4.56 Gear Ratio

BJ'naKJ · **Posted:** Fri Dec 08, 2006 1:59 pm

I see all the talk of swapping the 3.73 to 4.10. What about a 4.56 gear swap? At least one online shop shows it as available for the KJ drivetrain.
After installing 245/75s, I would like to get at least back to the original gearing, but something lower might work even better.

allyrand · **Posted:** Fri Dec 08, 2006 2:11 pm

You can go 456 in the rear of the KJ...and thats the largest size gear set that will fit the Corp 8.25...on the front, your out of luck tho..the largest you can go is 410...but I would bet running 410s would do pretty well with a 245 size tire

detroit_doc · **Posted:** Fri Dec 08, 2006 2:16 pm

If you search my posts I did the calculations. 4.10s with 245/75/R16s gives you a slightly lower over gear ratio than 235/70/R16s with 3.73s...

Let me see if I can go dig it up...

detroit_doc · **Posted:** Fri Dec 08, 2006 2:22 pm

Here you go...

I'm interested in doing 4:10s but wanted to get an idea of how it would compare to 3.73's with stock tires. So with the help of the discount tire calculator (http://www.discounttire.com/dtcs/infoTireMath.dos) and a little bit of math I came up with a comparison. I figured I'd post it incase anyone else was interested.

This data is for 60 MPH, using a 42RLE with an overdrive ratio of 0.69:1...

Stock 235/70/R16 / Stock 3.73 gears
Wheel RPM: 718.48
718.48 x 3.73 x .69 = 1849.1
1849 RPM @ 60 MPH

245/75/R16 / Stock 3.73 gears
Wheel RPM : 682.64
682.64 x 3.73 x .69 = 1756.8
1757 RPM @ 60 MPH

245/75/R16 / 4.10 gears
Wheel RPM: 682.63
682.64 x 4.10 x .69 = 1931.2
1931 RPM @ 60 MPH

So it looks like 245/75/R16 with 4.10s is a really good match. It should perform slightly better than 3.73's with stock tires. But it's not so low that you're going to hurt your freeway driving. Also according to the discount tire calculator your spedo with read 5% low with the 245/75/16s versus the 235/70/16.

BJ'naKJ · **Posted:** Fri Dec 08, 2006 2:44 pm

allyrand wrote:

You can go 456 in the rear of the KJ...and thats the largest size gear set that will fit the Corp 8.25...on the front, your out of luck tho..the largest you can go is 410...but I would bet running 410s would do pretty well with a 245 size tire

That's what I thought I'd read somewhere, but the following supplier lists a 4.56 specifically for the KJ D30:

http://www.rocky-road.com/kjdrive.html

Gris · **Posted:** Fri Dec 08, 2006 2:49 pm

I've been in email contact with Rocky-Road recently to discuss this. He has parts liste don his web page that WILL NOT work, he has never tried to install these gear by his own admition and he sells various other parts and accessories that are no longer manufactured or other proved to be crap.

I asked him to update his page to correct, at a minimum, the gear section so that people won;t be buying the incorrect parts and was ignored.

BJ'naKJ · **Posted:** Fri Dec 08, 2006 5:59 pm

Gris wrote:

I've been in email contact with Rocky-Road recently to discuss this. He has parts liste don his web page that WILL NOT work, he has never tried to install these gear by his own admition and he sells various other parts and accessories that are no longer manufactured or other proved to be crap.

I asked him to update his page to correct, at a minimum, the gear section so that people won;t be buying the incorrect parts and was ignored.

Thanks for the heads up. I e-mailed them too about that gear. We'll see what they say...

OzLtd · **Posted:** Fri Dec 08, 2006 6:52 pm

In saying this, I wonder if its just a simple small amount of clearance that is the issue as to why we cant install 4.56's ?

Has ANYONE ever tried or had the front diff open to look at and / or check / measure clearances ? AL ? :lol:

I'm sure theres a simple answer as to why.

unixxx · **Posted:** Fri Dec 08, 2006 9:14 pm

Apparently, the shaft of the D30a pinion gear is longer. This forces you to buy the front ring and pinion gears from Mopar, who only make 3.55, 3.73, and 4.10. The only reason they even make 4.10 is for use in four cylinder Libertys.

Jeepin Al · **Posted:** Sat Dec 09, 2006 10:15 am

I have a Dana 30 out of a YJ and an extra Dana 30A I will be dissambling this weekend to find out what in the HE doulble tooth picks is going on!

Just maybe the pinions are the same, I will post something Sunday night. The next thig I will look at is makeing the stell Dana 30 bolt in with the Dana 30A axles. The saga continues........

Al

OzLtd · **Posted:** Sun Dec 10, 2006 1:21 am

Jeepin Al wrote:

I have a Dana 30 out of a YJ and an extra Dana 30A I will be dissambling this weekend to find out what in the HE doulble tooth picks is going on!

Just maybe the pinions are the same, I will post something Sunday night. The next thig I will look at is makeing the stell Dana 30 bolt in with the Dana 30A axles. The saga continues........

Al

sounds like a plan Al.

SO, in saying all of the above, if you went out and bought an ARB air locker kit off the shelf for a TJ, you could put in it a KJ right ? (sure you might have a few seals and odd bods and ends lying around at the end, but I take it the hemisphere and internals are the same bar the pinion length ? yeah ?

unixxx · **Posted:** Sun Dec 10, 2006 2:20 am

The carriers and carrier bearings are the same. This is why you can use almost any D30 locker/LSD in the D30a. The only lockers that don't work are those that require a special diff cover to operate them.

Jeepin Al · **Posted:** Sun Dec 10, 2006 10:12 am

As far as I know, you can go buy any Dana 30 locker and put it in the front of the KJ. The way I understand it, ARB recommends not putting their locker in the front due to the recent rash of self destructing 30A cases. Several of the memebers of LOST do have ARB lockers in the front and are extremely happy with them, and I have an off the shelf True Trac in the front of mine. I will be working on the KJ today, and the YJ Dana 30 axle.

Al

OzLtd · **Posted:** Sun Dec 10, 2006 6:28 pm

Jeepin Al wrote:

As far as I know, you can go buy any Dana 30 locker and put it in the front of the KJ. The way I understand it, ARB recommends not putting their locker in the front due to the recent rash of self destructing 30A cases. Several of the memebers of L.O.S.T. do have ARB lockers in the front and are extremely happy with them, and I have an off the shelf True Trac in the front of mine. I will be working on the KJ today, and the YJ Dana 30 axle.

Al

I also know a few people who have ARBs in the front and no issues whatsoever. It all comes down to the driving style, not the product.

let us know how you go today Al.

Stu

Jeepin Al · **Posted:** Sun Dec 10, 2006 11:02 pm

OK everyone, the right, Dana 30A from the KJ, the left Dana 30 from YJ

Right KJ, Left YJ

Interesting, so that puts this to rest, it appears a stock Dana 30 pinion will not fit the KJ, BUT the ring gears look the same.

Now what?? Al

Jeepjeepster · **Posted:** Sun Dec 10, 2006 11:25 pm

Wow, that pinion gear is alot bigger than the 30's.

When you regear, does it just get a different ring gear but uses the same pinion gear? Or do both get replaced?

2006KJSPORT4x4 · **Posted:** Mon Dec 11, 2006 12:04 am

Talk about your scaled down models....jeez....now thats a stinker....

OzLtd · **Posted:** Mon Dec 11, 2006 1:36 am

Jeepjeepster wrote:

Wow, that pinion gear is alot bigger than the 30's.

When you regear, does it just get a different ring gear but uses the same pinion gear? Or do both get replaced?

Its not a radio controlled car man, of course you have to change both !! lol!! (not bagging you!)

Al, why dont you look at getting a good driveline shop to splice together the shaft off the D30a to the D30 pinion gear ? Thats not impossible......

jason thompson · **Posted:** Mon Dec 11, 2006 1:52 am

Jeepin Al wrote:

OK everyone, the right, Dana 30A from the KJ, the left Dana 30 from YJ

Right KJ, Left YJ

Interesting, so that puts this to rest, it appears a stock Dana 30 pinion will not fit the KJ, BUT the ring gears look the same.

Now what?? Al

I would try to use the standard 30 center and have some one build some outter tubes that will work with the IFS stuff
you would get the strength of the cast 30 center and never bend a tube also keep the smoth ride of the IFS

I do not think that you will be able to use the tubes from the 30A in the standard 30 center cause they will need to be welded in those little holes on the center and alum. and steel dont like to be welded togeather

OzLtd · **Posted:** Mon Dec 11, 2006 5:02 am

jason thompson wrote:

I would try to use the standard 30 center and have some one build some outter tubes that will work with the IFS stuff
you would get the strength of the cast 30 center and never bend a tube also keep the smoth ride of the IFS

I do not think that you will be able to use the tubes from the 30A in the standard 30 center cause they will need to be welded in those little holes on the center and alum.

what 'tubes are you referrng to ? The D30a doesnt have any 'tubes' as such. ? Its a bearing and seal arrangement then into the CV's ?

upon looking at this pic, it seems clear to me that trying to do a steel D30 pumpkin 'swap-in', isnt going to work without alot of fab, time (and money if you have it).

I think the best bet is to get the D30a pumpkin strengthened up by welding in some more gusseting. There is plenty of space and areas that could be added too ? Around the pinion shaft area seems to be the weak point, so a cradle / brace welded on, in alloy would more than strengthen it. See the lines going East - West, you could add heaps of North - South lines to GRID it up.

4.56 Gear Ratio

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