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2004 Allison Changes

1727 Views 9 Replies 5 Participants Last post by  Diesel Tech
I found this paragraph about a change to the 2004 Allison.
A modulator valve body and external wiring harness to control the modulator were added to modulate the main oil pump pressure. This reduces oil pump pressure at engine idle speed and therefore lowers the operating noise level of the transmission and substantially increases transmission cooler flow at idle.

Although no torque rating increases were mentioned, it would make sence that if the pump pressure could be decreased at idle, it could also be increased during WOT, and help to increase the holding capacity of the clutches.

I was just wondering if you have heard anything about this change or any other changes to the Allison for 2004. Also I was planning on installing a shift kit in my Allison, and am concerned that the kit might have issues working on a 2004.
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Amric, yes, the 04 allison will incorporate a modulator valve, I am not sure if it is current 04 stuff or will cordinate with the new engine. Basically, what they are doing is getting rid of 'overage fluid' which is fluid that does not have a purpose, its not shoved through the cooler and just goes back to sump. With the new setup, all fluid will go through the cooler, this will take away the heat build up from idling to long in gear. This will decrease the noise level also because, as stated, the pressures will be lower. I dont know if the opposite will happen as far as greater fluid pressure on the top side of things. I know that with the addition of the modulator valve, the shift kits will have to be redesigned to accomodate it. I think TTS and TransGO are already working on it.

Amric, hope you can make it to Grand Rapids Oct 11 for Diesel Day! Dyno will be on hand.. lots of performance goodies and hog roast..
dmaxalliTech said:
With the new setup, all fluid will go through the cooler, this will take away the heat build up from idling to long in gear.

What would it take to retrofit to an 02?
This the exact problem I fight in the summer stop n go traffic.
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I just took delivery on an '04 dually and would like to know if my allison has the new mod. Any way you might find out if its currently in the '04s or coming with the new motor?


Bob, My sources tell me its 04 model year, so it should have the updates.

Chris, I dont know what would be involved to update yours.. Not sure if its a simple deal or has lots of slightly different things...I havent seen an 04 apart yet.
Well I've had two '04's apart already and they made the transmission change with the '04 production start date. The new transmission is rated for 600 ft/lbs. We have been testing our transmission upgrade kit and torque converter, so far everything is working just fine with the new modifications Allision has made. So it looks like or kit will work in the '04 model just as it has in the early transmissions.
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Diesel Tech said:
The new transmission is rated for 600 ft/lbs.

Is this in relation to the 520ft-lbs that the 2003 was rated? Should I assume it can take 80 more ft-lbs than an 03 before limp mode?
Steve, thats good to know. I am giddy to get that kit, I want to have mine upgrades asap. Looks like we well be selling a few for you... Looking forward to doing business with ya!

The 01 - 03 trans. was rated at 520 ft/lbs of flywheel torque and the new trans. is rate at 600 ft/lbs. I believe this was necessary to handle the increase in torque output GM will be releaseing in the near furture. So yes, it will handle 80 more ft/lbs without going into limp mode. One must remember that if you add 80 ft/lbs to the new motor it will most likely go into limp as GM is rasing the flywheel torque in the new motor, but , if you've got an '04 now you can add the 80 ft/lbs and everything will adapt right in. We have run our 80 RwHp Tow program with no problems on the new transmission and the Race program at 120 RwHp and it handles it. The Race program has maxed it out so I would still recommend upgradeing if you plan to go to something greater than 80 RwHp. With the Race program you have to drive it for awhile before it adapts in properly so if you put it to the floor right away you will still hurt the new style transmission.
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