What do I need on the D30 if I put 4.88 gearing on the D35?

[Kuhn]

What gear ratio do I need on the D30 up front if I put 4.88 gearing on the D35? Also, is this gear ratio too extreme for my axles (with 35s)? ...I do go a little heavy on the skinny pedal when I'm late for work (5 days a week), but I don't rock crawl... Only hill climbs and mudding. Thanks for any and all input... but no, I will not put smaller tires up front.

[89ltd]

well now, I would think you would have to have the same gear ratio on the front as you have on the back. Have you ever worked on gears before? I think you would just change the ring and pinion gears, buy the kit, it comes with a zillion spacers for setting it up. I have 3.07 gears right now, sucks on take off but good gas milage, at 60 mph it revs about 1450 rpm.

[bdiamond69]

different axles does not really matter. lots of vehicles come stock with different front and back axles in them. but you have to have the same gear ratio in both thats what matters.
so if you put 4.88 in the back you have to do it in the front.

[branden0502]

the onyl way you can have a differant gear setup in the front and rear is if you NEVER engauge 4-wheel drive. things will go flying and you will end up in jeep hell if you engauge 4x4 with differant gears in the front and rear.

so only change the rear all you want, just dont put it in 4x4. and if you order 4.88's for the the front make sure you get revearse rotation too. 4wheelparts.com has a good deal on gear set ups. front and rear with install kits for somewhere around 400$. you'd have to check to make sure.

as far as 4.88 with 35's. that is as big a tire as i would go. 2.5, 4.0? whats under the hood?. if u have the 2.5 4.88 with 35 is the limit. if you have the 4.0 you should be ok. but if you want to go any bigger you might want to look at 5.13 gears. esspecially if you have the 2.5. but if you go 5.13 i think you will need a new carrier. i think that the housing will still work. but that is another ball game

[Kuhn]

Well... I need to think a little more before I start a thread! Thanks for all the responses. And, Branden, I didn't know you had to worry about reverse rotation. I will definately check out 4wheelparts.

Btw. I do have the 4.0. I am putting cams for 10% more tq (with everything that takes), headers, magnaflow cat, and borla muffler. And eventually I want to add a centrifugal supercharger, bore and stroke to 5.0L and add some nitrous after that (on a throttle position switch)... plans for plenty of hp. I just haven't found the cash for the D60 and various driveline parts I'd need to handle the power. Feel free to PM with and questions or suggestions about this.

[branden0502]

look at it this way....look at your rear axle...then the front....the front one is the oppisite of the rear.....hence revearse rotation...

your gonna put notrous on a jeep?????

[Kuhn]

yeah the reverse rotation does make sense. And yes, nitrous. lol I've done a couple hill climbs where the Jeep just couldn't push anymore. Gearing is one answer... but it's also my daily driver, so I need to keep the gas mileage at a decent level while cruising at 70mph. Nitrous is good for some high end power to get going, and then the supercharger and cams will help with some low end torque. So when I win the lotto I'll be able to build my Jeep right. lol

[fredjacksonsan]

Same ratios in all axles, unless you're driving one of these:



And I think with nitrous you're going to blow up the Dana 30 in the front, and probably the 35 in the back as well.

[Ray H]

Originally Posted by Kuhn

yeah the reverse rotation does make sense. And yes, nitrous. lol I've done a couple hill climbs where the Jeep just couldn't push anymore. Gearing is one answer... but it's also my daily driver, so I need to keep the gas mileage at a decent level while cruising at 70mph. Nitrous is good for some high end power to get going, and then the supercharger and cams will help with some low end torque. So when I win the lotto I'll be able to build my Jeep right. lol

Your Jeep does not use reverse rotation gears, its standard rotation only.
The lowest gears you can get for the TJ D30 and D35 is 4.88s.
Some axles use 4.88s and some use 4.89s. Thats ok, they are basically the same and work fine together.

[Kuhn]

ok so no reverse rotation... time to research. lol And I will be getting a D60 or D44 for the rear and D44 for the front... And nitrous is way down the list of things to waste my money on. There are so many other things to do... But if I have it on my Jeep, there will be a good, practical reason for it. Thanks again for all the input.

[branden0502]

how do you figure there not revearse rotation? back it up please

[Kuhn]

Ray's know what he's talking about in the past... helped out a lot. Either way, I will be researching and I'll update with an answer... But that might be a couple months away.

[Ray H]

Originally Posted by branden0502

how do you figure there not revearse rotation? back it up please

All I can say is that I know that no TJ came with a reverse rotation (also known as high pinion) front diff. The CJ didnt have rev. rotation, the YJ did, most model year XJs had rev rotation, but no TJs.
If you need proof im sure you can do some research and compare part #s.

EDIT: I'll get you started. Actuually heres a couple write ups that Kuhn may be interested in.
http://www.4x4wire.com/jeep/tech/axle/tjhpd30/
http://homepage.mac.com/rv6a/hpd30.html
and heres the scoop on Jeep D30s.http://www.jeeptech.com/axle/d30.html
As a side note, the Rubicon has a D44 in front, it is also standard rotation.

[Kuhn]

Ray comes through as usual!


lol cheers

[4x4grey88]

Hey Ray,

Thanks for the links.

I am looking into changing out my 3:77 (OEM) to 4:88's I found that purchasing a complete 4:88 axle from a friend, that is moving up to D44's, is cheaper then having the gears installed at 4wheelparts.