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I swapped my T-150 for a T18a last year. As stated, the high hear is the same 1:1 ratio. The low gear however gives my '81 CJ5 a whole new dimension in off roading. I live in Northern California and we have plenty of rocks here. The crawling is a whole lot easier now. As far as mud and sand goes, 2nd, 3rd and 4th have the same ratios as my T-150 had so there is no difference there. I run a AMC 258 i6 / 4.2l , T18a, Dana 20 , and 3.54 gears. I have no problem running up the highway to the Rubicon, crawling the trail and then returning home afterward on the highway. I have 31" tires that I like for maneuverability off road. It's not a daily driver but could be. I really like the T-18 . I don't use first unless needed and then it's worth its weight in gold, and believe me, it's heavy.
1979 CJ-7 with a fiberglass body and 1982 wide track axles, 258 I-6 with a 1995 4.0 head, HEI distributor, Motorcraft 2100 Carb, T-18 wide ratio tranny, Super Lift Springs and 33s, a 1997 BMW 328i, and a 2010 REDLINE CONQUEST TEAM Cyclocross Bike. :)
If you want it to drive like a smooth car, use the car tranny. If you want it to drive like a jeep, use the T-18 . My T-18 doesn't shift sloppy at all, but it does have a bit of a dump truck feel to it when shifting.
My only real complaint is the unsyncronized first gear. If using 1st as 1st instead of starting out in 2nd, I need to shift early, give a good pause between 1st and 2nd, and make sure the clutch is all the way in if I don't want to hear it grind. I'll live with that for the ultra low 1st gear ratio and the bullet proof reputation of a T-18 .
I swapped my T-150 for a T18a last year. As stated, the high hear is the same 1:1 ratio. The low gear however gives my '81 CJ5 a whole new dimension in off roading. I live in Northern California and we have plenty of rocks here. The crawling is a whole lot easier now. As far as mud and sand goes, 2nd, 3rd and 4th have the same ratios as my T-150 had so there is no difference there. I run a AMC 258 i6 / 4.2l , T18a, Dana 20 , and 3.54 gears. I have no problem running up the highway to the Rubicon, crawling the trail and then returning home afterward on the highway. I have 31" tires that I like for maneuverability off road. It's not a daily driver but could be. I really like the T-18 . I don't use first unless needed and then it's worth its weight in gold, and believe me, it's heavy.
I think that's some good input for the T-18 , your Dana 20Transfer Case I would guess would be a 2.0 gear unless you put the D-18 gear set in there or a teralow gear. Would be interested to know what gears you have.
I have seen posts here that talk about 80-90 and even over 100 crawl ratios which for most vehicles is way to low. Anywhere in the 60-80 range for a vehicle that is driven daily is more than capable.
For anyone who has a Jeep that's looking for better freeway drive ability then look to the Transfer Case for your gear help.
In my 65 I have the 6:32 T-18 gearbox and what makes my gearing so good is I use a large hole Dana 20Transfer Case with the D-18 2.46 gear set inside w/ off set drive backed by the Warn 25% Overdrive .
In low gear I'm at 66.38 crawl ratio, and then shift to OD it goes to 49.78 in low gear........lt's like having 8 speeds in low range.
Anyone looking to upgrade to a Borg Warner T-18 in the future there is a 76-86 AMC 304 -401 V8 bell housing on E-bay #1583572644 right now at .99 cents..
My only real complaint is the unsyncronized first gear. If using 1st as 1st instead of starting out in 2nd, I need to shift early, give a good pause between 1st and 2nd, and make sure the clutch is all the way in if I don't want to hear it grind. I'll live with that for the ultra low 1st gear ratio and the bullet proof reputation of a T-18 .
1978 CJ7
Silver paint with black hard top on 33" radials & eagle alumium rims. Good looking ride and have done lots of work to make it look and run great.
Stock equipment is 258 carb, power brakes, power steering, hard top & hard doors (per vehicle gross weight) tilt steering wheel, big brake package with large rotars & drums, T18 Trans with low 6.4 granny gear, Dana 20 transfer, Dana 30 front axle, Dana 44HD rear axle with 3.73 gears. True Trac ft & rear.
I was around jeeps in the 70's and drove a 1973 Jeep Truck. My family had 4 jeeps at the time. We also joined a jeep club back then too. So about 6 years ago looked for a Jeep CJ and found the vehicle above.
I have a 1978 CJ7 that came with the optional T-18 1b Transmission , 3.54 gears, AMC 258 i6 / 4.2l one barrel. With 33" tires I wanted a bit more pep and the mileage was awfull. First trip home after purchase took 3 tanks of gas and ran out of gas once in the middle of the night... fun trip. Glad there was a second car with me.
After motor rebuild, weber carb, borla header, MSD Igntion, TeamRush Tune Parts, Aux Grounds. Mileage went to 23 mpg from a guess of single digits. VERY drivable and have taken trips of 800 miles rt and done great... 65 mph is in the 2300/2400 rpm range.
I have found with AMC 258 i6 / 4.2l and other posted stay in the 2100-2400 range and 20-24 mpg is attainable.... very attainable.
Recently put True Trac in the front and back with 3.73 gears. My ring gear Dana 30 had a few teeth with damage and had access to a Dana 44 with 3.73 gears from early 70s... This was the best path I could come up with..... I was temped by 4.10 gears but more money for change and I did not want to give up my hwy mileage mpg performance. With gear change I recurved my Duraspark Distributor, re Jeted Weber 34, and almost done with my set up super tune....
200 mile hwy trip to wheel I got 20.6 mpg with 1/2 hr of low speed stop/go traffic leaving town and then doing 65-70..... speed limit 70. ON way "back" no traffic but went 70/75 and got in the 19.6 range mpg..... pretty good for higher speeds. tac was in the 2500-2600 range
Another trip about 80 miles went slower in the 55-65 range and tried to keep tac in the 2100-2400 rpms and got 22 mpg
This past wkend went/drove to a MS Fundraiser with a bud and his TJ fuel injected 4 cylinder & 33's. We filled up drove there/back and filled up again..... we both use the same amount of fuel. We tried to get good mpg, coasted to lights, was hwy drive at 50/55 mph and we got amost 24 mpg. Gentle driving and trying to get good mileage...
I am very pleased with my set up.... I drive mostly on the road but the trails are hundreds of miles away RT... If my Transmission did not have the granny gear 6.32 I would have gone with the 4.10 axle gears to help with the off road needs.... That means would need a 4 speed for road maners and most likely a OverdriveTransmission or Overdrive adapter...
Offroad happy with the 3.54 or 3.73 gears...... I can puts along on trails in 1st grannsy or 2 second.... Just at the idle most times eps when in the granny gear. I like my set up.
It also helps to have a sound engine... many post the AMC 258 i6 / 4.2l limit is about 2500 to 3000 rpms.... Mine will do 4000 and 4400 (red line in book) pretty easy and more pep than stock parts.... the extra rpm range will help with 3.54 or 3.73 axle gears. With out the extra rpm range would not have been happy with the 3.54 gears.....But when you got on it and used the extra rpms it was a beast...
IMPORTANT......
If you are not supper pleased with the T-18 shifting..... Try the AMSOIL MTF, Manual Transmission Fluid... I have been pushing the use of GL4 in the Manual Jeep Transmissions for the past 5 years or so..... I was using the right suff Dyno GL4..... THERE IS NO COMPARISON ON HOW THE T-18 SHIFTS WITH AMSOIL MTF.... It no longer shifts like a 'truck" Transmission ... Try it , the AMSOIL MTF you will be impressed!!
Here are some shifts with my T-18 .... used as 3 speed road gears...3.54 axle gears
Keep in mind 4000+ rpms with the AMC 258 i6 / 4.2l in second/third gear is like 64 mph... petty fast
If your axles have never been opened most likely you will have a data tag affixed to the bolts on the cover. That will give you the current gear ratio. If not the tooth count is stamped on the ring gear side face.
Next time you drain your fluid at either end, get a flashlight and a piece of chalk and count the gears.........on both the ring and the pinion...........now you know the gear ratio in both the front and the rear.
I think that's some good input for the 
