Allison 5sp: Cores / Swaps

sneaky98gt

Member
Nov 5, 2013
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Hello all.

I have a 2003 Duramax (Chevrolet), and I've got some questions regarding transmission cores / swaps.

So, I don't want to start a debate on the merits of a DIY transmission build versus paying a professional to do it, but I'm planning on building my own sometime later this year with parts from Mike and/or Evan. There's nothing wrong with the current transmission (minus having 200k+ miles), but I bought the truck specifically to play with (eventual goals of running competitively in 7.70), so a built trans is the very first mod on the list of many.

After some consideration, I've decided it'd be better to get a core to build versus pulling mine out and building it. This way, I've got a much more relaxed time-frame that I can really go at my own pace without rushing. Plus, if anything goes wrong, I know I've got a known good trans I can go back to to get the truck back on the road. That's worth a little extra money, IMO.

That said, my questions:

1. I know there's differences from '01-'02, '03-'05, and '06-up. But I also read somewhere that there's mid-year changes for '03 also. What are those differences, and how can I easily identify what I've got in my truck (early or late)? And followup: how could I identify a core labeled as an '03?

2. What's a decent price for a core?

3. Bonus question I just thought of: since I've got the choice, is there any year model that's "better" than the others? Or are they all roughly the same?


I ask these questions because a local junkyard has an Allison out of an '03 for $700. That seems like a decent price to me, but I'm unsure if it's a direct swap for my truck, or if it might take a little extra work (not necessarily opposed to that).

Thanks!
 

Mike L.

Got Sheep?
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Aug 12, 2006
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Fullerton CA
Cooler fittings changed mid year '03. Early fittings will have orange clips holding the cooler line to the fitting and late will have purple clips. Another way to check is; early ( orange clip ) use 3/4-14 threaded fittings and late ( purple clip ) use 7/8-14 .
 

sneaky98gt

Member
Nov 5, 2013
109
20
18
Cooler fittings changed mid year '03. Early fittings will have orange clips holding the cooler line to the fitting and late will have purple clips. Another way to check is; early ( orange clip ) use 3/4-14 threaded fittings and late ( purple clip ) use 7/8-14 .

:thumb: Awesome. You are the man. I'll check mine tonight.

Any other changes? Or just the fittings?

Thank ya sir!
 

sneaky98gt

Member
Nov 5, 2013
109
20
18
Looked yesterday, and I didn't see any orange or purple clips. They just looked like a typical silver zinc coating to me (I didn't actually pull them out).

That said, I'm about 95% sure they were 7/8" fittings. They were quite large.

On top of that, by actually crawling under the truck and looking, I realized that they connect to the bell-housing anyway (versus the transmission case itself). So if the core that I buy isn't the same, it's just a simple matter of swapping the bell-housings. Problem solved.

I think I'm gonna spring for that local core. The more looking I do, the more I realize I'm not going to find one for much, if any, less than $700, and if I do, the chances of it being local are slim to none.