Do I need to re-gear?

[JMT]

@GregBelleville I agree with Jerry about the front lunchbox locker. Also, while it may be rare, I broke a front axle stub in a stock Dana 30 running 33’s with a lunchbox locker.

 

[JasterMereel42]

Ok #1 replace that shitty-filtering K&N with a good air filter like from AC-Delco, Purolator, etc. K&N air filters are absolutely the WORST at actually filtering out the harmful stuff like silica, dust, dirt, etc. You will not lose ANY power, none whatsoever, by replacing the K&N. The TJ's factory air intake with a conventional paper element air filter like from AC-Delco is not restrictive (!) will easily flow more air than the engine can consume at wide open throttle and redline rpms. The below is from an ISO 5011 certified lab test of various air filters. Notice the lab's last sentence below, bolded for emphasis.

View attachment 452967

But let's get to what is likely the reason for your lack of power, let's take a look at your axle ratio. If your TJ has the dreaded 3.07 ratio that's the reason. With the wrong axle ratio for the size tires being run your engine rpms will be too low and the engine won't be able to generate enough power for the size tires being run.

There's a tab bolted to your differential at its 9 o'clock position. The below tag indicates the gears inside the axle have a 3.73 ratio. What does your tag say? 3.07? 3.73? If it's a 3.07 you would pick up a significant boost in power by regearing to a lower axle ratio like 3.73 or 4.10. Regearing will raise the engine rpms up enough to produce enough power for your 31" tires.

View attachment 452969

That tag is supposed to be on the rear diff? It is on the front of mine.

Also, mine says 3.73 and the RPMs are about 2300-2400 at 60mph on the freeway with 33" tires with the 32RH. It feels underpowered. I'm thinking about going with a re-gear to 4.10 or more. How much do these usually cost?

 

[OldBuzzard]

That tag is supposed to be on the rear diff? It is on the front of mine.

Both diffs get a tag from the factory. But they're often left off when changing the lube or other work is done.

Also, mine says 3.73 and the RPMs are about 2300-2400 at 60mph on the freeway with 33" tires with the 32RH. It feels underpowered. I'm thinking about going with a re-gear to 4.10 or more. How much do these usually cost?

Your profile doesn't tell us about your Jeep. Year, transmission?
You'll more likely want 4.56 for a manual tranny, or even lower gearing for an automatic, depending on which one you have.

 

[JasterMereel42]

Both diffs get a tag from the factory. But they're often left off when changing the lube or other work is done.


Your profile doesn't tell us about your Jeep. Year, transmission?
You'll more likely want 4.56 for a manual tranny, or even lower gearing for an automatic, depending on which one you have.

I've got a 3 speed 32RH.

 

[GregBelleville]

I've got a 3 speed 32RH.

I think general wisdom around here is to not go any deeper than 4.10 gears with the 32rh, otherwise highway rpms will be too high.

 

[OldBuzzard]

Check this:

Recommended gear ratio for 32RH transmission and 33" tires?​

 

[JasterMereel42]

Check this:

Recommended gear ratio for 32RH transmission and 33" tires?​

Looks like I need to regear to a 4.10 ratio. Thanks!

 

[iKrea]

You're struggling up Donner Pass because you're only running 4.56 with 35's which is on the verge of lugging for that size tire. Really, 4.88 would have been a much better choice. I ran 35's and 4.88 with the AX-15 which is not geared quite as low as your 6-speed is and it did fine regularly going up to my local mountains. If you live at a higher altitude 5.13 would be a great choice too. Many would recommend 5.13 for your transmission and 35's even if you don't live at a higher altitude.

Wait, so papa Jerry, i’ve been doing some serious thinking, would I benefit from re gearing my 33” for 4.56? i’m about to pull the trigger on a complete rebuild for the front and rear axle, i live in Canada and almost always have to use the Highway to get anywhere so the speed limit is 60mph, would it give me any downsides, i’m also planning on sending the jeep to Madagascar for a big trip, so please lend me your expert opinion

 

[L J]

Wait, so papa Jerry, i’ve been doing some serious thinking, would I benefit from re gearing my 33” for 4.56? i’m about to pull the trigger on a complete rebuild for the front and rear axle, i live in Canada and almost always have to use the Highway to get anywhere so the speed limit is 60mph, would it give me any downsides, i’m also planning on sending the jeep to Madagascar for a big trip, so please lend me your expert opinion

Jerry has left the building and won't see or answer your post. I suggest starting a new thread of your own to get feedback.

 

[JMT]

Wait, so papa Jerry, i’ve been doing some serious thinking, would I benefit from re gearing my 33” for 4.56? i’m about to pull the trigger on a complete rebuild for the front and rear axle, i live in Canada and almost always have to use the Highway to get anywhere so the speed limit is 60mph, would it give me any downsides, i’m also planning on sending the jeep to Madagascar for a big trip, so please lend me your expert opinion

33’s with the NV3550 should be regeared to 4.88. Same for the AX-15.

 

[steelhd]

Wait, so papa Jerry, i’ve been doing some serious thinking, would I benefit from re gearing my 33” for 4.56? i’m about to pull the trigger on a complete rebuild for the front and rear axle, i live in Canada and almost always have to use the Highway to get anywhere so the speed limit is 60mph, would it give me any downsides, i’m also planning on sending the jeep to Madagascar for a big trip, so please lend me your expert opinion

I think Jerry got fed up and left the site. One thing you can do is compare your Jeep as it came stock with your proposed tire size and gear ratio to see how it compares.
http://www.grimmjeeper.com/gears.html

 

[jjvw]

Wait, so papa Jerry, i’ve been doing some serious thinking, would I benefit from re gearing my 33” for 4.56? i’m about to pull the trigger on a complete rebuild for the front and rear axle, i live in Canada and almost always have to use the Highway to get anywhere so the speed limit is 60mph, would it give me any downsides, i’m also planning on sending the jeep to Madagascar for a big trip, so please lend me your expert opinion

Jerry was misguided on gearing. You want 4.88.

 

[GregBelleville]

Jerry was misguided on gearing. You want 4.88.

4.88 with 33s and a 32rh, I think this is the first I've seen those gears recommended with that trans and tire size, which is what I've got as well.

What would rpms at 70 mph be, seems like they'd be way too high with 4.88s.

 

[jjvw]

4.88 with 33s and a 32rh, I think this is the first I've seen those gears recommended with that trans and tire size, which is what I've got as well.

What would rpms at 70 mph be, seems like they'd be way too high with 4.88s.

IKrea has a nv3550. 488 for 33s is correct.

 

[GregBelleville]

IKrea has a nv3550. 488 for 33s is correct.

Whoops, got confused between posts and thought that recommendation was for the 32rh, sorry about that.

 

[Mudflat]

That's what I thought, 3.07 is just a terrible ratio. Jeep made it a standard ratio thinking it would help the mpg rating but it has to be driven so much more aggressively that the 3.07 doesn't help the mpg in the least. I'd regear it to 4.10 which is the ratio the Rubicon came with with the manual transmission for its 31" tires. It'll be a great performing Jeep after regearing the axles to 4.10. Highway rpms will be ideal.

I agree.

 

[iKrea]

Jerry was misguided on gearing. You want 4.88.

Are we anti jerry wth happened

 

[iKrea]

IKrea has a nv3550. 488 for 33s is correct.

4.88? okay so with 4.88 would i be able to run 35s

 

[jjvw]

4.88? okay so with 4.88 would i be able to run 35s

35s would be better with 513

 

[jjvw]

Are we anti jerry wth happened

I am a proponent of understanding how and why things work.