.

Thanks on the T-case check. Interesting.

OK, so I have some basic dimensional data to compare the stock Allison MT654CR automatic 5 speed to the Fuller RTO-12513 13 speed trans. The 13 speed dual countershaft trans lists as 3/4" shorter, 3/4" wider, and 7.5" shorter on height. The Fuller weighs 70 pounds more. I need to double check the width dimension, as the Allison info may have included the bell housing? If not, then we are good to go I don't see any clearance issue. If anybody has their trans out or is crawling under their truck today, take a tape measure and grab the width of the trans, not including the bell housing. Otherwise I will do it later this evening. Thanks.

The 13 speed fuller has a large 4 bolt clutch inspection window of which a hydraulic release actuator is available to be used for, and is available used for low cost, even an air assisted one I believe as an option, to reduce pedal force. Volvo and Freightliner both used a hydraulic clutch, so parts are available, new and used.

I doubt that fuller only weighs 70 lbs

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gringeltaube said:

According to the parts book and UOCs, the part number for the propeller shaft assembly (TC-to-fwd rear axle) only changes depending on the wheelbase and if it was made by DANA or ROCKWELL.
No changes between V; D & Z-models.

... which makes me think that the T-case always remained in the same position.

Click to expand...

The A2's use a much longer jack shaft (transmission to T-case) than the A0/A1's. I think you are correct in the T-case remaining in the same place across all three models. The 8.3 block is shorter than the NHC250 block so they compensated with the jack shaft length. This extra room between the transmission and T-case would open up more possibilities for different size transmission without having to move the T-case. I think this is what Jeff was getting at.

For reference, the picture is of an A0/A1 jack shaft. I don't have and A2 jack shaft to measure but from pictures it appears to be about 3 times longer.

You Snapper Head, I fixed it. Weighs 70lbs more.

So, correction to above, as expected. The Allison measures about 13" wide at the body and pan flange. But, there seems to be adequate room for a much wider trans. The front prop shaft seems to hang well below the area the trans would occupy. The 13 speed is 6" wider total, or 3" per side.

I would lose the PTO driveshaft, but could possibly run it direct off the Fuller PTO mount.

The trans to transfer case shaft on my a2 is significantly longer than posted above for the a1 and first gen. I measure about 19" from center-center of the U-joints.



Looking easier to swap the clutch housing on the Fuller to a smaller SAE #2 bell, as the engine mounts would need to change significantly if I swapped the engine flywheel housing to an SAE #1. This will limit me to an SAE #2 14" clutch vs the larger SAE #1 15.5" clutch, but Eaton has 14" clutches rated to 1400ft-lb, which exceeds the ISL's 1200ft-lb rating.

At this point, since the trans is only supported from the engine, I may be mating up the ISL with the 13 speed ahead of time, and dropping it in as one piece. I wasn't going to do this, but once I realized the Allison would just be floating in space after yanking the 6CTA engine out, may as well just yank them both.

What is this doubled up linkage rod from the T-case shifter to the trans? A lock-out to keep the T-case range selector from moving unless trans is in neutral?

The T-case does not look terrible to lower if need be. Some steel plating would do it. It would slightly worsen the rear driveshaft angle, but oh well. Would also have to lengthen the shift lever arm.

For the PTO you might run into clearance issues. If so an option would be to install a PTO angled adapter to rotate it downwards for clearance.





Looking more and more like it's a pretty direct swap minus the clutch controls (simplified with hydraulic setup as you mentioned).

Swamp Donkey said:

For reference, the picture is of an A0/A1 jack shaft. I don't have and A2 jack shaft to measure but from pictures it appears to be about 3 times longer.

View attachment 678559

Click to expand...

This is my issue with changing trans in the 819

74M35A2 said:

So, correction to above, as expected. The Allison measures about 13" wide at the body and pan flange. But, there seems to be adequate room for a much wider trans. The front prop shaft seems to hang well below the area the trans would occupy. The 13 speed is 6" wider total, or 3" per side.

I would lose the PTO driveshaft, but could possibly run it direct off the Fuller PTO mount.

The trans to transfer case shaft on my a2 is significantly longer than posted above for the a1 and first gen. I measure about 19" from center-center of the U-joints.

View attachment 678618

Click to expand...

Okay the front prop shaft can be swapped for a 939 or 939A1 shafts that have the hanger bearing to gain more clearance.
And you and Swamp thing are right about me saying that the extra room on the 939A2 is because the motor and transmission are moved forward , and thereby gives more room for extra-long transmission.

74M35A2 said:

Looking easier to swap the clutch housing on the Fuller to a smaller SAE #2 bell, as the engine mounts would need to change significantly if I swapped the engine flywheel housing to an SAE #1. This will limit me to an SAE #2 14" clutch vs the larger SAE #1 15.5" clutch, but Eaton has 14" clutches rated to 1400ft-lb, which exceeds the ISL's 1200ft-lb rating.

At this point, since the trans is only supported from the engine, I may be mating up the ISL with the 13 speed ahead of time, and dropping it in as one piece. I wasn't going to do this, but once I realized the Allison would just be floating in space after yanking the 6CTA engine out, may as well just yank them both.

Click to expand...

Yes it is easier to remove motor and tranny together anyhow.

74M35A2 said:

What is this doubled up linkage rod from the T-case shifter to the trans? A lock-out to keep the T-case range selector from moving unless trans is in neutral?

Click to expand...

Not sure what doubled up linkage you're talking about? There's only one linkage that goes to the transfer case unless you are using a wrecker transfer case that has a PTO.

74M35A2 said:

The T-case does not look terrible to lower if need be. Some steel plating would do it. It would slightly worsen the rear driveshaft angle, but oh well. Would also have to lengthen the shift lever arm.

Click to expand...

Look in a minute but I think if you drop the drive shaft angle on the rear by dropping the transfer case an inch or so would help the angle, but I will look.



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We may be keying in on the key to making this work. I already back-dated my front prop shaft to the earlier one with the carrier bearing. My spline joint was worn and had a bad vibration that would go away when the front drive was engaged.

So now, my front prop shaft has mor angle because it goes to the cross member bearing, then straightens out and heads to the front axle. This is why it seems like I have more clearance to fit a wide trans, because, I do.

Transfer case looks easy to lower if need be. The 13 speed is looking good so far! I don't even know how to drive one! Ha! This will be sweet. Studied it on paper, we should be good to go. I'll wear a 10 gallon hat and overalls my first time.

The 13 popper has an angle PTO adapter on it already, and I think 2 PTO ports to chose from, side and bottom.

74M35A2 said:

What is this doubled up linkage rod from the T-case shifter to the trans? A lock-out to keep the T-case range selector from moving unless trans is in neutral?

Click to expand...

Do the linkages you're talking about look like the ones in the picture?

There was a reverse lockout MWO. It was a kit added to keep the transmission from going into reverse if the T-case was in low range.

That is it exactly.

Some new info from digging all day long. I really don't want the nightmare of trying to do hard clutch linkage rods, so I am leaning toward hydraulic for ease of installation.

I want to keep my engine side SAE #2 flywheel housing as to not change rear motor mount style and location, so, I need an SAE #2 clutch housing for the RTO-12513 trans. Somewhat rare to use SAE #2 with a twin counter shaft trans, but they do make it. I selected Eaton clutch housing p/n 4305199, which is cast iron (no need to support rear of trans, but if you use an aluminum housing you will), and has a separate offset window to install a hydraulic clutch slave actuation fork (5th pic below, hydro slave @ 7pm window). Required Eaton actuator lever is p/n A-7414 (third pic below). Does not include the slave cylinder itself. For that, I am going to use an air-assisted Volvo unit, which those that update say only requires 12lbs of pressure to actuate. Of course it also works without air, but at a higher force. Below is a pic of the standard hydro actuator (first pic) and then the air assisted one (second pic). Can even get a roller tipped fork (4th pic)!

I need to check clutch availability and cost before pulling the trigger on spending $ for above and below mentioned items. Eaton website does say a 14" (SAE #2) clutch is available in a 1400ft-lb rating (ISL is 1200), so we should be good? Wonder where the shifter will poke through the floor? Can always make some custom shift lever bends.....
I still need to check firewall clearance to add a hydro clutch master cylinder pedal. Guessing PCB is in way, but that can easily be evicted to another location. I'm down to only using half of it anyway now with a modern starter that has an integrated low current mag switch on it (IMS). I will likely buy the hydro clutch master and pedal and install it first in the truck as it sits now, before going any further. If it fits well, then we are off to the races on rowing and splitting gears, starting in the basement of course... With a 2 speed t-case, I'm thinking 26 forward and 4 reverse speeds? Come get some of that, Catfish!!! Where is that 10 gallon hat?

Mechanical is easier... just need a really big left leg. Seriously, the box I sent you has plenty of room under the floor of a M936A2 series. You're way over thinking this.

There are hyrdo clutch slaves cylinders that do not mount on the firewall.

Master cyl mounts to firewall, slave on clutch housing.

I want a nice easy clutch pedal so I can comfortably drive to your house and do a 3 gear grabbin' hole shot on your lawn.

Most are built into the pedal, like this one:

https://www.heavytruckparts.net/det...&vendor=1821960&store=1&fc=1&fp=1&searchnum=1

Right ratio for that clutch you spec'd, right bell housing for it, right master, right slave,.

Well, does not mount where you think it does

There are others that mount under the floor board.

You can have 78 forward gears and 26 reverse gears--- all sounds good shortbus--- but it does you no good if you cant keep FUEL in your truck--- baaahhhhaaaaaa

I wouldn't worry so much of the placement of the transfer case but the placement of the fuel hand!!!

I'll just stick the shifter handle out the back window.

I have more homework, the Eaton Solo clutch may not be a single disk like I thought, which may be OK. Also something about hydraulic and self adjusting play or don't play well together?

If the m939 series cab is the same length from front/rear as the m809 series cab then this will give a pretty good idea of where a forward mounted shifter pops up through the floorboard.

Tons of room to add clutch pedal on inside firewall. Will check under hood soon, it was raining out, but should be no show stoppers.