Allison 6sp: Stock or mod it?

MaxPF

JAFAWAM
Jan 12, 2011
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Cliff notes: Cummins in a K5; Max engine torque 650-750lb-ft; truck weighs 6500lbs; No racing or pulling (except the occasional stoplight drags to pass a slowpoke); no heavy towing (rarely 8000lbs, more common 4000lbs); plenty of wheeling; 37's, 4.56's, 203-205 doubler

Trans is a 6 speed (I got parts to fix the basket case). The engine and intended usage is very tame compared to what most of you do. I'm thinking leave it stock, but I wanted to see what you all think.
 

Mike L.

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Aug 12, 2006
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I would not leave it stock. I would at least bump the pressure up, eliminate knock down at the converter flow valve and put a Transgo jr in it.
 

MaxPF

JAFAWAM
Jan 12, 2011
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Mesa, AZ
I would not leave it stock. I would at least bump the pressure up, eliminate knock down at the converter flow valve and put a Transgo jr in it.

Transgo Jr. is easy enough. Are there kits for the other 2 items you suggested?
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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I would not leave it stock. I would at least bump the pressure up, eliminate knock down at the converter flow valve and put a Transgo jr in it.

That's what I had suggested to him was a TRANSGO lock-up boost valve, Jr, and upgrade the C3's while he's in there. Figured that would give him a nice kick in holding power for a small budget.
 

MaxPF

JAFAWAM
Jan 12, 2011
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Mesa, AZ
Big time drum wear at the stator support rings. The benefit is good at a price. Need to address this or your drum will go to shit.

I saw you mention this in another thread, along with the C2 steels beating up the drum. Any reason why a guy couldn't have the drum vacuum carburized? That would give a surface in the 60-62 Rockwell C range, and is a clean process. Nitriding is also clean and would probably prevent the stator ring wear, but I doubt it would protect against the C2 steels since nitride cases are thin compared to a carburized case. Maybe something to experiment with :dontknow:

For now, I want upgrades that won't shorten the life of the hard parts or cause undue wear. Like I said earlier, compared to most of you guys my engine is low torque, and it's not going to get the snot beat out of it. Durability and longevity are what I need.

Mike, I will give you a buzz tomorrow. Thanks!
 

MaxPF

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Jan 12, 2011
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That's what I had suggested to him was a TRANSGO lock-up boost valve, Jr, and upgrade the C3's while he's in there. Figured that would give him a nice kick in holding power for a small budget.

Yeah, i know. Just thought I would get multiple opinions :D
 

THEFERMANATOR

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Feb 16, 2009
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Yeah, i know. Just thought I would get multiple opinions :D

Unstand, I'll admit I'm no expert. Just thought I would ask you before what your plans were as I would hate to see you go through all that you have to get it to work and have an internal failure in it later, ESPESCIALLY since you already have it apart now.

And thye single disc converter I was talking about is the TRANSTAR A7XL. It's only a single clutch lock-up, but the 1.63:1 stall in it should match your engine ALOT better than the stock 2.01:1 that came in the DMAX. And I have seen it for $400 after core from a few places.
 
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MaxPF

JAFAWAM
Jan 12, 2011
182
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Mesa, AZ
Unstand, I'll admit I'm no expert. Just thought I would ask you before what your plans were as I would hate to see you go through all that you have to get it to work and have an internal failure in it later, ESPESCIALLY since you already have it apart now.

No prob, I appreciate it :hug: The mod I was concerned about was the converter flow valve and boosting the pressure after reading Mike's comments about stator ring wear. It wasn't until after I talked to him that I understood the wear is only a problem if you are running a LOT of pressure. He's gonna hook me up with the stuff I need for a modest boost in pressure, so I should be in good shape.

And thye single disc converter I was talking about is the TRANSTAR A7XL. It's only a single clutch lock-up, but the 1.63:1 stall in it should match your engine ALOT better than the stock 2.01:1 that came in the DMAX. And I have seen it for $400 after core from a few places.
I will look into it. I am going to hold off on the converter for now and run this low mile stocker to get a feel for it's stall and get a better idea of what I want from it. I have an extra core I got with this parts trans, so I can get a built converter, send that one in for the core charge, and swap converters at my leisure.

Speaking of mods, I need a 32 spline output shaft for my Alli to mate with the 203-205 doubler. Since I have a batch of doubler shafts heading out to be splined I figured I would throw the Alli output in with the lot.

r-IMG1817.jpg


The fat part at the top will end up being 32 spline 24/48 diametrical pitch, which is the same as a TH400 and 4L80E. I had to do this since 29 spline inputs don't exist for 203 range boxes. I gotta say though, the metal the stock shafts are made of only measured 28 rockwell C; it's fairly soft, which also means it's not particularly strong (130ksi according to my Machinery's Handbook). I have a 2wd output that I am going to do a test hardening operation on to see if it is a hardenable alloy or not. If it isn't I will probably throw the 4WD shaft in with the doubler shafts to be carburized, so it will at least be resistant so spline wear. I blueprinted it already so I can make one out of better material later if it becomes necessary. :frank: