4.56 or 4.88 gears?

TJJeepGirl

TJJeepGirl

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Mt. Sterling, Ky
Okay guys I need help! Just installed a ford 8.8 rear end with 3.73 gears. I still have my stock dana 30 with 3.07 up front. So with that it's time to re gear everything! I have read several forms and it seems everyone says go with the 4.56 or the 4.88. The question is which one? Or should I go with something different? I have a 4.0 with a built stroker kit. I consider it a 4.7 now lol. And I have a 3 speed auto trans. I just upgraded to 35's. I do daily drive my jeep. Mostly around my town, but it has been from KY to FL twice. I do trail ride some. But when I do its mild riding with mostly playing in the mud. So what gears would be best for my setup?
 
32rh/34"/3.73 = 2765rpm @ 75mph
32rh/34"/4.10 = 3039rpm @ 75mph
32rh/34"/4.56 = 3380rpm @ 75mph

Grimmjeeper.com

4.56 and 35s feels a bit high even for me. 35s don't measure 35" when the Jeep is sitting on them, btw.
 
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jjvw said:
32rh/34"/3.73 = 2765rpm @ 75mph
32rh/34"/4.10 = 3039rpm @ 75mph
32rh/34"/4.56 = 3380rpm @ 75mph

Grimmjeeper.com

4.56 and 35s feels a bit high even for me. 35s don't measure 35" when the Jeep is sitting on them, btw.
Click to expand...

Thanks for the formula! This is my first jeep and build. I just don't want to throw $1,000 in gears I won't like.
 
jjvw said:
32rh/34"/3.73 = 2765rpm @ 75mph
32rh/34"/4.10 = 3039rpm @ 75mph
32rh/34"/4.56 = 3380rpm @ 75mph

Grimmjeeper.com

4.56 and 35s feels a bit high even for me. 35s don't measure 35" when the Jeep is sitting on them, btw.
Click to expand...
4.56 is the equivalent to the factory RPM with stock tires and 3.73's. You don't have to change the speedo gear with that gear swap to correct the speedometer.

If I was insistent on running 75 on a continual basis, I'd go with the 4.10's.
 
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TJJeepGirl said:
Thanks for the formula! This is my first jeep and build. I just don't want to throw $1,000 in gears I won't like.
Click to expand...
Part of your happiness will be determined by the RPM you believe the 4.0 should be or can be run at with no issues. If you think you should stay around 25-2600 RPM, you won't be happy unless you want to drive a lot slower than before.
 
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I'm also considering regearing to either 4.56s or 4.88s. I have a 5 speed manual and my 5th gear is useless on the highway, can't hold speed. I've got a heavy right foot too so my usual 80mph on the highway is around 2900 RPMs, and I need to get that lower. I have 35's too, so we're in the same boat.
 
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Don't forget the effect ratios have on your trail, off roading too.

I had 33s and the 3.07s. I never used 5th on the highway but in 4LO, 5th could hit 60mph. It was like a Mustang on forestry roads. Not using 5th on the highway was a compromise I was willing to make.

And that '87 YJ got 25mpg all day long in 4th on the Interstate. My TJR struggles to hit 20mpg.... ever.

But I agree, the bigger the tire, the smaller the engine, the heavier the vehicle, the more sensitive it will be to the rear end ratio choice.
 
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billiebob said:
... I never used 5th on the highway but in 4LO, 5th could hit 60mph.
Click to expand...
That's definitely not good for the 4Lo planetary gearset inside the transmission, its gears are screaming when used at higher speeds like that. The owner's manual cautions against using 4Lo at higher speeds like you mentioned.
 
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Jerry Bransford said:
That's definitely not good for the 4Lo planetary gearset
Click to expand...
I drove it like that for 15 years and sold it with 300K miles. Never had a problem with any of the driveline, including the Peugeot 5 Speed Tranny or Transfer Case.

But yeah gotta try 3.07s, 33s, 4LO... you'll love it in the mountains, off road.
 
TJJeepGirl said:
Okay guys I need help! Just installed a ford 8.8 rear end with 3.73 gears. I still have my stock dana 30 with 3.07 up front. So with that it's time to re gear everything! I have read several forms and it seems everyone says go with the 4.56 or the 4.88. The question is which one? Or should I go with something different? I have a 4.0 with a built stroker kit. I consider it a 4.7 now lol. And I have a 3 speed auto trans. I just upgraded to 35's. I do daily drive my jeep. Mostly around my town, but it has been from KY to FL twice. I do trail ride some. But when I do its mild riding with mostly playing in the mud. So what gears would be best for my setup?
Click to expand...


I don't recall you mentioning whether you have an Auto or a Manual (?).

I'm running 35's with 4.56 gears, in a Manual (5-Speed), a 2004. I'm thinking equivalent performance/RPM's in an Auto, would suggest 4.88 gears (?).

Anyhow, here in Texas, where average posted speed limits are between 75 and 85 mph on the highways, the RMP's can get a little annoying for me at high speeds, for the long hauls. In which case, I'm glad I chose 4.56's, vs the 4.88's which I came close to getting. In 1st gear and 4x4 Low, it climbs the rough stuff real nice.

I'm like 50/50 on road-time vs wheeling. If I were wheeling more than 50% of the time, I'd go with 4.88 gearing (in the Manual). But, and again, for the present I'm real happy with the 4.56's.

*I see your reference to "3 speed auto trans," now.
 
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You mentioned that you have a stock Dana 30 in the front. Are you keeping that, or do you plan on upgrading it in the foreseeable future? I'm only asking because you said you just installed an 8.8, I'm guessing to upgrade from a Dana 35.
 
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