Allison TCM tuning

496GasJob

New member
Aug 4, 2015
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New Hampshire
ok, so I recently bought a 2002 2500hd with an 8.1/ally combo. this truck really did not impress me from the get-go. my last truck was a 2wd reg cab 2500hd 6.0 and was significantly faster than the 8.1. don't get me wrong, the 8.1 tows my trailer pretty good and I can still get 10.5 mpg pulling 9k on back roads, but it still struggles on hills at times and I tow quite often.

so far, I've installed a 180* t-stat to slow down oil consumption (was 1 qt per 1k miles, now down to less than 1/2 qt), installed delco iridium plugs gapped to .045, I've replaced the air filter with a k&n, replaced crank and cam sensors as they are known to shit the bed and cause lack of power. it just seems like this truck should have WAY more power than it does. especially considering off the line my buddy can leave me in the dust with his crew cab long bed 454 with 250k miles.

now I talked to someone this past weekend who has owned 2 8.1 trucks, 1 tuned, 1 not... needless to say he convinced me to tune mine. I found somebody local who will dyno tune my truck for $450 but he cannot touch the Allison.

Now as far as Allison tuning goes, I Just want to know if it's worth finding someone who can tune my TCM along with the PCM. I HATE how the Allison downshifts. in 5th gear, I punch it and it unlocks the T/C, wait a second... then downshifts to 4th, wait a second.... then 3rd, and finally by the time it drops to the gear I want, I can't pass that car doing 35 in a 50. Shifts also seem way too soft. it just feels like it slides into every gear and i'm afraid all the bands and clutches will burn off as soon as I get it tuned

any tips and tricks from somebody who knows these trucks, on how I can get more power and better shifting out of this truck will be greatly appreciated. and don't say ZF6 swap.... that's on the to-do list:D
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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Well there are no bands to burn off as the ALLISON is a clutch to clutch trans, and being a clutch to clutch trans is why it shifts the way it does. The ALLISON cannot simply go from 5th to 3rd, it has to follow a sequence of 5th to 4th, change the shift solenoids accordingly, check the pressure switch outputs to verify, then 4th to 3rd, change the shift solenoids accordingly, and reverify the pressure manifold switch outputs to verify the solenoids stroked the shift valves. For an ALLISON to shift is not a simple process with the all clutch to clutch direct gear engagement of the ALLISON. It is designed for strength and longevity, not performance and fast shifts. I'm not sure on the 8.1L as you may be able to tune it to lep, but it is never going to snap down 2 gears in an instant, it is impossible by design of the transmission. Cutting some of the shift energy management may help with the lazyness as the ALLISON pulls power during shifts, but if you pull it to much you will just kill your ALLISON with tie ups from it trying to shift to quick. The 4L80E behind a 6.0L CAN snap through the gears like you're describing, but an ALLISON will never be able to just snap through multiple gears for a downshift.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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If a Allison does not shift like your stating, something is not tuned right or something is hurt inside. Even my fully built trans that sees 600-800hp will shift like a stock trans. No bangs, no hits like a built trans from yesteryear

I would do a compression test on your rig. See just how healthy that motor is
 

496GasJob

New member
Aug 4, 2015
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New Hampshire
I would do a compression test on your rig. See just how healthy that motor is
I bought the truck 5 months ago with 84k miles. I just assume it's healthy but it did tow a 15k camper its entire life. I will probably check the compression soon

and, THEFERMANATOR thanks, I did forget the Allison has no bands.. I didn't realize it can't skip gears like the good ol 4l80's. guess that's something I have to deal with
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
3,492
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Central OH
Something is wrong for sure, my brothers '01 2500hd long bed with 8.1/Alli was no slouch. It would eat a stock dmax. Maybe check the MAF sensor...

Could you flash a newer OS in the tcm like we do the diesels? That might help some, especially with it unlocking the TC during a downshift.
 

496GasJob

New member
Aug 4, 2015
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New Hampshire
only code the truck has generated in the last 5 months was a Mass air flow code. can't remember the details but I cleaned the MAF and it hasn't come back now for over a month... but I do part out these trucks so I have like 4 or 5 of them just kicking around. I think i'll swap one into my truck tonight for the hell of it... I mean, hybrid, if you say your bro's was quick then something is wrong here. one of my buddies was thinking about 8.1 swapping his 89 dually till he rode in mine, now he's looking for a 6.0 lol
 

WolfLMM

Making Chips
Nov 21, 2006
4,005
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AL
What all did Mercury marine change in them to get 425hp? Just tossing out ideas.
 

496GasJob

New member
Aug 4, 2015
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New Hampshire
Well I swapped out my MAF sensor with one I had kicking around and it runs exactly the same but generated the same code it did over a month ago, "mass air flow circuit/range performance", so I know this sensor is bad, i'll try a different one tonight.
And as far as I know, marine engines are their own animal. probably different head porting and a cam that can't practically be run on the street. I contacted Raylar Engineering and I was asking about their BP-202 towing/RV cam. looks like i'd see a noticeable difference in power, especially down low. it is on my to do list so I bought a car I can drive this winter while she's under the knife.
 

Big Block 88

Multiple choice muscle
Nov 3, 2008
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Kansas when I am home
A 6.0 will never out perform the 8.1 unless the 8.1 is down a few holes. My armored burb overseas was an 8.1 and weighed a bit over 11k fully equiped that thing would still haul ass. That said burbs didnt use the alli either.

Yoir sig says u want to do a zf swap to get away from the alli... I love hand shakers but man i think that is a mistake swapping out one of the best autos ever for a marginal zf that you cant even find parts for
 

496GasJob

New member
Aug 4, 2015
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New Hampshire
yeah well from what I hear, the gears are much more evenly spread out in the zf6 compared to the nv4500. I am actually picking up an nv4500 this weekend to put behind the 8.1 going in my 96 1/2 ton. maybe i'll change my mind about the zf6 once I take the 96 for a few good drives
 

496GasJob

New member
Aug 4, 2015
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New Hampshire
so I got my tune today. initial run on the dyno was 230hp and 267ft lbs. after tune was 255hp and 314 ft lbs. I expected a lot more and think my numbers should be higher overall. anyone think these numbers are low? also my throttle response is horrible even though it showed up in the PID's as matching dead nuts with pedal position. I am not thrilled and plan to do a DBC conversion and have it re tuned. also a raylar cam
 

496GasJob

New member
Aug 4, 2015
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New Hampshire
The guy was able to fix my throttle issue. ended up being a throttle "tip in" adjustment. basically maxed it right out and now it acts like a normal dbw setup. half second lag but no longer "eases" into the throttle when you punch it. i'm happy with the way it drives other than the fact it seems slow, but I guess I have a lot more work to do before I beat my cousin's tuned LBZ :D. raylar cam swap soon enough.