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Discussion Starter · #1 ·
I'm only running around 2100 rpm on the highway with the pedal on the floor. Does this seem right or should there be an adjust made on the linkage? I have a 4.2l w/5 speed running stock gears and 31" tires. This is on flat ground,it will go a little higher downhill.
 

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How fast... mph.... and how fast mph / rpm will it go in 4th.
 

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This is not unusual. The new Jeep Renegade, 9 speed automatic, hits top speed in 5th. each subsequent gear results in both slower speeds and lower rpms. Same with the Audi S8, 8 speed automatic and top speed is in 5th. In both vehicles those gears are direct. All the following gears are overdrive gears.
 

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Discussion Starter · #4 ·
61 mph according to the gps. I honestly haven't paid much attention in 4th. It is reved a little higher but not a whole lot.
 

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My '87 YJ with 30s 5th gear worked fine. When I put on 33s I never used 5th. 4th would hit 90mph. 5th lost speed even at 60mph. I had the 3.07 ratios. I think you should be able to hit 80+mph in 4th.

What is your rearend ratio?
 

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Discussion Starter · #6 ·
Thanks for the info! I also have the 3.07 gears and I just thought that it should run a little higher on the highway,of course a flying brick isn't meant for speed!
 

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Nuthin to do with the brick. Your 31s just pulled the rpms down too far from peak power.
Use 4th gear more
 

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max 2100 rpm and 61 mph? you have something wrong. when I first bought my 4.2 and the motor was still stock I hit 95 mph, didn't check the rpm's.
I'd check the cat, it probably partially plugged.
 

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Discussion Starter · #10 ·
5000 miles on the motor and new exhaust from the manifold back. The cat was deleted when it was installed. I thought it was maybe just the gearing. I did notice the cable doesn't look to me like it pulls far enough.
 

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2100 rpm at 61 mph? Doesn't sound right at all. I'll run that rpm and mph in 4th, 5th and 60 mph is approx. 1600-1700 rpm. (4.2, 3.07's, 31's).
 

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your speedo may not have been recalibrated for your larger tires, and you may be going 70 mph
 

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If I remember correctly I would run 60 mph in 4th gear at a little over 2000 RPM's. When I first purchased my jeep my 5th gear was useless unless I was going down hill. I thought this was normal considering I had 32x11.50 tires. I wouldn't even shift into 5th unless I was on flat ground and doing over 60 mph. However, after a good friend set my timing correctly and made adjustments to the carb, I now shift into 5th at 50 mph and I am able to accelerate and climb hills in 5th. The jeep is also much more responsive. It was a world of a difference! You should be able to turn 31's with no problem if everything is running right.
 
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