Diff 2.73 or 3.07 diffs

[Fonchy]

Im going to start my build and I have 2 sets of diffs, one is a 2.73 and the other a 3.07. Which one should I use, is going to be a daily driver. Thanks in advance

 

[Manic Mechanic]

Depends on tire size and Transmission I run 31s and 3.23


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[Belizean]

I have 31s and 3.54 and like that.

 

[Fonchy]

Sorry forgot that part, AMC 258 i6 / 4.2l inline 6, T-5 tranny, right now I have 31 on, im not going to do a lot of 4 wheeling. The 2.73 has solid axles and the 3.07 has a 2 piece. I have a donor CJ7 with the 3.07s, it has a 350 Chevy and auto tranny and I want standard, the 258 has a t5. I want to run the 350 but I don’t have and adapter nor a tranny that will handle it, or drive shaftswhat are you guys input

 

[Manic Mechanic]

I'm currently running the AMC 258 i6 / 4.2l T-5 combo and it's great. If ur not wheeling it the 350 is nothing more than extra weight gas and noise and bragging rights.

Go with the 3.07 258 t5 combo swap over the one piece shafts from the other axle there the same. You will be much happier in the long run and easier to get parts since you don't have to say I need parts for this that and the other.



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[boney]

I have the AMC 258 i6 / 4.2l , a T-5 and 2.73 axles on 31" tires. The jeep came with a T-4 but at some point someone put in the 5-speed. Frankly, on flat ground the engine doesn't have the poop to push 5th gear. I just run in 4th. I've attached a screen shot of my final drive worksheet for the 2.73 and 3.07 axles with 31" tires. Numbers under the RPM is speed in a perfect world. I don't have a tach, so I just guess by how much I have to step on the pedal to keep it going.

 

[Fonchy]

I have the 258, a T-5 and 2.73 axles on 31" tires. The jeep came with a T-4 but at some point someone put in the 5-speed. Frankly, on flat ground the engine doesn't have the poop to push 5th gear. I just run in 4th. I've attached a screen shot of my final drive worksheet for the 2.73 and 3.07 axles with 31" tires. Numbers under the RPM is speed in a perfect world. I don't have a tach, so I just guess by how much I have to step on the pedal to keep it going.

View attachment 75644

I have the same mine came with 4 spd and was change to 5 spd, I can goi in 4th great if I go to 5th it feels like someone just thru an anchor and starts to slow down

 

[TSB8C]

The T-5 is not a good tranny and that engine won't do much in an Overdrive gear. The 2.73 gears will leave you with no torque to speak of, so getting up to speed will take forever. Basically it'll be a dog that can't get out of its own way. I'm running a 420hp fuel injected 350 with a 700R4 auto (also has overdrive) and 4.56 gears with 35" tires. I run about 2200 rpm at 65mph on the freeway and get about 15mpg in 2-high normal street driving. But I can also accelerate quite well in houston traffic. It'll spin those large MTs in 4-high if I want to. Normal daily driving in 2-high can spin 'em in first and squeak 'em again in 2nd with the shift kit.

 

[TSB8C]

Went back to edit my prior post and it was too late. Please scratch my statement about the T-5 not being a good tranny. Got mixed up on the AX5 vs AX15, not the T5. Rest of the post is accurate though.

 

[DB80CJ5]

Sorry forgot that part, 258 inline 6, t5 tranny, right now I have 31 on, im not going to do a lot of 4 wheeling. The 2.73 has solid axles and the 3.07 has a 2 piece. I have a donor cj7 with the 3.07s, it has a 350 Chevy and auto tranny and I want standard, the 258 has a t5. I want to run the 350 but I don’t have and adapter nor a tranny that will handle it, or drive shaftswhat are you guys input

I think figuring out what you want to do with your Jeep is really the most important thing you can do prior to your build so kudos for thinking about this before you start. If you are doing mostly street driving that T-5 will handle the 350 without any issues. I have a 343 with 400hp 4:56 gears and 35'' tires and have not had a problem out of my T-5 Transmission and I romp on it every chance I get. It really depends on how much you want to spend. As far as gears go, lots of good advice here it really comes down to do you want speed and gas mileage or lots of torque and fun. If you are building a CJ7 you can make just about any engine trans combo work, if you have a CJ5 the rear driveline kind of limits your trans choice. Good luck with your build.

 

[Fonchy]

I think figuring out what you want to do with your Jeep is really the most important thing you can do prior to your build so kudos for thinking about this before you start. If you are doing mostly street driving that T-5 will handle the 350 without any issues. I have a 343 with 400hp 4:56 gears and 35'' tires and have not had a problem out of my T-5 trans and I romp on it every chance I get. It really depends on how much you want to spend. As far as gears go, lots of good advice here it really comes down to do you want speed and gas mileage or lots of torque and fun. If you are building a CJ7 you can make just about any engine trans combo work, if you have a CJ5 the rear driveline kind of limits your trans choice. Good luck with your build.

Well people don’t build jeeps with gas mileage in their heads, I just want a good daily driver or weekend beach vehicle and if a trails comes then some trails riding will be good, I want some umpfff when Im on the highway. If i could use the 350 that will be a bonus, now saying that where can i get a bell housing or adapter for the 350/T-5 combo, would it be better to run with the 2.73 or use the 3.07. someone posted i could change the 1 piece axles from the 2.73 to the 3.07 but the 2.73 is a wide axle and the 3.07 is short axle.

 

[Manic Mechanic]

Well people don’t build jeeps with gas mileage in their heads, I just want a good daily driver or weekend beach vehicle and if a trails comes then some trails riding will be good, I want some umpfff when Im on the highway. If i could use the 350 that will be a bonus, now saying that where can i get a bell housing or adapter for the 350/t5 combo, would it be better to run with the 2.73 or use the 3.07. someone posted i could change the 1 piece axles from the 2.73 to the 3.07 but the 2.73 is a wide axle and the 3.07 is short axle.

I said that. But it was my understanding that they were both wide track. If one is narrow and the other wide then it's a no go. I just ordered a new set of Yukon one piece shafts for my 20 (344+tax from Amazon). I can't speak to the T-5 holding up to a V8 but advanced adapters is the place to go for adapters and know how. If they don't make an adapter then it's probably not a good idea.

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[DB80CJ5]

Well people don’t build jeeps with gas mileage in their heads, I just want a good daily driver or weekend beach vehicle and if a trails comes then some trails riding will be good, I want some umpfff when Im on the highway. If i could use the 350 that will be a bonus, now saying that where can i get a bell housing or adapter for the 350/t5 combo, would it be better to run with the 2.73 or use the 3.07. someone posted i could change the 1 piece axles from the 2.73 to the 3.07 but the 2.73 is a wide axle and the 3.07 is short axle.

Do a google search there are a few places that sell them. Just a thought you may want to sell your 350 and source a 360 AMC motor they make about the same power. You can get good HP out of a AMC 304 , but you need to change aftermarket heads, 300 HP is not hard to achieve with either of those engines, and if you can find a 401 you can make big horsepower, but those are hard to find and my 343 is even harder to find. but all these blocks are the same, they use the same distributors and accessory drives and the heads are interchangeable too. It is just a lot easier to fit an AMC engine in. I assume one of your jeeps has the straight 6? don't dismiss it with an aftermarket head, cam, and intake you can get good power and a ton of torque from them. I believe it would suit what you want to do with it. You said you want to go to the beach well if you are driving on sand, you need lower gears, sand sucks up horsepower like nothing else. so look at the chart one of the other members gave you in the post. I think a 3:73 would work well with a 33'' tire. I run 4:56's with 35' and mine screams at 70MPH, if I put scout axles I'm going to go to a 4:11 for better street ability. I would use the wide axles and change the gears if you want. You can use what you have and change them after good thing about jeeps is you have good access to them. My CJ5 is quite the adventure at 70 MPH, wider is safer at highway speeds. Just remember more HP higher gear, low HP power low gears. Everything is a trade-off. I'm sorry I can't give a straight answer, best advice is to do your homework look at cost versus reward, and how much work you can/ are willing to do.

 

[Manic Mechanic]

If money is not a problem ditch all of the engine options and LS it.

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[TSB8C]

The LS option is a great option for sure. But since you already have the 350, that is also a great option as the 350 has near every part and customization option readily available at any local auto parts store. Easy swap, easy setup, easy to work on, etc. Since the T-5 has an Overdrive gear, your streetability should OK. I run about 2200 RPM at 65 on the highway with 4.56 gears and the 700R4's overdrive with 35" tires. In terms of adaptor options for the T5 to a Chevy 350:

Adaptor plate (if you already have a bell housing)

Bell housing adaptor

 

[Fonchy]

Ok so this is what I’m thinking, use the 350 with adaptor plate for T-5 and use the 2.73 gears, is going to be for Highway driving for the most part, this is what I have gather reading all the comments, thanks for all the comments

 

[Patrick]

There are two tee fives, one of which is the World Class. If it’s not the World Class, then it’s not advisable to use behind any healthy vee eight engine.

 

[Fonchy]

There are two tee fives, one of which is the World Class. If it’s not the World Class, then it’s not advisable to use behind any healthy vee eight engine.

Which one is it, i think i have the regular T-5

 

[Patrick]

I don’t know which Transmission you have.

Find yourself in this chart. If you are anywhere other than the green, then it’s going to disappoint. Take time and do things right.