Slow top speed

Drew

Drew

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Joined
Apr 2, 2017
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10
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Florida, United States
I have an issue in that whenever I am at top highway speed, around 70 or 80 mph, my jeep can't seem to accelerate past it. I can floor it and it just will not go beyond 80 in 5th gear. If I go up a slight incline or even if I am driving into heavy wind, it will start slowing down with my foot still to the floor.

Thoughts?

2004 Jeep Wrangler X, 4.0L
 
Jack up the rear axle. Mark the driveshaft and tires. Rotate both tires one revolution and count how many times the driveshaft spins.

Or look for a ratio tag on the diff cover.

If you've got no power now with the current gears, 33's will be even worse.
 
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GASnBRASS said:
Jack up the rear axle. Mark the driveshaft and tires. Rotate both tires one revolution and count how many times the driveshaft spins.

Or look for a ratio tag on the diff cover.

If you've got no power now with the current gears, 33's will be even worse.
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This would tell me what, the gear ratio?
 
Drew said:
This would tell me what, the gear ratio?
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Yes, the number of times the DS spins would indicate the ratio. So if it spins just a hair past 3, it's 3.07 gears. If it's 3 and 3/4 turns, it's a 3.73. Just past 4 would be a 4.10 gear, and so on. Or plug your vin into the link @Brantley posted and see what the build sheet says.
 
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I just got back from my first trip with new lift and 31's from stock. 750 miles DEN to LAS. Not only did the high winds blow me around, but I actually had to waive truckers by on the hills. Lift made it worse in winds and 31's robbed top end power. I will be checking gears tomorrow.

Sent from my SM-G928V using Tapatalk
 
Brantley said:
It's most likely stock, and if it's a Dana 35, will be 3.07 gears which is a terrible ratio
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This isn't true at all... In the 2.5l TJ's, Dana 35's came with 4.10 gearing and even optional 4.56 gearing in 1997. On the 4.0, they came with 3.73, 3.55, or 3.07.

Drew, your speed and power will definitely suffer if you upgrade tires. 33's are not only taller, but usually wider than 31's and therefore much heavier. Either re-gear, or get used to going slow while you save up for one.
 
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PStov98TJ said:
This isn't true at all... In the 2.5l TJ's, Dana 35's came with 4.10 gearing and even optional 4.56 gearing in 1997. On the 4.0, they came with 3.73, 3.55, or 3.07.

Drew, your speed and power will definitely suffer if you upgrade tires. 33's are not only taller, but usually wider than 31's and therefore much heavier. Either re-gear, or get used to going slow while you save up for one.
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He has an X which means it's a 4.0, and he has a 5-speed. In an 04 4.0, the only options are a Dana 44 with 3.73, or a Dana 35 with 3.07.

3.73 with 31's isn't ideal but I don't think he'd be complaining too much about it. He most likely has 3.07.

He for sure has a 4.0 and 5-speed and in 2004, the only ratios he could have stock are 3.07 or 3.73.
 
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Brantley said:
He has an X which means it's a 4.0, and he has a 5-speed. In an 04 4.0, the only options are a Dana 44 with 3.73, or a Dana 35 with 3.07.

3.73 with 31's isn't ideal but I don't think he'd be complaining too much about it. He most likely has 3.07.

He for sure has a 4.0 and 5-speed and in 2004, the only ratios he could have stock are 3.07 or 3.73.
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You're statement is correct for his specific set up. Just wanted to clear it up that not all dana 35's came with 3.07 gears. I only commented because I missed the details of his Jeep at the bottom of his post and misinterpreted what you were saying. My apologies.
 
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Look on your axle's differential cover at its 9 o'clock position. There will be a steel tag there with your axle ratio embossed into it. You can see this tag is indicating the axle has a 3.73 ratio inside.

Axle Ratio.jpg
 
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By checking out my VIN on Brantley's post, I learned that my 2005 4.0 automatic has a Dana 35 3.73. Upgrading to 31's definitely cut my top end power a bit, but I have plenty of low end. I guess I will leave well enough alone. If I ever have to go into the rear end, I can upgrade to 410's. For now, I will just have to peddle faster when going uphill... :p
 
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LeePTI said:
By checking out my VIN on Brantley's post, I learned that my 2005 4.0 automatic has a Dana 35 3.73. Upgrading to 31's definitely cut my top end power a bit, but I have plenty of low end. I guess I will leave well enough alone. If I ever have to go into the rear end, I can upgrade to 410's. For now, I will just have to peddle faster when going uphill... :p
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Not that you're looking to do it yet, but if you ever really want to regear for the 31's, 4.56 would be more appropriate and really with that terrible overdrive, 4.88 isn't that insane of a choice either, which would put the rpm right at 2700 at 70, perfect in my opinion.

I certainly would not go to 4.10. That's how Jeep geared the 4-speed Rubicon on 31's and I've heard plenty of people complain about it.
 
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Drew said:
It's a 3.07 dana 30. The lowest gearing for dana 30 is 3.55 correct?
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No, you can get Dana 30 gears as low as 5.13 if you want. I have 31's with 3.73 gears and this is a low as I would go for 31's. Since you have a manual tranny I would put 4.10 or 4.56 gears in. If you plan to go up to 33's you should go with 4.88 or 5.13.
 
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