5 to 6 speed conversion

[02CCSB]

anyone know how I would go about this? or am I forced to buy a locked TCM? I doubt a simple OS re-flash would do it.

Yes I have a valve body.

[THEFERMANATOR]

If you have a 01-05 DURAMAX truck with a 5 speed and want to make it a 6 speed, you are pretty well limited to the SUNCOAST kit. The 6 speed valve body will not just drop into a 5 speed and then have a 6 speed OS flashed in(tried this). You have to use the 5 speed style solonoids which means you have to run the kit. And if it is a 01-05 truck, there is no factory or ALLISON flash to enable 6th gear. If you have an 06-07 MD with a 5 speed, then yes it can be flashed to a 6 speed by ALLISON, or if you have a 8.1L you can swap in an 06 TCM, 6 speed valve body, modify the wiring harness, and have a 6 speed.

[02CCSB]

Hmmm...OK... I get what you are saying about the solenoids, makes sense.

It's an 02. Access to various VBs is not an issue, but, without that software for the G solenoid, I'm SOL...

[THEFERMANATOR]

The G solenoid has nothing to do with the 6 speed as the SUNCOAST 5-6 speed kit doesn't use it(but they do use a G solenoid type valve body). The problem is having the 6th gear pipe installed in the valve body which means you have to start with a 04-05 5 speed valve body to be able to install one. Then you have to have the software to command the extra shift of the C2 and C4 clutch pack for 6th gear. ALLISON has the TCM OS, but they won't pass it up and I doubt it is even on there servers for download if you had access to the ALLISON DOC. For an 01-05 to get 6th gear, your only option is the SUNCOATS kit if you want everything to work like stock(some have installed a GEN IV 6 speed TCM and made the other changes, but it still won't work as designed as the GEN IV TCM will be working in default mode without receiving the GM high speed can bus data protocol messages from the BOSCH ECM). I looked into this myself last year(even bought the 6 speed valve body and associated components) to only find out the software was a hurdle not easily overcome.

[LB72004]

what about the cost (suncoast kit) vs the benefits? is it worth it? do you get that much better MPGs????

[Wheelz]

Would it not be cheaper to sell your tranny and tcm and buy a 6spd with tcm? Or is there a lot of other stuff that would still need to be done?

[THEFERMANATOR]

The 6 speed TCM is a GEN IV ALLSION TCM, and there is no known OS for it to communicate with the older 01-05 J1939 can bus they used as the newer GEN IV OS uses GM LAN high speed canbus.(don't hold me to the exact descriptions of each com system as I get em mixed up easily). You can put one in and hook it up, but it won't talk to the ECM and leave you in limp mode so its sort of pointless. There is a reason that SUNCOAST sells this kit as it is the only way to put a 6 speed behind a LB7 or lLY and have a true 6 speed. And yes it is a locked TCM, so you can't make any shift point changes to it. If you have an 8.1L though, you CAN swap in a GEN IV TCM into it and 6 speed trans and wiring and have a 6 speed as the SUNCOAST kit doesn't work for gassers but the GEN IV 8.1L TCM does talk in low speed J1939 can like teh older 01-05 trucks used(all of the 8.1L's used low speed data).

[LB72004]

would one be able to run the 6 speed in a stand alone setup? just need to feed it throttle position right? is there anything you would loose hooking it up this way. i assume you would have to flash your ecm with a manual trans tune or at least turn off the codes.

[THEFERMANATOR]

would one be able to run the 6 speed in a stand alone setup? just need to feed it throttle position right? is there anything you would loose hooking it up this way. i assume you would have to flash your ecm with a manual trans tune or at least turn off the codes.

No tap shift, no gear display in the cluster, no tow/haul mode, no coms with the ECM meaning no defuel, and probably end up with a fried trans. It could be done, but would be a disaster hence why those who have tried it didn't do it for long.

[killerbee]

If you have the modified valve body, I can supply the 6-speed (01-05) TCM.