Space Monkey

I got the following done:

D30
Sleeved - synergy
Axle Seals - Synergy
C-Gussets - Artec
Trussed - Artec
FLCA gussets - Artec
Synergy balljoints

$1400.00 out the door. And thats Canadian.

On a dana 30 the only differences are the axle tube thickness and the pumpkin size for the carrier. You can strengthen the outside of the diff and axle all you want but the real weak point is the ring and pinion. I would not go deeper that 4.88 in the D30 or you are sacrificing strength of the gears for a little more low end power. Low end power that causes gears to break. Since i have a 2012 6SP im only going with 4.56 gearing for 35" tires. Perfect for DD and weekend warrior.


If you are going to get trussed then get it sleeved first. It will ensure the tubes dont bend due to the welder.

Grimscale

for what it's worth:
I have a 2011 JKUR with the 3.8 auto and Cooper Discoverer STT 35x12.50 R17.
I eventually decided on going to 5.38s for the gears for two reasons:
1) I plan on bumping up to 37s once these 35s are done.
2) speaking with the owner of the shop that did the gears, who also has extensive knowledge of transmission rebuilds, he advised I go with the 5.38s to reduce the strain on the transmission. He has seen numerous Jeeps some in with blown autos because they weren't geared right.

Real world experience?

The Jeep has so much more "get up and go" than it did even with the stock tires and gears. It no longer hunts for gears when driving up a mild hill against a headwind. I also only lost approx. 1.5MPG switching tires/gears like I did.


I would HIGHLY recommend 5.38s, or, if you truly feel that's too much, 5.13s. Don't go anything less, I think you'd end up regretting it.



And $1600? Is that just for the gear change? I think I paid in the neighborhood of $1100 for mine.

nthinuf

You have a 3.8, 3.73's and 35's, right? Pressing the OD button will show you what 5.38's with od/on feels like. (using the rpm chart, just divide the number from the rpm by .69 to get the od/off rpm's. There is only 12 rpm difference between 3.73 with od/on and 5.38 with od/off).

So, at 70 mph, pushing od/off will put you about 120 rpm more than 5.13's, and 239rpm more than 4.88. Close enough to get a good comparison.

And regarding the strength issue with the tiny pinion - way back in the day, many people were worried about that. But, it just hasn't turned out to be a big problem. 5.13's are certainly thinner and weaker than 4.88's, but if you are spinning big tires and catch a rock, the strength difference between the two is a non-issue. They will both snap, or more likely, they will be ok and you will lose a shaft/joint.


For my 4-door auto, I went to 5.13 with 33's (32" measured), then up to 35's (33.5" measured), then swapped in a front d44 and went to 5.38 with the 35's, and finally to 37's (35.5" measured). 5.13's with the 35's was ok, but I actually liked the slightly higher rpm with 5.38's and 35's.

djlarroc

Glad to hear this from someone in CO. I was about 80% for 5:38, but still not sure if I'd like 5:13 better. I came back from Moab 2 weeks ago. Had to climb the Eisenhour pass in 2nd gear around 4k RPM. It sucked! Currently on 33" (32" measured) tires with stock 4:10s.

nthinuf

From the example I used with a 35" that measured 34", there is only 120 rpm difference between the ratios. I would be willing to bet that if you drove two otherwise identical jeeps, one with 5.13 and the other with 5.38, you wouldn't be able to tell the difference.

An extra 120 rpm isn't going to kill the mpg's, and it isn't going to kill the engine any faster, but it will help with hills and might keep you in OD a little longer, which is a good thing.

As far as the mountain passes go, it is still going to suck! 5.38's help, but they aren't magic and certainly can't overcome the physics of a weak engine with bad transmission ratio trying to push a loaded down JK that is lifted and has big tires. The only way you are going to pull the passes at speed is to add more power.

djlarroc

I agree with you. I had also been considering some kind of boost to help the 3.8, but just not really finding the info I want. In the meantime, the gears will probably keep me happy. I just don't want to ever keep my engine over 4k RPMs for an extended period of time. I will accept climbing the passes at 50 mph with 5:38s and 3rd/4th gear.

petef550

I have an 09 with a 6 speed on 37 inch Nitto mud grapplers ( really like 36's ) and I have 4.88's and it's perfect on the highway and around town.

Jeep757

I have an 08 3.8 manual running 33's(32 measured) and trying to decide between 4.10 & 4.56. Still sick but do plan to lift (2.5) and add front bumper and winch

CornFed03

I'm going to run 5.13's on my 2015 Rubicon. Going to work my way up to 37's after the 35's get worn out. I've got a 6-speed though. Makes a little bit of a difference.

Offroad

$700? I had my Artec truss and gussets + install all for $370.00