Time for a re-gear
Thread Starter
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Joined: Mar 2020
Posts: 857
Likes: 123
From: Prescott, AZ
Digging up this old thread. I really can't recall if you completed your transition to 5.13s or not. I was looking for another thread in which you were talking about this 3.6L in general lacking power and just wanting, or having, to keep it up around 4500 rpm. I know there was another thread but kept landing on this one due to my search.
Anyhow, I'm hitting the point of being tired of these 4.88s when it comes to towing my trailer. Had to hook up the utility trailer this week and it's amazing what a turd this is even with an empty 5x10 utility trailer behind it. The last few big trips I've taken with my trailer it's really set the thought in my head that you're gonna be running high rpms regardless of being geared properly and having to downshift constantly or by just generally being undergeared. That leads me to my recent potential resolution flirtations.
I have always been anti forced-induction. I have a friend that has a RIPP and though he loves the thrill ride, he's struggled with shifting issues for years and trying to get it tuned properly. He's been through the gammit and the last attempt he put the brakes on the effort at $500 in labor for attempting to get it nailed. I have another buddy that has had all sorts of setups, Sprintex, Prodigy, RIPP. I've contemplated if taking that dive might be the answer to my issue but both of these guys tell me no, it's not worth it. I've seen first hand the additional wear on the engine and the unreliability, and they tell me on that top end I'd only be seeing ~2lbs boost and that isn't going to make the difference. It's generally a lot of money for a gamble and I agree it's just not worth it.
That leads me back to gearing. The time and effort to go to 5.13s from 4.88 will never be worth it, and that extra 100-150 rpm isn't going to make a hill-of-beans difference in my towing performance IMO. That leads me to contemplate 5.38s. That would be pretty undergeared for my 37s. It's not really a DD these days, but it does see long trips on the interstate every now and then when I go on adventures. I drove it to work this morning and forced it to stay in 4th gear. Traveling ~80mph put the engine around 3700rpm and that is where I estimate I'd land with 5.38 gears. I think I could stand the engine noise as my jeep is about as utilitarian as it gets, but one thing I thought about this morning was oil pressure. Running that rpm range puts my oil pressure up in the mid-70s, completely normal IMO and not a concern when downshifting, but I'm kinda thinking that could be a concern if that is just where it is all the time vs. short periods of downshifting.
If I'm running that high constantly do you guys think I am just asking for premature engine failure?
Anyhow, I'm hitting the point of being tired of these 4.88s when it comes to towing my trailer. Had to hook up the utility trailer this week and it's amazing what a turd this is even with an empty 5x10 utility trailer behind it. The last few big trips I've taken with my trailer it's really set the thought in my head that you're gonna be running high rpms regardless of being geared properly and having to downshift constantly or by just generally being undergeared. That leads me to my recent potential resolution flirtations.
I have always been anti forced-induction. I have a friend that has a RIPP and though he loves the thrill ride, he's struggled with shifting issues for years and trying to get it tuned properly. He's been through the gammit and the last attempt he put the brakes on the effort at $500 in labor for attempting to get it nailed. I have another buddy that has had all sorts of setups, Sprintex, Prodigy, RIPP. I've contemplated if taking that dive might be the answer to my issue but both of these guys tell me no, it's not worth it. I've seen first hand the additional wear on the engine and the unreliability, and they tell me on that top end I'd only be seeing ~2lbs boost and that isn't going to make the difference. It's generally a lot of money for a gamble and I agree it's just not worth it.
That leads me back to gearing. The time and effort to go to 5.13s from 4.88 will never be worth it, and that extra 100-150 rpm isn't going to make a hill-of-beans difference in my towing performance IMO. That leads me to contemplate 5.38s. That would be pretty undergeared for my 37s. It's not really a DD these days, but it does see long trips on the interstate every now and then when I go on adventures. I drove it to work this morning and forced it to stay in 4th gear. Traveling ~80mph put the engine around 3700rpm and that is where I estimate I'd land with 5.38 gears. I think I could stand the engine noise as my jeep is about as utilitarian as it gets, but one thing I thought about this morning was oil pressure. Running that rpm range puts my oil pressure up in the mid-70s, completely normal IMO and not a concern when downshifting, but I'm kinda thinking that could be a concern if that is just where it is all the time vs. short periods of downshifting.
If I'm running that high constantly do you guys think I am just asking for premature engine failure?
The big thing is that our engines are just under powered as you know and it’s worse with gear, armor, and big heavy wheels/tires. I honestly feel like the only real solution is a v8 swap. It’s spendy but once my engine dies, I’m putting a v8 in my Jeep.
As far as the premature wear, I think you’ll be fine. Just remember that even with the engine being at 6k rpm’s at times is still within normal limits. I let my engine rev to 5500 all the time if I’m getting up to speed on an on ramp. I don’t have any concerns if I’m cruising at 4500rpm (keeping engine temps in sight) for a few minutes while climbing a hill on the freeway.
Thread Starter
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Joined: Mar 2020
Posts: 857
Likes: 123
From: Prescott, AZ
Come to think of it Russ, it’s not so much about cruising at a couple hundred rpm lower. It’s more about mechanical advantage with a better gear ratio that makes it easier for the engine to turn the tires. 4.88 to 5.13 may not seem like much but imagine pedaling your bike and changing just one gear up/down when needed. It’s not that much difference in gearing but your legs definitely feel it and pedal easier.
JK Enthusiast
Joined: Dec 2020
Posts: 150
Likes: 20
From: White Rock, NM.
I would suggest not to go with Yukon. They induction harden their pinion and that leaves the threaded side vulnerable to damage during install. It's fine after the install.
Basically what that means is that during the hardening process, the pinion is held by the threaded side and while the rest of the pinion gets the hardening treatment, the threads do not.
As you can imagine, I learned this the hard way. So for a first time install, I'd stay away from Yukon. Unless they have changed since about 2 years ago.
The whole process is really frustrating and really gratifying and really sucks when you fail, but it's a failure only if you give up. So do it and do you research.
Also, I would strongly recommend you pull the axles. It's much easier that way.
I have 5.13 with 35's and they work great for me. And the gears are Yukon. It was a monumental PITA to get them fitted. But only until I figured out the thread issue, then it was easy.
Basically what that means is that during the hardening process, the pinion is held by the threaded side and while the rest of the pinion gets the hardening treatment, the threads do not.
As you can imagine, I learned this the hard way. So for a first time install, I'd stay away from Yukon. Unless they have changed since about 2 years ago.
The whole process is really frustrating and really gratifying and really sucks when you fail, but it's a failure only if you give up. So do it and do you research.
Also, I would strongly recommend you pull the axles. It's much easier that way.
I have 5.13 with 35's and they work great for me. And the gears are Yukon. It was a monumental PITA to get them fitted. But only until I figured out the thread issue, then it was easy.
Last edited by Junkyard junkie; Jul 28, 2022 at 08:04 PM.