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Old 04-25-2008, 05:52 PM   #1 (permalink)
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Gearing, what would you do?

I figure this isn't real hardcore so it is going here. I am looking for some people that may have dealt with a similar gearing situation.

I have a dilemma. It comes to my gearing in the YJ.

I have a D60 rear with 4.88 and was planning on re-gearing my front D44 to 4.88 in the next few months (it is currently 3.55)

I have ran the calculations, and with my 37's (actually measure 36") at 60mph

3.55 gears = 1400 RPM
4.88 gears = 1900 RPM

at 70 mph

3.55 gears = 1620 RPM
4.88 gears = 2230 RPM

Now I know these numbers don't really affect how it will perform on the TRAIL.

My intake setup puts the my power range at idle to - 5,500 RPM or so.

I have a 700R4 with the 355 V8.

With 4.10 gearing, 700r4, V8 and 33's I NEVER had a gearing issue, in fact I rarely needed 4 low. (no rocks around here) I always was able to keep my wheel speed up..

The 4.88's keep me in the same power band as what I had, the 3.55's will lower my RPM and make it more drivable on the street -- I was always a little over geared before. Better mileage maybe too.

I was offered a open 3.55 D60 with 90% of the disk setup (all new, just needs pads and caliper brackets) for my drum braked 4.88 D60 with a worn out limited slip.

Benefits are that it has disks, = lighter, it has open carrier = more locker options, and it would be cheaper then re-gearing the front 44 to match.

Benefits of my axle are it is already installed and it has 4.88's that I KNOW I will be happy with.

Short term looks like I would benefit from the 3.55 geared axle, but I am not sure about long term. What would you do?

Some questions that have come up from other people I have asked:

My buddy ran 3.73's with a manual and it was terrible, why in the world would you even consider 3.55 with 37's?

The 700R4 has essentially a 9:1 first if you count the multiplication of the torque convertor, and that is before you reduce it again if I use 4 low. This is harder on the tranny however through the heat build up. My tranny was built by a very reputable person with some upgrades and has less then 15k miles on it. I also run an aftermarket cooler.

Why would you want a jeep on 37's streetable at all? Why are you running it on the street?

I am running 37's on the street because I don't have a tow rig and trailer. I drive my rig there and back. It will also tow my flatty around.


I am really looking for people with actual experience with this setup or similar.

When I had 4.10's and 33's it was geared enough I could lift the front wheels in a parking lot pretty easy, 4.10s V8 and 30's was dangerous as you would touch the gas and it would want to come around on you in a corner.

The jeep:
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1994 Wrangler -- 6.0 Chevy, 700R4, D44, D60, 37's
1946 CJ2A -- 225V6, T98, D18 & 34's

Last edited by jeepfreak81; 04-25-2008 at 05:53 PM.
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Old 04-25-2008, 10:30 PM   #2 (permalink)
bjb
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I had 3.54s with 35s and it was ok on and off the road with the v8/auto+4/1 low. I now have 4.10s with 38s and it works about the same (maybe alittle better). With the OD in your 700 I'd sure go with the 4.88s. A v8 will turn 3000 all day long and get about the same mileage as lugging at 1500. You're only driving to and from the trails the 2-5 gallon difference a trip is still under $20. And you'll have a much better setup off road (unless ya are running 100+ in the desert).
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