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Re-gearing/Axle swap

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ducktapeguy

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Looking for opinions. Current drive train is AMC20/Dana 20 w/TF999 and Dana300. I'm on 31" tires right now. Right now it's tolerable, but highway RPM's are around 1900-2000 on the freeway. Ok on flat stretches, but not great especially when I start going up hills. I usually have to shift to 2nd on long uphill climbs.

I should probably re-gear to 3.54 or 3.73. I probably won't ever go larger than 31" or do any hard core off roading, just looking for something better for freeway driving and light off road. A re-gear would probably cost $2k+, since it would require a carrier swap on the AMC20 + parts and Labor, which is a lot for something that doesn't get driven that much. And I'd rather not dump that much money into an AMC20 so I've been looking at getting a Dana 44 rear which would probably cost just as much to setup, but at least it feels better than dumping money into the AMC.

The other option is I found a set of AMC20's and Dana30's with 3.31 gears for <$1000. I figure another few hundred to swap out bearing and seals and I'd have slightly better gearing that what I have now, but I'm not sure if it's worth the cost to do that just to be slightly better on the highway. Would it be worth the money to go from the 2.73 to 3.31? Or should I wait and just invest in the proper gearing? How would this affect highway mileage?
 
I would keep my eye open for a used set of better geared axles. Does the set you found have 1 piece axles? Good chance if you found a set of axles that have been regeared, good chance it would have 1 piece axles swapped in. The 3.31 gear are most likely stock gears with original parts inside. Regeared units will usually have mostly new bearings.
FWIW you probably have an AMC20 and a Dana 30(typo I assume)
 
I had 4x4Land change the 2.73s to 4.10s this past spring. Should have done it 20 years ago. 4.0, T-5 and one pc rear axles. Mileage is about 15-16 on the highway now at 2400 rpm at 65-70.
 
I run a 4.2 with a TF999. 31 inch tires, and I just installed 373‘s, and I’m happy with them. I cruise 65 without no effort. A lot happier than the 331s that I replaced.
I also have an another Scrambler with the TF 999 behind a stroked Golen 4.6…I’m running 31” tires with 4:10’s. It hasloads of power, but the RPMs run a little high when driving over 65 MPH. 55MPH is the sweet spot.
 
barrys said:
I would keep my eye open for a used set of better geared axles. Does the set you found have 1 piece axles? Good chance if you found a set of axles that have been regeared, good chance it would have 1 piece axles swapped in. The 3.31 gear are most likely stock gears with original parts inside. Regeared units will usually have mostly new bearings.
FWIW you probably have an AMC20 and a Dana 30(typo I assume)
Click to expand...
Yes, I meant Dana30. Not sure if they're one-piece, I'll have to ask

I typically cruise around 65-70mph, above that and I'm more worried about handling than the rpm. I'm just not sure what RPM I want to be at on the highway. Around 2500 seems to be the general consensus, but with 3.31's I'll be around 2400, 3.54 puts me at 2560, and with 3.73 that puts me around 2700 (all @65mph).

I guess I have to decide whether a few hundred RPM is worth the effort and cost to change. I did a mental breakdown of my options

Gear Ratios

2.73 (current setup)
Cost - $0
Pros - Not a whole lot
Cons - Gearing too low for climbing hills. Right now I've been using 3rd as almost an overdrive for flat freeways, on hills I shift in 2nd and bring my rpms up to about 2500@55mph, but at 65mph the engine feels like it's screaming.

3.31
Cost - Around $1k
Pros - Cheap and easy. Axles would swap right in. Brings me to a slightly "better" highway rpm, but still may not be ideal.
Cons - Keeps the AMC20

3.54/3.73
Cost - $2.5-5K depending on parts and if I do all the work myself. If I re-gear I'd probably swap to a different axle instead of dumping money into the AMC20, and both front and rear would need re-gearing. If I were going that far I'd also look into getting wider axles maybe from a YJ?
Pros - Puts me at an ideal gearing and a stronger axle
Cons - Cost and labor involved is significant.
 
TexasAg77 said:
I had 4x4Land change the 2.73s to 4.10s this past spring. Should have done it 20 years ago. 4.0, T-5 and one pc rear axles. Mileage is about 15-16 on the highway now at 2400 rpm at 65-70.
Click to expand...

What size tires are you running? Wouldn't the overdrive on the T5 and 4.1's put you at an effective 2.73 gearing again (0.68 x 4.10)?
 
ducktapeguy said:
What size tires are you running? Wouldn't the overdrive on the T5 and 4.1's put you at an effective 2.73 gearing again (0.68 x 4.10)?
Click to expand...
31” tires. 2900 in 5th at 70 or so. Sweet spot for power in a 4.0. Use 2,3 and 4th in town.
 
My ‘82 was a 4cyl jeep and came with 4.10 axles. It had a T5 / 232 I6 and I felt the gear ratios were great, just wish I had more power.
 
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