Offroad Trailblazers and Envoys

STD DISCONNECT OR AWD VERSION.....

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by larryk » Thu Aug 11, 2016 1:30 pm

Just putting together all the parts to swap my front diff....along with ball joints, Aarms, CV's, etc while Im in there...

My question has to do with the disconnect. I have a 4x4 TB, and it has the standard (ie PCM controlled) disconnect on it. I have both a standard, and an AWD version floating around....which would you guys suggest I install? I dont really see how much having the standard disconnect makes a difference, as the differential and axles are still spinning with the wheels. About the ONLY things that get less wear, are the pinion bearings, front Ujoint, and transfer case front output/chain.

Help me evaluate the benefit of a stronger disconnect (AWD version) that isnt going to fail trying to shift/lock, vs the extra wear of having the front parts spinning.....even when the Xcase is in RWD mode

Thanks
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by KingBird » Thu Aug 11, 2016 3:30 pm

Well, I'm kinda biased since mine came with the AWD sleeve but in my opinion, the standard disconnect is just more parts to fail.

Oddly enough I've experienced a stretched chain, but it was from the TB transfer case that I installed. Now it has the chain that I pulled from my awd transfer case that has more than 140k miles on it...

I'd go with the AWD sleeve, just my 2 cents.
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by bartonmd » Fri Aug 12, 2016 8:12 am

The AWD sleeve is by far better at making the whole disco stay together, being that the lifted CV angle puts an angle thrust on the gears, which doesn't seem to lend itself to longevity of... anything in the disconnect. The AWD sleeve is not only much stronger, but also keeps the shafts and bearings all in a line, rather than twisting on the bearings.

Having said that, when I went to the AWD sleeve I lost like 1.5-2mpg, so there's that... There actually is quite a difference from spinning the ring/pinion and front prop shaft all the time, even if it is only coasting.

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by larryk » Fri Aug 12, 2016 10:55 am

bartonmd wrote:The AWD sleeve is by far better at making the whole disco stay together, being that the lifted CV angle puts an angle thrust on the gears, which doesn't seem to lend itself to longevity of... anything in the disconnect. The AWD sleeve is not only much stronger, but also keeps the shafts and bearings all in a line, rather than twisting on the bearings.

Having said that, when I went to the AWD sleeve I lost like 1.5-2mpg, so there's that... There actually is quite a difference from spinning the ring/pinion and front prop shaft all the time, even if it is only coasting.


1.5-2mpg? Really that much? Wow/ I typically get, driving around town, 12-14 and on the highway, maybe 20? So I guess its a matter of losing 10% or more mileage, or having a stronger disconnect. BTW, I do have a front strut spacer lift.....and the CV's are clearly near bind at full droop. I havent had issues yet, but if it starts chewing them up.....

Why didnt GM just go with the end of axle (at the hub) disconnect on these trucks? You figure it would get better mileage if NOTHING was turning, and also be easier to service and stronger. Sigh
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by bartonmd » Fri Aug 12, 2016 11:49 am

Hub disconnects aren't on anything other than Super Duties and 1993 and lower Dana axles. Pretty much anything IFS has a center disconnect, and a lot of the later solid axles, as well. They got away from disconnectable hubs so the hubs can be smaller.

Yeah, I used to be able to get 20mpg highway (lifted with 30.5" all terrains), but put in the AWD disco and went to 31" all terrains at the same time. Now, I'm at like 16mpg highway.

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by HARDTRAILZ » Fri Aug 12, 2016 3:36 pm

I have a rebuilt AWD disco in the garage, but still on my rebuilt regular one and cant justify a swap until failure, but even then i am not sure it is worth the MPG loss.
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by TBYODA » Fri Aug 12, 2016 7:16 pm

How can we know the AWD caused the mpg loss when two items were changed at the same time. More likely the bigger tire's are contributing to the mpg loss IMO.
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by KingBird » Fri Aug 12, 2016 8:28 pm

I'm on 30" tires (currently) AWD sleeve, 3" lift, 3.73s and tune.

I get 17 on the highway at 75-80, but if I keep it around 65 I average 20-21 on the highway. In theory, taller tires would move that 20-21 mpg to 75-80.

Just saying, it depends on what you do behind the wheel more than anything.
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by HARDTRAILZ » Fri Aug 12, 2016 8:41 pm

.5 inch tire size change is the difference in my tires new or close to wear bars. I don't see that much swing in mpg.
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by Trail X » Sun Aug 14, 2016 6:56 pm

I didn't see any change in mileage when I went to the AWD sleeve, and that was back during the $4 gallon gas, so I paid close attention. My tires on the other hand really killed my mileage. I see no downsides with the sleeve. If your TB is lifted and your standard disco bites the dust, go with the AWD sleeve.

KingBird wrote:I'm on 30" tires (currently) AWD sleeve, 3" lift, 3.73s and tune.

I get 17 on the highway at 75-80, but if I keep it around 65 I average 20-21 on the highway. In theory, taller tires would move that 20-21 mpg to 75-80.

Just saying, it depends on what you do behind the wheel more than anything.


If only the air resistance didn't go up by a power of 2 with speed, maybe your theory would have a chance... that and maybe if you didn't have to contend with an automatic transmission that always wants to shift down into 3rd gear. :fro:
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by KingBird » Mon Aug 15, 2016 10:14 am

That's why I said "in theory"
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by bartonmd » Mon Aug 15, 2016 3:37 pm

TBYODA wrote:How can we know the AWD caused the mpg loss when two items were changed at the same time. More likely the bigger tire's are contributing to the mpg loss IMO.


I didn't do them at the exact same time. I just don't have enough long highway mileage data in between to say a definitive "this cost an x.xx% loss." In the couple months in between them, the "this tank was this" on my commute (80 miles/day, mostly highway) is what gave me the general idea above. You can see what difference it makes on your vehicle, though. Drive around in A4WD and see what it does. Same thing.

I did have a pretty good reference on my old Cummins W250, as well. Having the hubs locked in, with the T-case in 2WD, took me from 18 highway to 16 highway, and back when I disconnected them.

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by TBYODA » Tue Aug 16, 2016 11:02 pm

bartonmd wrote:
TBYODA wrote:How can we know the AWD caused the mpg loss when two items were changed at the same time. More likely the bigger tire's are contributing to the mpg loss IMO.


I didn't do them at the exact same time. I just don't have enough long highway mileage data in between to say a definitive "this cost an x.xx% loss." In the couple months in between them, the "this tank was this" on my commute (80 miles/day, mostly highway) is what gave me the general idea above. You can see what difference it makes on your vehicle, though. Drive around in A4WD and see what it does. Same thing.

I did have a pretty good reference on my old Cummins W250, as well. Having the hubs locked in, with the T-case in 2WD, took me from 18 highway to 16 highway, and back when I disconnected them.

Mike

Yep been with my red neck AWD sleeve since December 2014, didn't see much loss. More from my mud tire's and roof rack. I really need to open the disco and take look for wear.
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by bartonmd » Wed Aug 17, 2016 11:41 am

TBYODA wrote:Yep been with my red neck AWD sleeve since December 2014, didn't see much loss. More from my mud tire's and roof rack. I really need to open the disco and take look for wear.


FWIW, my tire change was from 245/70-17 to 265/70-17. That's the only difference, other than the spacers. Both 10-ply BFG all terrains.

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by DirtyBacon04 » Wed Aug 17, 2016 3:49 pm

My mpg loss didn't get significant until I installed the RTT, that's when highway economy dropped nearly 3mpg
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by Grimor » Fri Aug 19, 2016 4:17 pm

If I'm already at 13, will it drop me to 11?lol
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by bartonmd » Fri Aug 19, 2016 4:27 pm

Grimor wrote:If I'm already at 13, will it drop me to 11?lol


No, it would be a percentage, and not even a straight percentage, because your engine doesn't get straight percentage mpg change vs. change in load, because of the throttle and intake manifold vacuum.
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by Grimor » Sun Aug 21, 2016 2:48 am

I know, i was just kidding. I should try to figure out what made me go from 22 to 13 in just a couple weeks

those were the weeks I swapped rears and went from 3.42 to 4.10 and mostly stock tire size to 35 and new bumper
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by KingBird » Sun Aug 21, 2016 12:13 pm

Damn, those had to have been two awesome weeks, new gears, tires, AND bumper? I'm jealous!
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by navigator » Sun Aug 21, 2016 2:32 pm

running 4.10s, 33s and the AWD sleeve I average about 13.5-14.5 mixed driving. If I take off easy and drive like I have no brakes I pick it up a bit but I normally just drive.
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