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I have the model thrity diff out of my 81cj5. I plan on rebuilding it for now. If I run a 9.5 by 31 tire would I need to change my gear it is 2.73. I use it on back roads and trips into the city 20 miles on the highway. I would like to keep the highway speed but still do some humble 4x4ing. It has the AMC 304 so lots of power.
1986 cj7 258, t-176 4-speed, d-300, moser one piece axle in back in amc 20,G2 4.10 gears front and back, detroit truetac front and back,G2 4340 chromoly front axles in a d-30, 4" rough country lift, 33" tires
I would think that with the AMC 304 and 31's 2.73s would be fine and if all else fails on the tail you always have 4l. Depending on what Transfer Case you have quadtrac on some i think dont have a 4l. Also not sure what modles came out with that Transfer Case , I'm no expert by far. My jeep had 33's no lift and 2.73 and the AMC 258 i6 / 4.2l and 4l was a must on the trail, till i Put in 4.10 Unless you plan on putting bigger tires and a lift on I would think the 2.73 would be fine. Just my opinion.
I have a AMC 304 with T-15 3 speed and Dana 20 . My Ratio is 4.27 with 33" tires.
Plan on swapping in a granny Low T-18 or SM465 for the granny gear in the future, but for now, the ratio I have going is awesome for light trail riding and a little more aggressive wheeling.
I would recommend changing your ratio a little, but it really is all up to you... And you may be able to retain the current ratio in the diffs while still increasing your crawl ratio...
How does it do in 4L now when you take it on the trail and put it up against a small challenge? If you find it's hard to clime something or "lacks power" I would recommend changing gearing.
What do you currently have? Tranny, and Transfer Case , we know already you have the 2.73's and 31's... I ask, because if you want to still keep your current gearing, you may be able to do a tera low package for your t case and gain your low crawl ratio there instead too...
That above link is one of them out there that will allow you to play with options a while before making a decision...
1986 cj7 258, t-176 4-speed, d-300, moser one piece axle in back in amc 20,G2 4.10 gears front and back, detroit truetac front and back,G2 4340 chromoly front axles in a d-30, 4" rough country lift, 33" tires
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Since you have the axle out here is a link on how to put a zerk into your axle to repack the bearings I don't know how good of a job it would do but its something to read and look at. Easy Bearing Repacking
73 CJ5 4.0 head on a 258, HEI, Holley Projection w/ 4.56, Detroit lockers Narrowed D44 front and full float D44 rear T14 w/ D20 4 wheel discs, 38.5 Boggers
your mistaken, 2.73 is the most common factory gear ratio for the later cjs, 3.73 factory gears are almost unheard of with the exception of 4cyl jeeps, then I think they are actually lower than that.
1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
I would get 4.11 gears. What tranny do you have? If you have an Overdrive you could even go a little lower than that. If you have or plan to swap in a granny low such as a T-18 you could go much taller than that.
Check out this chart and shoot a gear ratio in the green.
Edit: What tire size do you have now? Going to 31 inch tires may not make a big jump. You could install the tires first to see how you like the gearing. In the '80s the gearing was very tall. If you swap out the tires and decide to get lower gears then get 4.11.
That's my 2 cents.
I double checked the tag and it said 272 49-18. There just seems to be no info on that gear option. I will count it when I open it up after I sand blast it.
1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
Sorry Busadave9 Old age taking my sharpness away. Hard to say the tack is a small one hard to see standing still let alone at speed. I went for a couple of ripps and went in restore mode. I wanted to get the steering fixed etc to much wobble to keep it at 65 one thing leads to another. I will have to wait and see what rpms are after and then make a better informed choice on gearing. For now it will work. It is just the fact that I have not seen that gear combo talked about anywhere
1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
Irregardless of what they are now 4.11 gearset will give you about 2900 rpm at 65 mph. I would think that should work out. Regearing can be a big job or if you have someone else do it, it can be expensive. I would first get the tires then decide if you need lower gears.
If I regeared I would have to consider a axle swap to a better axle hate to regear then do it all over in a couple of years. Your right I will get it up and running then figure out needs etc
1979 Jeep CJ5 with 304 V8, T18 Transmission, Dana 20 Transfer case with TeraLow 3:1 gears, 4.88 axle gears, Detroit Locker up front and Ox Locker in back with 1 piece axle shafts, 36" SuperSwamper SX Tires, Shackle reversal, MileMarker Hydraulic winch, MSD 6A ignition.
Plenty of options 
