Gear Ratio Question

[myZ71]

How do you know which gear ratio your truck has?  I have an old body style '99 and would like to know the gear ratio plus what size engine mine has (ie 4.8/5.3).

[Shaners]

You should have RPO codes in your glove box.  Here are the ones for the rear gears...

 

GT4 3.73:1 Rear Axle Ratio

GT5 4.10:1 Rear Axle Ratio

GU4 3.08:1 Rear Axle Ratio

GU6 3.42:1 Rear Axle Ratio

 

 

There should be a sticker on your fan shroud under the hood or somewhere close that has the motor displacement on it.  Or you could go by the RPO codes in the glove box...

 

L35 4.3L V6 Gasoline Engine SCPI

LM7 5.3L V8 Gasoline Engine SFI GEN III

LQ4 6.0L V8 Gasoline Engine SFI GEN III

LR4 4.8L V8 Gasoline Engine SFI GEN III

[dmdbit]

If your truck is the old body style like the 88-98 then you most likely have either the 350 or 305.

 

                          mike b

[myZ71]

Does anyone else out there have an old body style that is a 1999 model?  Does anyone know if this is common?  It says it is a 1999 model on my registration and I'm pretty sure that it is, just want to know if anyone could shed some light on the issue.

[myZ71]

Does anyone else out there have an old body style that is a 1999 model?  Does anyone know if this is common?  It says it is a 1999 model on my registration and I'm pretty sure that it is, just want to know if anyone could shed some light on the issue.

 

Went and looked, I've got the 3.42 gears (GU6) and the Vortec 5.7L 350 V-8.  How much improvement would I have to change to a 3.73 gear and how much would it cost?

Thanks for the help on the truck!!

:thumb:

[silverado man]

Does anyone else out there have an old body style that is a 1999 model?  Does anyone know if this is common?  It says it is a 1999 model on my registration and I'm pretty sure that it is, just want to know if anyone could shed some light on the issue.

Yes there the early 99's were the old style.  They didn't introduce the new style until later.   So yours would be an old style 99 then.

[Shaners]

3.73 gears would make the truck much more drivable especially when towing.  It would also cause the motor to rev a little higher and therefore less downshifting on the hills.

 

If your truck is 2wd and you are somewhat mechanically inclined you could do the swap yourself and it would be fairly easy.

 

Several guys in here have changed gear ratios to give more power when towing or to make up the difference of larger tires...