regear questions

[LGR]

So after my lift i'm going to be looking into regearing my 00' XJ..Its a inline 6 thats going to have 33" tires and i'm pretty sure its 3.55 now but not 100%.

My questions are...

What gearing would you all reccomend for driving 70% on road use the tires and such i will have? I'd like to have it balanced and as close to factory. Using the handle gear ratio guide on the site it looks like 4.27 would be it for 33" tires.

Also, what would somthing like that cost on both axles or a ball park on how much it would cost? I don't really know any mechanics in my area so I don't want to get swindled on the job. I don't have the know how to do it myself either.

last...if anyone knows a good mechanic around northern NJ that they could reccomend.


any help would be great. Thanks

oh yeah 35 up front and a 8.25 in the rear

 

[bchcky]

are you going to keep those axles? this is one of those times you need to make an honest no BS assessment. regearing can cost a lot of money to get it done right. if you think you might upgrade from your 30/8.25 combo in the future, hold off on re-gearing. do it once, do it right. if you're set on keeping those axles for a good LONG time, maybe 4.56? depends on how much highway driving your on-road driving includes? 4.56 might be too much if you do mostly highway.

 

[Bounty__Hunter]

I'd recommend 4.56, best to error a little on the lower side. Charts and formulas only account for changing tire height, the engine will still be strained due to the added rotating mass of larger tires. Gearing slightly lower that recommended helps overcome this and keep the jeep fun to drive on the road.

I'd recommend keeping your stock axles, you have the larger 297x ujoints in the front axle (same as D44) and the 29spline 8.25, both decent setups for weekend wheelin duty on 33" tires.

Expect to pay around $1000 to have a shop regear both axles, parts and labor. There's a mech. around here that does an $850 package special, which is about the best you'd find.

 

[GaryMB]

4.11 is pretty much the standard gear ratio for 33" tires. With the engine you have, I really don't see a problem with power or acceleration with 4.11 gears. With 4.56, your highway rpm will be almost 300 higher than with 4.11's. 4.11 would be my vote, but if the Jeep doesn't see many highway miles, then 4.56 might be the better choice.

 

[pushead]

4.11 is pretty much the standard gear ratio for 33" tires. With the engine you have, I really don't see a problem with power or acceleration with 4.11 gears. With 4.56, your highway rpm will be almost 300 higher than with 4.11's. 4.11 would be my vote, but if the Jeep doesn't see many highway miles, then 4.56 might be the better choice.

Your rpms will not be that high. I run 4:56 and 35"tires and only hit 2500 rpms at 70mph.

 

[Bounty__Hunter]

4.11 isn't a standard for 33" tires, there's too many variables such as engine and transmission type, and type and amount of wheelin, to consider. The XJ has an overdrive transmission, consider 4.56 for on and offroad performance.

 

[LGR]

4.11 or 4.56...

what ratio puts less stress on the engine and drivetrain?

I would just like to be as close to the factory style driving as i can.

 

[Utah_jeepster]

4:10 if your going to stick with 33's. 4:56's is too low for a daily driver on 33's. Your best gas mileage will be around 2800-3000 RPM. 4:56's will have you running near 3200RPM.

First off the costs vary for this transplant, but expect to pay any where from 99-200$ for gears/ per axle. there is a big difference here but you get what you pay for. I paid 200$ and mine came with a master install kit, an 80$ value. BTW you will need a master install kit per axle(new shims, crush sleeve,oil slingers, seals, and ring bolts).

Second not sure on the ford 8.8 but with your dana 30 you will need a new carrier, 3:93 gears is the lowest you can run without changing carriers.
They can be any where from cheap to dang pricey! ARB's are running from 700$ or so.
Most shops charge some where around 200-450$ an axle to re-gear and install a new carrier.
This isn't your backyard mechanic type of work, it takes some specialized tooling to set your back-lash, and pinion depth. Not to mention your 'C' clip clearance if you have that type of rear axle.

So if you never had the pleasure of diving into a differential I woulds suggest you look for a competent mechanic. If your installing a selectable locker or a clutch type ask this mechanic if he installed one before. If he hasn't then find one that has! There nothing like a regular type of limited slip differential, each one has its own special quirks, from slotting bearing seats for oil drainage to special pre-loads on clutch types.

Your local 4X4 shop who sells selectable lockers should know the right mechanic to take your jeep to.
I hope this clears some of your questions up
Utah

 

[GaryMB]

Your rpms will not be that high. I run 4:56 and 35"tires and only hit 2500 rpms at 70mph.

According to this tire/gear chart http://www.4wheelparts.com/4wp/assets/!!!---CHARTS---!!!/chart_gear-ratio.htm,
the difference in rpm between 4.11 and 4.56 with 33's is 298rpm.

4.11 is probably the most practical and commonly used gear ratio with 33's, unless you are dealing with an older underpowered or heavily modified vehicle, where engine size, weight, and transmission gears are of more concern.
The Cherokee, weighing in at a max stock curb weight of 3,400lbs and with 225lb/ft, would be all but bogged down with 33's and 4.11's. I agree with Utah_Jeepster, your best gas mileage will be with 4.11's. As for the strain on the engine, 4.11 will be slightly more strain starting from a stop, and 4.56 will cause more strain at highway speeds due to increased rpm. I don't see 4.11's causing any considerable strain on the engine compared to stock, but a 300 rpm increase on the highway will accelerate engine wear by about 10% over 4.11's.

 

[Bounty__Hunter]

According to this tire/gear chart http://www.4wheelparts.com/4wp/assets/!!!---CHARTS---!!!/chart_gear-ratio.htm,
the difference in rpm between 4.11 and 4.56 with 33's is 298rpm.

Also, according to that chart, both 4.11 and 4.56 are within the green range indicating "Daily Driver, Best Overall Performance". Let's not forget that the above referenced chart is based on a manual transmission in 4th, or 1:1 gearing. That would be like his XJ staying in 3rd gear all the time and not using overdrive. Take advantage of that overdrive and gear that jeep for performance, go with 4.56.

To me, 3.55 to 4.10 isn't enough of a performance change to justify the $$ and time involved in a gear change. Make it worth your while.

If you had 3.07 stock then 4.10 would be an easier pill to swallow.

 

[currupt4130]

Heres the ultimate gear calculator, and at the bottom you can adjust your rpms and speed adn see what your results will be. This should help. It may be more info than you want, but what you want is in there too
http://www.grimmjeeper.com/gears.html

 

[GaryMB]

Corrupt, that is the most thurough gear ratio/tire size calculator I have ever seen; it's gone strait into the bookmarks. With all the options for trannies, tires, and axle ratios, it got me thinking about modding my Jeep...

 

[redrooster]

All these graphs, charts and calculators are nice and all, but as a general rule of thumb...If you want it to drive like a daily driver then use the following. You increase the tire size by 20% then change your gear reduction by 20%. Then it is up to you to round up or down based on whether you want to err towards off road prowess or highway performance.
BTW...Personally, I would go 4.10 with the automatic (torque converter will help you out off road). If you wanted to increase the off road performance at a later date, then you could put a 4:1 in the transfer case.

 

[Bounty__Hunter]

All these graphs, charts and calculators are nice and all, but as a general rule of thumb...If you want it to drive like a daily driver then use the following. You increase the tire size by 20% then change your gear reduction by 20%. Then it is up to you to round up or down based on whether you want to err towards off road prowess or highway performance.
BTW...I would go 4.56.

Well put. But would you agree that changing the ratio by the same percentage of change in tire height only accounts for a change in tire diameter, thus keeping rpm's relatively the same at any given speed? What about the added tire mass, 33"s are a lot heavier than OEM 28"s. Wouldn't most jeepers want to err on the lower gear side to help get those heavier tires moving?

 

[GaryMB]

It's a compromise; 4.56 for better low speed performance and 4.10 for better highway performance and fuel economy. The 4.56 would help with the increased mass of the tires, but if it were up to me, I would look elsewhere to compensate for this...such as engine mods and weight reduction, but that's another story. I really don't think there would be a need to compensate for power loss with 33's and 4.10's on a 4.0L Cherokee, though...the Jeep would still be pretty quick and go slow offroad. It just comes down to personal preference.

 

[Bounty__Hunter]

I've got 32" and 4.10 in my MJ with the same AW4 auto the XJ uses, and it isn't slow enough on the trail, be even worse with 33" tires.

 

[redrooster]

Well put. But would you agree that changing the ratio by the same percentage of change in tire height only accounts for a change in tire diameter, thus keeping rpm's relatively the same at any given speed? What about the added tire mass, 33"s are a lot heavier than OEM 28"s. Wouldn't most jeepers want to err on the lower gear side to help get those heavier tires moving?

Whoa, you are causing me to use brain cells that have dissipated since I took my last power transmission class.
It is my understanding that: It does account for the changing tire diameter and engine RPM should also remain constant. Here's where we disagree, lowering your gear ratio also increases the amount of torque at the wheels. Reduction gearsets are torque multipliers, effectively. Therefore, lowering your ratio increases torque. You are correct that most wheelers will favor to the lower gear.
Where the rotating mass of a heavier tire comes into play is in relation to axle shaft strength (and braking power, but we'll leave that alone). Increased torque coming from lower gear sets plus the added rotating mass of larger tires can be beyond the strength of the shaft. This is why when you see an axle break, it is usually due to an abrupt tire stop with the engine at considerable RPM's (ie. hopping or suddenly finding traction).