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Proper gearing


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In my XJ I'm running 4.10's with 31" tires. The revs are a little high at highway speeds but still well within reason. I think you would be happy with 4.10's at a minimum and probably better off with 4.56's. Your clutch will thank you.

 

Have you checked any of the gearing calculators?

 

4.56's will put you at 2200 rpm in 5th gear at 65. 35's are a heavy tire and take some umph to get moving. It's nice to have the snappy throttle response that proper gearing gives.

 

We get approximately 19 mpg with the XJ, the engine doesn't have to work as hard as it would with the stock 3.07's. And yes, my speedo gear has been corrected.

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Thanks guys for all the help. :cheers: I have a 8.25 chrystler with 4.10s in it now but I'm having a real hard time finding a 4.10 dana 30 to match the front. Ive been thinking of regearing the front and rear to 4.56s and i swear ive seen kits on ebay for around $350 for both front and rear gears and set-up parts. Any one have any idea if there is a posi unit that will fit into a 88 dana 30 HP that came in jeeps from the factory that will accept the 456 gears? Also my buddy says he has a dana 30 out of a grand cherokee that has some sort of posi in it and he claims it is some sort of hydraulic posi....any ideas what he is talking about? and or if it can drop into the hp dana?

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IMHO, 4.10s are the minimum and 4.56s or 4.88s would be best for 35s for either daily driving or long distance driving. But at 4.88 and lower, the pinion gets mighty small. I had 3.73s and 33"s a while back and it was a downshift marathon going up mountain roads.

 

I currently have 4.56s and a 4:1 transfer case so the crawl ratio with an AX15 in first gear is close to having 5.89 gears and a standard 2.72 low range transfer case.

 

In regular 2wd I still downshift going up a steep hill on the highway. I think if I still had a standard NP231 then I'd be better off with 4.88s. Still drivable long distance and decent crawl ratio.

 

Here's a calculator to help you decide: http://www.rocky-road.com/calculator.html

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Thanks guys for all the help. :cheers: I have a 8.25 chrystler with 4.10s in it now but I'm having a real hard time finding a 4.10 dana 30 to match the front. Ive been thinking of regearing the front and rear to 4.56s and i swear ive seen kits on ebay for around $350 for both front and rear gears and set-up parts. Any one have any idea if there is a posi unit that will fit into a 88 dana 30 HP that came in jeeps from the factory that will accept the 456 gears? Also my buddy says he has a dana 30 out of a grand cherokee that has some sort of posi in it and he claims it is some sort of hydraulic posi....any ideas what he is talking about? and or if it can drop into the hp dana?

 

Yep, most of the aftermarket companies sell just about any ratio gears, carriers, and lockers for the HP D30. Also, there was a stock 4.56 geared Cherokee, 84-88 I think. IIRC it was the 4cyl with an automatic combo. Rare, I've never seen one in a yard that still had the axles.

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Also my buddy says he has a dana 30 out of a grand cherokee that has some sort of posi in it and he claims it is some sort of hydraulic posi....any ideas what he is talking about? and or if it can drop into the hp dana?

Sounds like it's the front diff out of a '99 or newer Grand with QuadraDrive. In the full QuadraDrive system, the transfer case is a full-time case, and the front and rear diffs are "gerotor" actuated units. They have clutches, but they work sort of the opposite of the older Jeep TracLok system.

 

With TracLok, the clutches are engaged and held by spring pressure. When the two wheels on the same axle need to rotate at different speeds (like around a corner), if both tires have traction, the tires develop enough torque to cause the clutches to slip.

 

With QuadraDrive, the clutches are normally UNlocked. When the two wheels on the same axle turn at different speeds, the mechanism actuates a hydraulic "gerotor" pump inside the diff that pushes the clutches into engagement, locking up the axle. It's a great system, and I always wondered if it could be retrofitted to an XJ or MJ Dana 30. But ... I saw the price for one of the units and quickly lost interest in trying it.

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Well my buddy said I can have the grand chero diff for free because of a bent axle tube but I'm sure I can salvage the carrier. Ill take a real close look into if it atall is possible to swap something in. It will be a little while before I can grab it but ill post what I find. :wrench:

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Also, there was a stock 4.56 geared Cherokee, 84-88 I think. IIRC it was the 4cyl with an automatic combo. Rare, I've never seen one in a yard that still had the axles.

 

4.56's came under 87-89 XJ/MJ's with the 2.5 and AW4 trans....pretty rare combo, but they do exist. The D30 under my MJ came from one out of my local junkyard

 

4.56's with a 4.0/AX15 and 35's is just about perfect for me.

 

Jeff

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