Replacing 3.55 with 4.56 - Dana 30 Chrysler 8.25

[Mudderoy]

What you're not realizing with that scenario is that a vehicle uses more fuel to get going from a stop than it does while maintaining highway speeds, especially if it's overgeared for the tire size (IE: 33's on 3.55's). That's one of the main reasons the "city" mileage rating is always so much lower than "highway" mileage ratings.

If he's going to be doing almost all highway driving with very little stop and go driving, you have a valid suggestion to for an MPG experiment. If he runs into stop & go traffic, the experiment's results be get more and more skewed every time he stops and has to get going again.

Plus I don't have to mention that driving with an overgeared axle/tire combination is very hard on an automatic transmission because of excess heat. Also, it's hard on a manual transmission's clutch due to excess slipping needed to get the vehicle rolling.

Gears are worth the effort. Period.

eace:

I live in the Houston area, and I use I-10 to go to and from work. I have a 20 mile commute that takes anywhere from 20 minutes to 1 1/2 hours. I do the stop and go every day.

Also I have a PM from a guy that is running the 4.56 and he does 3200 rpm at 80 mph. I'll probably be going to 33's eventually to 4.56 sounds pretty good.

 

[300$XJ]

If you plan on upping the tire size you could go 4.56, 4.10's will get you back very close to the stock set up for rpm's on the 32's. alljeep.com has some good prices and they will beat the compeditor! They also sells Yukon and Precision, not sure what else, Tell them Les told you about them and he might even give ya a discount! Ask for Wayne if you call!

 

[Mudderoy]

If you plan on upping the tire size you could go 4.56, 4.10's will get you back very close to the stock set up for rpm's on the 32's. alljeep.com has some good prices and they will beat the compeditor! They also sells Yukon and Precision, not sure what else, Tell them Les told you about them and he might even give ya a discount! Ask for Wayne if you call!

That is what I found as well. I liked the stock performance but thought the 4.56 might have a little more "getty-go", and I knew I wanted a larger tire later. I actually thought about the 4.88 for a little bit.

I'll go ahead and ask, is it really a bad idea to try and change the ring and pinion yourself? I mean I can read directions... I hate spending $400 to $700 of good Jeep upgrade money just to have the gears changed.

 

[cal]

I'll go ahead and ask, is it really a bad idea to try and change the ring and pinion yourself? I mean I can read directions... I hate spending $400 to $700 of good Jeep upgrade money just to have the gears changed.

If you have to ask, you shouldn't do it yourself.

:edit:

That is to mean that if you don't fully know and understand why it is that people say go to a pro, you are nowhere near ready to tackle the job. Its the *ONLY* task I pay someone else to do.

 

[waxer]

Amen

 

[300$XJ]

I will be having someone show me how to do it when I do mine! I could prolly figure it out but that is the one thing I have never done! I know you have to get some gear meshing compound and use that to make sure you have the correct mesh between the dears to they all work properly. But that's about all I know, I'm sure I could do it with some good instruction, but I'm gonna opt for help when the time comes. You know that the more getty-go is gonna mean higher rpm's which in turn is gonna drop your milage back down. Let me know how the 4.56's do, I'm running about the same set up as you it sounds and I don't care for the 3.55's much at all and was gonna go to the 4.10's, but am curious to know what you think about the 4.56.

 

[stewie]

in early march i changed from 3.55 to 4.56. i talked to Dave at DesertFab and he gave me a great deal on yokon gears and master install kit for my 30, 8.25 as well as a new carrier for my 30.

if you have 3.55 and are going to 4.56, you will need a new carrier. if you are going from 4.10s to 4.56 then the carrier you have will work fine.

i have an aussie locker and i can say it would probably be easier to do with the ring gear off the carrier- you have more room to get the parts and your fingers in there. but it is possible to do at a latter time.

with 4.56 on 31s, i like the pep that i have. i am actually able to use overdrive on the freeway and i dont have to worry about having to floor it to get up to freeway speeds. i can pass vehicles with confidence instead of wondering if ill be able to make it.

contact dave (AZXJ on the boards:
{ http://Desertfab.com/
480-288-4213
[email protected]
pm AZXJ for a quote on any parts or services... } copied and pasted from his sig) he is a great retailer with great products and outstanding customer service. and no, i do not get anything for saying so.

 

[ratcat]

You are right, but you are also wrong.

One thing you lose sight of is starting from a light or dead stop in first gear. You have to waste a lot more energy getting started. Also there is a much bigger jump from 2nd to 3rd then there is from 3rd to 4th. If you are driving around in third all the time and have to downshift, your RPMs will make a much bigger change requiring much more fuel.

BTW...after having several jeeps with several different gear sets in all of them. Changing the ratio to 4:56 will net you much much better fuel mileage. As long as you don't expect it to be stock.

I really didn't "lose sight" of anything. I mentioned your point in my post. I get 15 mpg running in 3rd gear. I drive 24 miles to work 2/3 on the highway. I suggested the experiment if he also drove mostly highway.

It could also be a good indicator if the 32's were the only/main cause of the reduced mileage. Not suggesting he's making this mistake, but I've seen many people complaining of extra bad mileage that aren't considering the inaccuracy of their odometers after bigger tires. I haven't corrected my speedo so I just add 10% to my miles when I check the mileage. That's actually spot on from the stock tires to the 32's

Please also notice that I didn't ever suggest that the regear wasn't a good idea. I will regear eventually too as I would like to use all 4 gears in my tranny and have the extra grunt from a stop. It's simply that regearing can be sort of costly and if his main reason to regear is to get better mileage my suggestion would be a good short term fix.

My results suggest that the lugging in OD at highway speeds effects the mileage more that the starts and stops. This also seems logical to me as until the converter locks up the initial ratios are variable anyway.

on edit: I did the math backwards I think. It seems the jump to OD is a bit less than 2 to 3. Maybe 1.5 compared to 1.3.