37" on Rubicon 4.10 axle ratio. Auto shifts aggressively.

Dubaibentzen

Dubaibentzen

New member
A question for those running 37" tires.

I have just installed 37" tires on a set of Rubicon axles with 4.10 axle ratio. The acceleration is off course not the same as stock.(I know 4.88 or 5.13 will be better... I'll get there...)
But now when I drive, the automatic shifter makes a sudden "jump" when going in the last gear. This is typically on the highways after accelerating and the when it wants to "settle" in the last gear for cruising. Took my wife for a drive today, and she asked me: "Wow - is that normal?" Also happens on slight hills.

Anything I can do for now to fix it, or is that just the way it is until I regear?

Help appreciated :thumb:
 
mudmobeeler

mudmobeeler

Caught the Bug
Interesting, Im trying to figure out how the hell to get 37s on my jeep and will most likely have to rock the factory axles and 4.10 gears for a bit. Gonna watch this thread.
 
A.J.

A.J.

Active Member
Dubaibentzen said:
A question for those running 37" tires.

I have just installed 37" tires on a set of Rubicon axles with 4.10 axle ratio. The acceleration is off course not the same as stock.(I know 4.88 or 5.13 will be better... I'll get there...)
But now when I drive, the automatic shifter makes a sudden "jump" when going in the last gear. This is typically on the highways after accelerating and the when it wants to "settle" in the last gear for cruising. Took my wife for a drive today, and she asked me: "Wow - is that normal?" Also happens on slight hills.

Anything I can do for now to fix it, or is that just the way it is until I regear?

Help appreciated :thumb:
Click to expand...

Just to clarify. You are saying the shift lever jumps? Or the vehicle feels like it jumps/lurches going in to highest gear?

As far as running 4.10's with 37"s I would turn the overdrive off always. Highway driving it will just be shifting up and down all the time. Overdrive will be worthless unless you are going downhill above 70mph with a tail wind.
 
MTG

MTG

Caught the Bug
I assume this happens after revving at high RPMs? You have a 2013, just manually shift into the last gear. For what it's worth I had 4.10s for a long time with 37s. Drove across the U.S. and did plenty of wheeling. Would have never changed, except that I live at altitude and drive up a pretty large hill every day.
 
Dubaibentzen

Dubaibentzen

New member
A.J. said:
Just to clarify. You are saying the shift lever jumps? Or the vehicle feels like it jumps/lurches going in to highest gear?

As far as running 4.10's with 37"s I would turn the overdrive off always. Highway driving it will just be shifting up and down all the time. Overdrive will be worthless unless you are going downhill above 70mph with a tail wind.
Click to expand...

Shift lever stays the same. It's an 2013 JKU Sahara Automatic transmission. I swapped the axles from a 2014 2 door Rubicon. I used a Procal to set the axle ratio to 4.10 and have set the tire size to 36. Maybe I should measure it again more precisely.

It's just the car that makes kind of a bump when it comes to a rest after the acceleration.

How do I turn off the overdrive?
 
Dubaibentzen

Dubaibentzen

New member
MTG said:
I assume this happens after revving at high RPMs? You have a 2013, just manually shift into the last gear. For what it's worth I had 4.10s for a long time with 37s. Drove across the U.S. and did plenty of wheeling. Would have never changed, except that I live at altitude and drive up a pretty large hill every day.
Click to expand...

Yup, it's after revving at high RPMs
 
DWiggles

DWiggles

Caught the Bug
get out and actually measure your tires, then as a double check, compare your speedo to a GPS (phone GPS works fine) to make sure you have the tires programmed correctly. this should help a lot :yup:
 
DWiggles

DWiggles

Caught the Bug
wayoflife said:
You're measuring too high. You need to measure up to the shoulder, the point where the sidewall turns 90 degs and becomes the tread. OR, you need to measure from the center of your wheel to the ground and x2.
Click to expand...

This :thumb: Almost there!
 
Dubaibentzen

Dubaibentzen

New member
wayoflife said:
You're measuring too high. You need to measure up to the shoulder, the point where the sidewall turns 90 degs and becomes the tread. OR, you need to measure from the center of your wheel to the ground and x2.
Click to expand...

Thanks. I'll measure again and run the procal again.
 
A.J.

A.J.

Active Member
Dubaibentzen said:
Shift lever stays the same. It's an 2013 JKU Sahara Automatic transmission. I swapped the axles from a 2014 2 door Rubicon. I used a Procal to set the axle ratio to 4.10 and have set the tire size to 36. Maybe I should measure it again more precisely.

It's just the car that makes kind of a bump when it comes to a rest after the acceleration.

How do I turn off the overdrive?
Click to expand...

You just choose 4 as your highest gear to shift to. 5th is overdrive. You do this manually with the shifter. Earlier models have overdrive button. Get calibration right first though as others have said.
 
Coop

Coop

Caught the Bug
What psi are you running in your 37s? The shops always air them up over 40 psi. You will want to run under 30.
I ran 4.10s with my 37s for a while and my 5th gear would not engage much at all, but it didn't shift hard like you described when it did engage.
Have you changed your fluid on your tranny?
 
Dubaibentzen

Dubaibentzen

New member
I have now measured from ground to center x 2 and came up with 17.5 x 2 = 35. I have done the Procal again and set the tires to 35. Speedo is now correct.
Not sure if fluid on the tranny has been changed.
It still shifts a but abruptly, but only in the last gear. It's probably the overdrive, and I will live with it for now and see if it gets better once I regear to 5.13.

Anybody with 5.13 having issues with overdrive on 37" tires?
 
jeeeep

jeeeep

Hooked
did you already have a procal tune on it for your other tires before the 37's??

you don't want to let it jump on that last gear or you could cause greater transmission damage. you may want to lock out OD
 
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Dubaibentzen

Dubaibentzen

New member
jeeeep said:
did you already have a procal tune on it for your other tires before the 37's??

you don't want to let it jump on that last gear or you could cause greater transmission damage. you may want to lock out OD
Click to expand...

No procal before. I bought it used with everything stock and went straight to building. As soon as the 37s were on I Procalled it. How can I lock out overdrive, when it's an automatic 2013. There's no OD button.
 
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