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Old 08-23-2014, 10:40 AM   #1
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Concerned with highway power on grades (06 rubi)

My new-to-me 06 rubicon runs great on the highway... up until I attempt much of an uphill grade. Can easily tool along around 70 on the flat but cannot get it to nudge above 60 on inclines even when floored. In fact often times flooring it does virtually nothing, as though it has no passing gear whatsoever. When it DOES jump into the passing gear, the RPMs spike really high but the jeep gains no momentum at all.

Only 30k on the rubi. The 32" tires (so I have been told by my local jeep dealer) are a factor, but it truly feels like a powertrain issue.

I have 3 months on the extended powertrain warranty, but the jeep dealer is most unhelpful as it doesn't have any codes in the system. Whatever happened to mechanics actually knowing how to diagnose issues?

Anyone have an idea of what to check out? I am not expecting a drag racer. I understand that jeeps are not the best on the highway. I simply want to maintain a decent MPH.

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Old 08-23-2014, 10:59 AM   #2
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Larger tires are likely the issue,
If it still has factory gears in the differentials, and larger than stock tires that's what happens

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Old 08-23-2014, 11:16 AM   #3
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Look at the tire sidewalls yourself to confirm what size they are, you don't have to go by what the dealer said. The biggest issue is the transmission has such a steep Overdrive ratio that it drops the RPMs too much in an attempt to wring out every last MPG.

Start using your Overdrive button to turn the Overdrive off for climbs. I use mine so much that I don't even have to look, my hand goes right to it.

You can always regear your axles to a lower ratio to restore the power your Rubicon had before it received its larger tires. The larger the diameter the tire, the less power you have.
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Old 08-23-2014, 11:24 AM   #4
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After reading a number of posts here on gearing, and watching a friend with his XJ and 3.73 gears with auto trans and taller tires, I would guess it is tire size and gearing combined. Friend's XJ did the same thing. Climbing hills on the highway, it would simply not remain in high gear, and speed was limited as it jumped back and forth, either screaming or bogging. A change to 410 gearing did wonders.
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Old 08-23-2014, 11:25 AM   #5
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Banks sidewinder turbo could help too, and if you plan on lifting it and going bigger tires, I'd consider doing the gears once for the tallest tires you plan on running.

Let's see a pic of the jeep!
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Old 08-23-2014, 11:26 AM   #6
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Its very likely your tire size. I run 33's with the same 4.10 gearing you have, but with a 5 speed manual. On the longest steepest highway climbs in Colorado I have to drop into 3rd gear and the best I can do is 53mph while nearing 4,000rpm.

Other than a regear of the axles, stay out of overdrive and keep your speed/rpms up before the climb. On the highway, your Jeep is a momentum vehicle like an old British roadster (except it won't corner nearly as well).
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Old 08-23-2014, 11:28 AM   #7
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Banks sidewinder turbo could help too, ...
What is the cost of forced induction vs. a regear?
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Old 08-23-2014, 11:28 AM   #8
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Banks sidewinder turbo could help too, and if you plan on lifting it and going bigger tires, I'd consider doing the gears once for the tallest tires you plan on running.
I wouldn't consider a turbo to be the correct fix for an improper tire size and axle ratio combination. The fix for that is to regear the axles... which typically costs $1200-1400.
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Old 08-23-2014, 11:49 AM   #9
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I wouldn't consider a turbo to be the correct fix for an improper tire size and axle ratio combination. The fix for that is to regear the axles... which typically costs $1200-1400.


I didn't say it was a fix, I said it would help with the low power these jeeps have on the open road.

I wouldn't consider telling someone to buy an oem fuel pump assembly a fix for low power at 65 mph, but you did it anyways.
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Old 08-23-2014, 11:56 AM   #10
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Hi kids... before this thread goes to hell let me say..keep on topic and any personal attacks will get you a vacation...
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Old 08-23-2014, 12:03 PM   #11
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If you want to see what 10% lower gears would be like ie changing your stock rubi 4.11 to 4.56 try running on the highway wit about 8% smaller tire diameter ( a little than 10% as the lighter tire also helps)

Just to get a feel for the power change you can make only the back two smaller for the test as long as you stay out of 4wd

If you like the change go to all smaller tires or regear if it don't float your boat skip spending money on the gear change

And FYI the fuel pump for power loss at 65 was described as massive sudden power loss with a miss
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Old 08-23-2014, 12:14 PM   #12
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I had the same issue as I was running 35" tires on my the with stock gears
The main way to fix this is to change your gears I went to 4.88 in mine and they work wonders so much more power
There should be a pic attached with proper tire size to gear ratio

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Old 08-23-2014, 12:22 PM   #13
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Such charts are very misleading since they don't often give the RPMs that you can actually expect to see. For example, that chart says you can expect slightly higher RPMs with an automatic transmission. That's true with the 3-speed automatic used up through 2002 but you can expect significantly lower RPMs with the 4-speed automatic (via an Overdrive) that is used in 2003 and newer TJs.

I've yet to see a fixed chart that was anything but 100% misleading in the hands of an inexperienced Jeeper or shop guy. The proper axle ratio depends on way too many factors including engine size/power, transmission type and ratios, vehicle weight, and if it's going to be driven on mountainous terrain or in flat areas.

For a few examples of various correct ratios for 33" tires: the recommended ratio for the 2.5L engine with 5-speed is 4.88 for 33" tires. With the 4.0L engine and 5-speed with 33" tires, it'd be 4.56. With the 4.0L and 3-speed automatic with 33" tires, it'd be 4.10. With the 4.0L engine, 4-speed automatic and 33" tires, it'd be 4.88.
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Old 08-23-2014, 12:27 PM   #14
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Quote:
Originally Posted by lumpy85 View Post
Banks sidewinder turbo could help too, and if you plan on lifting it and going bigger tires, I'd consider doing the gears once for the tallest tires you plan on running.

Let's see a pic of the jeep!


The tires are 255/75/17s.

edit, found cord:
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Old 08-23-2014, 12:39 PM   #15
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Quote:
Originally Posted by Jeep_tj_ View Post
I had the same issue as I was running 35" tires on my the with stock gears
The main way to fix this is to change your gears I went to 4.88 in mine and they work wonders so much more power
There should be a pic attached with proper tire size to gear ratio

Attachment 1418066
Are my 32"ers really that whacky for stock 06 rubi gears? I am actually pretty darned content as the largest I'd wish to have on it.
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Old 08-23-2014, 12:58 PM   #16
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No, it came with 31s to start with.

My '06 Rubi with 6 spd manual will climb up Monteagle Mtn on I-24 in 6th no prob. I'm still running stock size 245/75-16.

I believe your auto OD gear is much higher than the 6 spd manual's, so I would expect it to drop out of OD, but then you should have decent power.

Are you sure it still has the Rubi axles with 4.10 gears under it? Have you checked to see if the lockers work? There have been cases of these being pulled out and sold.

You could also have plugged cats.
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Old 08-23-2014, 01:05 PM   #17
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Are you sure it still has the Rubi axles with 4.10 gears under it? Have you checked to see if the lockers work? There have been cases of these being pulled out and sold.
I haven't checked the gears myself, no. Lockers however, I did check. Only changes from stock that I know of were the wheels/tires, lift and bumpers.


Relatively noobish here, but no idea what cats are in regard to a wrangler.
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Old 08-23-2014, 01:11 PM   #18
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If you have the Rubi axles, then you should still have the 4.10s.

Cats are the catalytic converters. There are 2 by the engine on 1 above the skid plate.

If they fail and plug the exhaust, it will seriously limit the engine's pwr.
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Old 08-23-2014, 01:27 PM   #19
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The over drive is not great for interstate speeds, especially with hills. I just drove a 2006 unlimited rubicon with 275-70-16's back to Kansas City from Los Angeles, it sucked at anything but flat or down hill.

I prefer the 6 speed on the highway, I know I'll get ripped on, since the auto is almost always preferred on the trail,


A handy calculator,


Gear Ratio Calculator


I posted the difference with the 42rle and the nsg370 all stock, for an rpm comparison
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Old 08-23-2014, 01:37 PM   #20
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You would need 4.88's to match the 6 speed rpm. With my old lj rubi 6 speed, I never felt like I needed more power on the hiway, you may want 5.13's
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Old 08-23-2014, 04:55 PM   #21
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Would a superchip programming help out matters?
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Old 08-23-2014, 05:02 PM   #22
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Would a superchip programming help out matters?
Not at all. Search the forum for what we think about chips, cold air intakes, throttle body spacers, etc. None will help you.
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Old 08-23-2014, 06:51 PM   #23
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If your wanting more horsepower, its gonna have to be a supercharger, turbocharger, stroker, or v8 swap!

If you want more zip on the highway, regear.




Good looking jeep btw!
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Old 08-23-2014, 07:58 PM   #24
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I have a 04 rubicon and had 33x15x12.50 and never had a problem on hills on the highway I would cruise at 70-75 mph up hill. My rubicon is auto and now have 35in Mtr with Kevlar and now have significant drops going up hill but like the other guy said just turn off overdrive and it's fine. But remember if it's a rubicon they come stock with 33's and should not be a problem at all
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Old 08-23-2014, 08:04 PM   #25
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...But remember if it's a rubicon they come stock with 33's and should not be a problem at all
Incorrect. Rubicon's came stock with 245/75r16 which is roughly 30.5” in diameter. Pretty tiny right?
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Old 08-23-2014, 08:20 PM   #26
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Hard to believe they were that small but 32's or 31in diameter wouldn't kill you on highway hill climbs
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Old 08-23-2014, 08:40 PM   #27
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I have roughly the same setup as the OP, it doesn't like hills on the highway in OD.


to answer your question that I missed earlier. Banks turbo kit is 2950.00, so double the cost of gears at least, I haven't had gears setup in a while, I know some get them setup cheap, some pay through the nose!
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Old 08-24-2014, 01:53 PM   #28
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I took the same hill (mountain) highway route last eve with OD switched off. Helped out a bit.

Unrelated, but when looking underneath I noticed that it already has blue spacers on the hubs. Explains how it has the JK rims on a TJ. Spacers are a no-no in Utah, but I suppose since it is more of a "adapter" from one lug pattern to another it will pass muster.
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Old 08-24-2014, 01:59 PM   #29
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Not at all. Search the forum for what we think about chips, cold air intakes, throttle body spacers, etc. None will help you.
I was thinking more along the lines of it setting up the CPU correctly for the tire size, trans shifting and speedo
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Old 08-24-2014, 02:02 PM   #30
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Have you checked all the usual tune up items: plugs, air filter?

It should climb hills in 3rd OK.

You also should be on the look out for the Oil Pump Drive Assembly (OPDA) issue with it. Affects '05 and '06s. It is in the spot the distributor was in on the old 4.0s. Right side of the engine, looks like a distributor without the cap and wires. They are known to seize up.

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