axles

Larry R. · **Joined:** Sun Jan 21, 2007 1:35 am **Posts:** 92

Does any one know which axles are in the crd's? Also what gear ratio's are availble, I'm thinking of re-gearing for milage (have 3.73 gears now).

fastRob · **Posted:** Thu Jul 31, 2008 11:26 pm

With 2 overdrive gears in the transmission what are your goals?
Do you want bigger tires or smaller tires?
I like the Jeep axles for the Rubicon with lockers, discs and 4.10's at a very reasonable price but with bigger tires the mileage would surely suffer.

A build sheet using your VIN from the dealer or Jeep.com would tell you exactly what the factory build was.
Mine are corporate 8 1/4", whatever that means.

tjkj2002 · **Posted:** Thu Jul 31, 2008 11:54 pm

Larry R. wrote:

Does any one know which axles are in the crd's? Also what gear ratio's are availble, I'm thinking of re-gearing for milage (have 3.73 gears now).

You have the Chrysler 8.25.If you are 4wd you can only go as low as 4.10's since that is the lowest ratio for the D30A front diff you have,and yes you need to regear both F/R axles at the same time.At the present time only 2 people make the 4.10's for the D30A,Dana/Spicer and Precision gears,many make the gears for the 8.25 like Precision gear,Richmond,Yukon,and Motive gear but stay far,far away from genuWHINE gears(they whine no matter what).If you happen to be 2wd you can go to 4.56's in the 8.25.

kdlewis1975 · **Posted:** Fri Aug 01, 2008 12:06 am

I've had the same idea...changing the gears out with the goal of gaining fuel economy. It would seem that we could increase our highway mileage on the freeways by gearing a little taller and running the engine at lower RPM. I've wondered what is available too. I think Libby's with the six-speed came with something like 3.55's probably to make up for it's lower overall ratio. I think that would would reduce engine speed by about 200 rpms. For those of us with the '06's we wouldn't want the limited slip varieties because of the ESP.

Sir Sam · **Posted:** Fri Aug 01, 2008 12:52 am

kdlewis1975 wrote:

I've had the same idea...changing the gears out with the goal of gaining fuel economy. It would seem that we could increase our highway mileage on the freeways by gearing a little taller and running the engine at lower RPM. I've wondered what is available too. I think Libby's with the six-speed came with something like 3.55's probably to make up for it's lower overall ratio. I think that would would reduce engine speed by about 200 rpms. For those of us with the '06's we wouldn't want the limited slip varieties because of the ESP.

No, KJs only came with 3.73s and 4.10s. There are many gear options including 3.55s for the 8.25 rear. There are no ring and pinion sets for the front end as the D30A uses a different length pinion gear.

I am looking at this from the same angle as you are.......going 3.55s for highway cruising. the 3.55s for the rear aren't a problem, its the front that is the problem.

Uffe · **Posted:** Fri Aug 01, 2008 8:34 am

I can't help but comment on this.

Changing diff ratios for highway mileage on a 4wd?? What on earth has possessed you guys to consider that as an option?!

Buy a TDI if you want fuel economy improvements on the highway - you'll be surprised in a positive way when you make the change. On the other hand you will most likely be disappointed if you change diffs and don't gain a single MPG because the main factor at highway speeds is the air resistance, not the drivetrain resistance.

Try a better diff oil if you want to fuss about with diffs, I really don't think it will help you enough for the price two new diffs for it to be worth it!

Sir Sam · **Posted:** Fri Aug 01, 2008 9:28 am

Uffe wrote:

I can't help but comment on this.

Changing diff ratios for highway mileage on a 4wd?? What on earth has possessed you guys to consider that as an option?!

Buy a TDI if you want fuel economy improvements on the highway - you'll be surprised in a positive way when you make the change. On the other hand you will most likely be disappointed if you change diffs and don't gain a single MPG because the main factor at highway speeds is the air resistance, not the drivetrain resistance.

Try a better diff oil if you want to fuss about with diffs, I really don't think it will help you enough for the price two new diffs for it to be worth it!

But Uffe by the same right you could look at how long it would take for a TDI to pay for itself as a second car for it to be worthwhile. New gears cost far less than a TDI would.

Then throw in things like the 400 mile drive to where you are going wheeling, and having the higher gears becomes attractive to some of us. All my cherokees have 3.55s, for my MJ I will be mated to 3.55s, so its not like 3.55s are just ungodly high gears.

tjkj2002 · **Posted:** Fri Aug 01, 2008 10:08 am

Sir Sam wrote:

kdlewis1975 wrote:

I've had the same idea...changing the gears out with the goal of gaining fuel economy. It would seem that we could increase our highway mileage on the freeways by gearing a little taller and running the engine at lower RPM. I've wondered what is available too. I think Libby's with the six-speed came with something like 3.55's probably to make up for it's lower overall ratio. I think that would would reduce engine speed by about 200 rpms. For those of us with the '06's we wouldn't want the limited slip varieties because of the ESP.

No, KJs only came with 3.73s and 4.10s. There are many gear options including 3.55s for the 8.25 rear. There are no ring and pinion sets for the front end as the D30A uses a different length pinion gear.

I am looking at this from the same angle as you are.......going 3.55s for highway cruising. the 3.55s for the rear aren't a problem, its the front that is the problem.

Actually they make 3.21 gears(standard on '08 KK's) and 3.55 gears(only on 6 speed KJ's) for the D30A as inaddition to 3.73's and 4.10's.

By adding higher gears with the same tires is basically the exact same as adding larger tires with the stock gears,you will loose MPG's in a KJ and have that feeling of power lose.Also you will be adding extra stress on the tranny and t-case.

Sir Sam · **Posted:** Fri Aug 01, 2008 11:20 am

tjkj2002 wrote:

Sir Sam wrote:

kdlewis1975 wrote:

I've had the same idea...changing the gears out with the goal of gaining fuel economy. It would seem that we could increase our highway mileage on the freeways by gearing a little taller and running the engine at lower RPM. I've wondered what is available too. I think Libby's with the six-speed came with something like 3.55's probably to make up for it's lower overall ratio. I think that would would reduce engine speed by about 200 rpms. For those of us with the '06's we wouldn't want the limited slip varieties because of the ESP.

No, KJs only came with 3.73s and 4.10s. There are many gear options including 3.55s for the 8.25 rear. There are no ring and pinion sets for the front end as the D30A uses a different length pinion gear.

I am looking at this from the same angle as you are.......going 3.55s for highway cruising. the 3.55s for the rear aren't a problem, its the front that is the problem.

Actually they make 3.21 gears(standard on '08 KK's) and 3.55 gears(only on 6 speed KJ's) for the D30A as inaddition to 3.73's and 4.10's.

By adding higher gears with the same tires is basically the exact same as adding larger tires with the stock gears,you will loose MPG's in a KJ and have that feeling of power lose.Also you will be adding extra stress on the tranny and t-case.

As far as I can tell the KK ring and pinion is different from the KJ ring and pinion.

I had not checked the part numbers for the KJs with the NSG370, I will have to look into that.

And its not a given that we will loose any gas mileage, just like its not a given that we will gain any gas mileage, there are too many factors that come into play, I think that its worthwhile to switch to 3.55s in a CRD and see what happens. When I found out the CRD had 3.73s I was a little surprised, generally that is lower than you see with many diesels.

And uffe, its not about rolling resistance, the idea is that since the CRD makes more torque lower in the powerband that you can drop the engine rpms for a given speed and consume less fuel while still having a vehicle that is not lugged down.

Once again though, theres alot that comes into this, tire size, engine speed, transmission ratios, etc.

DarbyWalters · **Posted:** Fri Aug 01, 2008 11:29 am

Taller tires (very tall) will hurt aerodynamics. Adding a slightly taller tire will sometimes improve mpg after you adjust your numbers for the change. I went to 235/75/16s which made an ~4% diff in overall gearing which results in the same as throwing in a 3.58 gear set. Tires is the easiest and cheapest way to make a difference.

ATXKJ · **Posted:** Fri Aug 01, 2008 1:44 pm

Uffe - Austin to Colorado - 900 miles, Austin to Moab 1200 miles (one way) - highway gears are reasonable as long as I don't tow.

Sir Sam - most of the diesels around here are trucks and they come with 4.10/4.11's - for towing - in fact It's assumed if you have a diesel you're using it to tow.

Although I'd bet CRD's have 3.73's because most Liberties have 3.73's and adding another gearset to the distribution channel was too expensive for Chrysler.

With tires - weight is also a factor especially in town - when I went from stock to MTR's I lost 2-3 mpg - but I think they're a lot heavier than Darby's Hercules.

Sir Sam · **Posted:** Fri Aug 01, 2008 5:16 pm

ATXKJ wrote:

Uffe - Austin to Colorado - 900 miles, Austin to Moab 1200 miles (one way) - highway gears are reasonable as long as I don't tow.

Sir Sam - most of the diesels around here are trucks and they come with 4.10/4.11's - for towing - in fact It's assumed if you have a diesel you're using it to tow.

Although I'd bet CRD's have 3.73's because most Liberties have 3.73's and adding another gearset to the distribution channel was too expensive for Chrysler.

With tires - weight is also a factor especially in town - when I went from stock to MTR's I lost 2-3 mpg - but I think they're a lot heavier than Darby's Hercules.

trucks yes, that are really setup for towing, but with most smaller diesels, such as the navara terrano and patrol have a final drive closer to that of 3.55s.

DarbyWalters · **Posted:** Fri Aug 01, 2008 6:13 pm

My Hercules TerraTrac ATs in 235/75/16s with a higher weight rating were only 2-3 pounds heavier per tire (from memory)...and they are MUCH better in wet/dry/offroad...

I also went with all Aluminum Skids to keep the weight down...and they actually make the underside "smoother" for aerodynamic improvements (just a guess...not scientifically tested...lol)...

Larry R. · **Joined:** Sun Jan 21, 2007 1:35 am **Posts:** 92

At 55mph I get 20mpg, if I speed up to 62mph to get the second overdrive and slow down to 57mph I gain 4mpg. This is why I think a gear change would be worthwhile. To take advantage of the low end torque, since the f-37 recall screwed with the shift points.

tjkj2002 · **Posted:** Fri Aug 01, 2008 6:58 pm

Larry R. wrote:

At 55mph I get 20mpg, if I speed up to 62mph to get the second overdrive and slow down to 57mph I gain 4mpg. This is why I think a gear change would be worthwhile. To take advantage of the low end torque, since the f-37 recall screwed with the shift points.

Going to a higher gear set will screw up your shift points even more,your TCM will only learn so far within a specified range,going to a higher gear set will be out of that range and the best torque range of your engine for cruising at higway speeds.

The CRD doesn't make that much more torque then the 3.7,about 70-75lbs -ft or torque,yes it is made at a lower RPM but the CRD will be effected,though not as much,as a gas KJ would by adding a higher gearset and keeping the same size tires.Spending a $1000 for a slight loss of MPG's and no other benifit doesn't make much sense but by all means do it,then I get to laugh when your start complaining that you spent all that money and lost mpg's.

Your driving a 4300lbs brick that is 4wd,be happy with 20-25mpg's since no other vehicle in the KJ's class with the same capibilities does not get that kind of mpg's.

Larry R. · **Joined:** Sun Jan 21, 2007 1:35 am **Posts:** 92

A friend of mine works at a Jeep dealership, he said it would be know problem setting the computer for the higher gear set. So your shift points will be un-affected, this leads me to believe some came with 3.55 gears.

Uffe · **Posted:** Sat Aug 02, 2008 4:41 am

You can nearly get an old TDI for the same money as you will have to shell out for those gears + labor costs (your own time at least).

1200 miles on highway with a 4wd??? Is that an argument at all?? Minimum 44MPG on the TDI vs maximum 33MPG on the KJ, if you do that much highway driving, why don't you consider that change?

The gears are for economy right? Why not spend your money more wisely and do the math: Gears may give you 2-3MPG boost while the TDI will give you at least 11MPG boost (worst case TDI vs best case KJ).

DarbyWalters · **Posted:** Sat Aug 02, 2008 11:09 am

tjkj2002 wrote:

Going to a higher gear set will screw up your shift points even more,your TCM will only learn so far within a specified range,going to a higher gear set will be out of that range and the best torque range of your engine for cruising at higway speeds.

The CRD doesn't make that much more torque then the 3.7,about 70-75lbs -ft or torque,yes it is made at a lower RPM but the CRD will be effected,though not as much,as a gas KJ would by adding a higher gearset and keeping the same size tires.Spending a $1000 for a slight loss of MPG's and no other benifit doesn't make much sense but by all means do it,then I get to laugh when your start complaining that you spent all that money and lost mpg's.

Your driving a 4300lbs brick that is 4wd,be happy with 20-25mpg's since no other vehicle in the KJ's class with the same capibilities does not get that kind of mpg's.

The CRD puts out AT LEAST 25% more torque and at a much lower rpm range. That is not just a little bit by any means. If the 3.7L put out 295 ft pounds, a different gearing would help it most likely also. The thing is the COST including INSTALLATION would be a cost you would need to recover. The other thing is AERODYNAMICS at higher speeds...once over about 65mph, the Liberty is at a disadvantage. I would not be laughing at anyone who tried it tho...

DarbyWalters · **Posted:** Sat Aug 02, 2008 11:12 am

Uffe wrote:

You can nearly get an old TDI for the same money as you will have to shell out for those gears + labor costs (your own time at least).

1200 miles on highway with a 4wd??? Is that an argument at all?? Minimum 44MPG on the TDI vs maximum 33MPG on the KJ, if you do that much highway driving, why don't you consider that change?

The gears are for economy right? Why not spend your money more wisely and do the math: Gears may give you 2-3MPG boost while the TDI will give you at least 11MPG boost (worst case TDI vs best case KJ).

It is not that simple Uffe...people are still paying on thier CRDs...an older TDI is not just the cost of that vehicle but any needed repairs...for some, the size of the CRD is what we need and the TDI won't meet those needs. There is a lot more involved than simple mpg math.

kdlewis1975 · **Posted:** Sat Aug 02, 2008 11:15 am

Oh, I agree that adding a different gear would be a pricey proposition. But since we're talking about cost, you have to consider the price of buying another vehicle and paying for the cost of taxes, title, and insurance on a yearly basis. When I bought the CRD, I was single and I intended it to be my do-it-all vehicle. I thought it would be something that had the potential to get 30 mpg highway and therefore would be an acceptable vehicle for a 20 mile commute to work. Rather than own a separate truck for hauling things for the house I just bought, I figured I'd find a utility trailer so that I could have a miniature tractor/trailer combination. I also wanted something 4-wheel drive since it snows an appreciable amount here, and I attest that the ESP works very nicely.

Since I bought the Jeep, I've bought a house, I've gotten married, I have a daughter on the way, and I can't exactly afford to add a third car at this point. My wife's vehicle brought to the marriage is a 2006 Suzuki Grand Vitara...talk about underpowered and poor fuel mileage. Unfortunately, both are too new and have too much negative equity at this point, so a trade-in isn't exactly and option at this point. I've perused the auto listings and you just don't find a VW TDI in this area for a low price that isn't already very old and/or ragged out. When I bought the CRD, I also expected to keep it for a very long time and with the price of diesel, a couple of MPGs better would pay off over the long term. One could also argue that making the engine turn fewer revs would also add to the longevity. CRD owners often remark that they get their best economy when they keep the tach under 2000 RPM. At 70 mph, my tach reads 2050...my speedo reads about 2 mph too high. I generally see about 27 mpg at 70-75 mph and 28-30 at 60 mph. It would seem that the best way to get a taller gear would be to simply change the gear instead of spending the money to put on bigger tires and a lift to accommodate them....it's not like this is necessarily inexpensive either. The aero issue is a whole other debate...doing the lift probably increases the drag...changing a gear doesn't.

If I was serious about adding new gears, I'd go to a junk yard and find wrecked Libby with a manual (see Wikipedia link below). Going "used" would probably be the most economical route to go. I still wonder if there would be a problem for our ESP equipped Libby's. I did wonder about what one could do about the shift points and recalibrating the speedo.

http://en.wikibooks.org/wiki/Jeep_Liberty/Gearing

These two links are actually from the above Wikipedia page, they could be interesting to play around with.
http://www.novak-adapt.com/knowledge/gearing.htm ...tests gearing scenarios
http://www.4lo.com/calc/geartable.htm ...relates tires sizes and economy

Thanks for the nice discussion thusfar....

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