4.56 gears vs. 4.88 gears for 33's

[4.0B2]

this guy has some good info...
i don't agree w/ ALL of it, but... still good stuff.

 

[legoms013]

All very true and valid points Hans.

You mentioned you would never run more than a 31's on the D35, maybe b/c of your driving style or something else.

My point is that many people have had good luck with the TTB D35 and up to 35's....so what would you go with if you were in my situation? 4.56's, 4.88's, or 5.13's considering that I will be on 35's in 2 years or less and no DD it anymore.

I only want to spend money on gearing for this D35 and Ford 8.8 (an explorer one mind you ) ONCE. With minimal regrets and optimum offroad capabilities.

I can live with un-ideal circumstances that this gearing will cause while I DD for a while until I get another car and this is no longer my main mode of transport.

I am not a lead foot offroader either. I believe in proper line choice coupled with proper throttle application to get you to your destination without breakage.

I look at it this way. If I have been able to live with 3.73s for 6 months commuting 60 miles per day, I should be able to cope with over gearing in the same manner that I dealt with under gearing.

 

[wahlstrom1]

You can always go up a gear (until your on the hwy) but you can't get a lower gear you don't have. I'd go 4.88's over 5.13's as I don't believe the D35 is capable of holding a tire that 5.13's require as mentioned a couple posts ago unless it's a crawl only wheeler.

There is a limited selection of gearing available for RBV's, short of an atlas or doubler (which will cause much more stress then lower axle gears) the lower gearing is required in our trucks as the tranny gearing SUCKS (3.40/3.72 first gears for manuals)!

 

[legoms013]

Alright now I am temporarily swung back to 4.88's. That seems to be more of a "fit all" for my needs.

4.56's: the pros outweigh the cons

4.88's: the pros = the cons

5.13's: the cons outweigh the pros

4.88, the winner (for now).

Unless someone gives me a good reason NOT to go 4.88.

 

[--weezl--]

well, i would go with 4.56 because based on what you just said, the pro's outweigh the cons... so there's more good things to happen with 4.56 then 4.88


lol, somehow i don't think you worded that

 

[wahlstrom1]

They're close enough that if your buying the same brand I'd go with whats cheaper...

 

[Bennybooster]

Just get the 4.88s, 5.13s will be too much

 

[HsOffRoad]

All very true and valid points Hans.

You mentioned you would never run more than a 31's on the D35, maybe b/c of your driving style or something else.

My point is that many people have had good luck with the TTB D35 and up to 35's....so what would you go with if you were in my situation? 4.56's, 4.88's, or 5.13's considering that I will be on 35's in 2 years or less and no DD it anymore.

I only want to spend money on gearing for this D35 and Ford 8.8 (an explorer one mind you ) ONCE. With minimal regrets and optimum offroad capabilities.

I can live with un-ideal circumstances that this gearing will cause while I DD for a while until I get another car and this is no longer my main mode of transport.

I am not a lead foot offroader either. I believe in proper line choice coupled with proper throttle application to get you to your destination without breakage.

I look at it this way. If I have been able to live with 3.73s for 6 months commuting 60 miles per day, I should be able to cope with over gearing in the same manner that I dealt with under gearing.

I am admittedly hard on stuff. I say I'd only run 31s because thats what I've found to be the best compromise of reliabiliy and off road performance for the type of wheeling I use my BII for. When you get used to running lightweight tube buggies with stuff like 1.5" diameter 4340 axleshafts, 9 3/4" ring gears, kingpins, and 1480 series steering u-joints made out of 300M alloy, you grow accustomed to being able to beat the snot out of things and be fairly confident that they will hold together. This is not the case with something like a D35 front TTB assembly - if you get aggressive, stuff goes boom.

We do a lot of long trips in very remote areas with these trucks. We may run 90 miles one way through the woods and only cross over 4 or 5 paved roads in the process. If you break an axle out there, you either have to stop and fix it (which means carrying spares, the necessary tools, etc...) or you are going to have a very difficult time getting the truck out of the woods to anywhere with civilization.

Sure, I could run bigger tires, and idle and winch the truck over everything at 1/2 a mile an hour and probably not break stuff, or run the front axle open or with a truetrac instead of a detroit - but none of those options really work for me. My BII is built for what I'd call "spirited woods bashing" (technical term, I know). The D35 axle (and the D44 for that matter) just doesn't hold up to big tires with lockers and that kind of use. It uses tiny wheel bearings that are an inch apart, 297X u-joints, a 7.5" ring gear, and 27 spline axle shafts. Personally, I'd rather be able to bash the truck and have it hold together (most of the time anyway) than run larger tires and have it break (especially considering that most of the time when you break a front shaft under load, the backlash rips the teeth off of the side gears in the detroit, and you have to pull the whole carrier out and rebuild it) - but again, that's personal preference.

Anyway, as for your gearing choice, The best advice I can give you is to do the following - calculate the mathematical RPM difference you will see on the highway with the 4.88 gear set and your current tires, and figure out what you would be running. Once you have the percentages figured out, spend a week alternating between running the truck at the RPMs you would need to run to attain your current highway speed with the new gears, and the slower speed you would need to drive to run the deep gears and keep the engine at the lower RPM... then see how much either of the two bother you, and use that to make your decision.

Personally, I run 4.10s and a 5 speed in my BII (2.9L) and it drives me nuts running the truck on the highway because I either have to turn the motor faster than would be ideal to keep up with traffic, or putt along and take forever to get anywhere. But, as stated, the manual transmissions that came stock in these RBVs have very high 1st gear ratios, so you need to run more gear to keep from beating up on the clutch. I'm hoping that swapping in a 4.0L flywheel and clutch assembly will help some of that (since it is heavier and carries more inertia), but I'll have to see how much that helps things when the truck ends up needing a clutch put in. The autos tend to have less of an issue with this, since the torque converter in essence multiplies the 1st gear ratio.

I'm in full agreement that if you plan to run 35s, having the extra gear will undoubtedly be nice - especially driving around town in high range. It will also work better off road (provided you can keep it together). If you can deal with the higher engine RPMS or lower highway speeds in the meantime, and go easy on the truck off road, I would say the 4.88s are proably the way to go. However, if a year from now you find that you are breaking stuff with your 35s and want to go back down to 33s, you are going to once again be forced to deal with the extra RPMS/reduced highway speed.

Ultimately, you are going to have to decide what is in your best interest for your particular situation. If yor plan is to start trailering the truck places in the future, go ahead and run as much gear as you need... just don't be surprised if you start having issues breaking stuff if you run more aggressive trails or use the truck hard.

I know that's probably not much help, but it's really going to be dependent on how the truck gets used, your personal prefernces, and our driving style.


-Hans

 

[4.0B2]

They're close enough that if your buying the same brand I'd go with whats cheaper...

2-300 rpms difference at 65 mph. Now why is 4.88 cheaper?? I noticed that to tho. It's like $50-75 cheaper. Is it bc demand for 4.56 is higher?

 

[-Nathan-]

problem with some people is that they dont have actual experience with gearsets. If I took a truck, and swapped out 3.73 to 4.10, and the owner wasnt told, guaranteed they could BARELY tell the difference. My point is that unless youve regeared, and know what parasitic drag and everything else does to affect they way your truck ACTUALLY feels and works with a different gearset, GTFO. Comparing numbers youve read off the interwebz means jack $hit.

Go 4.88 legoms13, youll have a much better wheeling experience, and feel like it really wakes up your truck, makes it exciting again.

 

[legoms013]

well, i would go with 4.56 because based on what you just said, the pro's outweigh the cons... so there's more good things to happen with 4.56 then 4.88


lol, somehow i don't think you worded that

Im thinking about the future, not just the present weezl. The pros equal the cons right now, and then when i run a 35" tire the pros outweigh the cons. I am not concerned with the cons right now, I can live with temporary misery if need be.

Again, I feel junkie, Nathan, and wahlstroms advice as the points I seriously consider, as their opinions are directly a result of their experiences and not confoluded by Internet banter. 4.88's it is then. I have decided.

Thanks guys!

 

[--weezl--]

ahh gotcha

 

[97fordrunner]

I ran 33's for a little while with my 4.88s and loved it with the 5r55e auto. the truck ran 65-70mph down the freeway in overdrive as opposed to having to run like you said up around 75-77mph to get to the point where it will stay in OD without shifting a ton. And it crawled like crazy and fuel mileage increased to as weird as it sounds but I think that was due to not working the motor so hard. Then I got a deal on 35's and still love the gears it still crawls really nice and can turn the tires on rock and mud. thats just my experience with them

 

[4x4junkie]

I disagree with this statement wholeheartedly. I can tell you from experience that you can definitely have too much gear.


There are multiple reasons for this:


First off, there is something to be said for wheelspeed, especially on certain obstacles/terrain. For instance, back when I had my shop, I ran supermod class tube buggies. I can guarantee you there are a lot of obstacles that you just aren't getting over trying to crawl with 5 transfer cases and 7.38 axle gears. Sometimes, wheelspeed and momentum are a must.

Second, there is an inherent strength issue with lower gear sets. As multiplication (the ratio) increases, the head of the pinion gets progressively smaller (with fewer teeth), and/or they try to add teeth to the ring gear, making the teeth smaller. This reduces the amount of area over which the load gets spread. It's a very simple concept to express if you try the following - First, interlock your fingers all the way, and try to spread your hands against one another in "shear" type motion. Now, slide your hands apart so that only the tips of two fingers are touching and try again. See the difference? With axles like the D35 which uses a 7.5" ring gear and no extra pinion support,this becomes even more of an issue thn it is with something ike a D60 or 10.5" 14 Bolt.

Third, the extra torque multiplication generates excessive stress on drivetrain parts. Let's assume for a moment that you are running a motor with 200 ft lbs of torque, a manual transmission with a 5.1 first gear, a transfer case with a 2.72-1 low range, and 3.73 axle gears. Simplifed to it's most crude form (not accounting for parasitic drag in the system, slip torque, shock loading, etc...) your 200 ft. lbs of torque becomes roughly 10,150 ft. lbs of torque at the tires. A stock dana 35 axle shaft is going to fail at around half of that torque, so if you ever wedge a tire, or shock load an axle under heavy throttle, you are going to grenade a shaft. Now if you are running the same setup with dual cases and 5.13 gears your previous 10,150 ft lbs of torque is now up around 38,000 ft lbs. It doesn't take a rocket scientist to realize that this is murder on axleshafts, the input/output shafts on the second t-case, driveline parts, gearsets, etc.

Adding larger tires only intesifies this issue because it increases slip torque, leverage, weight, & shock load on the drivetrain.

Personally, I'd never consider running anything larger than a 31" tire on something like a D35, and I'd never run a gearset lower than 4.10s. I"ve destoyed 4340 chromo 30 spline shafts with 31" tires and a bone stock 4.0L. You look at the break stength figures for the shafts, and you see that it really doesn't take much. (FWIW, really high gearsets like 2.73s and such tend to have the opposite issue - as the pinion head gets larger (assuming no carrier break), the ring gear gets thinner, and in certain instances, can become thin enough to enough to allow the carrier to deflecti under load. In genreal, gearsets in the 3.73 to 4.10 range tend to offer the best compromise for strength in most housing assemblies).


As for the tire stuff, Weezl, you really need to listen to what these guys are saying. If you get out a tape measure and go measure some tires, you will see that what the tire says on the sidewall has very little to do with how tall it acutally is. The advertised O.D. and C.S. numbers help a little, but even then, the height will vary quite a bit depending on rim width, inflation pressure, etc. I've seen off-brand RV stlye "Gound Hog" knockoffs that read 36" on the sidewalls that are only a hair over 33" tall with a tape. You can measure a 33 X 12.50- 15 TSL and a 33 X 12.50 -15 BFG Mud Terrain (both fresh out of the mold), and you wll find that they are NOT anywhere near the same size. It is VERY MUCH POSSIBLE for a tire claiming to be 33" tall and a tire claiming to be 34" tall to be the same height - or even for the 34" tire to measure smaller than the 33" tire.


-Hans

Good post. Though I don't disagree about the gear strength thing, one thing that needs to be taken into consideration is the fact most of the axle's other components (shafts, u-joints, etc.) tend to be weaker than even a 5.13:1 R&P set, so I don't see gearset breakage as something to really worry too much about (D30s OTOH have some issues with deep gears, but they also have a 3/8" smaller ring, as well as a smaller pinion shaft dia. too, which leads to more gear deflection). I've yet to see anyone who's broken a 5.13 D35 gearset and shown pictures of it, though I've seen plenty of broken shafts lol.

Also, your tires typically will slip long before the torque on your shafts ever could reach 38,000 ft-lbs. Though an exception might be is if your tire gets caught against an undercut rock ledge and wedges itself in there (or if you're on the throttle hard and bouncing, the shockload from which is what typically breaks stuff).



Legoms, What i would probably say is go ahead with whatever your gut tells you, be it 4.88 or 5.13, as either one will be a thousand worlds better than your 3.73s (FWIW, with the 5.13s and your auto's 0.75:1 OD, you should be turning around 2550 RPM @ 65 if my math is right (2400RPM w/35s)).
If you DO find yourself breaking stuff, you could always sell those axles and upgrade to something like a D60 (a locked D35 & 8.8 with good gears in it should not be hard to find a buyer for).
I think a D60 might be a bit excessive though if you're always one to pick your line and crawl it, rather than blast up stuff with a bunch of throttle.

A few guys here have ran 37s and even 38s on these axles and managed some decently long periods without issue doing some fairly decent rock trails. Though again it IS all in how you drive. You get too crazy with the skinny pedal and like said, things are bound to break.



BTW HS, You''l absolutely love the 4.0L clutch upgrade. The stock 8-7/8" clutch sucks donkey nuts, which is about all I can say about it.

 

[mhughes165]

i say put a small block in it and leave it 3.73's lol....then ull be gettin good mileage with no lack of power