Does improper gearing hurt engine?

H

hammonds42

New member
This maybe a dumb question but I am looking at an 08 jku x. It says that it has a 4 inch lift with 35 inch tires and geared at 3.21. While I was doing some research, I read the gearing should be more like 4.88 or better. This car has 76k on it. I am wondering if there are long term affects to the engine being geared this way?
 
Well, while it doesn't hurt it directly, it does increase load on all the driveline components, wearing them out much faster. Think of it as your jeep is permanently towing an invisible trailer....or permanently driving uphill. IF you don't regear, you'll spend the $1000 in fluid changes alone trying to keep up with the wear.
 
It will affect the engine but if its an automatic it will generally cause it to burn up the clutches in it faster than giving you motor problems. An auto will have so much slipage no matter what. With the bigger tires and stock gears the motor is going to be trying to work harder and will overpower the transmission causing it to slip more. Which will cause it to burn up.
 
Any time your engine is over-worked, it's not good for it. However, it's not going to spontaneously combust either. If you have the budget for the gears, do it.
 
I have an 08x. I regeared to to 4.88 when I put the 35 on. I also ran them same stock gears, 3.21, with 33, and my jeep dragged ass. So I would hate to see what it's like with 35. So if you get it, I would suggest jumping to 4.88 asap. Cause now my jeep is fine since I've done that
 
this is a good question cause i also bought a 2001 TJ that has a 4.5 inch lift with 33's. it has barely any miles on it but is my daily driver to work as well as my off road rig. As budget allows and because of the lift it already has i wanna upgrade the tires to 37's. would it be ok for me to re-gear her now with the 33's to accommodate the 37's or should i wait till i get the tires?
 
Since this is your DD, you may want to wait until you are ready for the 37s, as your gas mileage will be affected. Don't forget to get an AEV Procomp or equivalent before you regear.
 
Eezybreezy08 said:
I have an 08x. I regeared to to 4.88 when I put the 35 on. I also ran them same stock gears, 3.21, with 33, and my jeep dragged ass. So I would hate to see what it's like with 35. So if you get it, I would suggest jumping to 4.88 asap. Cause now my jeep is fine since I've done that
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Man mine is doing the same thing 33s with stick 3.21 is terrible. I can't wait to bump to a 4.88. Would a 5.13 be to much for a 35?
 
Clifford33 said:
Man mine is doing the same thing 33s with stick 3.21 is terrible. I can't wait to bump to a 4.88. Would a 5.13 be to much for a 35?
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5.13s would be overkill for 35's in my opinion if you want to drive on the highway. The RPMs would get pretty high and you'd burn more gas. For a trail rig, i don't think it'd be that bad. The other problem you start running into (if you run the D30 front still) is that the pinion gets really small and prone to breakage.

I just did the 3.21s on 35's for about 6 months and it really was just god awful. Made the switch to 4.88s just last week and I've been kicking myself since for not doing it sooner.
 
Lank said:
5.13s would be overkill for 35's in my opinion if you want to drive on the highway. The RPMs would get pretty high and you'd burn more gas. For a trail rig, i don't think it'd be that bad. The other problem you start running into (if you run the D30 front still) is that the pinion gets really small and prone to breakage.

I just did the 3.21s on 35's for about 6 months and it really was just god awful. Made the switch to 4.88s just last week and I've been kicking myself since for not doing it sooner.
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With the 08 and if it's an auto. The 5.13s would be about right and put it back stock feeling. However I agree that with the Dana 30, the 5.13s would be a small pinon. So you would want to be careful. If the OP was going to lock it or had a heavy right foot then the 4.88s might be a wiser choice.
 
Yeah I do a lot of highway and climb A lot of high way hills. Also have a heavy foot but I'm leaning on the 4.88s they seem just right. Any suggestions on brand?
 
mudmobeeler said:
With the 08 and if it's an auto. The 5.13s would be about right and put it back stock feeling.
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True, I forgot about the autos


Clifford33 said:
Yeah I do a lot of highway and climb A lot of high way hills. Also have a heavy foot but I'm leaning on the 4.88s they seem just right. Any suggestions on brand?
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All of them come from the same factory in Korea. There might be slight differences in handling when they get to the states but thats the extent of it. Some people on the forum recently were saying their Yukon's were noisy. I went for G2's just because the shop preferred them
 
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