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Unread 02-15-2006, 11:44 AM   #1
topfuel83
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What is a High Pinion Axle?

Ive heard people talking about putting high pinion axles under there Jeeps, but what actually is the high pinion axle? I know that when a Jeep is lifted, the axles are rotated up to correct the pinion angle. Does an aftermarket diff cover with a higher fill hole constitute a HP axle? I'm confused.

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Unread 02-15-2006, 11:49 AM   #2
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A high pinion means that the pinion is higher on the housing rather than towards the bottom. On a low pinion housing, the pinion gear turns the ring gear towards the bottom. A high pinion is the opposite, and since the pinion gear turns the ring gear towards the top, the gears are cut in reverse. This also means you need special gears for a HP housing. The advantages are that the gears are stronger and it gives the driveshaft more clearance as you can see in the pic below. Here is an article on a HP swap.

-Frank

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Unread 02-15-2006, 12:00 PM   #3
topfuel83
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Cool. That helps alot. Now is there a HP rear axle for a TJ? I sopose anything is possible, but is there a direct bolt in like the XJ D30?
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Unread 02-15-2006, 12:15 PM   #4
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I think some export TJs did have a HPD44 option, but I doubt you will find any here in the states. So technically there is no direct bolt in that you can find. However, there are some companies that make bolt on HP rears specifically for TJs, but you can make any work with some fabrication. Check out currie enterprises, they have some HP options and I think they explain which applications work best.

BTW, here is a LP30 (from stu's site) vs. a HP30:

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Unread 02-15-2006, 12:20 PM   #5
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Thanks. Not that I have the funds right now to play with. But now I at least understand what a HP axle is, and its applications.
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Unread 02-15-2006, 01:16 PM   #6
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This is what I was looking for. Its from Dynatrac's website, which is another option if you would like an axle made to bolt in. These are not the only options for aftermarket options, just the first two that came to mind.

Dynatrac's explanation:

Reverse Cut (high pinion) vs. Standard Cut (low pinion)

Perhaps the single most misunderstood axle term is reverse cut, often mistakenly referred to as reverse rotation. A reverse cut housing is not a standard cut housing turned upside down, it is a specially designed housing. The term "reverse cut" refers to the direction of the spiral cut in the ring gear, which is opposite that of a standard cut ring gear: Contrary to popular belief, it does not run backwards or in reverse. The principle behind a reverse cut is to strengthen the operation of the gear when it is used for a front driving axle application.

Hi-pinion or reverse-cut axles have also become very popular as rear driving axles in short wheelbase vehicles with suspension lifts because the higher pinion improves drive line angles so well. Dynatrac was among the first to pioneer this application and continues to offer the very best and strongest Hi-pinion axles available anywhere.

Standard-cut axles are often used as the front driving axles because of clearance issues, gear ratio availability, cost, or suspension considerations. However comparable reverse-cut axles have the distinct advantage of overall ring and pinion gear strength.

Reverse-cut axles should be used in the rear when higher ground clearance, reduced drive shaft angles or short wheelbase are desirable issues. Reverse-cut rear axles should be avoided for heavy GVW vehicles or heavy highway towing. Dynatrac has thoroughly tested Dana 44 reverse-cut, and Ford 8.8 reverse-cut, rear axles and found them to be weak and prone to failure in all but the very, very lightest duty applications. We can only recommend Dynatrac’s proven Dana 60 reverse-cut design as unquestionably dependable even under adverse situations.

The gear sets used in each type of axle are not interchangeable: Standard cut gears cannot be used in place of reverse cut, and vice versa. The housings, which have different lubrication passages, are also not interchangeable. However, differential cases (open, l/s, or locker) are compatible with both styles, as long as case spline count matches the axle shaft.
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Unread 02-16-2006, 05:26 PM   #7
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Quote:
Originally Posted by topfuel83
Cool. That helps alot. Now is there a HP rear axle for a TJ? I sopose anything is possible, but is there a direct bolt in like the XJ D30?
really you don't want a HP rear anyway. they're inheritantly weaker in the rear in forward gears than the low pinion design because of the way the stresses are distributed through the gears. the only advantage strength wise a HP rear would have is in reverse in which case it acts like a front axle. what you gain in ground clearance is counteracted by the loss in strength.
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Unread 02-16-2006, 08:32 PM   #8
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HP=stronger in front axles.Weaker in rear axles.That being said a HP 60 in the rear is pretty stout unless you run 40,s & up.
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Unread 02-16-2006, 09:58 PM   #9
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Quote:
Originally Posted by dirtgrip
That being said a HP 60 in the rear is pretty stout unless you run 40,s & up.
that's true. but considering he asked if there was a direct bolt in I don't think he's looking for 1 ton axles any time soon
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Unread 02-17-2006, 09:06 AM   #10
dirtgrip
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Both of my HP60,s were direct bolt-ins. All brackets were on & TJ width.Complete with disc brakes, 1 ton outers & large hubs.Plug & play.Terra CRD,s http://www.teraflex.biz/pages/product_results.php Search CRD
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Unread 02-17-2006, 11:42 AM   #11
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Since we are are close at hand to this topic, I 'd like to ask this question.

I have heard that in the case of a Dana 30 High Pinion axle, the carrier maxes out out at 3.55 (3.54) gears with lower gear ratio only available in the Low Pinion variety. I believe I was told this was due a smaller pinon gear needed to match a greater number of teeth on lower ratio ring gears, which is then physically bigger, and there isn't enough room inside the the carrier to clear the ring gear.

Can anybody confirm this, please?

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Unread 02-17-2006, 12:04 PM   #12
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That is not entirely true. There is a carrier break in all D30s, 3.55 and down, and then 3.73 and up. So, in a way its true, but by putting in the carrier for 3.73 and up, the problem is solved. The ring gear is positioned differently on the two carriers, so while there isn't enough room using the 3.55 and down carrier with numerically higher gears, the carrier designed for those gears allows enough clearance for them. This is also why they have thick ring gears, which can avoid the need for a different carrier in some cases. Go here for a list of carrier breaks.

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Unread 02-17-2006, 12:23 PM   #13
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Quote:
Originally Posted by Kerndone
That is not entirely true. There is a carrier break in all D30s, 3.55 and down, and then 3.73 and up. So, in a way its true, but by putting in the carrier for 3.73 and up, the problem is solved. The ring gear is positioned differently on the two carriers, so while there isn't enough room using the 3.55 and down carrier with numerically higher gears, the carrier designed for those gears allows enough clearance for them. This is also why they have thick ring gears, which can avoid the need for a different carrier in some cases. Go here for a list of carrier breaks.

yup, no problem getting lower gears for the HP 30. The manual 4cyl YJ's came stock with 4.10's. the lowest possible is 5.13's, though the lowest common ration between the D35 and the D30 is 4.88 IIRC.
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