Go Back   Jeep Garage - Jeep Forum > Jeep Platform Discussion > Grand Cherokee - WK2 -

Join Jeep Garage Today
Reply
 
Thread Tools Display Modes
 
  #1  
Old 07-20-2012, 06:19 AM
Member
My Jeep: 2014 5.7L WK2
 
Join Date: Jul 2012
Location: NYC
Posts: 405
Thanks: 0
Thanked 9 Times in 7 Posts
Rep Power: 1544852
trelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond repute
rear axle gears

Has anyone tried changing the rear axle gear ratio on a 12 GC Hemi Overland? Looking to go from 3.45 to 3.70. Some have told me I have to change both front and back others said only rear is fine. Does anyone know how much something llike this would cost? Any feedback greatly appreciated!!!!
__________________

__________________
Reply With Quote
  #2  
Old 07-20-2012, 06:38 AM
Member
My Jeep: 2012 3.6L WK2
 
Join Date: Feb 2012
Posts: 305
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 1364
tnjeep has disabled reputation
Re: rear axle gears

You have to have the front and rear ratios matching if you have a 4wd. If you got the 2wd version then just the rear has gears, the front does not. If I was spending the dough to change gears I would think about going closer to the 3.90 area if the stock is 3.45 maybe even closer to 4.10 if you want some real grunt off the line. But of course going to lower gear ratios will hurt mpg's as well as top speed will be lower.
__________________

__________________
Reply With Quote
  #3  
Old 07-20-2012, 09:06 AM
Member
My Jeep: 2014 5.7L WK2
 
Join Date: Jul 2012
Location: NYC
Posts: 405
Thanks: 0
Thanked 9 Times in 7 Posts
Rep Power: 1544852
trelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond repute
Re: rear axle gears

Got it!!! Thanks for the feedack. I understand that higher gears will lower top speed but do you have any idea how much? the consensus on the forums is that 3.70 is the best of both worlds........off the line and top end. I am most likely going to be installing a whipple twin screw in the next couple of months so I dont have to worry about losing on the top end side????
__________________
Reply With Quote
  #4  
Old 07-20-2012, 09:36 AM
Yadkin's Avatar
Senior Member
My Jeep: 2012 3.6L WK2
 
Join Date: Mar 2012
Location: Yadkin Valley, NC
Posts: 1,254
Thanks: 0
Thanked 19 Times in 19 Posts
Rep Power: 202408
Yadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond repute
Re: rear axle gears

As a rule of thumb, your top speed will be reduced by the same ratio of your gear change, for example 120mph x 3.45 / 3.70. Of course that assumes that your speed is governed by engine rpms.
__________________
Reply With Quote
  #5  
Old 07-21-2012, 10:23 AM
Member
 
Join Date: Jan 2012
Posts: 142
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 163571
bit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond repute
Re: rear axle gears

Quote:
Originally Posted by trelos78 View Post
Got it!!! Thanks for the feedack. I understand that higher gears will lower top speed but do you have any idea how much? the consensus on the forums is that 3.70 is the best of both worlds........off the line and top end. I am most likely going to be installing a whipple twin screw in the next couple of months so I dont have to worry about losing on the top end side????
I would not be concerned at all with loosing top end. The added gearing will probably help you to go faster as it will give you more torque to fight the wind resistance. And besides who cares if you top end drops from 160 to 145ish. How often are you really going to be going that fast?
Don't fear the gear, as someone already mentioned go 3.90 or 4.10's. Your mileage shouldn't be effected that much and it may even get better around town. And with the 6 speed transmission your rpms will still be very low on the highway.

Please update us if you get this done as I'm very curious about doing this someday myself.
__________________
2012 Laredo X 4X4, 5.7 Hemi, luxury package.
Mods: 2.5" RR lift,RR SuperSliders, ProComp 7036 wheels, 275/65-18 Wrangler Duratracs
My WK2 offroad:http://www.youtube.com/watch?v=AueMX...2&feature=plcp
Reply With Quote
  #6  
Old 07-22-2012, 06:24 AM
Member
My Jeep: 2012 3.6L WK2
 
Join Date: Feb 2012
Posts: 305
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 1364
tnjeep has disabled reputation
Re: rear axle gears

I am a big fan of 4.10 gear ratios. Have that ratio in my chevy truck with the smaller V8 (4.8) and it would pull of the line harder than my old work truck (chevy with a 5.3 and 3.73 gears). They also both got the same mpg's.
__________________
Reply With Quote
  #7  
Old 07-22-2012, 07:45 AM
Member
My Jeep: 2014 5.7L WK2
 
Join Date: Jul 2012
Location: NYC
Posts: 405
Thanks: 0
Thanked 9 Times in 7 Posts
Rep Power: 1544852
trelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond reputetrelos78 has a reputation beyond repute
Re: rear axle gears

Thanks for the feedback guys!!!! Shopping around for prices as we speak. It ain't gonna be cheap, I can tell you that much. I'll keep you updated.
__________________
Reply With Quote
  #8  
Old 07-22-2012, 12:54 PM
Yadkin's Avatar
Senior Member
My Jeep: 2012 3.6L WK2
 
Join Date: Mar 2012
Location: Yadkin Valley, NC
Posts: 1,254
Thanks: 0
Thanked 19 Times in 19 Posts
Rep Power: 202408
Yadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond repute
Re: rear axle gears

The only car I ever drove with 4.10's was my grandfather's '72 Olds. That car would destroy anything off the line, but it topped out at 85.
__________________
Reply With Quote
  #9  
Old 07-23-2012, 12:02 PM
Senior Member
My Jeep: 2011 3.6L WK2
 
Join Date: Dec 2011
Location: Olathe, KS
Posts: 1,016
Thanks: 0
Thanked 17 Times in 17 Posts
Rep Power: 3784
kkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond reputekkreit01 has a reputation beyond repute
Re: rear axle gears

I've had a Explorer Sport SOHC with 4:10s, and a Dakota Sport 318 with 3:92s. Both were much more thrilling off the line vs. my WK2 with super-high highway gears. At least the V6s should get lower gears vs. the Hemi (to help make up for hp/torque difference). The Pentastar would be so much better with a decent set of low gears underneath.
__________________
Reply With Quote
  #10  
Old 07-23-2012, 12:30 PM
Yadkin's Avatar
Senior Member
My Jeep: 2012 3.6L WK2
 
Join Date: Mar 2012
Location: Yadkin Valley, NC
Posts: 1,254
Thanks: 0
Thanked 19 Times in 19 Posts
Rep Power: 202408
Yadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond reputeYadkin has a reputation beyond repute
Re: rear axle gears

People buy the Pentastar over the Hemi to save gas, hence the tall gears. If you want to drag race get the Hemi.
__________________
Reply With Quote
  #11  
Old 07-23-2012, 02:44 PM
Member
 
Join Date: Jan 2012
Posts: 142
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 163571
bit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond reputebit50 has a reputation beyond repute
Re: rear axle gears

Quote:
Originally Posted by trelos78 View Post
Thanks for the feedback guys!!!! Shopping around for prices as we speak. It ain't gonna be cheap, I can tell you that much. I'll keep you updated.
Ya, it cost me $1500 to get the 4.88's put in my F150.
__________________
2012 Laredo X 4X4, 5.7 Hemi, luxury package.
Mods: 2.5" RR lift,RR SuperSliders, ProComp 7036 wheels, 275/65-18 Wrangler Duratracs
My WK2 offroad:http://www.youtube.com/watch?v=AueMX...2&feature=plcp
Reply With Quote
  #12  
Old 07-23-2012, 04:25 PM
ColdCase's Avatar
Senior Member
 
Join Date: Apr 2011
Posts: 1,446
Thanks: 0
Thanked 28 Times in 27 Posts
Rep Power: 26566
ColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond reputeColdCase has a reputation beyond repute
Re: rear axle gears

Quote:
Originally Posted by kkreit01 View Post
.. Dakota Sport 318 with 3:92s. Both were much more thrilling off the line
My 3.92 dakota sport sounded like it was going to explode on the highway at 70 mph.. not a very comfortable ride.

The stock rear end ratio for the V8 is 3.47, V6 3.06. I recall 2.73s and 3.13s being common street ratios years ago.

Overall top gear for the V8 is 2.32, 2.54 for the V6. The V6 has a 3.59 ratio first gear where the V8 has a 3.0 .

The STR8 uses the V6 transmission with 3.70 axle ratios.

Wonder if you could plug in the 3.70 STR8 Difs into the the base V8 housings? V6 housings? Quite a bit of difference between 3.47 and 3.70 gears (near 7%), it may be worthwhile.

Another trick is to use the smallest diameter tire you can get away with.

On the other hand, wonder if it would make more economical sense to just sell the base WK2 and buy a STR8 (if you can get one) rather than screw around with updating base? Bigger engine, more power, better gear ratios for stoplight racing... warranty in place.
__________________

__________________
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cherokee KJ rear axle ? roddaz Liberty-KJ and KK 0 03-26-2012 02:51 PM
jcmyers-4.88 gears and rear locker question jcmyers Wrangler-YJ, TJ & JK 2 03-19-2012 02:37 PM
Rear Axle Differential Mattaleca Suspension/Driveline/Brakes/Wheels/Tires 11 08-06-2011 09:29 AM
Rear Axle kevinswj Troubleshooting/Problems 0 10-10-2010 01:22 AM
Leaking rear axle chicago_jeepster_ Troubleshooting/Problems Discussion 10 05-05-2010 04:36 PM

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 07:49 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community

JeepGarage.org is in no way associated with or endorsed by Chrysler Group LLC.