Gearing after lift
JK Freak
Joined: Dec 2010
Posts: 946
Likes: 0
From: Philadelphia, PA
gears are pretty much optional u dont HAVE to do them but they will help u not feel sluggish, i have 35's right now with stock gears and u can feel the lose in power or whatever but its nothing unbearable ya know
i just saw ur doing a 4inch lift, u might wanna worry about ur driveshafts before gears
i just saw ur doing a 4inch lift, u might wanna worry about ur driveshafts before gears
JK Junkie
Joined: Nov 2010
Posts: 3,802
Likes: 3
From: Kitchener
Originally Posted by dillUSMC
gears are pretty much optional u dont HAVE to do them but they will help u not feel sluggish, i have 35's right now with stock gears and u can feel the lose in power or whatever but its nothing unbearable ya know
i just saw ur doing a 4inch lift, u might wanna worry about ur driveshafts before gears
i just saw ur doing a 4inch lift, u might wanna worry about ur driveshafts before gears
JK Junkie
Joined: Nov 2010
Posts: 3,802
Likes: 3
From: Kitchener
Originally Posted by dillUSMC
gears are pretty much optional u dont HAVE to do them but they will help u not feel sluggish, i have 35's right now with stock gears and u can feel the lose in power or whatever but its nothing unbearable ya know
i just saw ur doing a 4inch lift, u might wanna worry about ur driveshafts before gears
i just saw ur doing a 4inch lift, u might wanna worry about ur driveshafts before gears
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
Stickied to the top of this modified area are some faq's. Open the drivetrain section and look at the rpm charts.
Assuming you have 3.73's currently and not 3.21's, and assuming your 35's will actually measure 34":
Auto, 3.73, 34" tires = 1781 rpm @ 70 mph
That sucks, and you won't be happy at all, so you will live with OD turned off all the time.
The od gear is .69, so:
1781 / .69 = 2581 rpm @ 70 mph with od off.
Not optimal, but may be acceptable until you get around to new gears. Drive it and decide for yourself.
The driveshafts are the long tubes that run from the front and rear axles up to the transfer case. There are joints on both ends of both shafts. As you lift higher, those joints have to work at steeper angles than they were designed for, and it is not uncommon to have issues. These stock joints are not serviceable and not repairable, so the entire shaft has to be replaced. If you replace with another stock driveshaft, the same thing will just keep happening, so most choose to replace with an aftermarket shaft with different joints.
When you crawl underneath, you are looking for grease being slung out of those joints. It is pretty easy to tell if one is bad, as you can see and feel the grease at the joint and will also see a big ring of grease splattered across the undercarriage above the joint.
The general course of events is :
Lift, steeper angles cause the boots in the joints to pinch, boot eventually wears through, joint starts spitting grease, joint dries out, joint makes noise, joint seizes. If you happen to be at freeway speeds when it seizes, post a pic for us, we like carnage.Hopefully just the joint snaps, but it is not unheard of for to loose the gears and/or the tcase also.
Assuming you have 3.73's currently and not 3.21's, and assuming your 35's will actually measure 34":
Auto, 3.73, 34" tires = 1781 rpm @ 70 mph
That sucks, and you won't be happy at all, so you will live with OD turned off all the time.
The od gear is .69, so:
1781 / .69 = 2581 rpm @ 70 mph with od off.
Not optimal, but may be acceptable until you get around to new gears. Drive it and decide for yourself.
Why is that???? Learning here..... What are the driveshafts and located where ? I'd like to check the condition of mine out
When you crawl underneath, you are looking for grease being slung out of those joints. It is pretty easy to tell if one is bad, as you can see and feel the grease at the joint and will also see a big ring of grease splattered across the undercarriage above the joint.
The general course of events is :
Lift, steeper angles cause the boots in the joints to pinch, boot eventually wears through, joint starts spitting grease, joint dries out, joint makes noise, joint seizes. If you happen to be at freeway speeds when it seizes, post a pic for us, we like carnage.Hopefully just the joint snaps, but it is not unheard of for to loose the gears and/or the tcase also.
JK Junkie
Joined: Nov 2010
Posts: 3,802
Likes: 3
From: Kitchener
Originally Posted by nthinuf
Stickied to the top of this modified area are some faq's. Open the drivetrain section and look at the rpm charts.
Assuming you have 3.73's currently and not 3.21's, and assuming your 35's will actually measure 34":
Auto, 3.73, 34" tires = 1781 rpm @ 70 mph
That sucks, and you won't be happy at all, so you will live with OD turned off all the time.
The od gear is .69, so:
1781 / .69 = 2581 rpm @ 70 mph with od off.
Not optimal, but may be acceptable until you get around to new gears. Drive it and decide for yourself.
The driveshafts are the long tubes that run from the front and rear axles up to the transfer case. There are joints on both ends of both shafts. As you lift higher, those joints have to work at steeper angles than they were designed for, and it is not uncommon to have issues. These stock joints are not serviceable and not repairable, so the entire shaft has to be replaced. If you replace with another stock driveshaft, the same thing will just keep happening, so most choose to replace with an aftermarket shaft with different joints.
When you crawl underneath, you are looking for grease being slung out of those joints. It is pretty easy to tell if one is bad, as you can see and feel the grease at the joint and will also see a big ring of grease splattered across the undercarriage above the joint.
The general course of events is :
Lift, steeper angles cause the boots in the joints to pinch, boot eventually wears through, joint starts spitting grease, joint dries out, joint makes noise, joint seizes. If you happen to be at freeway speeds when it seizes, post a pic for us, we like carnage.Hopefully just the joint snaps, but it is not unheard of for to loose the gears and/or the tcase also.
Assuming you have 3.73's currently and not 3.21's, and assuming your 35's will actually measure 34":
Auto, 3.73, 34" tires = 1781 rpm @ 70 mph
That sucks, and you won't be happy at all, so you will live with OD turned off all the time.
The od gear is .69, so:
1781 / .69 = 2581 rpm @ 70 mph with od off.
Not optimal, but may be acceptable until you get around to new gears. Drive it and decide for yourself.
The driveshafts are the long tubes that run from the front and rear axles up to the transfer case. There are joints on both ends of both shafts. As you lift higher, those joints have to work at steeper angles than they were designed for, and it is not uncommon to have issues. These stock joints are not serviceable and not repairable, so the entire shaft has to be replaced. If you replace with another stock driveshaft, the same thing will just keep happening, so most choose to replace with an aftermarket shaft with different joints.
When you crawl underneath, you are looking for grease being slung out of those joints. It is pretty easy to tell if one is bad, as you can see and feel the grease at the joint and will also see a big ring of grease splattered across the undercarriage above the joint.
The general course of events is :
Lift, steeper angles cause the boots in the joints to pinch, boot eventually wears through, joint starts spitting grease, joint dries out, joint makes noise, joint seizes. If you happen to be at freeway speeds when it seizes, post a pic for us, we like carnage.Hopefully just the joint snaps, but it is not unheard of for to loose the gears and/or the tcase also.
I just got regeared in MAY I'd have to dish out all that cash AGAIN plus MORE????
Last edited by robsjeep9; Jul 23, 2011 at 03:29 AM.
JK Freak
Joined: Apr 2011
Posts: 847
Likes: 0
From: Texas
As I was told by the guys that i bought my lift from, JEEP - Just Empty Every Pocket 
I have an automatic with a 3.5", as they explained to me, I'll want to eventually change my front DS if i go off-road often. What happens is the front DS boot will rub on the transmission pan wear through the boot causing the shaft to eventually fail. Depending on how often and how aggressive you are off-road will determine how soon you'll need to replace it - they ran theirs for 3 years before having to replace. It all depends on how quickly it wears through the boot.
The replacement Front DS is not as big in diameter, but thicker walled making it stronger and no boot to worry about. If i would've gone with the 4" or greater lift, I would definitely need front and rear as the angle is steeper and the rear DS would separate during articulation.
I'm just quoting the experts....
I have an automatic with a 3.5", as they explained to me, I'll want to eventually change my front DS if i go off-road often. What happens is the front DS boot will rub on the transmission pan wear through the boot causing the shaft to eventually fail. Depending on how often and how aggressive you are off-road will determine how soon you'll need to replace it - they ran theirs for 3 years before having to replace. It all depends on how quickly it wears through the boot.
The replacement Front DS is not as big in diameter, but thicker walled making it stronger and no boot to worry about. If i would've gone with the 4" or greater lift, I would definitely need front and rear as the angle is steeper and the rear DS would separate during articulation.
I'm just quoting the experts....
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JK Newbie
Joined: Jul 2011
Posts: 49
Likes: 0
From: Melbourne, Victoria AUSTRALIA
Originally Posted by robsjeep9
Like he said..... It's bearable...,,, I added a Superchip first.... Eventually regeared to Yukon 5.13's BETTER for sure
I have the above and wasn't sure to go for 4.88 or 5.13 gears...
JK Enthusiast
Joined: Aug 2010
Posts: 415
Likes: 0
From: Kelowna, BC
I'm running 35 x 12.50s on a TF2.5" coil lift. Around town the power is ok, but offroad it blows goats!!!
I have front and rear Trutracs and rear gears sitting in my garage. I'm jyst waiting for the front gears to arrive. There seems to be a big back order on superior 4.56s for the D30. :(
I have front and rear Trutracs and rear gears sitting in my garage. I'm jyst waiting for the front gears to arrive. There seems to be a big back order on superior 4.56s for the D30. :(