Gears
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
Without a programmer the gears likely weren't compensated for either somewhat reducing the variance. In round numbers from 4.10s w/32s to 5.13s w/37s the speedometer is going to be around 5mph slow.
Even with a programmer to get the speedometer, shift points and gear hunting sorted out, 5.13s are nominally acceptable for 37s and an automatic. It also takes an additional 50% of wheel horsepower to go from 60 to 70mph, so as little as a 3 degree grade is going to kick you down and out of overdrive. That means something as small as an overpass on an otherwise flat freeway is going to spike your rpms at 3600+.
Even with a programmer to get the speedometer, shift points and gear hunting sorted out, 5.13s are nominally acceptable for 37s and an automatic. It also takes an additional 50% of wheel horsepower to go from 60 to 70mph, so as little as a 3 degree grade is going to kick you down and out of overdrive. That means something as small as an overpass on an otherwise flat freeway is going to spike your rpms at 3600+.
JK Freak
Joined: Feb 2010
Posts: 605
Likes: 0
From: Chesapeake, VA
Im about to regear and My buddy is doing it. So far I have 2 questions. I need to know what fluids to order and how essential the break it period is?
I have the Yukon Gear and axles. The basic install kit since i have 1k on my 2010 jeep. I also have a bearing separater and am ordering a rear ARB locker with the on board air.
Is there anything else i will need for the install?
Also I wanted to get them in before i go wheeling in nags head which is 100 miles away and wanted to wheel down there. Ill be staying there for a week. Well i calculated it out and i will need to install my gears and locker 2 days before i leave. Should i just wait and do the install when i get back??? i Really dont want too! =[
O yeah also any other essentials mods i should get. I run 35's on a Jeep X and I bought Evo gussets and plan to get a programmer eventually. Any other mandatory mods to keep it a DD and not breaking shit? thanks
I have the Yukon Gear and axles. The basic install kit since i have 1k on my 2010 jeep. I also have a bearing separater and am ordering a rear ARB locker with the on board air.
Is there anything else i will need for the install?
Also I wanted to get them in before i go wheeling in nags head which is 100 miles away and wanted to wheel down there. Ill be staying there for a week. Well i calculated it out and i will need to install my gears and locker 2 days before i leave. Should i just wait and do the install when i get back??? i Really dont want too! =[
O yeah also any other essentials mods i should get. I run 35's on a Jeep X and I bought Evo gussets and plan to get a programmer eventually. Any other mandatory mods to keep it a DD and not breaking shit? thanks
JK Enthusiast
Joined: Aug 2009
Posts: 180
Likes: 0
From: Las Vegas, NV
Without a programmer the gears likely weren't compensated for either somewhat reducing the variance. In round numbers from 4.10s w/32s to 5.13s w/37s the speedometer is going to be around 5mph slow.
Even with a programmer to get the speedometer, shift points and gear hunting sorted out, 5.13s are nominally acceptable for 37s and an automatic. It also takes an additional 50% of wheel horsepower to go from 60 to 70mph, so as little as a 3 degree grade is going to kick you down and out of overdrive. That means something as small as an overpass on an otherwise flat freeway is going to spike your rpms at 3600+.
Even with a programmer to get the speedometer, shift points and gear hunting sorted out, 5.13s are nominally acceptable for 37s and an automatic. It also takes an additional 50% of wheel horsepower to go from 60 to 70mph, so as little as a 3 degree grade is going to kick you down and out of overdrive. That means something as small as an overpass on an otherwise flat freeway is going to spike your rpms at 3600+.
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
Lets put it this way, the difference between 35s and 37s are greater than the difference between 5.13s and 5.38s. That said, if I'm rolling an automatic and I have a D44 front I would roll 5.38s even with 35s. Don't be afraid to twist the motor a bit and you won't see anything more than nominal efficiency decreases until you get over 2700rpm.
JK Super Freak
Joined: Mar 2008
Posts: 1,439
Likes: 1
From: Flyover Country
JK Newbie
Joined: May 2009
Posts: 94
Likes: 0
From: Corona, CA
Just for clarification.....as you didn't reprogram, are the speeds you are trying to reach (mentioned above) based on what the speedometer says, or based upon a gps, etc?
I ask, because with 37's, your speedometer is off by ~ 13.5 % or more (Depending upon what tires your's was calibrated for...), so you're really going closer to 75 when the speedo says 65 mph, etc.
And - you don't say whether the speed was hard to reach because the engine was winding out (RPM too high), or because it was too weak to even get the rpm to climb, etc.
For example, with 32's, 60 mph is around 2k rpm in 6th
37's would drop that rpm to ~ 1,730 rpm at 60 mph
5.13 gears would then RAISE that rpm by ~ 27.3 %, back UP to ~ 2,202 rpm at 60 mph
This means 5.13's have more than compensated for the 37's as far as final drive ratio...
...and you are now just fighting the extra drag and rolling resistance of the larger tires in addition to the gearing issues.
And - when your speedometer is telling you you're going 65 mph, you're actually going ~ 9.2 % more (After the tires and gears are corrected for...) or ~72 mph.
So, IF the above were correct, its 72 mph you are trying to maintain in the same way that you WOULD have tried to go 65 mph...making the jeep seem slower, etc.
If you did 5.38's instead of 5.13's, that would ADD ~ 4.6% to your rpm at any given speed, and make the speedometer off by that amount more than it was already off by.
IE: You'd be at 2,308 rpm instead of 2,202 in the above example....a difference of only 106 rpm.
I ask, because with 37's, your speedometer is off by ~ 13.5 % or more (Depending upon what tires your's was calibrated for...), so you're really going closer to 75 when the speedo says 65 mph, etc.
And - you don't say whether the speed was hard to reach because the engine was winding out (RPM too high), or because it was too weak to even get the rpm to climb, etc.
For example, with 32's, 60 mph is around 2k rpm in 6th
37's would drop that rpm to ~ 1,730 rpm at 60 mph
5.13 gears would then RAISE that rpm by ~ 27.3 %, back UP to ~ 2,202 rpm at 60 mph
This means 5.13's have more than compensated for the 37's as far as final drive ratio...
...and you are now just fighting the extra drag and rolling resistance of the larger tires in addition to the gearing issues.
And - when your speedometer is telling you you're going 65 mph, you're actually going ~ 9.2 % more (After the tires and gears are corrected for...) or ~72 mph.
So, IF the above were correct, its 72 mph you are trying to maintain in the same way that you WOULD have tried to go 65 mph...making the jeep seem slower, etc.
If you did 5.38's instead of 5.13's, that would ADD ~ 4.6% to your rpm at any given speed, and make the speedometer off by that amount more than it was already off by.
IE: You'd be at 2,308 rpm instead of 2,202 in the above example....a difference of only 106 rpm.
I figured if I went 5.38 I could run more in OD and have more RMPs so I would not downshift into 3rd on the fwy. I guess I would rather have the quicker pickup speed and be able to get better gas milage by having the overdrive actually work on the fwy.
Maybe that does not work that way.
Chido
JK Enthusiast
Joined: Aug 2009
Posts: 180
Likes: 0
From: Las Vegas, NV
Lets put it this way, the difference between 35s and 37s are greater than the difference between 5.13s and 5.38s. That said, if I'm rolling an automatic and I have a D44 front I would roll 5.38s even with 35s. Don't be afraid to twist the motor a bit and you won't see anything more than nominal efficiency decreases until you get over 2700rpm.
Thread Starter
JK Enthusiast
Joined: Feb 2009
Posts: 212
Likes: 0
From: York, Pa
I just bought 4 qts of Royal Purple Synthetic (Max-Gear) Gear Oil SAE 75W-90 for after my 500 mile break-in period.
Did I get a good Gear Oil? I have seen it alot on Spike TV's Xtreme 4X4.
And is 4 qts enough I have Riddel diff covers if that makes a diffence?
Did I get a good Gear Oil? I have seen it alot on Spike TV's Xtreme 4X4.
And is 4 qts enough I have Riddel diff covers if that makes a diffence?
JK Jedi Master
Joined: Aug 2007
Posts: 15,665
Likes: 4
From: Hammond Louisiana
I run RP, I have TeraFlex covers , took about 1.5 for the D-30 in frt. 2.5 or so in the rear, you may wanna pick up an extra quart just in case, I always buy a coupl ahead anyway. Maybe someone will chime in for the riddlers.