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post #1 of (permalink) Old 12-13-2002, 09:58 AM
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4.88\'s in a 97 TJ 4cyl

Hey guys,

Question.. I have a 97 TJ with a 4cyl and 35inch tires. And well, grandma passes me on a regular basis on the highway! I went to order a new set of 4.88's to get some power back, but the tech from my favorite 4wheel drive mail order company reccommended against them. He said the 4.88's were giving all sorts of problems in this model jeep and they were not selling them anymore. he talked me into a set of 4.56 gears.

Has anyone else heard of 4.88's being unreliable in this year jeep?

How much of a power difference is it between the 4.88's and the 4.56's?

The jeep is an everyday driver and my main reason for the change was better highway performance. Any feedback is greatly appreciated. [img]images/graemlins/smile.gif[/img]

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post #2 of (permalink) Old 12-13-2002, 10:24 AM
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Re: 4.88\'s in a 97 TJ 4cyl

RPM = MPH X Gear Ratio X 336 /Tire Diameter

So, on average that can translate to about 200 RPM less rotation at speed. Yep, over time that makes a difference.

1. As for unreliable? Well, it all depends upon the tire size, transmission gearing, transmission type, speed and driving habbits.
2. Most infor I've seen (no first hand info) says that pinion is gettin' pretty small for 35" tires.
3. That translates to too much tire to spin with too small /weak gearing.
4. Yep, I'd agree...if you'r hard on the gas pedal...
5. If you stomp on it... it's gonna grenade.
6. Would the 4.56 gearing be any better?
7. Yep... it's a help.
8. I'd give someone like Randy's Ring and Pinion, or another gearing comapny a call and talk to one of their engineers... NOT the salesmen... the engineer could explain the rational much better than I...

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post #3 of (permalink) Old 12-13-2002, 10:54 AM
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Re: 4.88\'s in a 97 TJ 4cyl

I had 4:88's in my 4cyl tj with 33's. Great off road and good for the road. Gave me fifth gear back and was good at highway speeds.
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post #4 of (permalink) Old 12-13-2002, 10:57 AM
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Re: 4.88\'s in a 97 TJ 4cyl

If it is a 4 dinger then and you have the stock axel in the back, it is a D35 (I am assuming that you have the stock rear) The 35 doesn't have very much room in there for tall gears, when you get up to 4.56's and 4.88's then gear teeth get smaller, the ring gets thinner, and the pinion gets smaller. When dealing with pieces of metal... smaller means weaker. And that is probably what the guy was telling you, they don't recomend them because they are weaker.
NOW, for you, who say that the jeep is on the road most of the time, and that you have the 2.5L and not the 4.0 I would tend to believe that your axels will hold up fine. As long as you are not dumping the clutch at 3-4K.
I am not sure if the TJ used a reverse R front 30, I know the YJ's did and that is a pretty strong unit. It should hold better than the rear.
As a general rule, if you jeep came from the factory with 27in tires, and 4.10 gears. Then if you run 33" a 4.56 will return you to factory rpm range, and 35-36 will be just about right with 4.88's

On an unrelated note, if you decide to regear, let me know I have a D30R, and D35 instal kits that have never even been out of the box, still shrink wrapped. They have been collecting dust, if you want them I will send them to you for a great deal. (however they are for YJ 30/35, I am not sure if the TJ is the same.
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