Opinion: Rear Diff Replacement Options

[FlyFish3rman]

Hi All,

I'm hoping to get your opinions on what to do with my rear diff. I have an 07 SWB TB non G80 8" with 3.42 gears. I'd really like to upgrade to 3.73s as I tow a lot in the summer through some pretty hilly terrain (I have a external trans cooler), and I could definitely use the extra gearing.

I'm envisioning two different paths (but maybe I'm missing something else).

Path (1): Buy a new 3.73 ring and pinon, and then have a professional do the install. I've never done a R&P swap, and don't want to experiment on my daily.

Path (2): Find a donor full rear end assembly in good working order (preferably the 8.6 with 3.73s) and do the R&R myself.

What path would you choose and why?

 

[flyboy2610]

Is this 4wd or 2wd? With 4wd you have to do both diff's.

 

[FlyFish3rman]

It is 4wd, but the front diff is shot. I've removed both CV shafts (covered the holes with Gatorade caps) and the front driveshaft. If I ever decide to repair the front diff then I'll account for the gear change in the repair. For now, however, I'm running 2wd and would like to change rear end gearing.

 

[Dr.Fiero]

Considering it's age? I'd get new gears (etc) and have a shop do it. If you just grab another assembly, even the newest one - it'll still be getting on in years and you'll have no idea on its history (little old lady who never drove over 55, OR was it some 16 year old who liked to do 5K tranny drops daily!).

 

[nicdaking]

Find a 8.6" from a ext or v8 equipped truck with the 3.73 it will be stronger but be sure to buy the right year (2005- or 2006+) abs sensors are different

 

[Mooseman]

For your 07, only an 06 to 09 diff will work unless you want your ABS and Stabilitrak to stop working.

I'm with @nicdaking on this one. AFAIK, 8.0 gear sets are non-existent except maybe from GM ($$$) and is a pretty involved job to get them set right. What you'll need to decide next is if you want a G80 locker or a limited slip. The locker will be from a TB or Envoy and the LS will come from a Saab 9-7x or a Buick Rainier. You could stick with the 8.0 if you get it from an I6 truck or go to the beefier 8.6 from an EXT or V8.

 

[TJBaker57]

One more item to look into. Will your PCM accept reprogramming for the gear change? I am fairly certain that earlier model years can not. I do not know about the 2007 though. I think there are "black boxes" available to handle such a conversion between the vehicle speed sensor and the PCM.

 

[Mooseman]

I'm "pretty sure" it can. 06+ according to this thread. The ABS can be adjusted via the Tech 2. PCM has to be recalibrated via a tune.

Can't calibrate the speedometer for new tires, but...

Has anyone come up with any type of speedometer modification idea's to let you know the speeds you're traveling with larger tires? I've read here that I cannot reprogram the speedometer in my '03, but I'd like to see if anyone has any other easy inventions that I can try. I ask because of a few...

gmtnation.com

 

[FlyFish3rman]

Thank you all for the replies.

I see that east coast gear supply (google search) has the GM 8.0" in 3.73 for $265 USD. Is that a good deal (subjectively speaking)?

I'd love to pick up a 3.73 8.6" assembly with a LSD or a Locker, but I'm in the rust belt, so finding a "nice" unit is tricky.

 

[TollKeeper]

Check LKQ as well.

 

[Mooseman]

And car-part.com. And if you have a pick-a-part nearby, it can be easily taken out yourself at substantial savings.

Just because it's from the rust belt doesn't mean it's FUBAR. Maybe the cover and the backing plates can rust through but the rest should be fine. Internally, it's sealed and lubed so no rust in there. As for wear, you can easily check the backlash via the pinion and open it up to check the internals. If it's been well maintained, it can last forever.

 

[JayArr]

I was always of the opinion that the mechanical parts were better in the rust belt because it was the body that caused the car to go to the yard. Out west and in warm climates the cars get driven until they don't run anymore and the body is still in good shape.

Don't discount a lower mileage rear end out of a rust bucket.

 

[FlyFish3rman]

Thank you all for your replies. I'm going to check out these websites and see if I can find a complete unit to swap out, and then send in my PCM to Lime-Swap for tuning.