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97 Tahoe front diff swap

n8in8or

n8in8or

I never met a project I didn’t like
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I’m more than likely doing some gear stuff to the Tahoe this spring. One of the things I’m seriously considering is a change from 3.73 gears to 3.42 gears. The easy way to do the front is to just swap the whole diff assembly. What years will interchange with my 1997? I found a diff out of a 1996 K1500 for a good price that I’ll probably pick up. Anything specific I should look for when looking at one? Anything I should proactively do to it before I put it in the truck? Thanks in advance!
 
If you haven't done it, now is a great time to upgrade to the 98+ electric servo actuator. 97 could be a spmut year from my reccection. If your truck came stock with a thermal actuator, then you have to use an early 97 or older diff, and use the spacer if you upgrade to the 98+ electric servo actuator. If yours came stock with the servo actuator, then you need to stick with one of them, or make sure you use only the electric servo actuator. You can interchange them from 88-06 trucks for the actual aluminum diff portion, it's the cast iron portion that bolts to it on the passenger side that changes from gmt-400 to gmt-800. And then just make sure and use the correct combo of actuator and spacer or no spacer for the passenger disconnect side. I hope I broke that down somewhat understandable.
 
THEFERMANATOR said:
If you haven't done it, now is a great time to upgrade to the 98+ electric servo actuator. 97 could be a spmut year from my reccection. If your truck came stock with a thermal actuator, then you have to use an early 97 or older diff, and use the spacer if you upgrade to the 98+ electric servo actuator. If yours came stock with the servo actuator, then you need to stick with one of them, or make sure you use only the electric servo actuator. You can interchange them from 88-06 trucks for the actual aluminum diff portion, it's the cast iron portion that bolts to it on the passenger side that changes from gmt-400 to gmt-800. And then just make sure and use the correct combo of actuator and spacer or no spacer for the passenger disconnect side. I hope I broke that down somewhat understandable.
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Yep, I think that makes sense. I’ll have to take a look at my truck and see what I have. Thanks for the info.
 
Just curious as to why swap the gear ratio? Running out of RPM /MPH the track?
 
WarWagon said:
Just curious as to why swap the gear ratio? Running out of RPM /MPH the track?
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2 reasons: 1. First gear runs out a bit too quick, so I’d like to try a taller gear and see if I like it better. 2. I’d like to run less RPM on the highway. I’m also going to switch from 265/70/16s to 265/75/16s to get a bit taller gearing overall, too
 
ak diesel driver said:
Even my 99 dually has the thermo actuator. Seems like it started sooner in the burb/Tahoe's. Seems like the push button transfer case got them
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Are you sure on that? GM has a tsb stating no vehicles made after 98 got them because the actual diff housing changed designs in late 97 to do away with the switch to tell everything it was locked in because the new style actuators had it built in. Push button shifting started in 96 and still used the thermal actuator, np246 with the full time option came out in 97, and it had the servo style, 98 they all went to it, then in 99 when all wheel drive became an option they used asolid plug to lock the disconnect in 100%.
 
Well I haven't actually paid much attention but it does take a bit for it to engage just like the TLAs do. I'll have to verify next time I'm under it.
 
IMO, going to a larger diameter tire is the best route however; you must consider the greater the aspect ration the more side to side motion the tire will have...your driving style will dictate if this is the best option for you.

Keep in mind advertised dia. & actual loaded dia. is always different, example my 295/75/16 is advertised as 33.5 however actual is 31.5
 
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FellowTraveler said:
IMO, going to a larger diameter tire is the best route however; you must consider the greater the aspect ration the more side to side motion the tire will have...your driving style will dictate if this is the best option for you.
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I have additional motivation to change my gears: the craptastic Superior Gear ring and pinion howl from 40-65mph despite being set up multiple times. Only AFTER I bought them did I find the negative reviews. I have a used set of GM 3.42 gears for the 14 bolt already.
 
n8in8or said:
I have additional motivation to change my gears: the craptastic Superior Gear ring and pinion howl from 40-65mph despite being set up multiple times. Only AFTER I bought them did I find the negative reviews. I have a used set of GM 3.42 gears for the 14 bolt already.
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Now the truth comes out.

Yes @FellowTraveler chainging tire size (taller) to see how it likes lower gears would be the easier way to test it out how the engine setup likes it before swapping gears.

IMO you should actually look for the 4.11 ratio: Quicker 60' track times. The big question I would have is the awful 3-4 shift RPM drop to get you over 100 MPH being reached sooner with the 4.11's. (Sleeper Stomping others on the street is best done under 100 MPH due to Felony speeding concerns.) The 4.11's tend to howl around 45 MPH so at least you would expect it. 1st gear gets this lead brick moving and then it's done it's part for the 60' time.

Maybe find a complete diff out of a junkyard that's ready to bolt in vs. trying to set the gears up to not howl. Disc brake conversion time? It takes a good bit of luck off the assembly line or someone who can tell by feel if the diff is set up properly.

Of course then you would have to be considering wider tires for traction at the track. Hard compromise with your need for skinny tires to sink through the snow/ice/slush... :p

It will be interesting to see how your torque curve combined with gearing changes your track times.
 
WarWagon said:
Now the truth comes out.

Yes @FellowTraveler chainging tire size (taller) to see how it likes lower gears would be the easier way to test it out how the engine setup likes it before swapping gears.

IMO you should actually look for the 4.11 ratio: Quicker 60' track times. The big question I would have is the awful 3-4 shift RPM drop to get you over 100 MPH being reached sooner with the 4.11's. (Sleeper Stomping others on the street is best done under 100 MPH due to Felony speeding concerns.) The 4.11's tend to howl around 45 MPH so at least you would expect it. 1st gear gets this lead brick moving and then it's done it's part for the 60' time.

Maybe find a complete diff out of a junkyard that's ready to bolt in vs. trying to set the gears up to not howl. Disc brake conversion time? It takes a good bit of luck off the assembly line or someone who can tell by feel if the diff is set up properly.

Of course then you would have to be considering wider tires for traction at the track. Hard compromise with your need for skinny tires to sink through the snow/ice/slush... :p

It will be interesting to see how your torque curve combined with gearing changes your track times.
Click to expand...

I hear you, but not exactly. I purchased the 3.42 gears a while ago when I first put this combo together and was disappointed at how quickly 1st gear ran out. But yes, my other motivation to do gears was to get rid of the stupid Superior (INFERIOR I say) Gears.

Of course I will hit the track to see how it affects things. I say it will at least be as quick. So if my acceleration stays the same, but I gain an RPM drop on the highway, then I'm happy. And if it's slower, well we'll see how much slower it is and that will determine my disappointment level. If anything, I think this will exacerbate my loose torque convertor and make me upgrade that next.....and then upgrade hard parts in the trans that I'll probably start blowing up. This upgrade stuff is a vicious cycle I tell ya!!

I've been looking for a complete diff for a while now and I haven't had any luck, so I'm finally pulling the trigger on this route.

I don't have to worry about tire width because I have a separate set of winter tires that I run in the yuck :wtf:
 
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