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2004 chevy trailblazer_ls
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113 Posts
Discussion Starter #1
I've been reading here for two weeks, and have spent 20+ hrs searching and combing threads. I've learned a lot. Thanks for all the informative threads.

The vehicle would be used primarily for a DD 4x4 in the winter and the occasional tow of 5000 lbs (race car and trailer, wet, when the car breaks). I generally drive to and from the track in the car.

I have a had a huge problem finding an 04/05 trailblazer with a 3.73 and locking diff. I've looked at dozens and everything seems to have the 3.42s. I've read that the Envoys come with 3.73s as base optioned, but they aren't really worth the extra 2 - 3,000 or so over comparative trailblazers... I really have no use for the "upgrades" the envoy gets over the TB other than the better gears.

Is it at all practical to swap the gears to 3.73s front and rear? Can you even get them at a reasonable price?

Should I start looking at envoys?

Are 3.73 TB really that hard to find?

Would the towing through the NE mountains cause a problem if I just grabbed a 3.42 TB and threw on a tranny cooler?


I'm a DIY type of guy, have rebuilt a couple motors, a few manual transmissions and have built up a couple suspensions. Never dealt with one of these before though and I'd like to avoid pulling apart something that has 40k that I just spent 10-11k on unless it's just the best route.


Looking for any input you guys might have, thanks in advance
 

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2004 chevy trailblazer_lt
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218 Posts
Not sure if you've bought yet, but I'm pretty sure Buick Rainiers came with 3.73's as the standard gears with the I-6, so you might want to look at those. The only downside is, you can't get selectable 4wd, you get either 2wd or permanent Awd, with is pretty much a 4wd Trailblazer stuck in A4wd. The other benefit of the Rainier is that you can get the V8 in the Short Wheel Base, which you could only do with those, 9-7X's, and '06+ TB's. Also, before I forget, Envoy's DID NOT come with 3.73's standard- I'm pretty sure that they came with all 3 gear choices just like TB's. And they don't really have any upgrades over the TB's, just different looks, and rear air suspension on SLT's. And depending on how often you tow, I don't think 5,000 lbs would be too much to tow- it is rated at more than that. And I wasn't aware that North East really had any mountains. Or is that Nebraska? Not sure. Anyways, I don't think you'll be doing any damage at all- just drop it in 3 if you're at all worried. May take a little longer to get rolling, but that shouldn't be a big deal. Hope that helped some!
 

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Southeast Chapter
2004 buick rainier
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5,864 Posts
:iagree: The rainiers, Bravadas; and 9-7x's all came with at least the 3.73 gears and most have the G80; right now all GMT-360's are going for around the same price so get what you think looks the best and what you would be happy with; but if you are going to be towing that weight i woudl really try to find one with at least the 3.73 if not the 4.10 gears and the g80 can bevery handy. have fun with your search and just let us know if you have any questions along the way:yes:
 

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Banned
2004 gmc
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26,181 Posts
All the gear options are available from Randy's Ring and Pinion and other differential parts suppliers, but changing the front is made more difficult by it being bolted to the SIDE of the oil pan, and a shaft going THROUGH to the passenger side. Lots of labor in that swap, even if you have experience shimming gears properly.

A tranny cooler is an excellent idea lots of members have done.

As long as you don't go to upsize offroad tires like 31-33", I'd think that 3.42s are fine, and should give you better mileage when not towing. Mountains from 6-12,000 feet would be a challenge, but that doesn't seem to be your territory. :cool:
 

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Banned
2004 gmc envoy_slt_xuv
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447 Posts
:iagree: The rainiers, Bravadas; and 9-7x's all came with at least the 3.73 gears and most have the G80; right now all GMT-360's are going for around the same price so get what you think looks the best and what you would be happy with; but if you are going to be towing that weight i woudl really try to find one with at least the 3.73 if not the 4.10 gears and the g80 can bevery handy. have fun with your search and just let us know if you have any questions along the way:yes:
I agree, I have a 3.73's on my Avalanche with a locker and I am not really happy with the towing performance. On the other hand I get great all aroung gas mileage for such a big truck with this combination. If towing is going to be your main priority I would go with the 4.10's
 

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2004 chevy trailblazer_ls
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113 Posts
Discussion Starter #6
thanks for the input guys, I'm still looking. I was ready to buy one a couple days ago but one of the guys at the dealership took it home and wrecked it... it was nice. Going to check out another one tomorrow morning. Looks like I'm going to be stuck with a 3.42 vehicle though, I just can't find anything with better gears.
I did find a few threads talking about swapping them, doesn't look too awful. If I'm not happy I can always switch them out.
 

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2007 chevy trailblazer_lt
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221 Posts
4.2 or 5.3??

The V-8 models only had 3.42 or 3.73 gears. I-6 models have the additional option of 4.10's These will KILL your daily mpg and are only really good if towing a lot.

I would recommend the 3.73's The Extra gearing is helpful and helps on acceleration. GET THE G-80 option!!! Locking diff is a God sent!!!!

Don
 

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2004 buick rainier
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109 Posts
if someone hasn't told you yet, you can check the gearing by looking at the RPO codes on the inside of the glovebox door,

GT3=3.42
GT4=3.73
I cant remember if 4.10s are GT5 or GTU, they are a rare option, except on the extended models.

5,000lbs is alot for the 4.2L, you may be happier with a V-8. The Rainer and Saab are the easist to find in the short model with a V-8. Rainers can be found for cheap, usually at trailblazer prices with Envoy SLT type options. If you are a city driver expect 12 mpg for the V-8, 15 for the I-6, gearing wont effect your city mileage.

As for gearing on the I-6, your best bet for 5,000lbs would be a model with 3.73s or better, and leaving it in 3rd, the max speed would be 60-65 mph, which is around 2600-2800rpm. You have to be careful not to be driving it with the torque convertor unlocked, it will burn up quickly. A model with 3.42s would likely unlock the convertor more often causing premature tranny failure. The 4l60 is the weak link as it is in all GM trucks.
 

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2004 chevy trailblazer_ls
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113 Posts
Discussion Starter #9
thanks for all the input guys, I appreciate it.

I'm waiting for the paperwork to finish up but i should be driving an 04 drk grey 4x4 TB with 3.42s tomorrow or wednesday, I even got a better price than I had originally anticipated.

I'll drive it around into the spring and then decide what I want to do with the diffs stereo etc..
 

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Registered
2002 gmc envoy_sle
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1,380 Posts
if someone hasn't told you yet, you can check the gearing by looking at the RPO codes on the inside of the glovebox door,

GT3=3.42
GT4=3.73
I cant remember if 4.10s are GT5 or GTU, they are a rare option, except on the extended models.

5,000lbs is alot for the 4.2L, you may be happier with a V-8. The Rainer and Saab are the easist to find in the short model with a V-8. Rainers can be found for cheap, usually at trailblazer prices with Envoy SLT type options. If you are a city driver expect 12 mpg for the V-8, 15 for the I-6, gearing wont effect your city mileage.

As for gearing on the I-6, your best bet for 5,000lbs would be a model with 3.73s or better, and leaving it in 3rd, the max speed would be 60-65 mph, which is around 2600-2800rpm. You have to be careful not to be driving it with the torque convertor unlocked, it will burn up quickly. A model with 3.42s would likely unlock the convertor more often causing premature tranny failure. The 4l60 is the weak link as it is in all GM trucks.
GT5 is the code for the 4.10 gears.
 
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