Manual Gear ratio?

LetFreedomRing · **Joined:** Mon Jun 28, 2010 8:51 am **Posts:** 268

I know I read this somewhere on here before (prior to me getting my liberty) but I can't seem to find it?

I know the automatics come with 3.73 ratios but what does the standard come with? I think I may have gotten a rare manual.

Do the manuals come with 3.55s? Or is that the 6-speed only?

HoosierJeeper · **Joined:** Sun Feb 15, 2009 8:23 am **Posts:** 1218

tjkj2002 · **Posted:** Wed Aug 11, 2010 6:43 pm

If you have the 5 speed manual you get 3.73's,only the 6 speed manual KJ's got the 3.55's.

infernicus · **Posted:** Wed Aug 11, 2010 9:33 pm

tjkj2002 wrote:

If you have the 5 speed manual you get 3.73's,only the 6 speed manual KJ's got the 3.55's.

I remember hearing this as well. But thought I read differently on my build sheet, guess I was wrong.
Why did they change the gears? How does that affect daily driving/off roading?

InCommando · **Posted:** Thu Aug 12, 2010 12:28 am

the 6 spd has the lowest crawl ratio found in the KJ, and that is the most common measure of "off road ability" when used in this context. They go 42 auto/45 auto/5spd/6spd in ascending order.

You can go here: http://www.grimmjeeper.com/gears.html
and enter the numbers for yourself to prove it. just pick your tranny/tcase/gear ratio/tire size & this (or several other websites) will prove it. Keep the tire size constant for a true reading.

Some people will talk about torque mutiplication with an auto, but they ignore the basic ineffeciences of the auto & the slippage on the convertor. There is a reason none of the calculators use that nonsense. A 3.7 automatic KJ DOES NOT deliver 590 ft/bs of TQ to the ground due to "2.5 mutiplication"... :ROTFL:

I guess tht is why all of the OTR trucks use auto's to more than double the torque of their engines.. :-)r

Now, if you can't handle driving a stick like so many people these days the auto is best off road. But that is because of driver shortcomings, not tranny shortcomings. The 6spd also has the highest top gear for increased MPG potential and enough gear choices to "split gears" and drive as effeciently as possible. Again, that is IF you an drive a stick. Drive a tankful keeping to a max of 1,800 - 2,000 RPM and no more than 65 MPH and you will be amazed at your mileage.

tjkj2002 · **Posted:** Thu Aug 12, 2010 1:20 am

InCommando wrote:

the 6 spd has the lowest crawl ratio found in the KJ, and that is the most common measure of "off road ability" when used in this context. They go 42 auto/45 auto/5spd/6spd in ascending order.

You can go here: http://www.grimmjeeper.com/gears.html
and enter the numbers for yourself to prove it. just pick your tranny/tcase/gear ratio/tire size & this (or several other websites) will prove it. Keep the tire size constant for a true reading.

Some people will talk about torque mutiplication with an auto, but they ignore the basic ineffeciences of the auto & the slippage on the convertor. There is a reason none of the calculators use that nonsense. A 3.7 automatic KJ DOES NOT deliver 590 ft/bs of TQ to the ground due to "2.5 mutiplication"... :ROTFL:

I guess tht is why all of the OTR trucks use auto's to more than double the torque of their engines.. :-)r

Now, if you can't handle driving a stick like so many people these days the auto is best off road. But that is because of driver shortcomings, not tranny shortcomings. The 6spd also has the highest top gear for increased MPG potential and enough gear choices to "split gears" and drive as effeciently as possible. Again, that is IF you an drive a stick. Drive a tankful keeping to a max of 1,800 - 2,000 RPM and no more than 65 MPH and you will be amazed at your mileage.

Manuals break more parts offroad,the clutch does not absorb the driveline shock like the TC in a auto can.Oh and that "slippage" in the TC in a auto is the torque mulitplication,it's called stall speed and why auto's do not need low 1st gears like manuals do.

Don't be hating since your 6 speed is weaker then a 42RLE,that is fact.

infernicus · **Posted:** Thu Aug 12, 2010 1:28 am

So what would happen if I were to re-gear to 4.11s.. is that possible in the 6spd?

tjkj2002 · **Posted:** Thu Aug 12, 2010 1:31 am

infernicus wrote:

So what would happen if I were to re-gear to 4.11s.. is that possible in the 6spd?

Yes

cmohr · **Posted:** Thu Aug 12, 2010 1:56 am

That 6 speed box is matched to the 3.55 gears, if you put in 4.10s you would probably have a top speed of 50mph....

My 2.5 CRD 5 speed manual came with 4.10's. I'm running 31/10.5/15's on it and gear ratio is good. In 4Lo the crawl is excellent, I reckon it could idle up a tree. But, Honestly on the highway I could do with an extra top gear, actually thought of putting on 32's to see what its like, since at the moment at 60mph revs at 2300, the CRD would happily still pull along at 1800 if it had the gearing. I currently get 22-23 MPG city driving, and 29-31 MPG Hwy.

LetFreedomRing · **Joined:** Mon Jun 28, 2010 8:51 am **Posts:** 268

tjkj2002 wrote:

If you have the 5 speed manual you get 3.73's,only the 6 speed manual KJ's got the 3.55's.

Ok thanks! That would explain why I have 3.73 axle on my build sheet. For some reason I thought I read that the 5 speed manuals came with 4.10s? :oops:

InCommando · **Posted:** Thu Aug 12, 2010 11:14 am

ALL 4 cyl KJ's got 4.10's, IIRC, so a 5 spd 4 popper may have had 4.10's.

As very few people are switching to 4.10's without adding taller tires that drops the final drive ratio back down, 4.10's and stock tires with a 6spd probably is a pretty rare thing. IF you did not change tires your RPM at 65 MPH would go from 2,193 RPM to 2,513 RPM's, hardly a huge difference. If you went to the ever popular 245/75/16's, the RPM # changes to 2,435. If you think you can't run your 3.7L at 2,500 RPM's all day, be sure you don't ever go over 50 MPH. :mrgreen:

Yeah, the T18, 435, etc... are all such weak trannies they break stuff internally constanty... :ROTFL:

manuals are, as a rule, stouter than an auto and suffer less from water damage or F-ed computer control & obvioulsy no convertor/lock-up issues like an auto. Again, auto's rock so hard that you constantly see them in OTR trucks, pro stock drag racers, earth moving machinary... :roll:

Drive train shock is controled by the driver. The key word there is DRIVER. Some people with no skill or finesse probably can't control themselves or their rigs. They are better off with slush boxes. :wink:

At least that " an auto makes 2.5 times more torque than a stick" stuff went away....

I know of no one breaking a 6spd in a KJ. I have power shifted and dumped the clutch on mine dozens of times w/o issues. I have read of many issues with the auto's, including water issues. I have a ton of off-road experience with 727's, the 45's granddaddy. Some little bit with a 518. Of course, some people can tear up an anvil, so actual mileage may vary.

infernicus · **Posted:** Sat Aug 14, 2010 2:26 am

Ok, so..
I have a six speed manual that has the 3.55s. Is it worth the time/money to switch out to 3.73s, since they are probably easy to find?
Would I gain anything to make it noticeable? Or just go all out to 4.10s?

Also, is it beneficial across the board? IE: lower rpms? faster speeds?

(In reality I don't know much about the benefits of the different gears.)

InCommando · **Posted:** Sat Aug 14, 2010 8:50 am

Gears are a bit confusuing. Gears that have a higher number, like 4.10, are referred to as being "lower." The higher the number, the lower the gears.

For on road:
As a general rule, that factory ratio is the most balanced for the power/effeciency trade off. Putting lower numbered gears (higher gears) in will lower your engine RPM at any given speed, but you may lose power and drop out of the most effeciencent RPM range if you just change gears. Putting higher numbered gears in can improve performance, especialy light-to-light performance, but at a cost of efficiancy due to running higher RPM's.

The best time to change ratios, IMHO, is when you put larger diameter (taller) tires on your jeep. You can pick a ratio that returns your vehicle to near the factory balance, or if you want to go more hard core off-road, you can go higher numerically. IIRC, 4.10 is as low as you can go with the D30a front diff.

If you have a 6spd, you can go to 3.73's and restore near factory balance if you go to a taller tire. The advantage is that you may be able to find used gears from someone switching from the factory 3.73's. I don't think aftermarket gears would be any cheaper. If you wished more light-to-light speed or slow speed off-road control, switching a 6spd to 4.10's would be ideal and would mimic an auto running 4.30 or 4.56 gears. :wink:

The factory crawl ratio of a 6spd KJ is almost identical to that of an automatic Rubicon. Putting 4.10's in a stock 6spd with no tire size changes would give you an outstanding 55:1 crawl ratio.

hooperswish · **Posted:** Sat Aug 14, 2010 2:13 pm

tjkj2002 wrote:

InCommando wrote:

Don't be hating since your 6 speed is weaker then a 42RLE,that is fact.

I don't know about that, but I do know that we 6 speeds get a beefier transfer case.

InCommando · **Posted:** Sun Aug 15, 2010 6:08 am

LOL. TJKJ argues that the 231 & 241 are the same t-case.... :ROTFL:

2006 KJ · **Posted:** Sun Aug 15, 2010 12:33 pm

from everything i've read my 6-speed has 3.55's.. a stronger t-case.. better crawl ratio.. and a few other electronic giz-mo's that auto's dont when in 4 lo (throttle raises, neutral start switch lets it start in gear.. few others). Also i can get away with running 265/75 mudders with steel wheels because of the real low 1st gear. I get 16 mpg now with the stock 3.55 gears... when i had stock jeep and stock tires/no lift/ no roof lights/ alum. wheels.. i got 20-23 mpg

however i DO want to go to 4.10's with my 32's.. i think it would make my jeep into a monster power wise and gas milage wise. i think it would be a waste spending all the $ to go to 3.73's.. if your changing gears go right to 4.10's

Manual Gear ratio?

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