Re Gearing After Lifting - Need Some Education

[604KJ]

Hello,

Im just about ready to drop some $$$ on the Tommudd 3.5" Econo Lift,
Tommudd's Econo 3.5" Lift Kit

But I've been reading through a lot of forums talking about re gearing to 4.10 since I'm looking to put the biggest tires i can fit without getting any rubbing or having to do some trimming. My question is, since i know nothing about this stuff, What is re-gearing & what does it do? Some forums I've read say if i do re gear i will end up losing top speed, but if i don't then it will eventually just wreck the Libby.

I'm confused if i need to do this or not, keep in mind, this is also my everyday vehicle so i prefer to do things right and keep it in good running condition.

Any advice to help educate me will be appreciated

Thanks,

 

[dude1116]

Hello,

Im just about ready to drop some $$$ on the Tommudd 3.5" Econo Lift,
Tommudd's Econo 3.5" Lift Kit

But I've been reading through a lot of forums talking about re gearing to 4.10 since I'm looking to put the biggest tires i can fit without getting any rubbing or having to do some trimming. My question is, since i know nothing about this stuff, What is re-gearing & what does it do? Some forums I've read say if i do re gear i will end up losing top speed, but if i don't then it will eventually just wreck the Libby.

I'm confused if i need to do this or not, keep in mind, this is also my everyday vehicle so i prefer to do things right and keep it in good running condition.

Any advice to help educate me will be appreciated

Thanks,

4.10 gears are referring to the gears in your axles (differentials). You need to replace both rear and front if you have 4x4. The way it works is like bike gears. The lower gear (4.10 is lower than 3.73, the stock V6 Liberty gearing) makes it easier for the Jeep at low speeds, more difficult to do higher speeds. Essentially, one is able to get more torque with lower gears, which puts less strain on the engine at lower speeds. 4.10s shouldn't effect your top speed dramatically, but it WILL effect your acceleration in a dramatically GOOD way.

Essentially, it makes it much easier for the Jeep to turn more weight in rubber.

 

[HoosierJeeper]

4:10 isn't a big enough change to effect the durability of your Jeep either way. But they should help get some low end torque.

 

[tjkj2002]

Re-gearing over comes (or reduces) the effects of adding bigger tires.When stock you have a overall final drive ratio,when you slpa on those bigger tires that final drive ratio has changed effecting the speedo,trans shifting,and generally building up to much heat in the whole drivetrain.Re-gearing to lower gears in the diffs helps bring you back into the OE speced final drive ratio reducing heat buildup but a pinion reset is required to bring back the trans shifting and speedo.

As long as you do not gear to low,and 4.10's is not to low for even 245/75R16's(31" tire), you will not loose any high end speed but gain back the low end that will be lost with bigger tires and stock gears.Also gains back alot of the mpg's you will loose,not all since the added weight of the bigger tires will always reduce mpg's.


When my KJ was still IFS and running 4.10's with 32" tires I could still do 100mph+,granted 4.56's would be much better for 32" tires on a KJ.

 

[LibertyFever]

IMO if you lift your Jeep and increase the tire size from a stock 28" tall to 31" tall regearing isn't really necessary.

However if you increase the tire size from a stock 28" tall to 33" tall then yes regearing would be necessary.

I have a YJ running on 33" tall tires. Regearing to 4.88's was necessary.

It is possible to run 33" tall tires on a Liberty. So after regearing the axles would you also have to reprogram the PCM for the larger tires and different gears? I would expect so.

sent from my Galaxy SIII & Tapatalk4 beta

 

[tommudd]

IMO if you lift your Jeep and increase the tire size from a stock 28" tall to 31" tall regearing isn't really necessary.

sent from my Galaxy SIII & Tapatalk4 beta

Sorry but have to disagree completely
Regearing when going to 31-32s does help a ton,
better mileage, better gearing on hills etc , runs cooler

Heck I'd still like to have 4.56s with my 32s !!!!!!!!

 

[tjkj2002]

IMO if you lift your Jeep and increase the tire size from a stock 28" tall to 31" tall regearing isn't really necessary.

However if you increase the tire size from a stock 28" tall to 33" tall then yes regearing would be necessary.

I have a YJ running on 33" tall tires. Regearing to 4.88's was necessary.

It is possible to run 33" tall tires on a Liberty. So after regearing the axles would you also have to reprogram the PCM for the larger tires and different gears? I would expect so.

sent from my Galaxy SIII & Tapatalk4 beta

I also must disagree.

When going to 245/75R16's(30.5" tires) on a KJ you should go to at least 3.91 gears,well no 3.91's for the D30A so 4.10's it is.Going to 32" tires puts you in the 4.10-4.27 gear ratio to bring back to stock.

 

[LibertyFever]

Very good guys, I must concede to your opinions because you clearly have more experience than I do.

I've regeared a YJ before. It wasn't that difficult but on a Liberty how do you get the front carrier out? Drop the entire center diff housing?


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[u2slow]

Very good guys, I must concede to your opinions because you clearly have more experience than I do.

I've regeared a YJ before. It wasn't that difficult but on a Liberty how do you get the front carrier out? Drop the entire center diff housing?

Ya, take whole front diff out. You can even drive it in the meantime. (I did when I had the diff out for seals, bearings, and Powertrax.)

I still have the stock gears... upping the tire size simply made 1st gear usable. With stock tires, 1st seemed too low, and 2nd too high when pulling away from a dead stop. Must be the auto's that need the gearing change to keep the shift points happy. :Frustrated:

 

[tommudd]

Doesn't matter if manual or automatic both benefit from installing lower gears

Easy to drop the front diff down out of a KJ
If you follow the service manual it says to remove half the front end but there are short cuts :hmm:

 

[604KJ]

So how does the re gearing process work? I would have to take it to a shop or something but what exactly would they do to it? Would it be better to take it to the dealer for this?

 

[tjkj2002]

So how does the re gearing process work? I would have to take it to a shop or something but what exactly would they do to it? Would it be better to take it to the dealer for this?

Taking to the dealership would run about $3000,any good offroad shop would do it for about half that.The most expesnive part of the whole deal on a KJ is the fact you must remove the front diff to re-gear and that is a 5.5 hour job in itself.

 

[TwoBobsKJ]

So how does the re gearing process work? I would have to take it to a shop or something but what exactly would they do to it? Would it be better to take it to the dealer for this?

NOT THE DEALER!

In essence, the stock gears in the front and rear differential are removed and replaced with the new ratio gears. It requires specialized tools and someone who knows what they are doing as the tolerances are very tight and must be done correctly the first time. If the vehicle is driven with poorly installed gears they are ruined - no such thing as "fixing" a bad installation. It has to be done over again with new gears.

Remember your 10 speed or 18 speed bike? There are two or three gears on the front spindle where the pedals are and 5 or 6 gears on the rear wheel. Regearing your Jeep is the same as swapping out the rear wheel gears on your bike - except a LOT more complex.

That said, a competent and trusted shop does this stuff everyday and will typically warranty the labor and gears.

Bob

 

[u2slow]

If I was going to have a shop do the gears, I would consider taking the front diff out beforehand to save on labour cost.

There's a good chance you'll need an intermediate shaft, bearings, and seals at the same time.

 

[604KJ]

I am now shopping around different shops for pricing, quite a wide range from 1500 - 3000+. What is the recommended ratio for me, running 31s right now and hopefully 32 or 33 next time i buy tires. The shops around here say they can only do 4.10...is that true and good enough?

 

[tommudd]

I am now shopping around different shops for pricing, quite a wide range from 1500 - 3000+. What is the recommended ratio for me, running 31s right now and hopefully 32 or 33 next time i buy tires. The shops around here say they can only do 4.10...is that true and good enough?

4.10s is it with stock front diff, rear can go lower
Can go 4.88 if you go to the JBA steel front diff
32s yes, 33s no way
32s and 4.10s works, been running them for over 80,000 miles
33s you'd need more lift, plus the steel diff and the 4.56s or 4.88s

 

[604KJ]

Cool, 4.10 it is. Thanks!

 

[ktmrider]

I am actually trying to find a front diff from a diesel. They are not that rare and the pricing on them less than what a gear set and installation would be. The rear can be done with the axle still on the Jeep.

 

[tommudd]

I am actually trying to find a front diff from a diesel. They are not that rare and the pricing on them less than what a gear set and installation would be. The rear can be done with the axle still on the Jeep.

Diesel/CRD ?

Look for 4 cylinder KJs for the front diff they had the 4.10s

Gas 2.4 KJ,auto or manual--4.10
Gas 3.7 KJ,auto--3.73
Gas 3.7 KJ,5 speed manual--3.73
Gas 3.7 KJ,6 speed manual--3.55
US CRD(auto only)--3.73
Now Export models
Export CRD with 2.8,auto--3.73
Export CRD with 2.5,auto or manual--4.10

 

[ktmrider]

Diesel ?

Look for 4 cylinder KJs for the front diff

I see..was not aware there was a 4 cyl gas.