Make sure you read all the threads about vibrations after re-gearing after you get the gears installed. Don't plan on much help from the guys at the shop that told you not to get 5.13 gears, they'll probably just laugh and say they told you so.
4.56 or 4.88 gears?
- Thread starter CHAWK
- Start date
Ditchdoc
Member
I have 456 and hate them. I was wheeling 33s on 307 they weren't the best but I could do 70 on flat ground. Now I'm stuck at 60 and the engine is screaming. To add insult to injury I have 6 nearly new 33s I have to wear out before I can go larger. I guess it just depends how far you drive to wheel.
According to your posts you have a 3 speed auto which is a whole different beast from the 4 speed auto. Nobody would have told you to pick 4.56 for 33’s. Though they would have pretty much all recommended 4.10 which is ~300 rpm lower on the highway. Not a lot of difference but with a 3 speed you just don’t have a lot of options for a good balance of power and comfy rpm cruising.
Ditchdoc
Member
I knew it be way over geared but thought it be livable till I go larger. I may change trannys anyway.
Yeah well that’s a shitty answer because if he gets vibes at 72 with 5.13 then he would have gotten them at 75.6 mph on 4.88 instead.
That’s typical of a shop. Truth is, I never hear different. The difference on here is that we are Jeep enthusiasts, they are jeep and shop owners. Most of us do our own work and don’t trust shops.
Math doesn't seem to be your strong point, maybe somebody could link to one of the 10 or 20 threads about vibes? I'm sure this guy will find them either way.
point me to where my math is wrong, professor. 4.88 to 5.13 is an extra 5% of gearing. Is not going to magically cause vibes that the lesser ratio would not have had. They are still there just at a different speed.
I’ve seen the threads about vibes,they aren’t new. there are plenty of them for 4.88 too. Even some for 4.56. As I already said, if you’re going to get vibes, they will start at a speed, and would have happened on the other ratios at the proportionate speeds.
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I have 4.56 gears with the 6-speed and with 33’s my vibes began at 64mph. When I moved up to 35’s they don’t come on till 67-68mph. If they happen at speed they will happen when the driveshaft reaches that speed.
Even with that I wish I was at 4.88 for the power and gas mileage. Vibes can likely be fixed with hubs.
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just shut up and pay attention
, I'm just kidding you man, but seriously do pay attention. I went through this in 2017. I have a different setup than you (33s on a 5 speed) and the dedicated Jeep-only-build-shop told me 4.10s were the best for me. With some trepidation I ignored them and listened to Jerry's & others advice at 4.56 and damn it if it wasn't spot on, in fact if I was going to fall off either direction from that ratio it would've been 4.88s, certainly not 4.10s. So all I can say is what everyone else has already said, ignore the 'experts' at the shop. By the by this is no dig on the workmanship of the shop I used, it was flawless on everything they did for me & it was a decent bit early on. They have a great reputation for good work & I continue second that, I've sent a few folks their way over the years. I have however questioned their judgment on gearing ratio recommendations however, that's something that the end user really has to decide based on their own preferences & intended uses.
I'm not suggesting any ratio, I'm suggesting fair warning should be given that these gears can cause headaches that cost in the thousands of dollars extra to fix and years to troubleshoot. There is proof of that here on this forum. Suggesting that a shop is full of it because they know this and want to avoid that is what I take issue with. Suggesting 5.13 as the obvious choice without a word of caution isn't what I'd do, that's why I posted suggesting researching the issues that arise.
You’re really picking. I’m on my phone and changed what I was saying in my sentence. Don’t worry, I edited my comment.
It’s still pretty obvious what I meant all along is that 4.88 to 5.13 is a 5% change in gearing and if you have vibes on one setup at a certain speed, then you would have had them on the other gears at the proportionately adjusted speed which is where my example of speed came from. I don’t understand what part of my math was so hard for you to understand.
And if the issues are bound to happen, then they will on 4.88 just as they would on 5.13, but at a 5% higher speed, so what do you suggest? The post is about gear ratio to choose.
The shop isn’t suggesting 4.88 because of vibes.
They are full of shit, they have no clue why we are recommending 5.13 which is due entirely to your 42RLE transmission. 4.88 would be fine for a 5-speed but not your 42RLE. 4.88 would "work" for your 33's but not as well as 5.13 would.So Jerry,
Dang I better go put a stop to them tomorrow because they are trying to tell me that’s what I need
As was already said at least several times NO they will not be too low for the highway or cause excessive highway rpms! I wish I had the same highway rpms with my 35's that 5.13 will give you for your 33's.
Believe it or not I just created a drive shaft rpm calculator inspired by this post. It is a common question to consider when deciding gear ratios and determining some other things. We've always known how to do the math but I figured it would be a good thing to have as a resource for people on our website. I haven't read this whole thread so some of what I'm saying might be redundant to other posts but here's my take. You want to gear your Jeep so that your drive shaft rpm at 60 mph is around 2,500 rpm at 60 mph. A lower number like 2,300 will gear your jeep for faster driving with less low end torque. A higher number like 2,700 will gear your jeep "lower" meaning you will be geared better for low speed off-roading and low speed torque, you'll be able to crawl better but it will require higher engine rpms to cruise at highway speeds. I think 2,500 is the best all around target but you can gear higher or lower as you wish. Just remember that low speed crawling and interstate driving are on two opposite sides of a see-saw, gearing for crawling means you make some sacrifices when it comes to high speed driving. You can find the calculator embedded on the bottom of this page.
https://4xshaft.com/blogs/faq/diagnosing-drive-shaft-vibrations
Also, if you gear to high (low number like 3.73 or 4.10) your drive shaft as well as your engine and everything else upstream from the pinion is going to have less of a mechanical advantage. This means they will have to work harder to move your Jeep forward, this puts more strain on things and makes you more likely to break a drive shaft when off-roading.
To answer your question more directly though @CHAWK I personally think you will be better suited with 4.56 and think 4.88 is too low (high number) for your tire diameter. 4.88 is what I'd expect if someone is running 37" tires. The problem with recommendations is often that people assume that they know what your needs and goals are, they might assume you are building your jeep for off-roading only. It is nuanced, and what is best for you is not necessarily what is best for the next guy. Either that or people don't understand what they are recommending in the first place.
To answer your question more directly though @CHAWK I personally think you will be better suited with 4.56 and think 4.88 is too low (high number) for your tire diameter. 4.88 is what I'd expect if someone is running 37" tires. The problem with recommendations is often that people assume that they know what your needs and goals are, they might assume you are building your jeep for off-roading only. It is nuanced, and what is best for you is not necessarily what is best for the next guy. Either that or people don't understand what they are recommending in the first place.
If you’ve driven the 4 speed 42RLE, you’d probably change to 5.13 as your recommendation….he has a very tall OD.Also, if you gear to high (low number like 3.73 or 4.10) your drive shaft as well as your engine and everything else upstream from the pinion is going to have less of a mechanical advantage. This means they will have to work harder to move your Jeep forward, this puts more strain on things and makes you more likely to break a drive shaft when off-roading.
To answer your question more directly though @CHAWK I personally think you will be better suited with 4.56 and think 4.88 is too low (high number) for your tire diameter. 4.88 is what I'd expect if someone is running 37" tires. The problem with recommendations is often that people assume that they know what your needs and goals are, they might assume you are building your jeep for off-roading only. It is nuanced, and what is best for you is not necessarily what is best for the next guy. Either that or people don't understand what they are recommending in the first place.
4.56 would barely be an improvement from the 4.10 he already had.
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