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8.1L/496 Tech

After owning a ZF6 8.1L, I would never own an allison (for myself) again. Two completely different trucks.

Unfortunately, GM ZF6 are expensive/rare. So my 8.1L/Nv4500/Np241 waits for the proper donor.
 
TRINDU said:
After owning a ZF6 8.1L, I would never own an allison (for myself) again. Two completely different trucks.

Unfortunately, GM ZF6 are expensive/rare. So my 8.1L/Nv4500/Np241 waits for the proper donor.
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What year 8.1 you have ? Inputs on maintenance ?
 
Bebop said:
Would you have by any chance a write-up or some extra infos on the crank sensor upgrade ?

No way to electronically "add" the 6th gear to the Allison ?
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For the crank sensor - Try and get some penetrating oil down the bore if you can ahead of time. I've always been told not to rotate the sensor to try and free it, only lift it by the flange as close to the body of the sensor as possible. There isn't a whole lot else to it. If you break the sensor off, you're pretty much going to be pulling the crank to push it through into the engine. The best way to access it is to lift the cab off. It's in a sucky spot to do in situ.

For the Allison - No way to do so with programming. While the 6th gear is mechanically present in the transmission, you'd need a new valve body and TCM to make use of it. Suncoast Gear makes a kit for this.
 
TRINDU said:
After owning a ZF6 8.1L, I would never own an allison (for myself) again. Two completely different trucks.

Unfortunately, GM ZF6 are expensive/rare. So my 8.1L/Nv4500/Np241 waits for the proper donor.
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Yes, for being a fat heavy pig, it's surprisingly peppy.

I've had a ton of folks want to buy mine. I always say no, even though I'd like to get rid of the rolling chassis. I'll keep it until I find the right '72 to drop the drivetrain in.
 
Russell said:
For the crank sensor - Try and get some penetrating oil down the bore if you can ahead of time. I've always been told not to rotate the sensor to try and free it, only lift it by the flange as close to the body of the sensor as possible. There isn't a whole lot else to it. If you break the sensor off, you're pretty much going to be pulling the crank to push it through into the engine. The best way to access it is to lift the cab off. It's in a sucky spot to do in situ.

For the Allison - No way to do so with programming. While the 6th gear is mechanically present in the transmission, you'd need a new valve body and TCM to make use of it. Suncoast Gear makes a kit for this.
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Seems like the vehicle I got isn't part of the TSB concerning the crank sensor. So I think it'll wait.
Cam sensor could be upgraded, but the PN for the 2002/2003 is still available, so I'm probably not doing anything about it for now.

10-4 on the trans stuff, definitely more work than what I'm trying to do.
 
Pulled my buggy about 400mi this weekend with it. 8000lbs total weight with trailer and spares. Cruise set a 70/75mph in the AL/TN mountains.

7.9mpg

The cruise control logic is pretty shitty which does not help with mileage. It waits until vehicle speed is 5 mph under set cruise speed and then holds it at WOT (and downshifts 2 gears in the process) until the vehicle speed is 3mph above set cruise speed, then goes back to normal operation. Rince and repeat.

I found that by making it downshift one gear before the hill, it didn't need to work as hard to keep up. Unfortunately, there is no button to block only 5th, so you have to play with the accelerator and get it right.

Need to fix the Tow/Haul button to see if there is a difference in terms of cruise control logic behavior with the Tow/Haul mode on. But I'm not holding my breath.
 
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Fix your tow/haul button. I just used my 01 Yukon with the 8.1 to pull a 23’ enclosed trailer with a sxs and all of our luggage, coolers, hunting shit in it and 5 adults in the Yukon on a 2500 mile round trip from Iowa to southern Georgia. In tow mode it shifted the way it should. We got 8-9 mpg.
 
4Eyedturd said:
Some days I jerk off to owning an 8.1/Ally truck for the big block power and same gas mileage my 6.0 gets. So far my 6.0 does what I need except getting better than 12mpg
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I've owned both, They drive completely different, The 6.0 liked to rev and the 8.1 was much more like a diesel, low and torquey. The allison makes the bigger difference. Actually grabs a gear and pulls as opposed to hunting and revving on every hill with the 4l80e. Overall I don't regret switching to the 8.1/allison combo.
 
Juztyn00 said:
I've owned both, They drive completely different, The 6.0 liked to rev and the 8.1 was much more like a diesel, low and torquey. The allison makes the bigger difference. Actually grabs a gear and pulls as opposed to hunting and revving on every hill with the 4l80e. Overall I don't regret switching to the 8.1/allison combo.
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I know the 6.0 is probably the most swapped motor ever, and I think they're great... but from a "bone stock truck from the factory" standpoint i don't really understand the purpose. It reminds me of the TBI years... 4.3, 305, 350... the 305 got 350 fuel mileage and had 4.3 power. :laughing:
 
45acp said:
I know the 6.0 is probably the most swapped motor ever, and I think they're great... but from a "bone stock truck from the factory" standpoint i don't really understand the purpose. It reminds me of the TBI years... 4.3, 305, 350... the 305 got 350 fuel mileage and had 4.3 power. :laughing:
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I towed a heavy gooseneck with both trucks, The 6.0 truck felt like it was working at 90% to do 70 mph with a load, The 8.1L truck feels like its working at about 40% with the same load... similar fuel mileage. Not scientific just seat of the pants feel. Don't get me wrong, my 6.0 truck served me flawlessly for years and my other reason for swapping it off was the need for an extended cab. I just like my 8.1 truck better now I have it.
 
Bebop said:
When do I need to be changing the Allison spin-on filter and the one in the pan ?
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I have an 04 2500HD Duramax with the Allison. My Truck has 290k on it. I bought it with 70k. At 100k, I drained the Dexron fluid, and replaced it with Transynd (co-developed fluid with Allison and Castrol engineers).

I change the spinoff every 15k. I change the fluid every 50k. Although Allison only recommends changing the internal filter upon rebuild, I change that every 100k.
 
Broncokyle88 said:
It should only take a half hour or so to fix the tow haul button. Pop the dash surround off, pull the steering column covers, find where the wires broke in the shifter, solder them, and route the wires with a little more slack in them. Or do what I did in my 2000 when the tiny ass wires got too short and slap a momentary push button switch in the dash and run two wires down to it where it will never break again.
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You can see through the torn booth that the wire is already dangling. I was thinking about adding some length to the splice as you're mentioning.

Juztyn00 said:
I've owned both, They drive completely different, The 6.0 liked to rev and the 8.1 was much more like a diesel, low and torquey. The allison makes the bigger difference. Actually grabs a gear and pulls as opposed to hunting and revving on every hill with the 4l80e. Overall I don't regret switching to the 8.1/allison combo.
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Yep, I really like how the 8.1 drives. Uphill in 4th gear at 3200rpm it has a very diesel-ish torque feel. Like you can't stop it.

My only complaint was that I can't seem to lock the trans out of 5th and let it run on 4th only, but maybe the tow?haul fix will improve that.

I've been buying a bunch of maintenance parts for it so I'll do the fix at the same time I'm spending a day working on it.

4RunnerGuy said:
I have an 04 2500HD Duramax with the Allison. My Truck has 290k on it. I bought it with 70k. At 100k, I drained the Dexron fluid, and replaced it with Transynd (co-developed fluid with Allison and Castrol engineers).

I change the spinoff every 15k. I change the fluid every 50k. Although Allison only recommends changing the internal filter upon rebuild, I change that every 100k.
Click to expand...

Awesome ! I'll look into that oil. Thanks.
 
Id like to get an 8.1 or gen6 454 with a 230ish cam, bored, with a stroker kit (496) in front of a 6L90E and 5.13 gears.Those zf6 trucks are unicons but would also be cool. That crank sensor thing is a bitch go buy one know. It will throw a ckp code and have no RPM signal when cranking.

photo31740.jpg
 
gmcxt said:
Id like to get an 8.1 or gen6 454 with a 230ish cam, bored, with a stroker kit (496) in front of a 6L90E and 5.13 gears.Those zf6 trucks are unicons but would also be cool. That crank sensor thing is a bitch go buy one know. It will throw a ckp code and have no RPM signal when cranking.
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Planning to take a big trip with the truck this December and do the crank sensor after that.
 
Dont buy a cheap crank pos sensor either. Buddys 6.0 truck had a ckp code and would randomly not start. He bought one, we threw it in, and no change. Spent the rest of the day troubleshooting before I finally asked him where he bought the sensor. "It was only $7 cheapest one Rock Auto had, way better deal than auto zone!" Swapped in a known good one out of a running truck and it fired up right away.
 
mjlogan88 said:
Dont buy a cheap crank pos sensor either. Buddys 6.0 truck had a ckp code and would randomly not start. He bought one, we threw it in, and no change. Spent the rest of the day troubleshooting before I finally asked him where he bought the sensor. "It was only $7 cheapest one Rock Auto had, way better deal than auto zone!" Swapped in a known good one out of a running truck and it fired up right away.
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I bought a crank sensor off rock auto for 5 bucks! it works, but the molding on the plastic required me to cut into the mounting bolt hole. They are over $100 new at cost and it was my sons car and I figured it would be worth a shot. that was 2 years ago. Win some and loose some lol.

....Also its for sale if anyone wants a 2003 vue for 1500.
 
What’s a decent price for a 170k mike 8.1 with an Allison? Supposedly running great till the truck was rolled. He wants $2500 for the whole thing or $1750 for the motor and trans
 
45acp said:
11mpg no matter what. Long freeway trip, all in town, all downhill at 50mph... it gets 11. They have a 9th injector and when the ecm senses low fuel usage it will kick on and spray gas down the side of the road.
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Specced for the RAAF.

 
gmcxt said:
I bought a crank sensor off rock auto for 5 bucks! it works, but the molding on the plastic required me to cut into the mounting bolt hole. They are over $100 new at cost and it was my sons car and I figured it would be worth a shot. that was 2 years ago. Win some and loose some lol.

....Also its for sale if anyone wants a 2003 vue for 1500.
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This. Even shit parts have a defect rates below 1%. Might as well just buy two.
 
Bebop said:
What year 8.1 you have ? Inputs on maintenance ?
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I owned 02-04 trucks. Check oil and drive. Update the crank sensor when you have the comfort to do it, and not on the side of the road. I'm still in the loop on all of them, the burban drinks oil but otherwise solid. I know welding rigs with 300k+. Shame GM caught the aids in mid-late 2000s and havent made shit worth owning since.

I flirted with 13mpg running 80mph. 10.5-11 in town. People who get single digits empty cant drive. That's what a 6.0L gets, I was never impressed with them.
 
Wondering if the B&S on the modern 496 is the +030 or +060 with a 4.250 or a 4.375 stroke crank.

I plan to pull my boat engine (1970's) LS6 454 standard bore and toss in a 4.375 stroker (8 counter weight) crank.
 
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TRINDU said:
I owned 02-04 trucks. Check oil and drive. Update the crank sensor when you have the comfort to do it, and not on the side of the road. I'm still in the loop on all of them, the burban drinks oil but otherwise solid. I know welding rigs with 300k+. Shame GM caught the aids in mid-late 2000s and havent made shit worth owning since.

I flirted with 13mpg running 80mph. 10.5-11 in town. People who get single digits empty cant drive. That's what a 6.0L gets, I was never impressed with them.
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I've got about 2500 miles on it now, averaging 12mpg empty.
I'll do the crank sensor and be happy.
 
Does that 6 speed also bolt up to the gen 3 small blocks?
 
That crank sensor on the 8.1 is just dumb. GM made a timing cover with both a crank and cam sensor and reluctor wheels for both 24x and 58x ECMs that go on the crank snout. I don't know what the original app was, but I have one on a gen 6 BBC I built. I don't know if it would be worthwhile (or possible) to swap onto an 8.1 with a stuck crank sensor or not, though.
 
Just did a big tune up on it.
All fluids, filters, swapped the plugs and wires (which appeared to be factory ones still) and it runs noticeably smoother at idle.
Fixed the tow/haul wires in the shifter.

Towing my buggy to RBD with it so I'm curious to see how this impacts mileage.

On the bad side, I removed a piece of trim and found that the rear doors had been bondoed pretty terribly and there are water bubbles underneath it. FML. Going to look for JY doors and swap them in, not sure I want to start digging and finding how bad this shit is.

Cab corners appear fine but same logic here, not sure I want to go start digging.
 
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