gear ratio help for a newbie

[HiItsRem]

I'm trying to build my truck to do a bit of drag racing, but, I want it to be a daily. I'm wanting to change my gear ratios out from a 2.72 to a 3.73 and I have no idea if I am supposed to change the t-case out if I swap gear ratios I know it's 1:1 but If I change the front and rear ratios would I need to do anything with the thing because on the tcase itself it says 2.72 and I have no idea if that is just a marking of the general gear ratio or not, I'm new to dealing with gear ratios and stuff like that and I've always heard growing up that once you change ratios you gotta replace the whole driveline and I'm just curious about that, I was hoping someone could help me on figuring out the best swap for a 10 bolt rear so I don't end up destroying my entire driveline. If anyone is curious it is a stock 4l60e K1500 1998 truck, if anyone asks for the sticker in the glovebox, good luck I have no idea what it says cause it's mostly scrubbed out and I can barely read any of the GM option codes. (I'm completely new to these kinds of specifics so please go easy on me) I know a fair amount of knowledge about these gmt400 trucks but the 4x4 driveline is where I don't know much about because I grew up in a 2wd 1ton that I spent a lot of time looking at and looking up info on

 

[Sean Buick 76]

Hi, no your axle ratios won’t be 2.73. Take a photo of the glovebox sticker which will list GT-4 or GT-5 etc for the gear ratio in the axles. If your actually drag racing then switching to 4.56 gears is typically the best bet unless you are making big power in which case a 4.10 gear can work well. Over 600 HP the 3.73 gear is fine.

 

[RichLo]

Your transfer case 2.72 gear ratio is the 4wd low-range gear ratio, 4wd High-range and 2wd are 1:1 ratio. No need to do anything with the transfer case when changing front and rear gear ratio's.

Yes the glove box code will tell you what the truck came with from the factory but that could have already been changed by a previous owner. If factory you probably have 3.42 gears. The best way to tell is to jack up the whole rear end and turn the driveshaft by hand. If it spins just under 3.5 turns for 1 revolution of the rear wheels then its 3.42, if it turns around 3 3/4 turns its 3.73, if its just over 4 turns its 4.10, etc.

4.10 is a good street gear, 4.56 is good if your putting 33" or larger tires on.

 

[Erik the Awful]

I'm trying to build my truck to do a bit of drag racing, but, I want it to be a daily... it is a stock 4l60e K1500 1998 truck

Never race a vehicle you can't walk away from. I've autocrossed my Mustang, but I've never had it to the drag strip because it's my daily driver. Keep your daily driver as reliable as you can, and buy a second vehicle for racing.

If you're looking to do some drag racing, you're really starting with the wrong truck, especially if it's an extended cab. Weight is your enemy. I'd look for a RCSWB C1500 and then strip out all the weight I could.

 

[HiItsRem]

Your transfer case 2.72 gear ratio is the 4wd low-range gear ratio, 4wd High-range and 2wd are 1:1 ratio. No need to do anything with the transfer case when changing front and rear gear ratio's.

Yes the glove box code will tell you what the truck came with from the factory but that could have already been changed by a previous owner. If factory you probably have 3.42 gears. The best way to tell is to jack up the whole rear end and turn the driveshaft by hand. If it spins just under 3.5 turns for 1 revolution of the rear wheels then its 3.42, if it turns around 3 3/4 turns its 3.73, if its just over 4 turns its 4.10, etc.

4.10 is a good street gear, 4.56 is good if your putting 33" or larger tires on.

Ohhh okay thanks a ton for the explanation on that!

 

[HiItsRem]

Hi, no your axle ratios won’t be 2.73. Take a photo of the glovebox sticker which will list GT-4 or GT-5 etc for the gear ratio in the axles. If your actually drag racing then switching to 4.56 gears is typically the best bet unless you are making big power in which case a 4.10 gear can work well. Over 600 HP the 3.73 gear is fine.

The sticker is super wore out and barely legible but if you can find anything in it go right ahead, would love some sort of explanation on what i have tbh

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[1998_K1500_Sub]

The sticker is super wore out and barely legible but if you can find anything in it go right ahead

Do I see a GT4 and a G80 on that sticker?

You've probably got the 8.5" rear on that half-ton. If so,... consider your options for a 9.5" rear end swap.

 

[HiItsRem]

Do I see a GT4 and a G80?

You've probably got the 8.5" rear. If so,... consider your options.

I know it has 10 bolts on it and I've heard nightmare stories on having a 10 bolt so I'm not looking forward to doing a 14 bolt swap from a 1 ton

 

[1998_K1500_Sub]

I know it has 10 bolts on it and I've heard nightmare stories on having a 10 bolt so I'm not looking forward to doing a 14 bolt swap from a 1 ton

If you swap then it doesn't matter what the sticker says

Looks like JB5 brakes too... pretty typical. The crappy JB5 rear brakes would get replaced with a rear end.

 

[Sean Buick 76]

3.73 gears in there are fine for all around use. 4.56 would be my pick if your drag racing as you say..