I'll start this build with a preface which I know will drive Charlie bonkers for having to wait.

Meet Jumbo...



This is a day or so after I purchased the truck in Feb of 2010 for around $7000 green backs. With the pending arrival of kiddo #2 we needed a bigger truck to hold us all as the ol' 87 F250 (6.9l diesel may it RIP) wasn't going to cut it anymore (not to mention it was drinking its own oil at the rate of a quart every 350 or so miles). I have always thought that the weak link of Ford's OBS workhorses has been the transmission and I have dreamed of upgrading the transmission ever since I bought the 97 in 2010.

Not to give too much away here in the first installment... but the RTO 6610 transmission has now been in the truck for 2 years and just shy of 20000 miles.

The people here will love this, I still wanna do something similar like this, just not sure on execution yet.

The Southern President

This should be interesting. I knew a guy that ran a military truck salvage yard that put a DT466 and 9 speed in a mid 80's F350. Could always tell when he was coming through town.

RTO 6610 is a ten-speed, right?

Ian,

You are correct. The RTO is a 10 speed... RT - Roadranger transmission, O - Overdrive unit, 66 - 660 ft-lb input torque, 10 - number of gear selections. transmission arrangement is a 5 speed gear box on front with a Hi/Low Aux range box in back.

Cj

Ooooooo
Cool truck build. Drum roll please!

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So, as I mentioned in the first post I have always dreamed of changing the transmission (which I consider as the main weak link of the Powerstroke power train) out for something a little more in the medium duty realm. Some months after purchasing Jumbo I found an ad for dead International t444e motor. From that engine I was able to get my hands on the flywheel housing adapter needed for any future conversion. My original plan was a TTC Eso 7 speed swap.
In the mean time I purchased a cnc mill and dragged it home to my place (this was with the good ol' ZF5 transmission). Trailer plus machine was around 21k (yah, I only exceeded the book GCR by a bit). As I was just on surface roads it wasn’t too bad other than having to really ride the clutch to get the truck moving and having to go into 4 wheel low to back the trailer into the driveway. The mill weighs in around 16000#.

The transmission swap really became serious in April 2016 while pulling my dad’s disabled truck home from Laramie, Wyoming. All told I was pulling around 15k and trying to keep the truck rolling at a reasonable pace was a bugger.

There is a reason that the 97 F350 was only rated for 11k towed weight (and it sits between the engine and rear axle). The trip home was rough, as finding a gear the engine was happy with that didn’t require me revving the engine into the stratosphere (how did Ford come up with the red-line for the 7.3??) to keep the boost up and the truck at a reasonable speed was tough. After arriving home, I promptly started doing some digging and found that someone had done an Eaton RTO 6610 swap in a Dodge Ram. Two weeks of trolling the web later I found a RTO 6610 on Craigslist and the adventure was underway. Two days and 1533 miles later, this was sitting in my garage...

[emoji102][emoji102][emoji102]

The Southern President

All right Doc... keep your eyeballs in your head .

It took me a year and a half to finally get to the point where I was ready to begin the swap.. I found one or two forums discussing Eaton-Fuller swaps that involved re-mating the transfer case to the transmission using a cut down yoke that was then bolted to a coupler with the correct mating splines for the transfer case. Not a bad idea, but it would have added a considerable length (4+ inches) to the whole transmission/transfer case combination. I knew that some transmission tunnel mods would likely be required, but I was hoping avoid modifying the body supports running under the cab that stiffen the cab.
First things first - breaking the huge nut loose (with a 6 some odd foot cheater bar – the aluminum bar is bolted to the output yoke).

Then, I got to work dismantling the auxiliary transmission case to have a look at the output shaft. This is a shot just after I divorced the case.

The RTO 6610 output shaft sure makes the original ZF5 transmission output shaft look puny. The splines (just visible at the top of the picture) on that guy are 2.25 inches in diameter. I didn't have enough hands to hold the other counter shaft. In low range there is approximately a 3 to 1 reduction. High range is direct drive.

Here is a shot of the main 5 speed gear box.

The left most (course cut) gears are reverse, the next set to the right is first gear. Second gear and third gear are on the next sliding clutch. Now things get a little odd. The next gear is 5th (this is an overdrive transmission) while 4th couples the input shaft straight to the main shaft. The shift pattern is:
R 2 5
1 3 4

How ironic that same transmission was in the LTL Ford trucks. My first new dump truck was a LTL with that in it. I spent a lot of money on that transmission, and fuel. Couldn't convince the drivers high gear was against the dash. They hated that truck. Said it was gutless in 4th (9th), screaming in 5th (10th) because they were shifting incorrectly, not looking at the shift pattern posted on the sunvisor

Great transmission tho, the gears were split apart just right with load on if driven properly.

My trucks either had big cam cummins or dt44 in them

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cjfisher said:

The left most (course cut) gears are reverse, the next set to the right is first gear. Second gear and third gear are on the next sliding clutch. Now things get a little odd. The next gear is 5th (this is an overdrive transmission) while 4th couples the input shaft straight to the main shaft. The shift pattern is:
R 2 5
1 3 4

Click to expand...

How does the overdrive ratio compare to the stock ZF-5? And I guess as a closely related question, what rear-end gears are you running?

It's been years since I drove a truck like that ('95 PSD with the ZF-5 and 4.10 gears) but my recollection is that when empty I'd have liked a taller "cruising" gear.

Ian,
The stock ZF5 was .79:1 OD, the RTO6610 is .80:1. Rear end is geared with 3:55s. I cruise at 65 mph at 2000 RPM. At 70 mph RPMs are 2200. With a 7.2:1 first gear I can start heavy loads just fine with the 3:55 axle gears.

Charlie,
The fellow I bought the transmission from described a truck about LTL sized. The truck ended up getting run over by a freight train which is how the RTO ended up homeless. It was originally just an RT-6610, but the fellow had it reconfigured to an overdrive unit. When I first did the swap I had a time or two where I forgot the shift pattern (the transmission quickly reminded me! ). And yes the splits are awesome - it is so easy now to keep the turbo spooled up. Pulling a load I'll rev up to 2500, after the shift I'm 2000 RPMs and I can get the turbo to spool right back up.

cjfisher said:

Ian,
The stock ZF5 was .79:1 OD, the RTO6610 is .80:1. Rear end is geared with 3:55s. I cruise at 65 mph at 2000 RPM. At 70 mph RPMs are 2200. With a 7.2:1 first gear I can start heavy loads just fine with the 3:55 axle gears.

Charlie,
The fellow I bought the transmission from described a truck about LTL sized. The truck ended up getting run over by a freight train which is how the RTO ended up homeless. It was originally just an RT-6610, but the fellow had it reconfigured to an overdrive unit. When I first did the swap I had a time or two where I forgot the shift pattern (the transmission quickly reminded me! ). And yes the splits are awesome - it is so easy now to keep the turbo spooled up. Pulling a load I'll rev up to 2500, after the shift I'm 2000 RPMs and I can get the turbo to spool right back up.

Click to expand...

Since there is no like button


Like

The Southern President

Thanks Doc.. how does the "Add to Doc's Reputation" button work up there in the right hand corner of each post (looks like a scale)? Is that form of 'Liking?"

Part Thrice:

Upon initial inspection it looked like the shaft had enough meat that I could cut it down and then re-spline it to fit the transfer case. I measured ten times and cut twice. Here is the test shaft I made out of aluminum. There was an opps from my using the cutter diameter as listed on the box.

After a bit of work on the lathe and cnc mill (yes that is a poor man’s indexer there on the end and the mill is the same one as seen on the trailer) and voila a revised output shaft.

I did not surface harden the areas I cut as I would have likely needed to re-heat treat the whole shaft and I was worried about warp-age.

The core of the shaft is already strong - Surface hardening it gives it better wear resistance. Eventually I’ll remake the whole shaft and heat treat and surface harden it. A quick shot of the Aux transmission with the gears in place - this is right before I put the case back together.

cjfisher said:

Thanks Doc.. how does the "Add to Doc's Reputation" button work up there in the right hand corner of each post (looks like a scale)? Is that form of 'Liking?"

Click to expand...

I'm not sure, it prolly does. I don't see that on tapatalk, which is another bad thing it.

The Southern President

That is some definite skill there CJ

The Southern President

The green beans in the right corner are the antique like button. You have to hit like 20 people before you can hit someone again. They are reputation points.

Used to be a red bean to take away reps back in the day. Cowboy9miliie and I got into a battle with another member, and we got him into negative reps.
That being said the management stepped in and shut down the negative reps part......

That being said......pfffftttttttt.

Nice job adapting. I love machine shop projects, and do miss the machine shop that was the wife and her father's that we had to sell back in 2012.
The city wanted the land for condos. Go figure

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dustybumpers said:

The green beans in the right corner are the antique like button. You have to hit like 20 people before you can hit someone again. They are reputation points.

Used to be a red bean to take away reps back in the day. Cowboy9miliie and I got into a battle with another member, and we got him into negative reps.
That being said the management stepped in and shut down the negative reps part......

That being said......pfffftttttttt.

Nice job adapting. I love machine shop projects, and do miss the machine shop that was the wife and her father's that we had to sell back in 2012.
The city wanted the land for condos. Go figure

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Click to expand...

I think they just disabled reps for that user. He can not give reps at all, and Noone can see his

The Southern President