Regearing

[Jeepmedic46]

just had my transmission rebuilt and the gentleman said I need to regear otherwise I’m going to burn the transmission out. It’s a 2000 Cherokee with the 4.0 and 3:55 gear ratio. Currently running 265/75/17 BFG Mud Terrains. Will I burn out my transmission?

 

[M Rose]

How long will your transmission last… not as long as it would if you put the proper gears in…

 

[tjZ06]

That's only about a ~32.5" tire, nothing crazy. Stock is about a 28" or 29". Not to mention tire size shouldn't "burn up" a transmission per say. Bigger/heavier wheels and tires will make you push through the torque converter a bit more, which creates heat, and heat is the enemy of an automatic transmission. And any added weight or power does mean the clutches that engage the planetaries have a slightly harder job. Regearing will counteract all of these issues, but again your tires aren't excessive and the trans should be fine especially if you add a good cooler.

-TJ

 

[Jeepmedic46]

That's only about a ~32.5" tire, nothing crazy. Stock is about a 28" or 29". Not to mention tire size shouldn't "burn up" a transmission per say. Bigger/heavier wheels and tires will make you push through the torque converter a bit more, which creates heat, and heat is the enemy of an automatic transmission. And any added weight or power does mean the clutches that engage the planetaries have a slightly harder job. Regearing will counteract all of these issues, but again your tires aren't excessive and the trans should be fine especially if you add a good cooler.

-TJ

Thank you, The way the transmission shop was talking I only had a couple of months to do a gear swap. I’ll put in a good transmission cooler. Will work on changing gears unfortunately working on a fixed income and had some unexpected things happen.

 

[MidOH]

Is that an XJ? Swapping in a manual transmission from a YJ is priceless.

This is a good excuse to invest in lockers or custom axles at the same time as regearing. I recommend an Aussie, Yukon, or Detroit auto locker up front. A selectable in the rear.

If you're careful, the auto trans will be fine. And just need another rebuild too soon. But it's not like it's going to smoke in 2 months.

Try to find a private shop that specializes in race cars and 4x4's. He'll be able to build up junkyard sourced axles for a fraction of the cost of new. A cut 8.8 rear is perfect for XJ/YJ's.

Dont fear the gear. 4.56.

 

[madcratebuilder]

A lot depends on how you use the truck. If you spend a lot time on unimproved tracks gears should be a priority. If you are mostly hiway and dirt roads, gears are not needed. A trans cooer and temp gauge would be a great investment.

 

[Shakes355]

So it's always a good idea to regear when bumping up tire size, regardless of what vehicle or transmission you have. That 4.0 is a torque machine at low RPM so Jeep was able to get away with those tall rear gears paired with the AW4. It was the best compromise for off road use and highway mileage.

That said, most XJs came with 225/70r15 (27/28") tires. 32's may not sound like a lot, but that's a big jump for the stock ratio. Depending on the gear you're in, you have dropped your running RPMs by 200-400. Not to mention the extra weight you probably carry.


So I'm inclined to agree with the shop. It's a lot of extra work being forced on the transmission. Is it an immediate concern? Depends on how you drive it, but probably not. But it will most likely shorten the life of your rebuild and provide you less margin for error if you need to beat on it.

Doing the calculations, you would need to jump up to 4.10/4.11's to get close to your stock numbers.

 

[Jeepmedic46]

I was thinking 4:10/4:11 gears. Would like to put 33s on but would have to regear to 4:56. Would put lockers in at the same time. Unfortunately no good shops around to do custom axles if I could afford them. Jeep sees mostly backroads to NH and Vermont to go fishing. Nothing challenging. Some highway. Going to put in a good transmission cooler and temperature gauge. Will have to figure out where to put that. Wonder if it would have been cheaper to put a manual in even though my wife said no before.

 

[M Rose]

I was thinking 4:10/4:11 gears. Would like to put 33s on but would have to regear to 4:56. Would put lockers in at the same time. Unfortunately no good shops around to do custom axles if I could afford them. Jeep sees mostly backroads to NH and Vermont to go fishing. Nothing challenging. Some highway. Going to put in a good transmission cooler and temperature gauge. Will have to figure out where to put that. Wonder if it would have been cheaper to put a manual in even though my wife said no before.

It would have been a lot cheaper to swap to a manual transmission… My manual swap on my Bronco (which would be more expensive than your XJ) was just under $1000.00 for all of the parts needed going from a AOD to a HD 1 ton ZF5 (very sought after transmission by Ford guys).
The NSG370 6 speed transmission found in 2005-2006 TJs can be had for as little as $600.00 from a junk yard. 5 speeds are easier to find and cheaper than that as well.

 

[MazeVX]

Well, as others said, regearing will help and makes sense for offroad. I would put a transmission cooler in anyway because heat kills your transmission...
But transmission cooler is way cheaper and even more effective on the highway so I would put that in first.

 

[Jeepmedic46]

Well, as others said, regearing will help and makes sense for offroad. I would put a transmission cooler in anyway because heat kills your transmission...
But transmission cooler is way cheaper and even more effective on the highway so I would put that in first.

Going to regear it as soon as I save up the money.

 

[Dilldog]

Gears that are not matched to tire size is a HUGE contributor to transmission failures. A combination of increased tire weight, and the tire being physically bigger thus causing the torque converter to not lock or unlock at appropriate RPMs/ speed puts more load on the transmission and builds heat, wich ultimately overheats the fluid and causes transmission failure.

If you are doing a lot of off highway or under load driving I would go for 4:10s. If you are good at keeping up on transmission services and you are primarily on the pavement, 3.55s would be OK. These rigs did come with 3.08s and the transmissions lasted just fine, not my choice but its a thing.

 

[smritte]

Going to put in a good transmission cooler and temperature gauge.

Cooler is a must and gauge will tell you everything.

Gears that are not matched to tire size is a HUGE contributor to transmission failures. A combination of increased tire weight, and the tire being physically bigger thus causing the torque converter to not lock or unlock at appropriate RPMs/ speed puts more load on the transmission and builds heat, which ultimately overheats the fluid and causes transmission failure.

This is the biggest reason for us wearing out auto trans. No one can properly advise you on the gearing unless they know not just your vehicle but how and where you drive. Are you bogging down the vehicle climbing hills? Yes? You need to regear.

What's your trans temp at with the "Correct" cooler? Yes there are diffrent designs, just adding one randomly may not be enough. Or it may be enough.

Most people don't want to regear and just accept any issues that come from it. Some will never notice any real difference and tell people not to regear thinking everyone is the same.

"I" prefer my trans temp to be at or below engine temp. The higher the temp, the faster you break down the additives in the trans fluid. Pushing over 250 degrees is where you start really breaking it down fast, 300 and up is death for ATF.
You really want to know how your trans is holding up? Send a fluid sample out to be analyzed.

My 04 TJ Rubicon. Stock build, 32" tires (at the time). The trans temp would hit close to 290 degrees driving into my local mountains. Changed out my radiator with an over sized trans cooler inside it. Temps were in the 240 range. A bit too high but I only saw that on steep mountain roads.

Later I went to 35's and my temps were 300 degrees. Regeared to 4.88's brought it back down some. Added a nice big Stacked Plate Derale cooler in front and that brought it down to around 220 degrees. Then I started pulling a trailer. Back up close to 300 on steep hills. Added another Derale cooler under the body with its own fan. Now my temps didn't go over 250 on hills with trailer. Later I ended up with 39's and 5.13 gears. The temp stayed good with and without the trailer.

All this means is, you need to know what temp your running at. The guy who built your trans probably has no actual knowledge outside of what he has seen rebuilding trans's for people.

 

[Dilldog]

Cooler is a must and gauge will tell you everything.



This is the biggest reason for us wearing out auto trans. No one can properly advise you on the gearing unless they know not just your vehicle but how and where you drive. Are you bogging down the vehicle climbing hills? Yes? You need to regear.

What's your trans temp at with the "Correct" cooler? Yes there are diffrent designs, just adding one randomly may not be enough. Or it may be enough.

Most people don't want to regear and just accept any issues that come from it. Some will never notice any real difference and tell people not to regear thinking everyone is the same.

"I" prefer my trans temp to be at or below engine temp. The higher the temp, the faster you break down the additives in the trans fluid. Pushing over 250 degrees is where you start really breaking it down fast, 300 and up is death for ATF.
You really want to know how your trans is holding up? Send a fluid sample out to be analyzed.

My 04 TJ Rubicon. Stock build, 32" tires (at the time). The trans temp would hit close to 290 degrees driving into my local mountains. Changed out my radiator with an over sized trans cooler inside it. Temps were in the 240 range. A bit too high but I only saw that on steep mountain roads.

Later I went to 35's and my temps were 300 degrees. Regeared to 4.88's brought it back down some. Added a nice big Stacked Plate Derale cooler in front and that brought it down to around 220 degrees. Then I started pulling a trailer. Back up close to 300 on steep hills. Added another Derale cooler under the body with its own fan. Now my temps didn't go over 250 on hills with trailer. Later I ended up with 39's and 5.13 gears. The temp stayed good with and without the trailer.

All this means is, you need to know what temp your running at. The guy who built your trans probably has no actual knowledge outside of what he has seen rebuilding trans's for people.

One should also note that it is possible to overcool a transmission as well. You really do want a transmission to run at around 190*F plus or minus 10*. This will ensure that the transmission will be running warm enough to cook out any or most of the condensation that will naturally occur during the heating and cooling. Minimum you want trans temps above 130* or so. Also its worth noting that most gauges go into the pan or the return line after the coolers. On average your fluid inside the transmission is 30-50* warmer. That said I typically worry when I see 200* and if I see 250* I'm replacing fluid as soon as possible. All that said, I would install a gauge first, or swing by an auto parts store and see if you can pull transmission temp from a scan tool. It is possible to simply grab a $50-100 scan tool and maybe be able to monitor transmission temp as well as much much more. I typically plug in my scan tool when I'm off pavement and keep the screen on with the live data displayed. It has kept me out of trouble a few times...

 

[smritte]

One should also note that it is possible to overcool a transmission as well. You really do want a transmission to run at around 190*F plus or minus 10*. This will ensure that the transmission will be running warm enough to cook out any or most of the condensation that will naturally occur during the heating and cooling

This is why I keep the radiator inline with the coolers. I don't think I have seen mine go under 160, even extreme cold once everything's warmed up.
You would be surprised how many people disagree with that saying it cant be too cold.

 

[Dilldog]

This is why I keep the radiator inline with the coolers. I don't think I have seen mine go under 160, even extreme cold once everything's warmed up.
You would be surprised how many people disagree with that saying it cant be too cold.

Yup, warming oil up is a seldom thought about advantage to coolant to oil coolers. They are great at maintaining an average temperature, but air to oil coolers can help cool more quickly and without transferring the heat to coolant. Even when its 100* outside, thats a lot cooler than 200*+ oil...

 

[MazeVX]

Talking about "overcooling" seems like my understanding that thermostatic control is usual and mandatory was wrong...
Oil coolers, whatever oil they may cool, should never used without a bypass flow thermostat that slowly warms up the cooler until it fully opens.
Coolant to oil coolers are very good thing especially in colder climates but adding stress to your coolant system as well, with some vehicles that can be a problem if you are in hot climate.

 

[smritte]

Coolant to oil coolers are very good thing especially in colder climates but adding stress to your coolant system as well, with some vehicles that can be a problem if you are in hot climate.

For this exact reason, I run a bypass system on my cruiser. Toyota designed my cooling system a bit subpar. Most of the year I don't run through the radiator unless I know I'm going into extreme cold. My setup is simple to divert through the radiator if needed.

 

[JDGreens]

I was thinking 4:10/4:11 gears. Would like to put 33s on but would have to regear to 4:56. Would put lockers in at the same time. Unfortunately no good shops around to do custom axles if I could afford them. Jeep sees mostly backroads to NH and Vermont to go fishing. Nothing challenging. Some highway. Going to put in a good transmission cooler and temperature gauge. Will have to figure out where to put that. Wonder if it would have been cheaper to put a manual in even though my wife said no before.

31's tires - automatic tranny - 4.10 gears
33's tires - automatic tranny - 4.56 gears
Personally if I had the chance to start over, a good running stock Xj no lift. Maybe some armor to protect the essentials. Because with all the never ending mods that money can buy. That money can be spent on so many adventures. You would be surprised at just how capable your rig is stock.

 

[Jeepmedic46]

31's tires - automatic tranny - 4.10 gears
33's tires - automatic tranny - 4.56 gears
Personally if I had the chance to start over, a good running stock Xj no lift. Maybe some armor to protect the essentials. Because with all the never ending mods that money can buy. That money can be spent on so many adventures. You would be surprised at just how capable your rig is stock.

I bought the Jeep with the lift. Would cost to much to put it back to stock.