6L80 in my M998

Mogman

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MAN, this is a COMPLETELY different animal!!!!!!

from 2900@60MPH to 1800@60MPH, same mechanical tach and same GPS speedometer! I hate that I am going to lose the tach when the turbo GEP goes in but then again you really don't need a tach when you are not on the edge of disaster all the time.

2150@70MPH I could not be more pleased, no more gripping the steering wheel tight in case she blows up!!

I do have some more tuning to do, I need to move the shift points down as I have to lift the throttle to get it to shift but the shift firmness feels about right.

Because of the tuning I cannot give a 0-60 time yet but she feels more perky for sure!

Also much like the DuraVee and its Allison the vehicle moves when put into gear at idle, with the TH-400 you had to give is some gas pedal to get it to move, I always thought the mantra that the HMMWV transmission had a special diesel TC was bull S%it, I suspect it was the same one used in gassers

YAY!!!!!

EDIT, I am having issues programming the TCM, this will get resolved meanwhile I fudged the TPS calibration in the controller and am getting an idea on how great this is, preliminary testing shows 0-60 in less than 20 sec, originally it was 27.4 and it cruises comfortably at 70, of course this is on flat road, the minuscule HP of the 6.2 is still there just not NEARLY as pronounced as with the TH400, BTW that 1800-2200 RPM range will be right up that GEP Turbo's alley!!!

AND of course this is a helmet top loaded with all kinds of stuff including front and rear winches and full off road gear so it is as aerodynamic as a brick and weighs in at over 7400LB
 
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MattNC

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MAN, this is a COMPLETELY different animal!!!!!!

from 2900@60MPH to 1800@60MPH, same mechanical tach and same GPS speedometer! I hate that I am going to lose the tach when the turbo GEP goes in but then again you really don't need a tach when you are not on the edge of disaster all the time.

2150@70MPH I could not be more pleased, no more gripping the steering wheel tight in case she blows up!!

I do have some more tuning to do, I need to move the shift points down as I have to lift the throttle to get it to shift but the shift firmness feels about right.

Because of the tuning I cannot give a 0-60 time yet but she feels more perky for sure!

Also much like the DuraVee and its Allison the vehicle moves when put into gear at idle, with the TH-400 you had to give is some gas pedal to get it to move, I always thought the mantra that the HMMWV transmission had a special diesel TC was bull S%it, I suspect it was the same one used in gassers

YAY!!!!!

EDIT, I am having issues programming the TCM, this will get resolved meanwhile I fudged the TPS calibration in the controller and am getting an idea on how great this is, preliminary testing shows 0-60 in less than 20 sec, originally it was 27.4 and it cruises comfortably at 70, of course this is on flat road, the minuscule HP of the 6.2 is still there just not NEARLY as pronounced as with the TH400, BTW that 1800-2200 RPM range will be right up that GEP Turbo's alley!!!

AND of course this is a helmet top loaded with all kinds of stuff including front and rear winches and full off road gear so it is as aerodynamic as a brick and weighs in at over 7400LB
Congratulations on the great progress!
 

Mogman

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I went for a 70 mile jog today and after fudging the TPS calibration it shifts pretty damn good, I would like to fine tune it a little but if I cannot I will not be too heart broken,

This conversion was worth every damn penny as far as I am concerned!!

Tooling along at 65-70 MPH I can barely hear the fan when it kicks in and do not have the large loss of power as the engine tries to twist the fan at a bazillion RPM.
 

Mogman

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I took the Detroit out for another run today 125 or so miles.

Now in the beginning I said that installing the 400+ HP Duramax made a big difference in the DuraVee but it was the 6 speed Allison transmission that really changed the game.

Well the 6L series transmission is very much just the little brother to the Allison and it changed the game on this machine, it is not even like driving the same kind of truck, I came out of Corpus tooling along at 75 MPH in the CENTER lane!!, no more being banished to the right lane only!!

It was also very comfortable and somewhat calm at 2300 RPM, I can barely tell when the fan kicks in, once I got out of town and in the clear I ran 25 or so miles on only the mechanical throttle lock with zero adjustments, it would cycle between 75 and 73 with the fan cycles and would slow to around 67 going up the overpasses then it would speed right up to 75 on the way down.

The top speed I have gone on open road is 80 and the stock 6.2L still had a little more to give, of course it's no DuraVee but the Detroit does also weigh 2200 lbs more than the DuraVee.

I was thinking it was my imagination that the shift time VS throttle position were magically getting better but Zero Gravity the vendor for the "this is not a stand alone controller" says it uses adaptive software and it will continue to fine tune itself, How COOL is that!

At this point had I not just purchased a 6.5L GEP turbo I might not consider it to be a needed upgrade.

I need to figure out how to do a video because words just cannot convey the change in how this truck performs.

Mogman out!
 
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Glider

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I have been following this thread from the beginning. I am very interested in this modification. How does your shifter work? Have you seen any negatives so far? When will you have a complete kit less transmission?(never hurts to ask, right?)

Congratulations!! It doesn't seem like it took long to do this considering you are the first!
 

Mogman

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Hey Glider!
OK, I of course had to add a 4sp shifter in case anyone did not follow along, I used a modified " BRACKET ASSEMBLY LINKAGE" like this.
4l80.jpg
That was for the 4L80, it bolted directly to the transmission pan using the existing bolt (pan) bolt holes, I did have to do some mods to it.
The rods are simply bent (one of them) 3/8 all thread using 4 of these "trunion" pieces.
Trunion.jpg
and the shift lever I detailed earlier, works great and the geometry is pretty damn close, MUCH closer than the $500 custom setup I bought for the DuraVee.
The details are shown in post #35.


I have had some interest in the custom components, basically it is just the shifter bracket and linkage, the flex plate mods, the clocking ring and the cross member, all the other components can be purchased over the counter, I am trying to find a machine shop to fab the clocking rings, the most difficult custom item, so yes there is a possibility of some form of "kit"

As far as down side.. The only things I can think of is the possibility that I may have to purchase an HP Tuner because my EFILive does not seem to want to read/write the TCM tune (HPT is what Zero Gravity uses) I have not given up yet and the fact that fudging the TPS calibration really helped and the fact this dang controller is tuning itself that is not even close to being on the front burner at this time.

Another thing which is not really a problem as much as "clean up" is the controller harness came with allot of "options" that will need to be removed to clean up the harness once I figure out what I will be using, there are many options, paddle shifter, manual shifting, various input/output options like torque converter lockup indicator, temp warning, it goes on and on, so now I just have the unused options bundled and tie wrapped out of the way, I will clean all that up when I do the GEP conversion.

I do not see ANY operational down side, being able to knock about 7 sec off of my 0-60 times pretty much proves my long time belief that the much newer designed 6L series is much more efficient than the old TH400.

I had an old friend that runs a multi generational and very successful auto shop in Beeville drive the Detroit, he was gone for almost 20 minuets (I was starting to get concerned) when he came back he said it felt as "natural" as any vehicle he had driven, like the 6L was engineered for the M998, he experienced no flairs or missed steps, and he has done TONS of transmission work over the years.

But back to the shifter, I have no idea what can be done with the drive positions other than OD, I have not even tried them, I would assume that other custom things can be done with them after being able to mod the TCM tune, the controller itself is capable of having two different programs that can be selected via a switch.
 

Glider

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I'm guessing OD is drive. P,R,N the same. If you pull the shifter to 1 is that 1st gear or a higher gear? Are all gears capable of being selected by the shifter?
 

Mogman

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P, R, N, OD is all correct, I have not even tried to see what the "lower" drive positions do, the are all available.
On the DuraVee the first two down from OD act just like OD, the last is just 1st gear
I am not familiar with what the original optional positions did in the OEM application.
 

Mogman

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Plans are to set up manual shifting, that would include three switches, one to activate manual shifting and two to control up and down, this would be great for off road, I am checking to see if converter lock would be able to be controlled manually, this would probably help me as I make the 62 mile run down the 4WD beach on the national seashore, being able to lock the converter would save allot of heat that would normally be developed by the converter "slip" during long heavy pulls in sand, right now it locks up around 35 MPH and then stays that way which works great on the street.

EDIT, I rarely ever use low range in sand, and the 6L first being 4.03:1 VS the 2.48:1 for the TH400 will make a big difference, low range would be really low in first!
 
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Mogman

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Well I never claimed to be a photographer but this piss poor video will give some idea of the 6L80 performance, notice the tach. drop to 2300 as I reach 75 MPH.
I could not find any of the little camera mounts so I did it by hand, this was at about 3/4 throttle.
I had to start to back off near the end so I would not be dogging the truck in the left lane as they were doing exactly 75 MPH

 

Mullaney

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Wow. The rpms do drop in last gear. I most definitely would consider this mod. Is there any concern with offroading and the converter lockup?
.
Didn't I read earlier in this thread where the plan is to be able to lock up the converter with a combination of manual switches.

Post #50 explains the highlights - with more to follow:
 

Mogman

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Zero Gravity informs me that manual shifting and paddle shifting is the same thing and it requires the TCM to have a Corvette tune so I would need to be able to read write the TCM tune to implement this, I did not get any answer to the question of manual lockup control.
So the read/write issue is moving back up in importance.
 

Mogman

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The transmission was in lockup from around 35MPH in this video, it shifted from 5th to 6th at 75 MPH, 5th gear is just a little lower than the 4l80s 4th gear OD 0.85:1 VS 0.75:1 for the 4L80,
6th is 0.67:1
This truck has the 2.56:1 diff. gears
 

Mogman

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Wow. The rpms do drop in last gear. I most definitely would consider this mod. Is there any concern with offroading and the converter lockup?
I do not think so, none of the other options (TH400 and 4L80) have lockup control, I would assume the 6L would automatically go in and out of lockup at the same tail shaft speed (35 MPH in high range) when in low range, it is actually quite seamless the only reason I know is because of the monitor software on my laptop. so rock crawling for example would all be done in non lockup mode.

There is a brake light input which inhibits lockup when the brakes are applied (I am not using it because it automatically unlocks under 35MPH anyway and of course the brake lights are 24V so a relay would be needed) BUT that could also be put to a switch to inhibit lockup at will.
 

Mogman

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Wow, I just read the 6L80 was built at the Willow Run facility, the same plant that built B24 Liberators during WWII, pretty cool!
 

Mogman

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I've been reading up on the 6l. Can it be shifted to all gears including park electronically?
I would assume so for the most part, but the Park is mechanical the rest of the driver involvment is a multi position switch, BUT you have to have an interface to the TCM like the TCM-2650. dragging all the signals out without the TCM would be a big problem, IF you pull all control off of the TCM (power) it will be in third gear only, the mechanical connection to park (the actual control of the parking pawl being the only driver input
 

Glider

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Zero Gravity informs me that manual shifting and paddle shifting is the same thing and it requires the TCM to have a Corvette tune so I would need to be able to read write the TCM tune to implement this, I did not get any answer to the question of manual lockup control.
So the read/write issue is moving back up in importance.
Do I read this correctly that if you have a mechanical shifter you can select all gears mechanically with a software change. Meaning you could have full control with the hardware you have installed.

If so you could remove the detents or what mechanism usually stops the shifter in a gear position between drive and 1.
 
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