3.8 auto gearing - JKowners.com : Jeep Wrangler JK Forum
 
LinkBack Thread Tools Display Modes
post #1 of 6 Old 02-04-2019, 12:31 AM Thread Starter
Rock God
 
b1pig's Avatar
 
Join Date: Jan 2008
Location: ray city, ga
Posts: 1,234
Garage
Feedback: 1 reviews
Send a message via MSN to b1pig
3.8 auto gearing

I suppose I'm just "thinking out loud" at the moment... Pondering my choices here.

I have a 07 Unlimited Rubicon. Put 35's on it last February. Still 4.10 gearing.

A coworker has a 08 Sahara, also on 35's. He came by my house so I could check out a "noise". Went for a ride. His rear ring and pinion are LOUD. Going to put a new set of gears in his. He bought his Jeep used from a dealership. Someone at some point put some valuable bits on it, but there are signs that it was half-assed along the way.

Case in point. Did the ole gear check by turning the tires and counting driveshaft revolutions. This Jeep literally has 5.13 front and 4.56 rear gearing. Checked it three times. So, he's just going to go 5.13 in the rear. The front seems fine, so he wants to just match whats already good.

I guess I'm going to get a good chance to see what it's like running 35's on 5.13 with an auto.

My long-term thoughts for myself, though.... I am seriously considering slowly collecting all the bits to do a LS swap. I have heard/read that the LS swaps tend to favor taller axle gears. While I don't think 4.88 would really negatively affect my Jeep later doing a LS, I can't say I have a timeline for actually doing it.

So, my questions revolve around anyone's experience having an LS whether with the 4L60 or 6L80 on lower gears in the 4.88-5.13 range on "only" 35" tires. Any real negative affects? Other than snapping D44 shafts going over a parking block at the mall?


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

'19 Ram 1500, '01 BMW R1100RT, '99 Fat Boy
needed: ̶b̶o̶a̶t̶ ̶a̶n̶d̶ plane
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
b1pig is offline  
Sponsored Links
Advertisement
 
post #2 of 6 Old 02-04-2019, 05:52 AM
Granite Guru
 
cjindna's Avatar
 
Join Date: Sep 2015
Posts: 261
Feedback: 0 reviews

With 35s, a 6L80E trans, and 4.88 gears you'll be north of 2,300 RPM at 70 mph. Nothing wrong with that per say. With the low 1st gear in the 6L80E you'll likely struggle to get any wheel speed in 4 low and find yourself running 2nd/3rd gear, again maybe no big deal.

As a point of reference, I run LS3/6L80E with 4.88's and 40" Nitto. Cruises 70mph at 1,900 rpm.
cjindna is offline  
post #3 of 6 Old 02-07-2019, 01:15 AM Thread Starter
Rock God
 
b1pig's Avatar
 
Join Date: Jan 2008
Location: ray city, ga
Posts: 1,234
Garage
Feedback: 1 reviews
Send a message via MSN to b1pig

i don't think that would be a horrible trade. we had a '04 tahoe... as i recall, it ran around 2200 at 70. i can turn the overdrive off and run mine up the interstate as it sits at 85mph if i wanted to, but i have no desire to do that.

i might just go ahead and regear it and suck it up if/when it comes to a conversion. at my rate, my 3.8 will outlast the rest of the Jeep.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

'19 Ram 1500, '01 BMW R1100RT, '99 Fat Boy
needed: ̶b̶o̶a̶t̶ ̶a̶n̶d̶ plane
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
b1pig is offline  
Sponsored Links
Advertisement
 
post #4 of 6 Old 02-07-2019, 03:15 AM
Rock God
 
Chipewa's Avatar
 
Join Date: Jan 2012
Location: Farmington Hills MI
Posts: 1,180
Feedback: 0 reviews

I have a 2007 LS3 6.2 6L80 with 4.88 gears. I have run BFG 37s (actual diameter closer to 35) and have liked it. Now running 39s. No problem at all with 4.88s. Very quick around town but sacrifices a bit in MPG on highway.

LS3 2007 JKU X - Red Rock, 2012 JKU Rubicon - Deep Cherry Red, 2001 TJ - Black
Chipewa is offline  
post #5 of 6 Old 02-07-2019, 08:47 AM
The Wheelin Man's Friend
 
RiverCityOffroad's Avatar
 
Join Date: Aug 2010
Location: Austin, TX
Posts: 8,649
Garage
Feedback: 60 reviews

If that Jeep doesn't have lockouts on the front axle and both driveshafts are in it I am going to say I seriously doubt it has different gear sets. The transfer case would have exploded almost immediately. You cannot have different gears in these things without major problems.

To answer your other questions, if the LS is a real thing then 4.88s are what I'd live with on 35s until you do it. If its a bit of a long, long, long term goal then put 5.13s or 5.38s in the thing. That 3.8 is gutless until you gear the crap out of it. 4.88s and 35s with a 3.8 Auto still hunts for gears in my experience in a mostly flat, near sea level area of Texas.

Marcus


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
RiverCityOffroad is offline  
post #6 of 6 Old 02-07-2019, 05:40 PM
Newbie
 
Join Date: Oct 2014
Posts: 8
Feedback: 0 reviews

Motech has a bunch of videos on youtube explaining which LS engine/ trans combos for certain gears and tire sizes to find the right one or even give them a call. As for gearing, I put 5.38s in when I did my tons cause I knew it'd be awhile before I could do an engine swap which is way down the line. The 42rle it needs as much gear as it can to hold at 2500rpm where the engine makes sufficient power to avoid downshifting and excessive heat etc. My engine/trans never left me stranded so as much as I talk shit about them I gotta give them credit. IMO that combo just cant handle the weight JK's are subjected to once modified. Even only on the 37s my trans still hunts for the right gear on the slightest hill and certainly won't hold on any large grade. Like you I'll slowly gather engine swap parts overtime as my 3.8 will give me plenty of time to do swap.

2010 Stone White JKUR
05+ Dana 60/ 01 14 bolt
5.38s/ Arbs
3 link/ coilovers
NJ-Rubicon is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JKowners.com : Jeep Wrangler JK Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Gearing on auto 2dr w/ 35s Trav977 JK General Discussion 11 01-07-2018 01:33 PM
12"+, rear auto locker, auto trans ledzep_06 JK General Discussion 9 02-28-2016 03:06 PM
Nav radio "auto-dimmer" doesn't auto dim? xjtrailrider Stock JK Tech Dept. 5 12-04-2009 04:33 AM
Yet ANOTHER gearing question thaduke2003 Modified JK Tech Dept. 22 10-08-2009 06:37 AM
Axle gearing, ratios, 35s, and model differences BADGER JK General Discussion 14 04-19-2009 05:37 AM

Posting Rules  
You may post new threads
You may 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 On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome