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mxunlimited 12-16-2012 08:20 PM

2005 rubicon unlimited
 
Help, 05 rubicon unlimited 33s automatic 4" procomp lift runs at 1900 rpm at 65 in o/d and won't hold it on flat ground w/o shifting back an forth. It has Gail banks header cat back cold air intake shouldn't it be at least hold its speed, tires are a/t

mxunlimited 12-16-2012 08:22 PM

Forgot to mention new to the site so take it easy on me

obiefox 12-16-2012 08:38 PM

1900 is too low a RPM to hold it in OD. Your options are to run a smaller tire or re-gear. Or just flick the OD switch on the dash. :)

With 33's your best gear is 4.88, even though you probably don't want to hear it. The 42RLE has a .69 OD.

You could go 4.56, but 4.88 would be the best choice. IMO.

4x4jeeptj 12-16-2012 08:44 PM

I've got an 04 rubicon. Automatic. 4" lift and 35" m/t tires. Stock 4.10 gears. I drive around town with o/d off. And once I get up to about 70 on the highway I turn o/d on and cruise at about 2100-2300 rpms. Don't have the money to re gear right now so driving with o/d off is the next best thing to do. If you got the $$$ 4.88's would be the way to go.

obiefox 12-16-2012 08:46 PM

65mph with 4.88 and 33's will put you at 2200 rpm

4.56 will net you 2000 rpm at 65

mxunlimited 12-16-2012 08:47 PM

Do you know what rpm would be at 70 mph with 4.88 and would that stop the tranny from searching so much for the right gear

mxunlimited 12-16-2012 08:50 PM

Sorry didn't scroll down far enough to see the rest of your answer. Do you know anyone running the 4.88 with my same tranny and if they like it

obiefox 12-16-2012 08:50 PM

Quote:

Originally Posted by 4x4jeeptj (Post 3111657)
I've got an 04 rubicon. Automatic. 4" lift and 35" m/t tires. Stock 4.10 gears. I drive around town with o/d off. And once I get up to about 70 on the highway I turn o/d on and cruise at about 2100-2300 rpms. Don't have the money to re gear right now so driving with o/d off is the next best thing to do. If you got the $$$ 4.88's would be the way to go.



with 4.10 and 35's you would need to go 75mph just to stay above 2000 RPM in OD

obiefox 12-16-2012 08:55 PM

I run 32's (31.7) on my AT rubi, but I'm sure others will chime in shortly with 33's and 4.88's to give you their first hand experience.

obiefox 12-16-2012 08:55 PM

Oh and I'm no math wiz...
Tire/Gear Calculator

4x4jeeptj 12-16-2012 08:59 PM

Quote:

Originally Posted by obiefox

with 4.10 and 35's you would need to go 75mph just to stay above 2000 RPM in OD

Well you need to remember with an auto trans there is slippage in the torque converter. Maybe that's why my guage shows a little above 2k.

4x4jeeptj 12-16-2012 09:00 PM

Quote:

Originally Posted by 4x4jeeptj

Well you need to remember with an auto trans there is slippage in the torque converter. Maybe that's why my guage shows a little above 2k.

Forgot to mention my speedo is off about 4-5mph so when it shows 70 it means 74-75.

obiefox 12-16-2012 09:15 PM

Quote:

Originally Posted by 4x4jeeptj (Post 3111715)
Well you need to remember with an auto trans there is slippage in the torque converter. Maybe that's why my guage shows a little above 2k.


Converter should be pretty much locked up in OD...

obiefox 12-16-2012 09:17 PM

Quote:

Originally Posted by 4x4jeeptj (Post 3111721)
Forgot to mention my speedo is off about 4-5mph so when it shows 70 it means 74-75.

Ah, there we go. That would explain it.

Take care
Kevin

UpTheCreek 12-17-2012 08:04 AM

Quote:

Originally Posted by mxunlimited (Post 3111568)
Help, 05 rubicon unlimited 33s automatic 4" procomp lift runs at 1900 rpm at 65 in o/d and won't hold it on flat ground w/o shifting back an forth. It has Gail banks header cat back cold air intake shouldn't it be at least hold its speed, tires are a/t

I have same but only a 2" budget boost. Won't hold overdrive either, especially bad in any head wind. Bought it with 33's but I am going back to the stock 245 tires. If you are keeping your lift, go to 4.88's or if you're planning on 35's in the future, just go 5.13's now and be done with it!

UnlimitedLJ04 12-17-2012 08:12 AM

you need at least 4.88 gears. many even go to 5.13s with 33s. the 42RLE auto needs deep gears to behave.

mxunlimited 12-18-2012 07:21 AM

Ok thanks for all of the good input, my tires are 305/70/16 and actually measure 32.2 so do you still think 4.88 and that should put me about 23 or 2400 rpm at 65 does that sound about right. I just dont want to make costly mistake, or mayby just say to heck with it and do a 4BT cummins swap. wouldnt that be nice


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