ALRIGHT IV GOT A 00' SILVERADO Z71 WITH A 5" LIFT AND 35" DICK CEPEK FCII. IM PLANNING ON SWAPPING OUT MY GEARS FROM THE HIGH 3.73 TO A MUCH LOWER 4.56. WHILE IM AT IT, I WOULD LOVE TO SWAP OUT THE LIMITED SLIP FOR A TRUETRAC OR AUBURN GEAR. HERES THE BIG QUESTION, DOES MY LIMITED SLIP HAVE ANYTHING TO DO WITH THE AUTOTRAC OPERATION. I REALLY DON'T KNOW HOW IT WORKS, I JUST KNOW I USE IT ALL THE TIME AT MY RANCH, FOR A LITTLE EXTRA GRIP IF I NEED IT. IM ALSO LOOKIN AT A 9.5" REAR END OUT OF A VORTEC MAX, BUT THATS FOR A LATER POST.  

I see no issues with the usage of a LSD. Your auto trac works with clutches engaging  front drive shaft when slippage is detected due to differences in wheel speeds. On gear ratio, 4.56 would be minimum I would suggest here and you would do well to consider a 4.88 as well if you use it in farm/ranch work a lot. Even a 4.88 is not as deep as it sounds and would only yield about 2100 RPM in OD at 65 MPH and with the drag of those tires and lift you really do not want any less RPM here if you want OD to be really usable.  

dam 4.88 sounds kinda steep, but ill do some research on it. thnks for the tech on the autotrac though.  

jnsaldana25:
dam 4.88 sounds kinda steep, but ill do some research on it. thnks for the tech on the autotrac though.

Check out link below as a 4.88 is not deep at all with 35's and OD nor should you feel that less cruise RPM is better here is this configuration

Click Here  

you'll be much more satisfied with the 4:88 than any other with 35's, although the 4:56 is about as close to corrected stock final ratio (4:27) as you'll get going from 30.5" tires to 35's.  

mudb8-.:
you'll be much more satisfied with the 4:88 than any other with 35's, although the 4:56 is about as close to corrected stock final ratio (4:27) as you'll get going from 30.5" tires to 35's.

While mathematically, a 4.56 is close to being equal to stock tires with 3.73's, the lift and bigger tires add drag so it take more HP to cruise than before and more power to accelerate and a a slightly deeper gear like a 4.88 will help "adjust" for this and restore near stock like over all performance with 35's.  

These guys are right. You don't want something comparable to stock on the chart because that doesn't take in to account the increased rotating mass, weight, etc. You want something a hair deeper and the 4.88 will give you what you need.

--Sean  

4.88's sound like a good choice, but as far as the differential; adding the autotrac or detroit locker shouldn't affect my autotrac right???????  

right  

mudb8-.:
right

I would have to say no on Detroit locker with autotrac. Stay with a LSD type diff. A Detroit does not have the ability to power both wheels properly in a turn. It is either 1WD with one coasting or 2WD both tires same speed with then skidding in a turn. This could maybe cause issues for your 4x4 drive system.  

yeah, i missed the detroit part, like snoman says.....lsd  

wow i never would have guessed that an up-grade would be ill advised here. well you learn something new every day right?