Gear change ? and detroit locker

[70jimmy]

I have a 14 bolt FF 10.5 ring gear with 4.10's I am comparing cost and benefit of gear change vs doubler, 4 to 1 etc. Front is a 3/4 ton 10bolt with upgraded shafts and its welded.

The rear has a detroit locker. If I change gears can I just order the ring and pinion and have it reset? Can I use the locker I have or do I need a different one with the new gears?

What determines whether you need a new carrier (like I know what that is).

thanks

 

[bot0611]

im not that sure but the carrier only changes the type of traction, posi, limited slip that stuff..

Let me know if im wrong

 

[chevyuser74]

u can keep your carrier and your locker, now depending on the Carrier break is 4.10-down or 4.56-up which is determined by the original gearing, determines whether u need thick gears or not

 

[deadlew]

Actually it is cheaper to get gears for the 14B FF with the 4.10 carrier than a 4.56 carrier. You will be able to keep your current 14B FF carrier and locker and get them set up.

PaulC

 

[Hogback Fabrication]

Whoa, lots of crazy info posted so far.

IMO, gear your axles for the street and gear your t-case for the trail. This gives you the best of both worlds, you won't see much off-road improvement by going to deeper gears in the diffs.

Next, your rear detroit and carrier will work no matter which ratio you choose. The detroit works with any ratio because it fits inside the carrier on a FF 14 bolt. The carrier split for a 14 bolt is 4.10/4.56 BUT there are thick gears made for this axle. If you want 4.56/4.88/5.13/5.38 gears, just order the "thick" gearset and they will work perfectly on your carrier.

As for what determines when you need a new carrier, it has to do with the thickness of the ring gear mounting flange. The lower (numerically higher) ratios need to push the ring gear closer to the center of the housing and hence require a carrier that is offset by a quarter inch or so. The "thick" gears basically take up all of that distance and allow you to use the low gears on the more common carrier.

Each diff has its own "carrier split" (well, 10 bolts don't but just about every other one does) which means that there are two or more carrier offsets used. Some of the aftermarket gear vendors offer thick gears for certain diffs so that you don't need to buy new carriers, but thick gearsets aren't offered for every diff (Chevy/Dodge D60's for example).

 

[70jimmy]

ok so next ? Using RPM calculator on Randy's Ring and Pinion site I show my current RPM's at 2485 at 65 mph, seems to be in an ok range for hwy. This seem like acceptable rpm to you? Runs good going down hwy in high range on the 205 Tcase, so I have been leaning more toward a T-case change.

But I don't want to do the Tcase change and then find out I still need to change R and P's.

FYI I am looking at the ORD doubler, Klune black box, Atlas 4 to 1 and JB conversions case.

Those who have any please let me know pros and cons. Obviously I would need crossmembers for the doubler and driveshaft mods.

Thanks

 

[bp71k5]

I've got 4.10's and the doubler in my 71. The 4.10's are nice for the highway. I think you'll be fine there.

If you are serious about the x-case change, any of those options give plenty of low gear.

 

[Greg72]

ok so next ? Using RPM calculator on Randy's Ring and Pinion site I show my current RPM's at 2485 at 65 mph, seems to be in an ok range for hwy. This seem like acceptable rpm to you? Runs good going down hwy in high range on the 205 Tcase, so I have been leaning more toward a T-case change.

But I don't want to do the Tcase change and then find out I still need to change R and P's.

FYI I am looking at the ORD doubler, Klune black box, Atlas 4 to 1 and JB conversions case.

Those who have any please let me know pros and cons. Obviously I would need crossmembers for the doubler and driveshaft mods.

Thanks

You're on the right track young Jedi...

Don't mess with the axle gears if you already know you're doing aftermarket t-cases. Deeper axle gears won't get you deep enough by themselves and you'll end up doing a Doubler (or whatever) anyway to get REAL offroad reduction. To add insult to injury....after paying to two sets of gear swaps and buying the Doubler parts.....you'll also need to swap in an OD tranny so that you can drive on the highway! Talk about spending the most money you possibly can!!!

4.10s with an Atlas-4 should be sweet. I'm sure you've already seen my buildup using that combo. It will crawl at 110:1 in low-low range, and will still cruise down the highway at only 2300RPMs at 65MPH.....and that's WITHOUT an overdrive transmission, just your basic TH400.

The real secret is going to be in your selection of transfercase setups. A traditional 4:1 Doubler isn't going to be quite deep enough with only 4.10s...so you're going to need to find a way to get more like a 5.x:1 or 6.x:1 ratio in the xfercase to make it perfect.

 

[6.2Blazer]

For whether to change the axle ratios or t-case (doubler) it completely depends on what you are trying to accomplish. Changing the axle gears will have the biggest effect on street driving, but t-case gears have more effect off-road (obviously when in low range). Axle gears can't come anyway close to altering the crawl ratio the way a doubler can. You could have to go from the current 4.10's all the way down to 8.20's to get the same crawl ratio, which obviously isn't possible.

If you are happy with the street performance of your rig (especially if you like to drive at 65 mph and it's already at 2,500+rpm) then definitely keep the 4.10's in the axles and get the doubler.

 

[h0wl0ngcanitbe]

[hijack]
can i ask what size tires your runnin im very curious about all this gear info, also what is a doubler?
[hijack off]

 

[Greg72]

[hijack]
can i ask what size tires your runnin im very curious about all this gear info, also what is a doubler?
[hijack off]

There are a couple of EXCELLENT threads in this forum that have discussed gearing in-depth. A quick search will give you a couple hours of educational reading.

A couple of quick points:

1. Tire Diameter has nothing to do with crawl ratio. It is only important when trying to calculate highway RPM... a larger tire will drop your highway RPMs compared to a smaller tire, all other things being equal. Larger tires DO add a lot of rolling mass (like 4 HEAVY flywheels) and will affect the "pep" of your engine. In other words, I wouldn't run 44's with 3.08 gears just because the highway RPMs looked good.

2. "Doubler" is the brand name of the Off Road Design's dual-transfer case product. Most of us here use it generically to describe any dual case solution. A single factory transfercase generally provides a 2:1 reduction ratio, so putting two of them together gives you 4:1 (or more) reduction for offroad crawling. Most factory trucks have an overall crawl ratio of around 30:1 - 40:1.....for more serious low-speed work, a ratio in the 100:1 - 120:1 range is more desirable. The simplest rule of thumb is to try to match your crawl ratio to your tire circumference measurement. This will give you 1" of forward motion for each engine RPM. (Ex: a 40" tire has a circumference of 125", so you'd try for a crawl ratio in the 125:1 range)

As you do the calculations for crawl ratio, you'll quickly realize that those kinds of numbers require more than a simple axle gear swap....you just can't get there without more reduction somewhere else. If you also want streetability, the problem becomes the balacing act of deep gearing vs. low highway RPMs.

 

[70jimmy]

Excellent explanation Greg!!! Thanks, yep doubler, underdrive type gear reduction is my choice now just to pick which one. Oh and find another money tree.

hOwlOngcanitbe: I am running 37" BFG Krawlers

 

[h0wl0ngcanitbe]

As always thanks for the great responses!

 

[kennyw]

1. Tire Diameter has nothing to do with crawl ratio. It is only important when trying to calculate highway RPM...

Tire diameter is much more than just the weight of the wheels/tires. It is also a major part of the overall gearing, but generally ignored when computing crawl ratio It shouldn't be.

 

[Greg72]

Tire diameter is much more than just the weight of the wheels/tires. It is also a major part of the overall gearing, but generally ignored when computing crawl ratio It shouldn't be.

True.

A particular crawl ratio does not guarantee the same performance across all vehicles. 100:1 will feel much different on a Jeep with 31" tires than it will on a K5 with 49" Iroks....

31" Tire Jeep w/100:1 crawl

Rate across ground at idle (850RPM): 69 ft/min
RPMs needed to reach 1MPH: 1100RPM

49" Tire K5 w/100:1 crawl

Rate across ground at idle (850RPM): 109 ft/min
RPMs needed to reach 1MPH: 700RPM


Clearly, the driving experience would be quite different between the two vehicles, even though the calculated ratio is the same. The Jeep is just about perfectly geared, and the K5 is probably wishing for something deeper.

The "1 inch of travel/1RPM" target is a method that incorporates the tire diameter into a crawl ratio calculation. Ideally, that means that at 850RPM, and tire is travelling 850 inches/ minute (or about 71 ft/min). For technical 4-wheeling, it is a speed that allows for good control, easy-to-modulate throttle, and reasonable forward progress across the obstacles.