Lower reverse gear?

[DaemonForce]

I'll get straight to the point: I drove around in deep snow this morning and got caught in a very dangerous snow bank, got flung off the road and SOMETHING wrecked the Eagle. I say wrecked because the wheel wells were packed with snow, I couldn't steer and most importantly, couldn't move until someone finally came along an hour later to winch me out. My concern is in the hour before someone helped me.

I was in 4WD the entire time. My engine held up great but none of the wheels would move AT ALL and I'm trying to figure out why this happened. Is it just snow/ice messing with stuff or does my gearing suck? I punched the snot out of the throttle nearing 900RPMs and I could feel the transmission engaged but no movement.

I have an A-904, NP129 and stock differentials. In reverse it looks like this:
Reverse gear: 2.2:1
Transfer case: 1:1
Differentials: 2.73:1

If my gearing is too high, I'm guessing the NP229 swap is a valid idea. What kind of ratio does the low gear offer in that case and does it make sense to do this? I need to hold off with the lift kit and a winch until I get a new welder. I really want to keep this car independent and capable since it's the last of its kind here in mid-Washington and after this morning it appears that I'm the only one crazy enough to drive around in the deep snow. :/

[mach1mustang351]

It doesn't take a lot of snow to wad up in front of the wheels and stop them.  I just about got stuck in a situation with an up hill start where I had to stop in a deep snow pile before merging into traffic.  I actually had to back down and use 4lo to get through it ( I have swapped in a NP242 among other things).  There are may ways to make a vehicle better in the snow.  Taller tires, more power, lower gears and more traction.  A lot of these are covered in other threads.  Just my thoughts.

[DaemonForce]

Sounds like another reverse issue I noticed yesterday. If I reverse in a lot of snow, it will cake inside the guardplates and freeze the shift linkages in place. Not fun.

I don't want to change anything that sacrifices mileage or torque. I like my differential gearing and I'm stalling on fixing my 2" drop(springs...). For years I've been interested in changing engines but now I'm curious if changing the transfer case can make this vehicle more capable. Options are the plan here. I just want a straight 1:1 high gear and then the lowest gearing you can imagine so that I don't need to count on outside help when I'm sitting on 2ft of packed snow and mud. I'm guessing any NP2xx case will help me if this happens again. I'd use a winch but I need to do a lot of modifications before that happens.

[captspillane]

All new process transfer cases are the same low range ratio (2.72 to 1). The only one that is different is the 241OR. Those are quite rare.  The only production vehicle to ever have that transfer case is the newer Jeep Rubicons like my 2006 Unlimited TJ. That has a 4 to 1 low range. A normal NP241 from a truck will have the usual 2.72 ratio. There are aftermarket kits that replace the entire internal gear set to give you the 4 to 1 low range, but they're more expensive than they're worth.

Taller tires do not help. Thinner tires do. A 2WD Model T with the thin bicycle tires is considerably more capable in snow than my Rubicon with all the axles locked. The 33x12.5 tires are incredibly impractical in every possible road surface except when aired down on very large boulders. A stock Eagle with a low range will put a Jeep with large tires to shame in a hurry. There are also "pizza cutter" tires that are tall while still being very thin. The thinner it is, the less resistance it has in snow, and you have to remember that it takes two additional inches of tire to gain one inch of ground clearence.

If you want reliable traction, the NP242 is the way to go. You can use the open differential in "Full Time 4WD" to retain the all wheel drive while having the locked differential in "Part Time 4WD" for severe conditions. The advantage of the 229 is that it avoids slip yoke driveshaft issues.

[carnuck]

Not having front and rear locked is why it didn't go (or you were high centered)

[DaemonForce]

Not having front and rear locked is why it didn't go (or you were high centered)

Can you explain this better? I know the NP129 doesn't have a high lock but what does that mean for my Eagle when it's at a dead stop and locked in 4WD?

[captspillane]

Being high centered means that you ran over a huge clump of snow and some of the car's weight was actually supported on the snow like a pedastal, thus taking weight off the tires and letting it lose traction easier. Its pretty common if you go full throttle into a very thick snow and the front of your car plows and compacts a huge pile ahead of you. In that case you would have a tire spinning someplace and you would benefit immensely from having a positraction rear and a locked output transfer case to make sure that the wheels that do still have weight on them are able to spin.

I disagree that his car would have moved if he had the front and rear transfer case outputs locked together, and even if he had front and rear axle locks. I've gotten stuck several times before because the transmission refused to transfer enough power to the wheels to make it move. Using low range is the only way to improve that situation besides switching to a manual transmission or changing the shift characteristics of the transmission. The 258 is a very humble engine and it can be overwhelmed. Think of it like this, if you push down on the brake hardcore at a red light, and then press the gas pedal to floor, your RPM's will increase dramatically and there will be torque applied to the wheels but the car won't move unless the engine overcomes the brakes. If none of his tires were spinning and yet he wasn't moving that's exactly what was happening. I've had it happen several times in automatic station wagons with 2.73 gears. A manual transmission and strong clutch will be able to apply the full torque of the engine until it stalls but an automatic is designed to apply some torque without stalling the engine. With low range, however, it makes up for the high axle ratio and it makes a dramatic effect on how much torque can be applied to the wheels.

[eaglefreek]

I have to also agree that you weren't high centered. If you were high centered, the engine would rev a lot higher than 900 rpms because a wheel(s) would be spinning. What is limiting you to 900 RPM is the stall speed of the torque converter. I've had similar situations happen to me trying to get over a small curb or rock. I couldn't get enough rpm to get over the obstacle. However, unlike you I was able to back up and get some momentum to get over them. I tried to get a higher stall torque converter when I was having mine transmission rebuilt but had limited time to fidn one because I needed it back on the road. The 258 in stock form gets its peak torque at 2000 rpm. At 900 RPM you aren't able to produce enough toque to move those highway gears. With a manual you would be able to slip the clutch to get the rpms up and have more torque available. Think of your rear gears as a lever. The lower the gears the longer the lever and the easier it is to get moving at low speeds. However, lower gears will cripple you at higher speeds. FYI, a lower gear will have a have a higher number. 3.55's are lower than 2.73's. I went off roading this weekend and having a low range case, saved me from having to be pulled over a couple obstacles.

You have a few options.

Add more torque to your engine by installing a different camshaft, bumping up the compression etc. I have the 4.0L head, Comp cams camshaft, MSD ignition, Motorcraft carb. I have 3.07's but with my taller tires my gear  ratio is about the same as have 2.73's with stock size tires. I still have trouble because of the low stall speed of the torque converter.

Find a company that can change the stall speed of your torque converter a few hundred RPM's.

Install lower gears in the axles. This will sacrifice MPG. However, in conjunction with an OD transmission, you can have the best of both worlds. Lower axle ratio and a reasonable final gear ratio.

Installing a manual transmission will give you a much lower first gear and a clutch that you can slipp to get RPMs up.

Install a transfer case with low range.


I already have a NP229. On my to do list is an overdrive auto transmission and a NP242 to gain 4 high lock.

[Sunny]

Taller tires do not help. Thinner tires do. A 2WD Model T with the thin bicycle tires is considerably more capable in snow than my Rubicon with all the axles locked.

I constantly try to explain that to people who come in to my work who always want super wide snow tires. Nobody ever listens. 

[carnuck]

Got sidetracked. Missed the part about only 900 RPM. I was assuming he was revving and not going. In that situation with the Eagle NP129, one tire spinning only would cause the VC in the tcase to burst if done for too long a time. Having a tcase that locks would stop that from happening. Having a low range would also allow more power to get to the wheels.

I wish I could put the 33/9.50/15s that are on my MJ on my Eagle wagon (but I don't want to mess with the body since it's so nice)