Author Topic: rear axle gearing  (Read 4523 times)

Offline gold84gmc

  • Frequent Member
  • **
  • Posts: 483
rear axle gearing
« on: July 28, 2007, 08:44:04 PM »
hi, i have an 84 gmc 2500 2wd with a th400, 350, and 14 bolt rear end. i was wondering if anyone knew what gear ratio it is/could be? and i would like to improve the acceleration while not sacrificing top speed or too much gas mileage, so what gear ratio would you guys suggest? thanks...i also have a 76 caprice with 3:08 rear end and im wondering if putting 3:73's would improve the acceleration/top speed? thanks.
92 buick century custom 3.3L

Offline Lt.Del

  • Andy aka:SgtDel
  • Senior Member
  • ****
  • Posts: 3864
  • DelbridgePhotography.com
    • www.delbridge.net
Re: rear axle gearing
« Reply #1 on: July 28, 2007, 09:17:09 PM »
Quote
like to improve the acceleration while not sacrificing top speed or too much

Ah, you want the best of both worlds.  If you ever figure out your desire, you will be rich.

The lower gears (higher numerically) will improve acceleration.  The higher gears (lower numerically) will improve top speed.

As for anyone reading this thread who knows your rear gear, good luck.  You can always remove the pan and count the gears.  The old fashioned was is jacking up the rear and put a chalk mark on the drive shaft and on a tire and see how many turns the wheel goes for each full turn of the drive shaft.  It should turn between 3 to 4 times for each drive shaft rotation.,..it is just how much past 3---1/4, 1/3, 1/2...etc...

Do you have the build sheet?  Also, on some rear axles...passenger side tube facing front, there should be a marking as to what the ratio is.  I have never found mine, but they are supposed to be there.

Quote
i also have a 76 caprice with 3:08 rear end and im wondering if putting 3:73's would improve the acceleration/top speed? thanks.

The 3.08 (higher gear) will be better for top speed.  The 3.73 (lower gear) is better for acceleration.   Putting the 3.73 in the caprice will not improve top speed...just use more gas at higher speeds-more rpms.  It will improve acceleration from a stop. It is a lower gear.

 



Offline cochese

  • Newbie
  • Posts: 15
Re: rear axle gearing
« Reply #2 on: July 29, 2007, 11:51:43 AM »
you may have already looked, but i found the gear ratio for my truck listed in the rpo list inside the glove compartment. 
1986 c-10
305 5.0 V-8

Offline DirtyLittleSecret

  • Registered Users
  • *
  • Posts: 106
Re: rear axle gearing
« Reply #3 on: July 30, 2007, 09:52:09 PM »
You should also have a ratio tag on your diff cover...
78 K20: fresh 350, SM465, NP205, 4" Pro Comp, & working hard!
65 Jeep J300: 13.5:1 383, TH400, NP205, mostly NOS. 
88 Toylet LandCruiser FJ62: LT1, 4L60e, 3" OME, Aussies.
06 VW TDi: DD@72mpg.