488s or 456s. That is the question

WK2JT

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4.56 gears are going in on Tuesday! I can't wait to drive it!

Any break-in procedure? I'm thinking just drive gently and vary the speed, then I'll probably change the fluid around 5 to 7k miles.

I also have to remember to set the Tazer to the new ratio.
You can do a google search. Lots of variations on the “correct” procedure, but all are very similar. The first 50 miles are critical. Very short duration trips first couple hundred miles. The gears are going to be tight and generate a lot of heat. You do not want to breakdown the gear oil and overheat the gears. Then progressively longer drive intervals until about 500 miles. Change the gear oil at this point and you should be good to go.

Most shops include the 500 mile gear oil change.
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OldButStillJeeping

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I didn't read the whole thread, so I apologize if I'm restating a bit.

On my TJ, which came from factory with 3.73 and 29" tires. Using the readily available chart found online and comparing tire diameter to ring and pinion... giving you RPMs, I installed 4.56 and it was perfect with 35's. Conversely, most TJ guys I knew went with 4.88 but we're revving into the higher 3s on the highway.

My YJ is rolling 35's thru a 3 speed automatic and 4.10's and I would have to redline the motor to go 85 mph. Heck, in 4lo I have to put the transmission into neutral just to stop it, because the brakes won't.

I've done a couple ring and pinion changes in my home shop on my Jeeps by myself. It's not easy. But if you can afford about $500 in tools; A guage, torque wrench, etc. Have common mathematics down pat, and you're dedicated. Triple check your work without cutting corners. It can be done successfully. A former Ford Mechanic who did diffs for a living schooled me.

My personal thoughts are, people tend to gear too low. Unless you're crawling rocks most of the time, or pulling stumps out of the yard, you will probably be over revving just to daily drive it. The mpg will be a joke.

I'm eventually going to put 37s on my Mojave with it's 4.10s and I think it will be fine as gold. But if I do change it, it'll be to 4.56.
 

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I didn't read the whole thread, so I apologize if I'm restating a bit.

On my TJ, which came from factory with 3.73 and 29" tires. Using the readily available chart found online and comparing tire diameter to ring and pinion... giving you RPMs, I installed 4.56 and it was perfect with 35's. Conversely, most TJ guys I knew went with 4.88 but we're revving into the higher 3s on the highway.

My YJ is rolling 35's thru a 3 speed automatic and 4.10's and I would have to redline the motor to go 85 mph. Heck, in 4lo I have to put the transmission into neutral just to stop it, because the brakes won't.

I've done a couple ring and pinion changes in my home shop on my Jeeps by myself. It's not easy. But if you can afford about $500 in tools; A guage, torque wrench, etc. Have common mathematics down pat, and you're dedicated. Triple check your work without cutting corners. It can be done successfully. A former Ford Mechanic who did diffs for a living schooled me.

My personal thoughts are, people tend to gear too low. Unless you're crawling rocks most of the time, or pulling stumps out of the yard, you will probably be over revving just to daily drive it. The mpg will be a joke.

I'm eventually going to put 37s on my Mojave with it's 4.10s and I think it will be fine as gold. But if I do change it, it'll be to 4.56.
where can I find the readily available chart?
 

Smess

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It’s down to the wire. I want 488 gearing. Just not sure I need them

The Jeep is the automatic eight speed version on 35/12.50s

I do light towing on occasion and will be on light trails

If you have either of these gears can you give me real world data
I am not sure why if a manufacturers Cafe rating is so important why every vehicle would not be geared to perfection.

To Mr Threadstarter:

https://www.bushwacker.com/blog/gear-ratio-chart

To Mr Threadstarter:

I have put 35's to start on every Jeep I have ever owned and the best match to me would be 4.10 for overall economy and performance

To Mr Threadstarter:

I have a Gladiator with Dana 60's and 4.88's and 40's and the Ultimate Dana 60 comes pre-assembled as a complete build in every gear option but 4.56 and I wish I had the 4.56 which we wanted but close the closest which is 4.88

THEREFORE BASED ON THE THREE BULLET POINTS ABOVE WHICH INCLUDE INFORMATION AND FACTS FROM GREAT SOURCES AND SO MANY YEARS OF LOTS OF PEOPLES EXPERIENCE EVERYTHING AND EVERY PERSON SUGGESTS AGAINST 4.88'S

BUT IF YOU DECIDE TO GO 4.88'S CAN YOU PM ME AND CAN I GIVE YOU MY ADDRESS SO I CAN BUY $5 WORTH OF WHATEVER YOU ARE ON SO I CAN ESCAPE FROM LIFE FOR AN HOUR OR TWO OR A DAY OR WHATEVER AND VISIT WHEREEVER THIS STUFF TAKES YOU BECAUSE I BET IT IS A VERY NICE EXPERIENCE- THANKS
 

OldButStillJeeping

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where can I find the readily available chart?
Here you go. This is from G2. Go to their website for more info.

I think you can find it on quadratecs website, and many, many, others.

Find your engines happy place in the RPM range at hiway speed and follow the chart. Maybe add a small amount for the larger tire and wheel weight.

You should be good

Screenshot_20210715-235237~2.png
 
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Smess

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Here you go. This is from G2. Go to their website for more info.

I think you can find it on quadratecs website, and many, many, others.

Find your engines happy place in the RPM range at hiway speed and follow the chart. Maybe add a small amount for the larger tire and wheel weight.

You should be good

Screenshot_20210715-235237~2.png
thanks, looks like the same chart as the link I posted with different font and colors
 

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This is the calculator I used to help me decide on my gearing. I find it very very close to my actual. According to this calculator, my 4.56 with 315/70-17 is just a little bit lower geared than a stock MaxTow. The reason I didn't also include a rubi or mojave is because those both come stock with larger tires.
 

DanW

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I am not sure why if a manufacturers Cafe rating is so important why every vehicle would not be geared to perfection.

To Mr Threadstarter:

https://www.bushwacker.com/blog/gear-ratio-chart

To Mr Threadstarter:

I have put 35's to start on every Jeep I have ever owned and the best match to me would be 4.10 for overall economy and performance

To Mr Threadstarter:

I have a Gladiator with Dana 60's and 4.88's and 40's and the Ultimate Dana 60 comes pre-assembled as a complete build in every gear option but 4.56 and I wish I had the 4.56 which we wanted but close the closest which is 4.88

THEREFORE BASED ON THE THREE BULLET POINTS ABOVE WHICH INCLUDE INFORMATION AND FACTS FROM GREAT SOURCES AND SO MANY YEARS OF LOTS OF PEOPLES EXPERIENCE EVERYTHING AND EVERY PERSON SUGGESTS AGAINST 4.88'S

BUT IF YOU DECIDE TO GO 4.88'S CAN YOU PM ME AND CAN I GIVE YOU MY ADDRESS SO I CAN BUY $5 WORTH OF WHATEVER YOU ARE ON SO I CAN ESCAPE FROM LIFE FOR AN HOUR OR TWO OR A DAY OR WHATEVER AND VISIT WHEREEVER THIS STUFF TAKES YOU BECAUSE I BET IT IS A VERY NICE EXPERIENCE- THANKS
I've got 4.10s now and 6th gear is just too tall. The general consensus I've gathered is 4.56 is the sweet spot for 35's and 4.88 for 37's. I went with 35's because I do a good bit of highway driving. It should be a little better, power wise, than it was with 4.10's and 33's from the factory, which I thought felt great.

I do think 4.88's would be fine in 6th gear but would make 1st just ridiculously short. I don't need 1st to be any shorter than it is now, so a little shorter won't hurt. A lot shorter will be just too much for me. At least that's how I'm thinking now. I'll never know for sure, but I'm betting it'll be ok with 4.56.

So I should be at about 2400 rpm at 75mph in 6th gear. The real challenge is not to gear it so that 1st is too short or 6th is too tall. If they had made 6th and 5th a little shorter, I wouldn't even think of re-gearing. When I was running the 315 KO2's, it was tolerable and I would not have re-geared. They were about 34.5" in actual diameter. The Generals I'm running now are 34.9 and it just barely hit the tipping point.

Really, though, the story won't be told until Tuesday evening when I drive it home with 4.56's. I'll chime in that evening with a report. Then I'll settle in and live with them a bit and will share out on them over the subsequent days and weeks, especially after getting them on the highway a bit and also doing some off-roading.
 
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