LS + 4L60E + 32's: 3.73 or 4.10 and carrier selection help - JeepForum.com
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post #1 of 16 Old 10-08-2019, 07:42 PM Thread Starter
jm302
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LS + 4L60E + 32's: 3.73 or 4.10 and carrier selection help

Hi All,

In the process of a frame-up resto-mod 1986 CJ7. I've got a TDK frame on order, so I've been taking this time to rebuild the drivetrain I will reuse. I just got done rebuilding the d300 and now the diffs are up. I'm going to completely re-gear them, change carriers and all bearings. The rear is getting disc and all of the front end components are being refreshed.

I've really been struggling with the whole gear thing. 3.73's or 4.10's? This CJ will see a lot more pavement than off-road (sorry) so I'm thinking 32" tires and 3.73's will not be an issue considering the power of the LS.

This also leads me to the carriers. Considering this CJ will mostly see pavement, an ARB air locker seems wayyy overkill. I was considering a posi unit for the rear and front, but that seems to not be a proper thing to do. Should I just bite the bullet and drop the $$ on the air lockers? I'm really stuck and would appreciate any thoughts. The key here is I only want to do this once!


Thanks!

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post #2 of 16 Old 10-08-2019, 08:01 PM
CSP
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Why would you even consider air lockers? Would you ever engage them? Are you aware that when locked they are essentially a spool?

Go here and determine what your RPMs are at any given speed with the two gear ratios. www.grimmjeeper.com/gears.html
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post #3 of 16 Old 10-08-2019, 08:12 PM Thread Starter
jm302
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I don't have a good reason to consider air lockers - which is why I asking opinions. Yes, I'm aware of what air lockers do and when you should use them. The likelihood is they will never get locked. I really didn't want to run open diffs in both front and rear. For example, in my F150, I've used the electronic locker several times instead of locking it in 4wd. Simply my thought process was - it would be there if I need it. Either way, I have to replace the carriers to support either of my gear selections.

I've looked at the RPM charts before. That's where I came up with 3.73 or 4.10 as an optimal gear ratio.

Maybe the difference is between 3.73 and 4.10 is not worth a conversation... I'm really not sure. The best way is to solicit feedback so I make an informed decision. Like I said - the end goal is not to do this twice. That's when stuff gets expensive.

I appreciate your response.
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post #4 of 16 Old 10-08-2019, 08:30 PM
REDnBLUES
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Keep this in mind. A new Wrangler Rubicon runs 4.10 standard with the 3.73 optional on the 6 speed or the opposite on the automatic. I have (or rather my wife does) a 2015 Hard Rock JKUR with an auto and 4.10's. I replaced the 32" tires to a taller tire that measures 33.25" and either way, it's fine on the highway or off road...and it's a V6. Our last wrangler had 3.73's and I would never do that again.

Your 4L60E will make it all good; go with your lowest gear and don't look back.

My cj7 goal build would be Eaton e-locker and either 4.10 or 4.56 gears.

Good luck with the opinions!

1977 CJ7 - LT1/700R4 Project
2015 JKU Rubicon Hard Rock - stock
2013 JK Sahara - gone
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post #5 of 16 Old 10-08-2019, 08:56 PM Thread Starter
jm302
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Quote:
Originally Posted by REDnBLUES View Post
Keep this in mind. A new Wrangler Rubicon runs 4.10 standard with the 3.73 optional on the 6 speed or the opposite on the automatic. I have (or rather my wife does) a 2015 Hard Rock JKUR with an auto and 4.10's. I replaced the 32" tires to a taller tire that measures 33.25" and either way, it's fine on the highway or off road...and it's a V6. Our last wrangler had 3.73's and I would never do that again.

Your 4L60E will make it all good; go with your lowest gear and don't look back.

My cj7 goal build would be Eaton e-locker and either 4.10 or 4.56 gears.

Good luck with the opinions!
Thanks! That was great info. When you said you had 3.73's and would never do that again - why was that? Did you see a considerable difference between the 3.73 and the 4.10's?

Based on the calculator (which is far superior to others I've used) linked by CSP, it seems at 70MPH, in 4th gear and 4.10's, I'd be at 2109 RPM.. That's a lot lower than I figured. I'm definitely leaning 4.10's now.

Those e-lockers are $$$ - sheesh. What I'm doing is by no means a budget-friendly build, but... ouch.

I'm super curious to hear from some folks that run a LSD in the rear.

Thanks!
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post #6 of 16 Old 10-08-2019, 10:54 PM
CSP
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Personally I would go with either a full case locker like a Detroit or Yukon Grizzly. If you don't like the characteristics of a real auto locker like those, the Detroit TruTrac is a GREAT limited slip. It has the lowest slip differential before it locks of just about all of the limited slips and is strong. It's also not a clutch type limited slip which will wear out and end up being more slip than limited.

My choice would be 4.10s with that transmission.
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post #7 of 16 Old 10-09-2019, 12:24 AM
REDnBLUES
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3.73 is too high in my opinion with your setup. Remember, you have automatic overdrive, which in this case is more forgiving. If you ever decide to go to a 33", you'll still be ok.

You asked why I would never do 3.73 again...I personally would not do it again in a JKU because the 4.10 just gives it more grunt off the line plus, excessive high speed is not usually a goal in a Jeep.

1977 CJ7 - LT1/700R4 Project
2015 JKU Rubicon Hard Rock - stock
2013 JK Sahara - gone
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post #8 of 16 Old 10-09-2019, 10:18 AM
BrutusBlue
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LS, 4L60e, 32’s, 4.10’s, Trutracs front and rear...done! Tire weight makes a difference too...on 32’s your not dealing with much of a difference between tire makers. Based on your use, pick a tire that’s lighter weight.

3.73’s are fine for 32’s with no overdrive on an LS motor. With overdrive, 4.10’s or lower. The LS motor will run at a higher RPM than anything else at highway speed but your gonna generate more heat that can find its way inside the cab.

Im building a CJ with LS, 4L on 33’s with 4.10’s if that helps you.

I daily drive a CJ with LS, no overdrive, on 33’s with 3.70 in the rear and limit my highway spurts. 4.10’s were too low for no overdrive.
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post #9 of 16 Old 10-09-2019, 10:28 AM
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Off topic...which LS motor?
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post #10 of 16 Old 10-09-2019, 10:38 AM
Cutlass327
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Brutus has the best setup listed - TruTracs, no lockers.



You never really said what the usage is going to be - weekend cruiser, daily driver, daily driver/weekend warrior... Unless it is the last one there, you don't need lockers. You said your truck has them, use it if you are doing something that will need lockers. Otherwise, even just open front and Trutrac rear will be sufficient.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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post #11 of 16 Old 10-09-2019, 01:36 PM Thread Starter
jm302
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Quote:
Originally Posted by BrutusBlue View Post
Off topic...which LS motor?
Gen IV LC9 5.3 - AFM and VVT Delete + new cam. Should be around 400hp/tq at crank.. A lot more than I need.
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post #12 of 16 Old 10-09-2019, 01:48 PM Thread Starter
jm302
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Quote:
Originally Posted by Cutlass327 View Post
Brutus has the best setup listed - TruTracs, no lockers.



You never really said what the usage is going to be - weekend cruiser, daily driver, daily driver/weekend warrior... Unless it is the last one there, you don't need lockers. You said your truck has them, use it if you are doing something that will need lockers. Otherwise, even just open front and Trutrac rear will be sufficient.
It'll be a weekend cruiser. My wife is an amateur photographer, so I intend to cruise around Western North Carolina (Smoky Mountains, BlueRidge Parkway, etc) and let her do her thing. It's about 105 miles to get out there. This is why I need something pavement friendly, yet still capable of hitting a trail if necessary.

Funny story (well I suppose it's funny now) - I got my F150 hella stuck today. Needed a wrecker to get me out. I was up in Little Switzerland and slid myself into a heap of mud in a parking area for a waterfall. I'll admit, it made me want front and rear lockers for the CJ. Had the F150 had a front locker, my one front tire with traction would have likely pulled me out.

I appreciate all the feedback - you all are a great help!
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post #13 of 16 Old 10-09-2019, 01:57 PM
Cutlass327
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"Little Switzerland?" There's a town near here, Sugarcreek, that goes by "Little Switzerland". It has the largest cuckoo clock in the US.

78 CJ5 302HO, T177/D300, 86 WT 30/44, Aussie F/R

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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post #14 of 16 Old 10-09-2019, 07:02 PM
BrutusBlue
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Quote:
Originally Posted by jm302 View Post
Gen IV LC9 5.3 - AFM and VVT Delete + new cam. Should be around 400hp/tq at crank.. A lot more than I need.
Good motor. Light weight, with good power. Im not a big fan of the drive by wire gas pedal in a CJ but you can make it work. If yours is the 2010-2011 LC9 5.3L then you can run a healthy cam...should have valve relief cut pistons. If yours is the earlier 2007-2009 LC9 without the relief cuts then you can run a nice single pattern cam with good results. Either versions, for sure dump the vvt/afm. The LC9 is the newer version of the L33 which was a Gen III 5.3L screamer.
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post #15 of 16 Old 10-09-2019, 07:41 PM Thread Starter
jm302
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Quote:
Originally Posted by BrutusBlue View Post
Good motor. Light weight, with good power. Im not a big fan of the drive by wire gas pedal in a CJ but you can make it work. If yours is the 2010-2011 LC9 5.3L then you can run a healthy cam...should have valve relief cut pistons. If yours is the earlier 2007-2009 LC9 without the relief cuts then you can run a nice single pattern cam with good results. Either versions, for sure dump the vvt/afm. The LC9 is the newer version of the L33 which was a Gen III 5.3L screamer.
It's a 2013 LC9 - I'm going to run the Holley Terminator X Max. At the end of the day, the X Max is not much more $$ and much simpler than dealing with that nasty wiring harness, learning HP tuners, buying the credits, getting a TAC module, etc. Plus it makes the earlier 4L60e possible. If the length was there I'd have the 6l80e.

Getting a DBW pedal to fit will take some fab, but I'm confident I can make it work.

I'm about to drop an order on 2 Trutracs and 4:10's, bearing kits and some extra shims.
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