4x4 Rear end swapped but gear ratios are off

[Kungfubenny]

Due to cost efficiency I swapped my rear end from an 06 Tahoe that was parted out.
After all was said done we test drove the vehicle only to realize the gearing ratio is different.

What steps can I take to match front end ratio the newly installed rear end (my guess is 4:10)
I have noticed an increase of speed off the line but I am unable to engage 4wd without front wheels binding.


Please any help is very much appreciated!!!

 

[strutaeng]

First step is to figure out what ratio you have (check glovebox for code), what ratio your swapped axle has and what you want to keep.

Similar to the rear, you can try swapping the front to match. Regearing your current front axle is another option, but that's not as easy and usually requires some specialized knowledge and equipment. You could take it to a shop to get it done also.

Lastly, you need your computer reflashed for the correct ratio, otherwise your speedometer and odometer will be off.

 

[Kungfubenny]

First step is to figure out what ratio you have (check glovebox for code), what ratio your swapped axle has and what you want to keep.

Similar to the rear, you can try swapping the front to match. Regearing your current front axle is another option, but that's not as easy and usually requires some specialized knowledge and equipment. You could take it to a shop to get it done also.

Lastly, you need your computer reflashed for the correct ratio, otherwise your speedometer and odometer will be off.

Thank you for the brief and informative response!!

Unfortunately my vehicle doesn’t have its factory glove compartment due to the car being stolen (thief scratched out the rpo codes and damaged the compartment) leading me to swap it out with another from lkq.

My best bet may be the latter, having the front end re-geared to the appropriate ratio and computer flashed when I can afford to do so of course.

I will eventually have a shop open up the rear to better determine what to match the front with as well as flash the ecm.

 

[strutaeng]

Thank you for the brief and informative response!!

Unfortunately my vehicle doesn’t have its factory glove compartment due to the car being stolen (thief scratched out the rpo codes and damaged the compartment) leading me to swap it out with another from lkq.

My best bet may be the latter, having the front end re-geared to the appropriate ratio and computer flashed when I can afford to do so of course.

I will eventually have a shop open up the rear to better determine what to match the front with as well as flash the ecm.

Understood.

You can just lift the truck up, put in neutral and count the number of driveshaft revolutions to make the wheels spin one revolution. Use chalk to mark a line on each to make it easier to see. A helper would also be good so they can keep an eye on the tire while you are manually spinning the driveshaft.

A 4.10 ratio requires the driveshaft to spin just a tiny bit over 4 revolutions per 1 tire rotation.

I hope this helps.

 

[S33k3r]

3.73 gears will be a tiny bit under 4 revolutions per 1 tire rotation. Also, you may have 3.42 gears, which was a standard at the time, I believe (in the front differential). My wife's Tahoe, which was totalled, had 3.42s.

(I don't blame my wife for totalling it; a car in front of her went spinning out on a rainy day and spun right in front of her. If we had thought ahead and added a dashcam...)

 

[Kungfubenny]

Thank you guys for responding! I was able to find an old photo of my rpo codes I took when I first got the truck. Gu6 is the code I found which translates to 3:42 gear ratio.
I do believe the diff that I swapped into my truck is 4:10 and have still yet to confirm that theory but I will be taking to a professional to have it matched once I can afford to, no off roading or 4 wheeling at all for now. Small price to pay in order for me to get back on the road.