutchinweasel]

I'm right there with you!

They say the first thing to go is your memory.

The second thing is...uh...the second thing is...uh...what were we talking about again?