Drivetrain Upgrades: Gears and front locker

As I’ve mentioned before, it’s good to have a solid build plan for your 4×4 regardless of if you’re building it for overlanding, rock crawling, trail riding, or even if you’re building it up for daily-driving street use.  When making the plan it’s a good idea to work backwards so that you don’t have to redo stuff or compromise on poor quality parts.  The main parts of Phase 2 of the build plan for the ECOA Wrangler hinged on the fact I wanted to run 33″ tires.  That one factor dictated things like the lift I would need to clear the tires, limited investments I’d need to make into things like axle shafts if I was going bigger, and kept the overlanding and street drivability I was going for.

Honestly, I didn’t order from them based on the name similarities.
East Coast Gear Supply has a solid reputation and being on the east coast i knew I’d have my order quicker than ordering from a mid-west or west coast supplier.
The team at ECGS was also very helpful in putting together a package that would work for the LJ and what I had in mind.

One of the more important things that I knew I’d have to do when going to 33’s was gearing.  It was always part of the plan when I went to 33’s, I just never realized how much I’d need them till I tried to tow the ECOA camping trailer.  Around town and on back roads it was fine, but the less-than-steller OEM transmission in the ECOA ’04 Wrangler Unlimited left a lot to be desired.  Here’s a brief install writeup on the gear package I went with and a little insight into why I chose the parts that I did.

If you haven’t read the previous piece on Differential Basics, now would be a good time to check that out.  That will give you some insight into the different types of differentials and their basic operation. With that in mind, the stock axle gear ratio in the 2004-2006 Jeep Wrangler Unlimiteds is 3.73:1. Stock differentials in the LJ is an open front with a limited slip in the rear.  Base LJ’s came equipped with 30×9.50r15 tires.  In comparison, the Rubicon package drops that down to a 4.10:1 ration.  Rubicons come with air lockers front and rear with the front functioning in an open position and the rear functioned as a limited slip when off.  Lastly Rubicons came with 31″ tall tires.

You’ve probably seen a chart like this in a parts catalog or online.
Charts like this are calculated with a 1:1 transmission gear (so no overdrive engaged).
Don’t worry too much about the numbers in the boxes.  Just focus on the colors.
Down the left = Tire Sizes
Across the top = Axle Gear Ratio
Yellow = Better gas milage
Green = Near OEM tire/gear ratio
Red = More power

Axle gear ratio  affects things like fuel milage, towing, acceleration, crawling (aka ‘crawl ratio’ when in low range), and to a certain degree driveline stresses.  Using the chart above you can see how but the 30″+3.73 and 31″+4.11 combinations for the LJ and LJ-R are in the green.  Some other model Jeeps came with a 29″+3.55 ratio which is also in the green.  So we’ll use this green area as our base point.

When I bumped my Jeep up to 31″ tires with the stock 3.73 gears I noticed three things:

    • Drop in engine RPMS at highway speed. Around 1800 RPMs in overdrive at 65 mph.
    • Loss in accelleration 
    • Loss in overall power – especially while towing
The last one was the most important thing to me.  When I tried to tow my camping trailer project on the highways I couldn’t maintain the speed limit at 65 MPH.  The Jeep just wouldn’t hold overdrive and it was struggling to keep up with traffic.  Some of this is due to the aerodynamics, or rather lack-there-of, of the trailer and it acting like a giant parachute behind the Jeep.  That said, even with the increase in drag the Jeep should be doing better than it was.  I was hoping to wait to do gears but I didn’t have a choice.  So let’s look at my options.
According to the chart above, there are more than a few possible combinations for me.  Too many actually.  So let’s simplify it down a little and cut out all the tires smaller than I run (so I’ll black out everything less than 30″) and also all the sizes bigger than I’d ever consider running (so I’ll black out everything more than 33″) and focus on my jump from 31″ to 33″.
Looks like I have some options, right?
Not that simple.  Some of those gear ratios are not commonly available on the market.
Something to consider if something were to break: “Can you easily find replacement parts?”

3.91 and 4.27 are not commonly available.
Also, anything 5.13 or deeper won’t work with Jeep’s OEM Dana 30 axle.
Now, conventional wisdom in the Jeep 4×4 world says my top two options for 33″ tires would be 4.11 or 4.56 gears.  4.11 gears would give me the closest-to-stock tire/gear ratio.  4.56 gears would give me a little more power to compensate for the larger tires.  That said, the transmission in the LJ is gutless.  It’s actually a Chrysler car transmission and should never have ended up in a Jeep behind a torquey motor like the 4.0 inline six.  After talking to a lot of people more knowledgable than me, as well as a few that have already done axle gear swaps, it was recommend that I consider 4.88 gears.  Given the slower speed nature of overlanding, coupled with increase weight in the Jeep and the addition of towing a trailer, the 4.88 gears would give me more utility over the conventional recommendation of 4.56 gears.  After doing a little math, my estimated engine RPMs, using the chart as source along with the OEM overdrive gear ratio of 0.69, should be around 2,200 RPMs at a highway speed of 65 MPH.  That’s a little over stock, much better than the 1,800 RPMs I was cruising at with the 31’s, so it sounded good to me.
With that in mind it was time to order gears.  Now, if you think you can just pick some parts form an online catalogue and place an order without talking to anyway please don’t.  That’s what I tried to do and I almost ended up wasting a lot of money.  Luckily one of the reps at East Coast Gear Supply saw my order come through the system and opted to give me a call.  After a long conversation about my goals for the LJ he ended up putting together a totally different package than I originally ordered.  So do yourself a favor when the time comes, just pick up the phone and call them!
So, what did I end up with?
Left = 4.88 ring and pinion sets
(Rear is “thick cut” to use my OEM limited slip – money saved)
Top Right = Solid Differential covers. Need to protect the investments
Lower Right  = Torque Masters “Aussie Locker” for the front axle
Not pictured = Master install kits for front and rear gear sets
When I mentioned my limited slip was slipping the rep recommended a new clutch pack.
This was big money saved since I had originally looked into a replacement limited slip at nearly $500.
Sadly I didn’t end up needing this… more on that later.

One of the most overlooked maintenance items on any 4×4 is differential oil
Lube Lockers negate the need for messy RTV sealant.
This speeds up the process and makes it more likely you’ll flush and change your gear oil.
And they sent me a shirt and some stickers!
Now, some of you are thinking, “Dean, you’re throwing money around again.  You keep saying budget-budget but here you are dropping another grand on parts.”  You can look at it two ways.  First, “You have to pay to play.”  I’ve said time and time again “budget” doesn’t mean “cheap.”  It means being smart with your money.  Second, “Money saved is money earned.”  The moment you consider opening your axles and doing gears it quickly becomes a slippery slope of other things to do under the justification, “while I’m at it I might as well do X, Y, & Z.”  It’s also very easy so say, “Well, I’m already spending $500 on a new limited slip, what’s a few hundred more for a locker.”  So let’s look at a few options I was considering:
  • Air lockers front and rear – good enough for a rubicon, good enough for me, right?
    • Pros – Much better for rock crawling and technical terrain
    • Cons – Expensive; Added driveline stresses mean upgraded driveshafts; more money
  • Aftermarket Limited slip rear, air locker front – Better than stock, and a little cheaper.
    • Pros – Cheaper than air lockers front and rear; selectable locker front adds utility over OEM open differential
    • Cons – Still fairly expensive; still requires upgraded front shafts
  • Aftermarket Limited Slip rear, mechanical locker in the front – What I REALLY wanted
    • Pros – Upgrade over stock; adds mechanical locker up front; don’t really need upgraded shafts if I’m careful
    • Cons – None really which is why it was my original plan.
  • Rebuilt OEM Limited Slip rear, mechanical locker up front – What I went with
    • Pros – Cheapest of my options that is still considered an upgrade; reuses rear limited slip which was money I didn’t need to spend and could be put toward the front locker
    • Cons – Still a lot of money at the end of the day, but considerably less than something like air lockers front and rear
  • Aftermarket Limited Slip, leave front open
    • This is what I originally ordered along with a gear and install kit.
    • Turns out I was way off and could save money on rear limited slip and put it toward front locker and the differential covers along with a new clutch pack.
Okay, back on track.  Installation.  I’ll be honest, I have a friend who is a professional mechanic and as a solid “you owe me” favor he offered to do my gears.  This was huge money saved on my part and also a way for him to support my No Highways Tour trip this year without him throwing me cash.  My catch was doing all disassembly and reassembly of everything but the gears (wheels, brakes, axle shafts, etc) which would allow him to focus on just the gears.  I highly recommend having your gears professionally installed.  Although you can do them yourself there are so many little things that can go wrong that it’s worth letting someone experienced do them.  Some shops will cut you a break on install rates if you bring them empty axle housings.  This is money saved for you but the tradeoff is more work.
Jeep on the lift ready for disassembly
A good habit for any overlander is to do as much work on your vehicle with the toolset you usually carry.
This not only familiarizes you with your tools but also let’s you know of any gaps you need to fill or any extra tools you never use and could get rid of.
My kit is a little excessive since I’m usually “that guy” with all the tools to work on anything and everything.
For more information on my toolset check out the writeup I did last year.
Rear torn down and ready for the gear swap.
Notice the black RTV “gunk” leftover.  I scrapped that all off in favor of the Lube Locker reusable gaskets.
Shot of the new ring gear (right) and pinion gear (left).
The pinion gear is turned by the driveshaft.
The ring gear turns the differential which rotates the wheels.
The ring and pinion combination transfers rotational energy from the engine to the wheels.
This is why it’s so vital to make sure they are setup correctly.
Empty Dana 44 rear axle housing.
And yes, I’m still working on cleaning all that RTV off at this point.
Toledo, we have a problem.
Just as we were starting reassembly of the rear differential my buddy noticed some missing teeth an abnormal wear in the spider gears of the OEM limited slip.  At first I really regretted not ordering ordering that replacement.  There was no way of knowing this was the issue causing my rear end to slip.  Also no idea how long it’s been like this.  Luckily my buddy had a spare D44 limited slip carrier at his house.  Remember, he’s a professional mechanic.  He has all kinds of goodies in his garage.  I do as well, I just didn’t have one of these.  Why is it you always have extra parts you don’t need and the extra parts you don’t need aren’t in your garage when you need them?  Someone get Murphy on the phone.
After a long trip to his house and back (and a stop for pizza and some other parts) we were back on track.
The dial indicator here is checking for backlash in the gears.  This is where being a pro really matters.
And yes… still working on removing that RTV.  I hate that stuff so much.
A shot of the front Dana 30 with new 4.88 gears and the Aussie Locker.
This one was a little cleaner since I had started on it the night before during disassembly
At this point I’ll confess there aren’t any more photos.  Reassembly was pretty straight forward.  The only unexpected thing was a fouled axle u-joint which was a P.I.T.A. to swap out.  I already had spares so  there was no need for yet another parts run.  Also, gear work is messy and I was already wasting enough time washing and rewashing my hands for the above pics.
First, when you’re ready to upgrade your gears and/or differentials don’t just rely on the internet for research.  Call and talk to the pros at a place like East Coast Gear Supply.  It’s what they do.  Also talk to mechanics because that’s also what they do.  Yes, it’s good to talk to fellow enthusiasts.  Case in point: My friend at Off Road Consulting and Training has a nice Rubicon LJ.  He’s also one of the most knowledgable Jeep people I know.  He and I spent a lot of time talking about gear ratios and stuff.  He recently went from stock Rubicon 4.11’s to 5.13’s for his 35’s.  Usually he’d be okay with 4.88’s but, like me, his LJ has the crappy 42LRE automatic transmission and he opted to go one ratio deeper.  Having that validity and his input was also very nice.  His input, along with the input from ECGS, and an online group of LJ enthusiasts is how I settled on 4.88 gears.
Second, investigate.  If something is wrong with your driveline figure out what it is.  All it would have taken for me to realize my rear limited slip was toast would have been a few minutes to pop the cover and look.  This would have confirmed it was something beyond just bad clutch packs.  If you’re not comfortable doing it yourself, consult with professionals.  This is one area where doing it yourself isn’t the best option.
Third, take your time and do it right.  In addition to the four hours I spend Friday doing the disassembly, my buddy and I spent twelve hours working on my Jeep Saturday.  Sure we wasted some time bullshitting, running back and forth to his place, eating pizza, and what-not.  Just know that this is a labour intensive job and can be compounded by things like busted differentials and secondary things like busted u-joints that come up with this kind of upgrade.
85 is the new 65… for now at least.
Until I get my new 33″ tires and the appropriate speedometer gear, my speedo is way off.
Forth, backup plans and a backup for your backup plan.  Right now I’m having to deal with 4.88’s and 31″ tires.  Both my primary hookup on 33″ tires and my backup plan fell through.  This was rather unexpected but “shit happens” as they say.  The Jeep is fine at low and medium speeds.  Honestly, it drives like a rocket now from zero to 55mph.  At highway speed though the lower gears have increase my cruising engine RPMs up to nearly 2500.  That’s a bit much for my liking.  That will correct itself when I get my 33’s, but for now I just have to deal with it.  I’ve just been in a tight spot trying to get everything line dup for the big trip this year and the deadline of being in Utah for Easter Jeep Safari.  In an ideal world I would have already had some 33’s rip-roaring and ready to go. 
I know it’s a lot, and given all the updates I’ve posted in the last month it looks like I’ve thrown a lot of money at my rig despite the “budget nature” of the build.   Such is the nature with pre-trip builds.  The nice thing for you is not all of these upgrades need to be made at the same time.  They can spread out over months or even years if you need to.  However, some upgrades go hand-in-hand like gears and tires if you want to do it right.  So that’s something to consider when you make your plan and start budgeting your money. If I wanted to stay on 31’s I could easily have opted for 4.56 gears and been fine.   Sadly I didn’t find out about the deal on 33’s falling through until AFTER I ordered my parts (I blame Murphy for that one too).
Anyway, most of the Phase 2 upgrades are done.  I doubt I’ll be pulling the trigger on any major upgrades this year.  Most of my remaining plans are all little things.  Now my attention can turn from the rig to the trip itself.  The time for talking about overlanding is done.  The time for adventuring is about to start… 2016 No Highways Tour, here I come!  First stop, Easter Jeep Safari 2016.