What rear end?

[dodger098]

Hey guys, I'm thinking of getting new gears in my truck for better mileage.  I've seen some posts about 3.21s being pretty good on the mpgs, is there a lower rating I could go with?

[dodgerider]

Don't you want to get a higher gear for better mpg?  I though someone here went up to 4.56s and got like 3 mpg improvement.  Dunno how that works though since you would run higher rpms i think.

[06Hemiman]

You want to turn the lowest rpms possible to get the best mpg.  There might be some Mopar 3.21s available from the 2nd gen trucks still.  Be really tough to find though.

[moparman]

You want to turn the lowest rpms possible to get the best mpg.  There might be some Mopar 3.21s available from the 2nd gen trucks still.  Be really tough to find though.

It was Mr Anderson that got the 4.56s installed and said that he got better mpgs with them plus he can now launch like a bat out of hell.  That's a win win in my book.

[markedman]

Yeah, he said that he's now getting 3-4 mpg better under 70 mph, less mpg over 70.  So as long as long as you can keep it under 70 you're ok.

[Cutter]

The object, as i understood, of 4.56 gears is it takes less power to get the vehicle rolling, less work for the engine and less gas.  However this would cause the engine to run higher RPMs so at higher speeds it would use more gas but less gas while accelerating. And also leave a lot of rubber on the pavement. 

[gman]

The object, as i understood, of 4.56 gears is it takes less power to get the vehicle rolling, less work for the engine and less gas.  However this would cause the engine to run higher RPMs so at higher speeds it would use more gas but less gas while accelerating. And also leave a lot of rubber on the pavement. 

Yeah, and from what I understand if you have one of those hemis that'll shut down 4 cylinders it'll leave those off more often since it's easier to move the truck.  I suppose it's an added bonus for you guys with 06+ trucks.

[diesel game]

The object, as i understood, of 4.56 gears is it takes less power to get the vehicle rolling, less work for the engine and less gas.  However this would cause the engine to run higher RPMs so at higher speeds it would use more gas but less gas while accelerating. And also leave a lot of rubber on the pavement. 

Yeah, and from what I understand if you have one of those hemis that'll shut down 4 cylinders it'll leave those off more often since it's easier to move the truck.  I suppose it's an added bonus for you guys with 06+ trucks.

That's pretty awesome.  Why can't Cummins do something like that?  When I'm unloaded cruising on the highway I doubt that I need more than 2 of my cylinders running.  Lets just shut them off.

[Mr Anderson]

Yeah, he said that he's now getting 3-4 mpg better under 70 mph, less mpg over 70.  So as long as long as you can keep it under 70 you're ok.

That's exactly right.  My 4.7L pulls my camper with no problems right now, and when I'm not towing I get better mpgs.  I don't know exactly why, but the engine runs a few hundred rpm higher and I get 3 mpg more than I used to.  Up to about 72 or so then I see the overhead start to decrease so as long as I'm under 70 I'm getting better mpg.

[dodger098]

Yeah, he said that he's now getting 3-4 mpg better under 70 mph, less mpg over 70.  So as long as long as you can keep it under 70 you're ok.

That's exactly right.  My 4.7L pulls my camper with no problems right now, and when I'm not towing I get better mpgs.  I don't know exactly why, but the engine runs a few hundred rpm higher and I get 3 mpg more than I used to.  Up to about 72 or so then I see the overhead start to decrease so as long as I'm under 70 I'm getting better mpg.

How's that thing when pulling, don't you have a trailer or something?

[05ram]

Yeah, he said that he's now getting 3-4 mpg better under 70 mph, less mpg over 70.  So as long as long as you can keep it under 70 you're ok.

That's exactly right.  My 4.7L pulls my camper with no problems right now, and when I'm not towing I get better mpgs.  I don't know exactly why, but the engine runs a few hundred rpm higher and I get 3 mpg more than I used to.  Up to about 72 or so then I see the overhead start to decrease so as long as I'm under 70 I'm getting better mpg.

How much was it to get the rear end redone?  If it saves you on gas money I might think about it.

[hemibob]

Hmm, this whole thing makes me wonder if I can get my rear end regeared.  My hemi gets me about 25 mpg highway, maybe 26.  If I could get something in the high 3s or low 4s in the rear I would probably net a few more mpg.  Has anyone heard of the rear in an LX car being regeared?

[Mr Anderson]

Yeah, he said that he's now getting 3-4 mpg better under 70 mph, less mpg over 70.  So as long as long as you can keep it under 70 you're ok.

That's exactly right.  My 4.7L pulls my camper with no problems right now, and when I'm not towing I get better mpgs.  I don't know exactly why, but the engine runs a few hundred rpm higher and I get 3 mpg more than I used to.  Up to about 72 or so then I see the overhead start to decrease so as long as I'm under 70 I'm getting better mpg.

How's that thing when pulling, don't you have a trailer or something?

If you'd read the message you'd see that it's a lot easier to pull my camper now.  I love the new gears.

Yeah, he said that he's now getting 3-4 mpg better under 70 mph, less mpg over 70.  So as long as long as you can keep it under 70 you're ok.

That's exactly right.  My 4.7L pulls my camper with no problems right now, and when I'm not towing I get better mpgs.  I don't know exactly why, but the engine runs a few hundred rpm higher and I get 3 mpg more than I used to.  Up to about 72 or so then I see the overhead start to decrease so as long as I'm under 70 I'm getting better mpg.

How much was it to get the rear end redone?  If it saves you on gas money I might think about it.

The cost was 600$ for the rear.  That includes cost of the gears too.

[markedman]

$600 for one side?  That's pretty spendy.  I don't think anyone could justify that price with gas savings now that prices are coming back down to reasonable levels.

[NitroNanny]

Hmm, this whole thing makes me wonder if I can get my rear end regeared.  My hemi gets me about 25 mpg highway, maybe 26.  If I could get something in the high 3s or low 4s in the rear I would probably net a few more mpg.  Has anyone heard of the rear in an LX car being regeared?

I think it would require more than just gearing on your part.  With the trucks they already have a couple models (srt, powerwagon) that come with a much taller gear ratio.  You would probably need to upgrade your driveshaft and rear axle to handle the extra torque from the regear.  I don't think it's as popular as would seem.