Bonanza

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Took us 3 days in a 110 degree shop, but we’re finally done. I wanted to post a few things, and my opinion, as I searched when I had a few tough spots and didn’t get much luck. Here we go!
  1. I am in 8th gear a lot, but my current results indicate 0 to slim gas mileage increase.
  2. It still felt peppier stock. I like the 4.88s better than the 4.10, but its still super slow. Was not a day/night difference.
  3. If you’re doing the install yourself, the crush sleeve portion of the install was very challenging. We ended up chaining the flange to the LCA.
  4. We didn’t not need to use different shims- same setup from the factory
  5. A bolt on one of the ring gears seized and we had to cut it out. Oof
  6. Overall, knowing what I know now, 4.10s were fine enough and I probably wouldn’t say this is a must-do. There’s just so much involved with a regear that I wouldn’t recommend it unless you really hate the driving experience. This is absolutely not a DIY project

Edit-- 200 miles in. So far so good, no leaks and no noises. Couple of things to note now that I've had some more seat time:

1. MPG improvement is [mixed]
2. Quality of life improvement is somewhat better-- it takes a lot less pedal, and a lot less pressure to both start off, and maintain any speed.
3. 4HI is usable. This is a big A-ha actually. Previously, I found 4hi to be fairly worthless. I used it a bunch this past weekend, as I could actually -go- without it bogging down or feeling like I needed to really give it gas.

Edit 2-- 500 miles in. MPG is 15.6. Bleh. Enjoying 4HI, but would be happier if the MPG increased instead of decreased.

Edit 3-- Did the oil change at 499.5 miles. Front was sparkling clean, which is to be expected from the lack of constant load. I did go into 4hi and 4lo, but it just isn't enough to get close to the rear. The rear's oil was much darker. The drain plug had a fair, but not excessive, amount of sludge with metallic crystals in it. No chunks, but more metal than I've seen in a drain pan. I pulled the cover to inspect the ring gear but I didn't see anything abnormal or even suspicious. (Even if I did, not much I could do, eh?) With 75-140 in now instead of 75-90, I saw a 19 mpg trip to work this morning all city. So we'll see how it goes.

Edit 4- Two gas tanks came and went after the oil change. MPGs are.... (drum roll).... 16.7. Literally the same as pre-gearing, to the tenth. I'm prepared to confirm that re-gearing from 4.10 to 4.88 will result in slim to no gas mileage increase.

Edit 5- Just filled up. 16.7 MPG per dash computer.
Edit6- 16.3 on this last tank. Camping trip up/down mountain, 4lo for some of it.

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Geoarch

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Took us 3 days in a 110 degree shop, but we’re finally done. I wanted to post a few things, and my opinion, as I searched when I had a few tough spots and didn’t get much luck. Here we go!
  1. Mpg improved a decent amount. I am in 8th gear a lot.
  2. It still felt peppier stock. I like the 4.88s better than the 4.10, but its still super slow.
  3. If you’re doing the install yourself, the crush sleeve portion of the install was very challenging. We ended up chaining the flange to the LCA.
  4. We didn’t not need to use different shims- same setup from the factory
  5. A bolt on one of the ring gears seized and we had to cut it out. Oof
  6. Overall, knowing what I know now, 4.10s were fine enough and I probably wouldn’t say this is a must-do. There’s just so much involved with a regear that I wouldn’t recommend it unless you really hate the driving experience. This is absolutely not a DIY project




C0036A0A-9E24-4B5A-9D05-10C2B564CC91.jpeg
I did that on my 70 Chevy II with a 327, but I was 20 years old and just out of tracked vehicle mechanic school and used the shop on the base. I would never attempt it now. Good on you.
 

glassjawkid32

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Took us 3 days in a 110 degree shop, but we’re finally done. I wanted to post a few things, and my opinion, as I searched when I had a few tough spots and didn’t get much luck. Here we go!
  1. Mpg improved a decent amount. I am in 8th gear a lot.
  2. It still felt peppier stock. I like the 4.88s better than the 4.10, but its still super slow.
  3. If you’re doing the install yourself, the crush sleeve portion of the install was very challenging. We ended up chaining the flange to the LCA.
  4. We didn’t not need to use different shims- same setup from the factory
  5. A bolt on one of the ring gears seized and we had to cut it out. Oof
  6. Overall, knowing what I know now, 4.10s were fine enough and I probably wouldn’t say this is a must-do. There’s just so much involved with a regear that I wouldn’t recommend it unless you really hate the driving experience. This is absolutely not a DIY project




C0036A0A-9E24-4B5A-9D05-10C2B564CC91.jpeg
What were the before and after numbers on your mpg?
 

Summitdan

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5.13:1 for me and my 37’s on the 3.6, but I’m at high altitude and tow frequently. It drives great. I see 8th gear frequently.
 


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Bonanza

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What were the before and after numbers on your mpg?
16.7 before, which is about on par, and 17.6 after 1 normal trip. It’s reading 20 mpg now, but that’s due to the break in driving— about 40 mph top speed.

This isn’t a “don’t regear” thread, but I know a LOT of people are on 4.10s and wondering if it’s worth it to jump to 4.88s. On my old Jeep, the jump from 3.21s to 4.56 was night-day. This, from what I can tell, is not night day. More of dusk-night difference.

In a vacuum, 4.88s are spot on and would be my choice if I ordered my Jeep from a menu. But here I am in the real world, with my own shop, wholesale prices, and someone helping me install. I think part of my apprehension is that my Jeep has 16k miles, and I pulled out parts that were pretty much new. I’d be much happier inside if I knew the seals and bearings were worn.

I will update the post after the breakin period and see how I feel. :)
 
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Bonanza

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If anyone else has done there own gears, I really want to know how you held the flange while giving it 360 lbs ft of torque. I didn’t see that in any install video or write up and is easily the hardest part. We borrowed an impact gun that resembled a Gatling gun and weighed about 50 pounds, but it still spun the flange. Lost about a half day trying to figure that out!
 

tommyp

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If anyone else has done there own gears, I really want to know how you held the flange while giving it 360 lbs ft of torque. I didn’t see that in any install video or write up and is easily the hardest part. We borrowed an impact gun that resembled a Gatling gun and weighed about 50 pounds, but it still spun the flange. Lost about a half day trying to figure that out!
They make pinion flange tools that you bolt on then put a pipe in them to anchor off to whatever on the jeep.

https://www.ironrockoffroad.com/product/yoke-tool.html



You can see it in use in this video for our axles it should link to the time where he is using it 10:30 or so in.

 
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Bonanza

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steve68

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Can you not hold the yoke with a large pipe wrench or adjustable or chain wrench,

Good post, I'm ready to regear and do a pedal commander,

really interesting that you didn't have to shim, getting the mesh and pattern is a big thing and requires great attention,

What brand of gears did you use? and what comes with them,

Thanks
 


Trailman

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When you say you found 4HI unusable prior to the re-gear, are you specifically referring to the 37s, or did you feel that way with 33s stock?

I use it all the time and it seems great to me, wondering if I'm missing something :p
 

Orange01z28

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5.13:1 for me and my 37’s on the 3.6, but I’m at high altitude and tow frequently. It drives great. I see 8th gear frequently.
I was waffling between 4.88 and 5.13 for so long but I ended up ordering 5.13

I got my 37s this week but i'm not able to do gears until the end of July so i'm getting a good feel for them on stock gearing. Since my new tires are XTs compared to MTs they're about the same weight so I hardly feel any butt in seat difference. However, I have not been offroad yet and have only been down here in the flatlands

I plan on buying a boat this winter so Im glad to hear 5.13 and 37s is a good combo

Oh yeah, 100% having this done by pros
 

COMPY

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You have to reprogramming the computer in order to the transmission shift fine ?
Is mandatory ?
 

Summitdan

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You have to reprogramming the computer in order to the transmission shift fine ?
Is mandatory ?
Definitely mandatory after a regear.
 

khockey02

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Thanks for the write-up. I agree, coming from 3.73 to 4.88 with 37” KO2s. There is certainly a quality of life increase driving through the mountains, towing, etc. but given the hassle and $2,000, I’d be happy sticking with the stock setup if I could go back. Especially if I’d had 4.10s

 

 
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