Some opinions and advice

[Rickalicka18]

If you haven't noticed already, I love getting multiple opinions on things, because just reading about it doesn't help me as much.. Lately I've been contemplating on just sticking with my current plan, going a little crazy, or just going big.... But I am intimidated by going bigger than my current plan... And it would really help to get some opinions and advice from people on this site, since no one knows trailblazers better than the people on this site.

Now to give some background I have some things that I WILL get done anyways. I have to replace cv joints, flip my ucas, replace my 4wd disconnect, switch my rims, change rotors & brake calipers & pads (upgrade to ext rotors basically), pcm of nc tune, dual exhaust, and cold air intake, For the things that will get done I will be taking full week off (if needed), get all the parts ready to go beforehand and leave it up on the lift the whole week and just go to town on it until its all done. But the problem is that its always in the back of my mind that I want to have bigger tires than 265/70/17s, so I came up with some options... Three options to be exact:

1. Stick with my current plan which is keep my gears 3.42, and put 265/70/17 tires. Then maybe a 2" body lift. (The quitters way out)
2. Change my diff gears out to 3.73 gears and put 275/70/17 tires on. What makes this "middle ground" option so appealing to me is the fact that it seems to be relatively easy and somewhat cheap to find 8.6 rear diffs with 3.73 gears already in. Although, I've already been told that 3.73 gears won't make much of a difference, I'm convinced my gas mileage will be way better with the 3.73 gears (over 3.42 gears) hopefully giving me above 15mpg as an average, give me peace of mind knowing my transmission and diff won't be overheating, and let me break the 32" tire mark... All while giving me the opportunity to convert to 4.10 later. I'd also buy a 3" body lift with this set up and have to do some trimming.
3. Last option is to just convert to 4.10 gears. (This is the "go big or go home" option). Doing this I would convert both front and rear diffs from 3.73 to 4.10. My only issue with this is the time, experience, and money factor. I've never cracked open a differential before and I don't know how long it would take to convert it. It sounds fairly easy to do though (Maybe someone could reassure me how easy it is....). This would allow me to put 285/70/17 tires on and I would most likely need to do some front bumper trimming. I also think my gas mileage would stay relatively reasonable staying above 15 mpg as an average. Also putting a 3" body lift on this set up.

Lastly, I've calculated option 2 will probably cost me around $600 more than option 1 and I wouldn't need to crack open the diff, just install it with everything else... Option 3 is about $1100 more than option 1 and I would have to open the front and rear diff to change the gears, which will most likely take some time and thinking to do. Anyways, these are my current options I came up with. Any input or advice is welcome. Thanks in advance.

[Jrgunn5150]

Ok, first off, you keep mentioning gas mileage, what are you doing with this thing? Is it your sole mode of transportation, and it need's to be reliable and economical? If so, I'm going to say take that money and buy a Honda, then the Trailblazer can be whatever you want it to be.

You can buy an entire diff with 4.10 gear's, and just swap them out. I would not waste my time on 3.73's. For that matter, I wouldn't waste my time on 4.10's. I'm seriously having attacks of consciousness over 4.56's. What I want to do is three link mine, with a Dana 44 and 5.13's. The primary purpose of mine is to wheel, so I'm a little different. I guess.

[Rickalicka18]

I didn't really put out a crazy number for average gas mileage... As I stated in the post above, I should be able to get 15mpg or higher with each set up, which isn't too much to ask for. My dads diesel pickup gets 14.5mpg and I would 100% be okay will fueling that up everytime. When It gets to the point where my whole life is spent at the pump then its not practical.. Tbh I'm getting around 15 rn, maybe lower, and I'm happy with it. I have no problem getting through a whole week on a full tank rn. In the future, this will be a more expedition orientated build, seeing mild offroad use, so it will see a good amount of highway miles and backroad miles. Right now, it serves as my daily driver though. I DON'T WANT NO DAMN HONDA!!! MERICA BUILT!!!

It will be more cost effective to buy an 8.6 diff with 3.73 and buy the 4.10 gears seperate, than buying a 8.6 diff with 4.10s already installed. A difference of about $250 maybe $300 which is worth it in my book, plus I gain experience in opening up the rear differential. If I could find one with 3.42 gears it would be even cheaper, except I can find any lol. I also have no interest in put 4.56 gears in. I believe JD has 4.56 and 285/70/17 for his combo, but I just don't feel that I need it. 4.10 will keep my rpm closer to stock than 4.56s. Although 300 rpm isn't that big of a difference, keeping the rpm closer to the rpm "sweet spot" will translate to stockish mpg. Someone mentioned the rpm sweet spots in the fuel mileage thread but I can't remember who haha... But it makes sense.

We do have different purposes for our trailblazer though, but that's alright. Thanks for your input.

[Jrgunn5150]

Have you been searching car-part.com?

I think for most people, who want to lift and run oversize tire's, 4.10's are adequate. If you want to regear your new rear, I would recommend taking the opportunity to upgrade to a real locker as well.

[Rickalicka18]

I absolutely agree with the locker idea. I'll look into that. I know that the diffs I was looking at had a g80, but a better locker is a good idea. I think I heard the g80 suck though haha

[Jrgunn5150]

I absolutely agree with the locker idea. I'll look into that. I know that the diffs I was looking at had a g80, but a better locker is a good idea. I think I heard the g80 suck though haha

On one hand, they've been sticking them in millions of axle's for decades. On the other, they are unpredictable, unlock at a wheelspeed above 20 mph, and are not rebuildable.

[Rickalicka18]

The g80 is the perfect locker for the average use of a vehicle, I think. It does what it suppose to do. I'm sure GM had the positives out weighing the negatives in the end, otherwise they wouldn't be using them I guess.

I will be upgrading though.

[Rickalicka18]

[quote="Jrgunn5150"]Have you been searching car-part.com?

I completely missed this for some reason haha... I did just check it out briefly and saw they sell 3.90 rear and front diff gears. Found that pretty weird. Does that sound right?

I'll be doing some more exploring of the site tomorrow... Holy crap its 1:34 am...

[Rickalicka18]

Thanks to Jr. I found a 4.10 axle local for $550. Seems like a good deal to me. I'll be following through with option 3 now.

[Jrgunn5150]

Thanks to Jr. I found a 4.10 axle local for $550. Seems like a good deal to me. I'll be following through with option 3 now.

Woot! Make sure to call ahead, those thing's aren't always up to date. And really stress that you absolutely want 4.10's and are driving hours, or whatever lol .

BTW, I don't think a 3.90 gear is even a ratio Chevy, or AAM ever used.

[Rickalicka18]

I'll find the link for it. I actually searched the wrong site at first, but while searching found that they make 3.90 and 4.30 ring and pinon gears for the front and back diffs..

Do you think if would be beneficial to change the front hubs. I know for a fact that they've never been changed and I'm at 160k

[Rickalicka18]

Heres the 3.90: http://www.carparts.com/details/Chevrol ... 85390.html

Heres the 4.30: http://www.carparts.com/details/Chevrol ... 85430.html

[TBYODA]

Heres the 3.90: http://www.carparts.com/details/Chevrol ... 85390.html

Heres the 4.30: http://www.carparts.com/details/Chevrol ... 85430.html

i would check your data a site deals with this kind of stuff like summit racing. I would trust catparts.com, summit should have better prices.

beside our front diffs is 7.2" ring gear and the rear is either 8.0" or 8.6" Not 8.5" like every gm 1500

[Rickalicka18]

Interesting... So you're saying that the 3.90 and 4.30 gears are for a gm 1500?

[TBYODA]

the gating factor is the front 7.2" ifs diff.

[Rickalicka18]

Oh okay, I see what you're saying now

[Jrgunn5150]

Heres the 3.90: http://www.carparts.com/details/Chevrol ... 85390.html

Heres the 4.30: http://www.carparts.com/details/Chevrol ... 85430.html

Those are for the rear, which doesn't surprise me since the same ring gear was used in alot of car's, and people race car's, so they may need silly in between ratio's.

I just meant factory ratios, a 3.90 or a 4.30 aren't ratio's you would see in a modern Chevy product going back my lifetime.

[Rickalicka18]

I know what you mean. They don't have those ratios for the front diff though

[Jrgunn5150]

I know what you mean. They don't have those ratios for the front diff though

Precisely, because it was never a factory ratio, and because we only share a front diff with S10's, and no one cares about S10's lol.

[moose1]

Fwiw I have the 3.73's and run 275/70/17 and mpg sucks. Avg.12.5