Duramax Diesels Forum Truck of the Week
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Old 09-12-2017, 07:28 PM
Bob H Bob H is offline
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Default 03 built 5 speed conversion to a 6 speed via OEM?

I know some of you will read the title and think you know what I'm asking, but I'm not asking how to put a 6 speed behind my LLY.
I'm swapping my LLY out for a LBZ and I have a stage 5 Suncoast built 5 speed trans that works great.
The trans I'll be getting with the motor/swap was a flood car,(not same truck as the engine) so getting reasonable deal on it. After cleaning obviously, I was going to swap valve bodies, PNDRL switches and wiring harnesses,(inside and out) and I'm not sure what else?
Questions: Any reason I can't do that and anything I am missing in "converting" my 5 speed to work as a 6 speed behind the LBZ?
Yes, the ECM and TCM will be from the LBZ along with all the other wiring.

Main question - can it be done and any reason I shouldn't?
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Old 09-12-2017, 07:48 PM
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Old 09-12-2017, 08:00 PM
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Take it easy on him. He's a naval officer and they haven't been doing too hot. At least in the Pacific anyways.

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Old 09-12-2017, 08:00 PM
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Quote:
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Will it never end?


Nope....
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Old 09-12-2017, 08:04 PM
Bob H Bob H is offline
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Hey - In my defense, all my previous searches turned up folks trying to put a 6 speed behind a LB7 or LLY which is a no-go and I'm fully aware of that.

And I did finally just find my answer - from Mike no less,(and really Ben right after him):
http://www.duramaxdiesels.com/forum/...eed+conversion

But in short - This will be a LBZ setup, I just don't want to waste my time/money spent on my existing built 5 speed if I don't have to. Appears I can use my 5 speed as the base.
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Old 09-12-2017, 08:25 PM
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Water in transmission is a huge huge issue.
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Old 09-12-2017, 08:36 PM
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You don't even have to swap valve bodies with your 5spd. As long as whatever TCM you use is set up for 6th gear.
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Old 09-12-2017, 08:44 PM
Bob H Bob H is offline
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Copy on the water inside the trans issue. Just want to know if physical parts work as I didn't intend to just swap it straight over and I see how that could be read-into my response - but even a thorough cleaning and solenoid replacement may not be enough.
The important part - I wanted to ID what parts had to be swapped. From the post linked, ben said:
"To make a 5-speed trans work with a 6-speed TCM (an actual factory 6-speed TCM), you'll need a factory 6-speed valve body, the 6-speed internal NSBU (technically called an IMS), and the 6-speed valve body wiring harness."
And Mikes comment before that one:
"Swap the valve body, internal harness, shift shaft and internal linkage and mode switch."

I'd rather not chase my tail when its installed back in the truck. I'm comfortable with custom/details required to make the swap work, but don't pretend to know it all and appreciate the thoughts/feedback.
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Old 09-12-2017, 08:45 PM
Bob H Bob H is offline
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Quote:
Originally Posted by PureHybrid View Post
You don't even have to swap valve bodies with your 5spd. As long as whatever TCM you use is set up for 6th gear.
I may not know much about this - but I am nearly 100% certain that is not correct at all.
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Old 09-13-2017, 05:13 AM
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Quote:
Originally Posted by Bob H View Post
I may not know much about this - but I am nearly 100% certain that is not correct at all.
You are correct. The 5sp & 6sp valve bodies are different, and the trim solenoids are different. Plus the IMS.

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Old 09-13-2017, 11:06 AM
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Quote:
Originally Posted by Bob H View Post
I may not know much about this - but I am nearly 100% certain that is not correct at all.
Does the 6spd tcm not read the solenoids correctly??? Is it because of the nsbu??? The valve bodies might be different but there's no extra hardware to activate 6th gear, it's in the tcm.
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Old 09-13-2017, 04:27 PM
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Quote:
Originally Posted by PureHybrid View Post
Does the 6spd tcm not read the solenoids correctly??? Is it because of the nsbu??? The valve bodies might be different but there's no extra hardware to activate 6th gear, it's in the tcm.
The solenoids are different and behave differently (I think its an impedance difference). 5 speed TCM running 4th gen 6sp trim solenoids doesn't play nice (ask me how i know ). I imagine 3rd gen 5sp solenoids would be equally unhappy with a 4th gen 6sp tcm. The solenoids are not interchangeable. And yes there is AT LEAST one hardware difference in the VB to allow the 6th gear. I'm sure you can find pictures of the two out on the interwebz .

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300.59' 3rd place first pull

Best 1/4 times:
Truck: 14.067 @ 96.29, weighing in at over 7200#
446.4RWHP/820.2RWTq
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Old 09-13-2017, 05:52 PM
JRein JRein is offline
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5 speed

6 speed

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Old 09-13-2017, 06:22 PM
Bob H Bob H is offline
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And that's why I love this board - tech brought.
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Old 09-14-2017, 04:52 PM
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And don't forget the f solenoid is completely different from 5 speed to 6 speed. 5 speed goes to 96% duty cycle at full lockup, 6 speed only goes to 67% at full lockup, and they do not interchange. You may also run into issues with your 03 base trans. Some 03's use the smaller cooler ports, and do not have the correct pump assembly for the g solenoid to function as that wasn't added until 04. Not sure what would happen if the g solenoid is commanded on without the correct hydraulic circuitry for it(but you could put a dummy solenoid in the pan to get around it).
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