Hello Jeep people! In need of some help for a gear change! I have a 2009 X JKU with 3.21 gears and an automatic transmission. Was needing some help choosing the gears to put. If anybody could recommend some kits that I can buy that come with everything I need. Trying not to spend a lot so just need a good deal. Was wanting to upgrade to 4.56 gears. Anything would help!

 

If I told you your JK with automatic transmission came with 3.73 gears, would it make a difference in your gear change plans?

 

 

I mentioned it because you may not see enough of a difference going from 3.73 to 4.56.

 

 

 

I'll leave that to those who know more about gear/tire relationships.

 

With the expense of regearing, do more research than reading replies in a single thread. For 3.8 auto's, 5.13's are very popular for 35's. So you are probably on the right track with 4.88 or 4.56 for 33's. (assuming you know that you will never go up to 35's or larger?)

Here are some charts a forum member put together a few years back. They use actual 'measured' tire height, not mfg spec. If you don't have the new tires, you might assume a 32" actual height for a 33" tire. You could also measure your current tires and get your rpm @ 70, then plug in the numbers to verify where you're at.



Then you could take it a step further. At 70mph, turn OD/Off and check your rpm's again. You should find that it's pretty darn close to the rpm of 5.38's on that chart. So, you instantly have an idea of where you would be with that ratio as well. Roughly 135 rpm between ratios, so you can make some guess-timates on the other ratios.

 

Are you having a shop do the regear, or are you doing this yourself? If you are having a shop do the install, you should just get quotes from the shops that include parts and labor. It really isn't any more than if you think you find a "good deal" on parts, and take everything to them as shops will typically get the parts at wholesale and not charge you additional (or a very small margin) for them.....while they make the margin on labor. Margin on parts is so skinny anyhow. Also, if a shop takes care of the parts in addition to labor, it will be much easier to deal with any warranty work should you need to. If you take parts to a shop, they usually won't help with warranty should a part fail. You're quite a ways down there in the tip of Texas. Around DFW regears are usually ~$1500+/- (that includes parts and labor) for reference. I would caution that re-gearing is usually not a mod you want to skimp on. You might find someone willing to regear both axles for $1000.....and if you do, you should question how they're doing it so cheap as it usually means cutting corners to save time.

If you are doing this job yourself, besides the gear sets, you should be buying master install kits that come with all the new parts you'd need (new ring gear bolts, shims, crush sleeve, bearings, etc.....). It's helpful to have proper set up bearings as well, but many will re-use the existing bearings and rheem them out just a touch.

If you do have a shop quote parts & labor, you should ask about the brand. A lot like preference in gasoline brands.....you may or may not have a preference. You can't go wrong with Yukon gears, but many shops will go with G2 or something else as they might have a lower cost to the shop. Just be aware of what you're buying so that if one shop quotes you a price that includes Yukon gears, and another shop quotes prices using G2, you can factor in your preference.

It's hard to go too low with that 3.8L. I'd think with 33s you might be better off considering 4.88s. You'd probably be fine even going as low as 5.13, but 4.88 is probably "more ideal".

Last comment....whether doing yourself or having a shop do it, read up on break-in procedure. It's important, and a lot of shops won't even tell customers about break-in procedure. Whether information is relayed to you by a shop or not, it is ultimately the owners responsibility to care for their vehicle.

 

I second everything resharp said ^, if the shop is doing your gears...let them order all the parts. Usually they kits will come with some little parts missing (just like some AR parts/LPK kits can be missing a spring/detent) and it's easier and quicker for the shop to deal with that. Plus if they stock the parts, there'll be no hiccup.