Checking out my options: '04 Avalanche Z71 Build?

[Stryder106]

Not to hijack this thread - but Drei - do you have any info on the spare tank that would fit in the original space for the spare? Someone told me a fuel tank from an F150 would fit - but when I looked at the tank and compared to the space - there was no way that was going to work. I have been spending a lot of time on my back laying under there trying to figure out the best use of that space.

 

[Sinfuzz]

Thanks for the massive amount of info @Stryder106 and @CrazyDrei super awesome stuff!

One of my biggest takeaways is accepting what a rig is, what it can and can't do. @CrazyDrei was awesomely troll like (I say in the best way possible) with his build thread shoving 37s where so many said they didn't belong. But, you keep the activity in check. @Stryder106 is similar in the way that he keeps the truck on trails it can do and it appears to rule.. I wanna run the Mojave Road now haha... These aren't SAS rock crawlers, but they can go places a Civic can't (to quote CD, i think) and they can carry a whole lot more than my JK ever will. Bonus, my wife and I could definitely sleep in the Avy, again, JK not so much.

One technical note, both of you brought up gearing and both of you have thoroughly made me question if I REALLY do want to top out at a 33" tire. I have 33s on my JK with 4:10 and I couldn't imagine it being any lower numerically and it's even a 6-speed. The 5.3 definitely kicks out more than the 3.8, but I'm really thinking if I go 35s on the Avy, I may also jump straight to 4.88, especially with Silver being a common spot to cruise around. Definitely going to look at those Eibach shocks as well.

You guys gave me a lot to chew on here. I'm excited to start building this thing and do some more exploring! Thanks again for all the info, I'll keep the thread updated with my progress.

 

[Sinfuzz]

An Av is basically a Suburban with the back roof cut off so any of the Suburban drivetrain mods should work (lifts, shocks, etc.) Given that you're in Michigan I would think that rust mitigation would be a top priority for you - here in dry Colorado it's not so much of an issue.

I got my truck with some rust already on it =\. It's not the worst, I am going to have to do something about keeping it in check though. Is there anything you can really do besides getting lots of car washes and under-body coatings?

 

[rayra]

POR-15, the better cleaning / prep you do, the better the results. Like dealing with roof tar, though. Gets everywhere if you aren't careful.

https://www.eastwood.com/paints/rus...pe=e&msclkid=b1f9267a0b9015bc07d47a3df0a3635c

 

[Stryder106]

Thanks for the massive amount of info @Stryder106 and @CrazyDrei super awesome stuff!

One of my biggest takeaways is accepting what a rig is, what it can and can't do. @CrazyDrei was awesomely troll like (I say in the best way possible) with his build thread shoving 37s where so many said they didn't belong. But, you keep the activity in check. @Stryder106 is similar in the way that he keeps the truck on trails it can do and it appears to rule.. I wanna run the Mojave Road now haha... These aren't SAS rock crawlers, but they can go places a Civic can't (to quote CD, i think) and they can carry a whole lot more than my JK ever will. Bonus, my wife and I could definitely sleep in the Avy, again, JK not so much.

One technical note, both of you brought up gearing and both of you have thoroughly made me question if I REALLY do want to top out at a 33" tire. I have 33s on my JK with 4:10 and I couldn't imagine it being any lower numerically and it's even a 6-speed. The 5.3 definitely kicks out more than the 3.8, but I'm really thinking if I go 35s on the Avy, I may also jump straight to 4.88, especially with Silver being a common spot to cruise around. Definitely going to look at those Eibach shocks as well.

You guys gave me a lot to chew on here. I'm excited to start building this thing and do some more exploring! Thanks again for all the info, I'll keep the thread updated with my progress.

I went 33" and can tell you that the 35" is much better. As for the gearing - just some info for you. My Av with the 35" tires and 4.88 gears really likes to cruise on the hwy around 60-64 mph. At 60 my RPMs are 2000. At 65 they are 2150. If I'm minding my Ps and Qs and just cruising along between 55-62 while FULLY loaded I can get 16.5MPG. Cruise at 72MPH and the MPG drops to ~13.5. I'm also about as aerodynamic as a brick with the roof rack and RTT.

Over summer I did a month long overland trip covering 4700 miles of dirt (4754 to be exact) and found myself in the Sand Dunes in Oregon along with some Jeeps and Toyotas (much lighter) - I aired down to 15psi and while they were winding out their engines to keep moving, I was simply chugging along at 1700rpm and never had an issue. I say that to make the point of thinking of everything in combination rather than individual components. My engine and exhaust mods increased HP and torque, but most importantly pulled the torque curve way down in the RPM band. A stock Av makes 96% of it's torque at 4600rpm. Mine makes 96% of its torque at 2200rpm. It behaves more like a diesel which is easier on rotating parts. I live in CA so what I can do is extremely limited due to CARB restrictions.

My Av has done everything I've asked it to do up to and including Level 7 trails. Mojave Road is definitely a cool trip. If you ever decide to plan it, let me know and I can give you a few side trips to do along the way.

 

[Martinjmpr]

Is there anything you can really do besides getting lots of car washes and under-body coatings?

Yeah, you can move to a warmer and drier part of the country.

 

[Sinfuzz]

A stock Av makes 96% of it's torque at 4600rpm. Mine makes 96% of its torque at 2200rpm. It behaves more like a diesel which is easier on rotating parts. I live in CA so what I can do is extremely limited due to CARB restrictions.

Is there info in your build thread on what you did? I must have missed that part, sounds awesome though.

 

[Stryder106]

Yes there should be.

 

[CrazyDrei]

Stryder106,

I am quoting your post because you have so many great points but this is more for OP and others who have not been there done that and just exploring options.

make the point of thinking of everything in combination rather than individual components.

This is probably the most accurate comment about GMT800 trucks I have ever seen on any forum and worth it's weight in gold.

My engine and exhaust mods increased HP and torque, but most importantly pulled the torque curve way down in the RPM band. A stock Av makes 96% of it's torque at 4600rpm. Mine makes 96% of its torque at 2200rpm. It behaves more like a diesel which is easier on rotating parts.

Cold air intake: $40 on eBay, long tube headers: $200 on eBay, re-flach the ECU like a flashpacq F5: $150 eBay and you have opened up the 5.3 to behave better then a 6.0.

My Av with the 35" tires and 4.88 gears really likes to cruise on the hwy around 60-64 mph. At 60 my RPMs are 2000. At 65 they are 2150. If I'm minding my Ps and Qs and just cruising along between 55-62 while FULLY loaded I can get 16.5MPG. Cruise at 72MPH and the MPG drops to ~13.5. I'm also about as aerodynamic as a brick with the roof rack and RTT.

I run 4.10 gears with 37" tires, Stryder106 runs 4.88 gears with 35" tires. I wanted 4.56 or 4.88 gears to turn my 37" tires, however for over $1,000 parts and labor for the new gears I had an opportunity to get a set of 4.10 for under $300 installed, could not pass it up and it does great empty but no where as efficient at 16.5mpg loaded. Go to bigger tires, keep your 3.73 gears, drive for 6 months, figure out what kind of driving you do and what you really need and upgrade from there. Don't fear the gear.

found myself in the Sand Dunes in Oregon along with some Jeeps and Toyotas (much lighter) - I aired down to 15psi and while they were winding out their engines to keep moving, I was simply chugging along at 1700rpm and never had an issue.

No replacement for displacement. Get a wide tire such as 12.5" or 13.5" wide air it down to 15psi and you will do donuts around Jeeps, drop it down to 10psi and you'll keep up with most side by sides, drop it to 5psi and you will never get stuck in the sand. I just got back from a day at the dunes and was running up 600ft hills at under 2,000rpm while my Jeep buddy was bouncing off the rev limiter.

Hope this helps.

 

[Sinfuzz]

Thanks again for all the info guys. It’s looking like we’re keeping the Jeep, but that’s becoming hers and I’ll just be driving and building the Avy.. I gotta unbury it, charge the battery up and get it to my buddies garage to start looking at it.

My wife and I are just excited to get it setup for camping out of to start. The build will start with some boring maintenance stuff, then move onto rebuilding the front end and suspension mods.

Really appreciate all your help. I’ll either keep this thread going with the build or start a new thread once it starts.

 

[Stryder106]

Hey Y'All - I entered this picture in a Best Shot contest. I took it of my Av and camping location last summer in the Hart Mountain Antelope Refuge in southern Oregon. This was Day 8 of a month long overlanding trek covering 4754 miles. I need 100 votes to make the next round. If you guys like the pic - I'd appreciate you jumping over there and voting for it. Overland Expo Best Shot 2019

 

[Burb One]

Hey ya'll. Looks like you're off to a great start. double to what everything Stryder says (his truck, and outlook are on point)

My idea with the truck is there's two ways to do things for any given part- extremely overbuilt custom, or overbuilt off the shelf. If I can find it and it works, I prefer off the shelf. I don't ever want to break something and not be able to find it in the local area of wherever I'm at in the country. Of course, sometimes you got to build it up yourself, and in those cases, build it so it will never break.

Only thing I would say is be careful with upgrading parts before thinking about what the next weak point is. RCV axles would be a big no-no on a 8.25 front end(and I would even argue a 9.25). Carrying and replacing a CV is a 20 min wheel-on job, vs. replacing a diff or losing 4wd out on trail. Same goes for the larger front tie rods. Personally, I'm a fan of the sleeves on quality tierods (Moog/ AC Delco) vs. the beefy units. We ran across a silverado recently on trail with some upgraded tie rods that had it's steering box ripped, Again, would much rather bend a tie rod and replace, then deal with that. Your next point of breakage after the tie rods are pitman/idler and then steering box. The steering box is pretty stout, and with some help the idler/ pitman are too. Of course, there's a point where if we were bending tierods all the time, then we'd re-think, but that's not the case. We run pretty fast and haven't had any trouble with the front ends with a combination of sleeves on quality stock size tie-rods, quality pitman arm/idler arm with cognito braces. The (not so) weak point is still the tie rods and I like it that way. For the CV's- if you go to a six inch lift you can fit a 2500 front diff and axles in there- if you stick with the 8.25 there's not much to do other than just be careful with what you're doing. The front end isn't that weak with stock tire sizes or even 33's if you stay away from the throttle pedal when stuck, it's the bigger tire sizes (especially with aftermarket uca and extra droop without limit arms) where it gets into trouble.

For the gas tank, look over on my build thread for some pictures. a 1996 F150 gas tank fits perfect where the spare is. Bought one with the built in pump and plumbed the output into the filler for the stock tank (got a gauge off ebay too!). Also the angle works perfect to plumb the aux fill into the stock gas cap door. In a pinch, if the main tank was ruptured, I put quick fittings on the output for both, and can confirm the f150 tank will run the truck.

For the brakes- Fronts- A HUGE upgrade is fitting the GMT900 brakes to the front end(look at my thread or around for the exact year that is best- can't recall off the top of my head). I can't say enough how much of a difference this made, with bolt on parts. Also- again the thing I love about it, is any part store in the country will have on hand replacement parts. I can recommend the AC Delco police line calipers, rotors and pads. Brakes are a tradeoff (bite, heat, noise, dust, etc.) and I think that line is the most aggressive- non squeaking pad for this truck I've found.) I think on rock auto for everything it was less than 400 bucks. The only downside is you need to be on 17's to fit in the wheel. (All three the Burb's have $150 craigslist GMT900 wheels). The rear brakes on a GMT800 suburban are the biggest ones that were fitted that will fit bolt on- (even bigger than latter year 2500.) For those just get some good calipers, pads and rotors (again AC Delco Police are what I recommend)

 

[rayra]

I'm not sure about that 900 front brake fitment issue, I'll have to tape my clearance next time I have the wheel off (next week, have new CVs and upper control arms on the way. When I was changing my wheel hubs last week I was laying there unbolting my CVs and was looking into and thru my front wheels and I seemed to have a great deal of vertical separation between the GMT900 brake upgrade and my factory 17" wheels. So much so that I think 16" rims would readily clear.
But my impression might have been skewed by my 2" wheel spacers. Have to get in and measure the inner wheel diameter at the back plane and compare it to the brake diameter at the hump of the calipers. And figure if an 1" smaller rim would still clear. Everybody says it won't, but it sure looks to me like it might. Maybe it's a wheel weight clearance issue, have had past trouble with my aftermarket 15" aluminum rims on my '85 C-10, with tape weights.

And Burb's comment about next weakest link is very true and triggered another memory / thought that I'm pretty sure I covered in my 'Hey Vortec Guys' topic, that of the factory idler arm. If you have a high mileage GMT800, just go ahead and replace it right now, at a time and place of your own choosing. The thing's grease fitting is near the top and with the factory skidplate in place to oil change tech will bother pulling the plate or the air intake chamber in front of the S-belt to get to the fitting. So the idlers are usually worn out and sloppy.

 

[Burb One]

The thing's grease fitting is near the top and with the factory skidplate in place to oil change tech will bother pulling the plate or the air intake chamber in front of the S-belt to get to the fitting. So the idlers are usually worn out and sloppy.

Seconded. Also- the moog problem solvers (HD) come with a remote hose so you can grease it in the future easily!

 

[rayra]

That is indeed a problem solver. Usually only see that sort of remoted grease fitting on construction or farm equipment.