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Strength difference between 4.88 vs 4.56 gears

L

lgorman00

NAXJA Forum User
Location
alaska
what are the strength difference between 4.88 and 4.56 in dana 30.
Is it better to stay with a 4.56 with locker for 35" tires
 
I doubt that there is any significant strength difference between the two gear ratios. Its like comparing apples to oranges (You cant). What gearing boils down to is getting the power from the moter to the tires. As you get bigger tires, your XJ will loose power to the tires. This is not to say the power is not there, im just saying that if you dont regear, you won't be able to harness the power that your XJ has. Regearing allows you to harness that power again after putting larger tires on.

I run 32" tires and have no power issues at all. I know that if I ran 35's, I would need to regear. When I go to 33's, I will most likely regear to 4.56's. 4.56's and 33" tires are a good (on road/off road) combination for those who like to wheel the blue trails(Intermediate) and use thier XJ's for a daily driver as well. The only problem with doing this is that if you want a multitask off road vehical, you will never have the best of either world. However, I am willing to make the sacrifice until the old (2000) XJ becomes a beater (In a year or two).

4.88 gears would be the way to go with 35" tires according to calculations; however, strength may be an issue with your Dana 30. That Axle will not take much abuse with 35" tires and 4.88 gears. You may want to think about upgrading your axle before going to 35" tires. You may be able to find a cheap D44 already geared low for cheaper than regearing your D30 and exsisting rear axle.
 
Last edited:
IntrepidXJ said:
i think he's more concerned with the size of the pinion and ring gear teeth between the two sets
Click to expand...


I didn't know that there was much of a difference between the two. Atleast no significant difference in strength. I suppose that one could have the pinion hardened making them stronger. But Why? the material is already strong.
 
HaZakated said:
I didn't know that there was much of a difference between the two. Atleast no significant difference in strength. I suppose that one could have the pinion hardened making them stronger. But Why? the material is already strong.
Click to expand...

oh, i never said there was a problem with the size, i just believed that's what Igorman was getting at.


goatman said:
There is nothing to be concerned about with 4.88 gears........the fears and negative comments are unfounded. It's like global warming......propagated by people who don't know based on what they've heard, which came from someone else who didn't know, but spoke on what they'd heard....and on and on.
Click to expand...
 
IntrepidXJ said:
well, 4.88 is the top for a d30....so that would be "way up in the gear ratio" for that axle
Click to expand...

What does strength have to do with regearing though in this situation? 4.56 vs 4.88


I think he is new and is a tad bit confused. Thats why I explained it. Hey, I learn something new everytime I get on here. The least I can do is give a little back.
 
Last edited:
HaZakated said:
I doubt that there is any significant strength difference between the two gear ratios. Its like comparing apples to oranges (You cant).
Click to expand...

You can most certainly determine strength differences between gearsets.

It is a long, drawn out set of equations, that most would become frustrated with before ever reaching the end.
 
Dirk Pitt said:
You can most certainly determine strength differences between gearsets.

It is a long, drawn out set of equations, that most would become frustrated with before ever reaching the end.
Click to expand...


take a glance at the {key} word in my first post......("Significant").........I know that the strength would vary slightly because the cut sizes are different between the two gears. I just don't think that it is enough to make a great difference. Mabey the apples to oranges phrase was a little 2 far. More like apples to apple trees...lol

What do you think about when you hear the word strength?...I think about tensile strength, modulus of elastitcity, Shear strength, Yield strength, Impact strength...etc, etc. I listen alot here on NAXJA. I usually stay to the side and just listen instead of speaking. I find that when I speak, there is always someone out there who makes it thier duty to prove me wrong. I see no sense in this. In this situation, I believe that this guy is new to XJ's and simply stated his question in a manor for which made sense to him, but not to long time XJ enthusiasts. Mabey I am completely crazy in making this assumption, but I think he should be more concerned with wasting his money than worrying about the strength between 4.56's and 4.88's. If he gears to 4.88 and goes to 35" tires and starts breaking axles left and right, he will have to spend more money on axles than what he could of spent just buying a set of dana 44's already geared low.



I am an advocate of learning from others mistakes. In most situations, I would have never said a word. In this situation I said a few. I hear people all the time talking about how they have to upgrade this and that if they want to do this and that. I am an advocate of overkill; however, Too much overkill is not nescesary. For example: There is no point in spending 5000$ on caging an XJ that will withstand impacts of up to 50,000 psi. That would be a waste of time and money unless you are just a very, very bad driver and plan on falling off a 100' cliff. I would estimate that on average, the maximum impact that an XJ undergoes in a roll over would be around 15,000psi.

What I am trying to say here is that in his situation, he need s more strength, but not from the gears, he needs more strength form the axle.

Have a great day.

Brian
 
Last edited:
HaZakated said:
take a glance at the {key} word in my first post......("Significant").........I know that the strength would vary slightly because the cut sizes are different between the two gears. I just don't think that it is enough to make a great difference. Mabey the apples to oranges phrase was a little 2 far. More like apples to apple trees...lol

What do you think about when you hear the word strength?...I think about tensile strength, modulus of elastitcity, Shear strength, Yield strength, Impact strength...etc, etc. I listen alot here on NAXJA. I usually stay to the side and just listen instead of speaking. I find that when I speak, there is always someone out there who makes it thier duty to prove me wrong. I see no sense in this. In this situation, I believe that this guy is new to XJ's and simply stated his question in a manor for which made sense to him, but not to long time XJ enthusiasts. Mabey I am completely crazy in making this assumption, but I think he should be more concerned with wasting his money than worrying about the strength between 4.56's and 4.88's. If he gears to 4.88 and goes to 35" tires and starts breaking axles left and right, he will have to spend more money on axles than what he could of spent just buying a set of dana 44's already geared low.



I am an advocate of learning from others mistakes. In most situations, I would have never said a word. In this situation I said a few. I hear people all the time talking about how they have to upgrade this and that if they want to do this and that. I am an advocate of overkill; however, Too much overkill is not nescesary. For example: There is no point in spending 5000$ on caging an XJ that will withstand impacts of up to 50,000 psi. That would be a waste of time and money unless you are just a very, very bad driver and plan on falling off a 100' cliff. I would estimate that on average, the maximum impact that an XJ undergoes in a roll over would be around 15,000psi.

What I am trying to say here is that in his situation, he need s more strength, but not from the gears, he needs more strength form the axle.

Have a great day.

Brian
Click to expand...

I understand exactly what you are saying. I was just pointing out that there is a way to calculate the strength difference between the two gearsets. Your first post made it sound impossible. I don't care what you said about significant differences, I was simply stating that you can determine the difference.

In this situation it's not necessary though since you will likely break a 4.56 just as easily as you will a 4.88.

What I'm saying is; if you know what you are doing, you can calculate the amount of input torque (within a range) a gearset can handle.
 
and I'm not quite following how your getting your roll over forces or pressures. It wouldn't require dropping off a 100' cliff to get 50ksi and 15ksi is pretty light, maybe a slow flop. A hrad roll can easily genrate 50ksi and of course that depends how much area it's spread over so really me should be talking about forces not pressures.
 
HaZakated said:
I doubt that there is any significant strength difference between the two gear ratios. Its like comparing apples to oranges (You cant). What gearing boils down to is getting the power from the moter to the tires. As you get bigger tires, your XJ will loose power to the tires. This is not to say the power is not there, im just saying that if you dont regear, you won't be able to harness the power that your XJ has. Regearing allows you to harness that power again after putting larger tires on.

I run 32" tires and have no power issues at all. I know that if I ran 35's, I would need to regear. When I go to 33's, I will most likely regear to 4.56's. 4.56's and 33" tires are a good (on road/off road) combination for those who like to wheel the blue trails(Intermediate) and use thier XJ's for a daily driver as well. The only problem with doing this is that if you want a multitask off road vehical, you will never have the best of either world. However, I am willing to make the sacrifice until the old (2000) XJ becomes a beater (In a year or two).

4.88 gears would be the way to go with 35" tires according to calculations; however, strength may be an issue with your Dana 30. That Axle will not take much abuse with 35" tires and 4.88 gears. You may want to think about upgrading your axle before going to 35" tires. You may be able to find a cheap D44 already geared low for cheaper than regearing your D30 and exsisting rear axle.
Click to expand...

You said you run 32 inch tires and have not regeared yet. I would presume you are running 3.55 gears in a dana 30?
Hold up a 3.55 pinion from a D-30 gear set to a 4.88 Pinion from a D-30 gear set and tell me there is no strength issues? Even from 4.56 to 4.88 there is a difference in pinion gear size and the amount of material available for the number of teeth. Yes, 4.88's in a D-30 are less strong that 4.56's in a D-30. The gears on the 4.88 D-30 are not much larger than the pinion shaft itself.
IMO 4.56's will keep the weak link at the axle shafts and u-joints where it is easier to effect repairs.
Base your decision on the crawl ratio you want to achieve. 4.56's will net (With an AW-4) a 34.9 to 1 ratio. 4.88 will net a 37.4 to one crawl ratio. Assumptions: AW-4, Stock 2.72:1 low gear T-Case.
I ran 4.56's with the D-30. Currently have 4.88's in the D-44. I upgraded the T-case to 4:1 for a better ratio.
Run the 4.56's.
 
3 tooth contact with 4.56's. 2 tooth contact with 4.88's. That is why the are said to be the weakest gearset for the Dana 30.
 
Call up dana ask them.... there is very little difference in gear strength. that is the point in using hypoid gears you can change ration and still keep strength. as for the pinion gear size issue. well it is a non issue as the weakest part much like splines on a shaft is the smallest diameter on the part (the pinion shaft). the most important part of any gear set is that it is installed properly most breaks are caused by improper setup or housing flex not a weak gear.
 
lgorman00 said:
what are the strength difference between 4.88 and 4.56 in dana 30.
Is it better to stay with a 4.56 with locker for 35" tires
Click to expand...

It is amazing how much non-information has been posted so far in this thread.

Get the ratio that you think is best for your gearing. There has never been any evidence posted on this topic to show that the 4.88's are weaker than the 4.56's. Never anything other than conjecture. Not even personal experience. The difference between 4.56 and 4.88 isn't very much. When considering strength, the increased rotation and leverage have to be considered along with the tooth contact area, so there could easily be no difference in strength whatsover. Jeeps used to come stock with 5.38 gears in D25/D27 which is the same gears as a D30, and they were standard cut, so arguably not as strong as the reverse cut XJ D30 gears.

Get what you want, and don't worry about it.
 
bj-666 said:
as for the pinion gear size issue. well it is a non issue as the weakest part much like splines on a shaft is the smallest diameter on the part (the pinion shaft).
Click to expand...

I've seen a handful of gears chip or break teeth, and never a broken pinion shaft.

Goatman said:
Jeeps used to come stock with 5.38 gears in D25/D27 which is the same gears as a D30, and they were standard cut, so arguably not as strong as the reverse cut XJ D30 gears.
Click to expand...

that guy that was with us in JV with the black CJ had 5.38 gears in a low pinion D30. he was on 36" Iroks with alloy shafts and said he never has had any problem with the gears.
 
Will you be running premium fuel?

Just thought I'd add to the nonsence.

But seriously. The strengh differences are not enough to really worry about. Just think of it this way. Drag racers have forever been running steeper gears with transbrakes and big slicks with multiple times the power that these Cherokees have and sure they will toast a set of gears on occasion but overall they hold up just fine. I understand that 4.88 is a little steep for racing but you get the idea.

But like someone said previosuly.....I would think about u-joints and axles way before breaking gearsets.
 
DaffyXJ said:
Hold up a 3.55 pinion from a D-30 gear set to a 4.88 Pinion from a D-30 gear set and tell me there is no strength issues?
Click to expand...

Strength difference? Sure. Put a gouge in the surface of one of your axleshafts, you'll get a stress concentration, and there will be a strength difference between the gouged shaft and an ungouged shaft.

Strength issue? I don't know. I run west coast rocks with an (open) HP D30 with 4.88s and 35s, and I'm not worried about gear strength.

With 35" tires, I would - and do - run 4.88s instead of 4.56s. With a locker I would look into getting aftermarket shafts.
 
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