4.88's installed, 6-spd Sport S, 37's - Finally

Jt-wrx

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Finally, Yukon Gears, got it back yesterday, have been working through break in now but can say it's worth it.

I can no throttle clutch crawl through drive thru now lol

Here's actual rpm data in both km/h and mph for Jeepers on both sides of the border.

*Sport S, 6-speed, 4.88, Mopar lift, 37x12.50 Falken MT's. GPS matched km/h, Tazer tire height 36.45", July 3, 2020.
Gearspeedrpmspeedrpmspeedrpm
4th110310012034501303700
5th110250012028001303000
6th110225012025001302700

*Sport S, 6-speed, 4.88, Mopar lift, 37x12.50 Falken MT's. GPS matched mph, Tazer tire height 36.45", July 3, 2020.
Gearspeedrpmspeedrpmspeedrpm
4th683100753450813700
5th682500752800813000
6th682250752500812700

My goal was 24-2500 rpm in 6th at 120 km/h (75 mph) and it does 2500 now. Goal achieved. I was driving essentially a 4-speed manual with the 3.73's and it was only happy on the street. Now i have fully useable 6-speed with no extra fluff at the top end, i don't want to do more than 75 mph in this thing.

3500 RPM Shifts
1st into 2nd = 25 km/h (16 mph)
2nd into 3rd = 47 km/h (29 mph)
3rd into 4th = 82 km/h (51 mph)

Note: with 3.73's and 35's...this 4.88's and 37's is now exactly 500 rpm higher for the same speeds.

Lastly, my Captain America dash light is coming on and saying the start/stop system needs service, even though i changed the tazer setting to 4.88's when i left the shop. Comes on after each start and get to about 40 km/h. Will have to dig into this, surely it's a simple fix. I have it disabled in the tazer settings so unsure whats up.

 

hjdca

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Thanks so much for this. This is the first rpm/gear ratio mapping with the six speed manual that I have seen. I was leaning towards 5:13s, but, your data tells me that 4:88s are fine.
 

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JT-wrx, from your experience, I'm thinking 35" tires with 4.88 gears would then be the right selection for those of us in a lot of mountain passes? I must admit my stock rubicon 6MT is piss poor at climbing and even worse at descending steeper paved highways.
 
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Jt-wrx

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I’ve done the breakin and now some towing. Jeep and trailer on scale went 8928 lbs. I know the Jeep alone with my gear and changes is 5150 lbs. So my aluminum 6’x6’x14’ triton dual axle cargo trailer I built vanlife style for camping and all the gear we drug along is 3400 lbs and me and the kids total the remaining 380 lbs. Trailer started life at 1800 dry. We had 3 mountain bikes, 3 paddle boards, fuels, foods, water enough to go nearly a week.
So towed all that about 550 kms, it was fantastic, 5th gear at 110-115 km/h (68-71 mph) was 2500-2700 rpm, cruise control very useful now and it was on and held most everything, only had to drop a gear on the bigger valleys where you crossed water. But this trip east of the mountains so fairly normal.
During breakin I was holding 6th gear at 120-123 km/h (75-76 mph) at 2500 rpm or 2550 rpm and held some pretty substantial hills on cruise, it’s make you smile useful. I feel like 35’s for my set up would be a little too short, too many rpm. I haven’t pulled the mountains yet with trailer but not even remotely worried I didn’t get enough gear. There will be more 3rd gear pulls no doubt and 4th maintenance for a lot of 60 mph type stuff and some 5th on the straights and valley floors.
I don’t do much hardcore off-roading if that’s what you’re asking but for the little bit I do this setup will be more than up to the task. If you want on 35’s and what I just described for abilities then get the next size under 4.56 maybe? 4.88’s would let you step up to 37’s no prob I guess. From recollection 4.88’s and 37’s is slightly stouter than stock 4.10’a and 33’s. I am beyond happy with my set up now.
 
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Jt-wrx

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Also, if I was imagining mountains without the trailer then it’s just not even a thing for my set up. I do think you’ll find 4.88’s and 35’s are going to rev too high for tastes at 75 mph in 6th. There’s good power from 24-2600 rpm. That’s where I wanted to land at that speed in 6th. Hope that helps.
 


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Understood. With the sad minivan motor and 16% grades, I think my best option may be the 4.88 even though I do go 80mph frequently.

It is sad to me that a 15 year old Nissan 4x4 is better at climbing and descending mtn passes. Once again, thanks for the Barbie minivan motor, Jeep. You will not be forgiven for this.
 
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Jt-wrx

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More to report on this towing expedition, i am back now, did approx. 700 miles. On the return trip, steady 15 mph headwinds kept me in 4th gear at 64 mph(3000 rpm) all the way home, average over the whole trip was 19.8 l/100km or 11.9 mpg. 5th gear would dog down to about to about 66 mph and seemed a little bogged, felt better in 4th at higher rpms, held hills and cruise control etc. Makes sense i'd lose a gear as 15 mph headwinds (23 km/h) against the flying brick are the real deal. ;)

Note: so i just watched the oil pressure gauge on the way home and ran the speed upward until it started to add the second stage and backed it off to that 64 mph(103 km/h) to where it only ran on the stage 1 oil pump 32-33 psi (stage 2 it jumps to 76-78 psi, somewhere a little over 3000 rpm).

Anyway, wouldn't want to tow more than about 4000 lbs with a jeep truck regardless of transmission. I felt this way about my pentastar 8 spd ram also, even though it had a 7200lb tow rating it was just so much more comfortable with about half that. I approach most towing situations like that, whatever the rating is, my goal will be half that. A supercharger would be nice if i needed to do this a lot. Probably get better mileage and always be able to run 70-75 mph barely ever requiring a downshift.

I live at about 4000' elevation if anyone curious. Magnaflow cat back is only engine type mod i have.

Overall i'm super happy, there's only so much a little pentastar brick can do. The 4.88's and 37's is the absolute right combo for me. Have read many times how big a difference this mod is but i totally understand it now. Towing did awesome, running empty is better than it was off the lot, she's got some pep in her step now, power and go all over.
 

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More to report on this towing expedition, i am back now, did approx. 700 miles. On the return trip, steady 15 mph headwinds kept me in 4th gear at 64 mph(3000 rpm) all the way home, average over the whole trip was 19.8 l/100km or 11.9 mpg. 5th gear would dog down to about to about 66 mph and seemed a little bogged, felt better in 4th at higher rpms, held hills and cruise control etc. Makes sense i'd lose a gear as 15 mph headwinds (23 km/h) against the flying brick are the real deal. ;)

Note: so i just watched the oil pressure gauge on the way home and ran the speed upward until it started to add the second stage and backed it off to that 64 mph(103 km/h) to where it only ran on the stage 1 oil pump 32-33 psi (stage 2 it jumps to 76-78 psi, somewhere a little over 3000 rpm).

Anyway, wouldn't want to tow more than about 4000 lbs with a jeep truck regardless of transmission. I felt this way about my pentastar 8 spd ram also, even though it had a 7200lb tow rating it was just so much more comfortable with about half that. I approach most towing situations like that, whatever the rating is, my goal will be half that. A supercharger would be nice if i needed to do this a lot. Probably get better mileage and always be able to run 70-75 mph barely ever requiring a downshift.

I live at about 4000' elevation if anyone curious. Magnaflow cat back is only engine type mod i have.

Overall i'm super happy, there's only so much a little pentastar brick can do. The 4.88's and 37's is the absolute right combo for me. Have read many times how big a difference this mod is but i totally understand it now. Towing did awesome, running empty is better than it was off the lot, she's got some pep in her step now, power and go all over.
Nice rig. I see this is an older thread. Any updates? I just went 37s and stock gears for now but looking to re gear soon.
 

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Did you ever figure out the ASS service light issue?
 


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I just re-geared as well 4.88 with 35's 6MT. So far still doing my break in however am also getting the captain America light once the jeep warms up and oddly.. rear camera doesn't work once the light is triggered.

I am taking the jeep back to the shop that installed it to take a look. They used flash cal to adjust.

I am curious what the shop can do.
 
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Jt-wrx

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ya that's what happened to mine, dealership had to do it, 4wp didn't know what to do with that for me

as for an update, i've been running these 4.88's on 37's for quite awhile and i love it, right choice, it's super fun to drive, my mileage is going down because it's too much fun to drive and i'm ripping the gears quite a bit more with the music from the magnaflow street side exit and how much zip there is, i drive more like my little redneck sportscar...so ya, i fully endorse this set up ;)
 

Food2000

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I took my jeep back and the shop that installed the Arb lockers and regear couldn't figure it out.

However i Fixed Auto-stop light /ess and rear camera not working.

Per the the below forum link, from my understanding at least for the 6 speed manual trans... there's a secondary battery and you have to take of the negative cable along with separating the two lines to the negative cable (1 for the secondary cable) and also unbolt the negative to the frame.

- per the forum discussion below, it seems they had the exact same issue with ESS / auto stop light and rear camera not working.

Wrangler Forums: https://www.jlwranglerforums.com/forum/threads/ess-broken-after-regearing.11852/

I called the dealership and they said $340 for the flash / reset (brutal). Just gotta take off the negative for a bit!

dfgd.PNG
 

cgflyer

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Nice rig. I see this is an older thread. Any updates? I just went 37s and stock gears for now but looking to re gear soon.
I'm mounting 37's on stock (4.10) gears soon and plan on running for a bit before I re-gear. How are you getting along?
 

cgflyer

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I took my jeep back and the shop that installed the Arb lockers and regear couldn't figure it out.

However i Fixed Auto-stop light /ess and rear camera not working.

Per the the below forum link, from my understanding at least for the 6 speed manual trans... there's a secondary battery and you have to take of the negative cable along with separating the two lines to the negative cable (1 for the secondary cable) and also unbolt the negative to the frame.

- per the forum discussion below, it seems they had the exact same issue with ESS / auto stop light and rear camera not working.

Wrangler Forums: https://www.jlwranglerforums.com/forum/threads/ess-broken-after-regearing.11852/

I called the dealership and they said $340 for the flash / reset (brutal). Just gotta take off the negative for a bit!

dfgd.PNG
Is this only required if you get the faults?

 

 
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