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‘06 Megacab
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Discussion Starter · #1 ·
I haven't seen many threads on accomplishing the swap or the experience of the journey. So for posterities sake, here's the good, the bad and the ugly of my swap.


Its been a number of years since I realized my 48RE was going to need some help. I looked at building the 48 or a manual swap for quite some time but then started to see the Allison conversions showing up which piqued my interest.

I enjoy driving a manual and the low gearing of the G56 would be ideal for towing in the mountains plus in/out of the steep, tight and slow roads to camping/riding areas. I also needed/wanted the taller overdrive of the 48RE to keep up with the flow of traffic at a reasonable RPM. It was the easiest route, but I'm not a fan of the harsh shifts of the built 48's I've ridden in. I put pen to paper for a comparison and in the end the Allison was the best compromise of what I wanted.

Unfortunately, the swap is no small task and was the biggest negative. The to-do list includes:
  • Bell housing adapter
  • Transfer case adapters
  • Cooler lines
  • Shifter bracket
  • Transmission mount bracket
  • Driveshafts
  • Stand-alone TCM and harness

I started researching my options for the controls, talking to CAConversions and Jason from TransmissionTuner. Both answered my questions and were very helpful, but I felt Jason would be the best fit for my needs and I pulled the trigger on his harness in 2018.
 

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Discussion Starter · #2 ·
I sourced a transmission from a recycler for 1100 with shipping. It was ugly from New England road salt and had plenty of miles, but none of it mattered since I would fully clean and rebuild. (Let me throw out the disclaimer right now... when it comes to before & after pictures I fail miserably. I always forget to take pictures.)




The next step was to tear it down for the clean up and rebuild. To make my life easier, I fab'ed an adapter for the engine stand that bolts in place of the PTO covers.



Tear down went smoothly and the internals looked much better than I expected. Clutches were worn but no significant burning or hotspots. Either way... its a serious pile of parts.

 

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Discussion Starter · #3 ·
The case clean up took a few hours of pressure washing and scrubbing with engine degreaser, simple green and aluminum wheel cleaner. (insert comments on lack of photos here)
After cleaning and drying, sprayed the case with a few coats of primer.




I was liking the olive drab green and almost disappointed to spray the cast iron grey.


 

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Discussion Starter · #4 ·
Rebuilding the transmission went fairly well except for two issues.

Following the ASTG manual with Suncoast's instructions, I had a two clutches that I could not get within specs. A call to Suncoast's tech support was just the ticket and I got the exact thickness clutch plates needed.

The other issue was during the shift kit install. A few of the bolt heads rounded off while trying to split the valve body. The material was just soft.


My go-to fix for stuck/broken bolts is welding on a nut. The focused heat causes the bolt to expand and helps it break free, plus a new(-ish) head to torque on.


Free at last!





Again, I'm no expert but it wasn't terrible to build and quite satisfying to see the final product.
 

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Just asking....the starter being on the passenger side, will that be a problem with the exhaust?
 
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Sorry if I missed it. What year Allison trans is that?

What Cummins/bellhousing are you going with?
 

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Discussion Starter · #7 ·
Swapping the 23 spline transfer case input for the 29 spline version was the next hurdle. The lock ring pliers in this pic simply did not open the ring far enough to properly remove it.


Do yourself the favor and find a set that opens 1".


Also, don't forget to swap over the pilot bearing from the old input gear... or else you'll have to disassemble this twice.

Don't ask how I know.
 

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Discussion Starter · #8 ·
Sorry if I missed it. What year Allison trans is that?

What Cummins/bellhousing are you going with?
I think it was from a 2007. Its actually from a truck with the 8.1L gas motor. I believe the input shaft speed continued to come from the pickup sensor in the bellhousing a year or two later than it did with the duramax due to a lack of GMLan/serial bus capabilities. The transmission is the same...torque converter and TCM tuning are the differences.
I decided to use the GM bell housing and one of the many available adapter plates for this.

Its a decision I am currently regretting.

Just asking....the starter being on the passenger side, will that be a problem with the exhaust?
Needless to say, the exhaust is the least of my issues. The exhaust hanger at the bottom of the down pipe does interfere with the adapter plate.
Again, I regret taking this path. It is not the path of least resistance and is the inferior option if I may be completely honest.

To start, it requires grinding of the block just for this plate to go on. Granted its just extra material, but I'm not a fan of it.

I tried to take as little as possible from the block and instead attack the adapter. In the end it was a compromise of the two.

My next issue with the adapter was the bolt holes being slightly off. The bolts with the alignment dowel were the only two to go in smoothly. The further away from those two the worse it got, the top two would not thread in. It required oblong-ing those six holes.

Next on the list of reasons this is not the best option, starter clearance. The exhaust is the least of the worries. There is barely enough room between the block, frame and motor mount for the starter to fit. Maybe there is a difference with the Ford 6.0 starter, but I think I have a 6.4 starter. I ground off some of the housing and the starter as part of the compromise. At this point F, the adapter plate.

Last but not least on my list of why to F this plate, the coolant line for the heat exchanger.


While I plan to squeeze out every BTU it has to give, I know a lot of people bypass the heat exchanger and delete this line. The Fleece coolant bypass seems like a popular option..... Correct me if I'm wrong, but I believe it installs in the freeze plug on the back of the block. Its hard to see that freeze in the picture as it is covered by this ridiculous plate.


I was getting cold feet about using this GM bell housing adapter over the past month or so... I should have listened to my gut. I'm sure using the SAE bell housings come with their own list of issues, but its can't be this bad. At this point I have to complete the swap, but once I'm done I'll CAD the adapters to fabricate locally. I want to toss this thing in the dumpster.
 

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Discussion Starter · #9 ·
Speaking of coolers, I went with the offering from Mishimoto.

Its a nice piece... but this swap intends to kill me by a death of a thousand cuts. Unfortunately when I opened the box to install it on Thursday, I was missing the thermostat and all the giblets to go with it.... most importantly the threaded cap. Tech support was able to have these pieced sent to me and in hand Friday afternoon.

A keen eye will have caught my mistakes making the stainless lines. Forgetting about the intercooler piping.
Fixed. Now they hug the radiator.
 

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Discussion Starter · #10 ·
In case anyone was wondering about Allison harness, Jason does an excellent job. I have to say the wiring is tidy and everything is nicely labeled.

It has been mentioned by @cumminsturbofreak in other threads, and I'll have to echo his words... Jason's customer service is top notch. We've been emailing back and forth over the past couple weeks and has been super helpful.

The next bit is not for the faint of heart. If you're squeamish about wiring... just look away.

I needed to add an additional wire to take advantage of Jason's newer cruise control solution, but I also did not want to drill a larger hole through the firewall. Instead, I added a Mil-Spec circular connector. FYI, its a size 22 shell and fits the clutch master cylinder hole perfectly.

For what its worth, I ordered the wrong strain relief. I reordered one in nickel to make sure it matched in the engine bay.

I cut the harness at the yellow wire strippers in the first pic and went about the tedious task.



I made a quick under dash mount for the TCM.

Interior half of the harness. Not nearly as nicely wrapped as Jason's work, but it will do.


Bolted in place with the harness


Shot of the firewall waiting for the transmission side of the harness. I even have 4 spare 16ga pins for later.
 

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awesome work sir. It was a pain, what you said about death of a thousand cuts, I think I felt every one. I'm a little over 20,000 miles in on mine, and I can't stop smiling, every time I drive it. It's worth it, for sure. My 2006 two door is next on my list, i'll use CAConversions again, might source a different adapter plate to keep the starter on the drivers side.
 
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Discussion Starter · #12 ·
That’s awesome to hear you’re liking the swap!!
I’ve been planning this for a few years... now I’m doing the work I’m anxious to get it on the road and be able to pull the toy hauler again.

I’m also glad I’m not the only one that fought a number of small issues. We’re there other pain points you’d care to share???
 
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Black93GT, thanks for sharing all the info and pics. 👍

Is that the CAConversions aluminum adapter plate you are using?
 

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Good to see , since I’ll be doing mine shortly!
Did you drill the case for the extra c3 oiling ?
 

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In case anyone was wondering about Allison harness, Jason does an excellent job. I have to say the wiring is tidy and everything is nicely labeled.

It has been mentioned by @cumminsturbofreak in other threads, and I'll have to echo his words... Jason's customer service is top notch. We've been emailing back and forth over the past couple weeks and has been super helpful.

The next bit is not for the faint of heart. If you're squeamish about wiring... just look away.

I needed to add an additional wire to take advantage of Jason's newer cruise control solution, but I also did not want to drill a larger hole through the firewall. Instead, I added a Mil-Spec circular connector. FYI, its a size 22 shell and fits the clutch master cylinder hole perfectly.

For what its worth, I ordered the wrong strain relief. I reordered one in nickel to make sure it matched in the engine bay.

I cut the harness at the yellow wire strippers in the first pic and went about the tedious task.



I made a quick under dash mount for the TCM.

Interior half of the harness. Not nearly as nicely wrapped as Jason's work, but it will do.


Bolted in place with the harness


Shot of the firewall waiting for the transmission side of the harness. I even have 4 spare 16ga pins for later.
Where are you mounting the TCR module?

I mounted my TCM on the passenger firewall where 03 TCMs were mounted.
928183

The black box mounted on the passenger battery tray is the fuse/relay box for the TCM and TCR.


I mounted the TCR module near the spot you mounted your TCM.
928184



I mounted the OBD port backwards under the emergency brake lever.
928185





This is where I came through the firewall with the wiring.
928186


I cut a hole slightly larger than the diameter of harness, then I cut the plastic plate on one side to allow the harness to be slipped in. I then used a grommet between the harness and harness to prevent wear.


As for mounting, I used Howard’s SAE 3 bell housing adapter. This allows one to keep the factory starter, adapter and flex plate. All you need to do is swap the bell on the trans. And best of all, no cutting or grinding!
 

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Discussion Starter · #16 ·
Is that the CAConversions aluminum adapter plate you are using?
No it’s not theirs. I believe it is from G Force.
Did you drill the case for the extra c3 oiling ?
No I didn’t. I was looking at it but from what I read, the waffle pattern of the friction plates and the shift kit increases fluid flow/cooling so isn’t as important of a modification.
This is where I came through the firewall with the wiring.
928186


I cut a hole slightly larger than the diameter of harness, then I cut the plastic plate on one side to allow the harness to be slipped in. I then used a grommet between the harness and harness to prevent wear
I like the braided sheathing much better than the corrugated. The harness are much slimmer that way. The way mine was built, it would not have fit through that hole as is.

The plan is to put the TCR module in the cavity behind the glovebox. I didn’t get to it yet... for now I want to be mechanically complete and tie in only the bare minimum to make it drivable while I’m in the shop. Once I’m back home, I’ll tidy up the last bits.
 

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I like the braided sheathing much better than the corrugated. The harness are much slimmer that way. The way mine was built, it would not have fit through that hole as is.
Mine is actually wrapped in corrugated, then sheathed with the braid. It looks tidy and is very durable, but it is an absolute bear to do wiring changes with a soldering iron. And I had to do that as the first variable pressure control beta tester. Made a few changes, like pulling the control solenoid wire from the TCM and routing it into the cab to be controlled by the TCR, adding a dedicated fuse/relay box, etc.

Reason why my loom is skinnier is due the TCM location being outside the cab.
 

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That’s awesome to hear you’re liking the swap!!
I’ve been planning this for a few years... now I’m doing the work I’m anxious to get it on the road and be able to pull the toy hauler again.

I’m also glad I’m not the only one that fought a number of small issues. We’re there other pain points you’d care to share???

Mounting the transmission. Mine is a triple disc converter, weighs a ton, as if the trans didn't weigh enough already - I had a hell of time trying to muscle it into place. My suggestion is finesse. My dad and brother in law went in the house after we tried to force it in place for an hour, and I made tiny adjustments here and there by myself and it slipped right in the sweet spot.

I used dave's transfer case adapter and I love it. The only tough part was putting the reluctor ring on the shaft. You talk about a pain in the butt. Had to freeze the shaft and heat the ring. Those are some tight tolerances right there. Sounds like you may not have to do that - if I do it again, i'll have someone swap the output shaft for me so I don't have to have an adapter ring.

I still have a little PTSD over the whole thing, but if I can think of anything else, i'll let ya know. It was hell getting it done, but damn it sure pulls hard right now. I'll swap the 4.10 out for a 4.56 in the next couple weeks. Finally got my kodiak back on the road with a new CP3 so I can put the dodge in the barn and get to work. It only turns 1700 or so at 80 so I figured i'd try out a taller rear diff with my 35's. good luck! Following.
 

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I still have a little PTSD over the whole thing
Me too.

But in my case, I stupidly used a floor jack to raise the Allison into the truck. And of course, I had the Allison fall off the jack onto me.

I was at least quick enough to shove it back on the floor jack before it broke anything.
 
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Discussion Starter · #20 ·
I have a triple disk as well and filled it too. This unruly beast put up a good fight today but in comparison, I’m cheating. I’m renting a lift at the auto hobby shop at the Air Force base and have the usage of a transmission jack. I wasn’t going to attempt it without one. The only downfall is being limited by their business hours.

I forgot which reluctor ring I bought. It’s large enough to have the ID of it machined to be an interference fit for my transfer case input gear. It’s a little too snug for my liking but it’s not coming off without persuasion. CAC does have that adapter to make things easy but it looks huge.
 
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