High- vs. low-pinion Dana 30 - available gear sets

I've been doing some consideration on my build, and came to the conclusion I have absolutely no desire to run larger than 31" tires on the vehicle for the forseeable future. In order to maintain gearing that is damn near stock with this tire size in mind, I've been considering installing 3.91's instead of 4.10's.

The only 3.91 gears I can find for a D30 are standard cut, which I assume means low-pinion D30... To my understanding, high-pinion D30's use a reverse-cut ring and pinion set. Can someone confirm this?

My dilemma is this... If my previous conclusion is indeed correct, I might have to rule out a high-pinion D30 swap into my rig seeing as I cannot for the life of me find a manufacturer of a set of reverse-cut 3.91 gears for a D30. Thus far I've looked at Superior Gear, Precision Gear, and a number of off-road suppliers, and have come up empty-handed thus far.

Can someone recommend a manufacturer of reverse-cut 3.91 gears for a D30 so I can proceed with this part of the build?

I guess I'll rephrase and simplify the question...

Are all HP D30s reverse cut? Furthermore, are all LP D30s standard cut?

Correct.
HP is also about 30% stronger.
The RPM difference between 3.91 and 4.10 would be negligable-the slight increase in available torque and the significan increase in strength would be well worth the swap.

Nick

Thanks for the reply, I'll work something out!

I did the math and came to the same conclusion. Then I couldn't find 3.91 gears for the front.(same again!) At the time, I'd decided to go with 4.10s. Even if you can find the 3.91s, they're going to cost more then the 3.73s or 4.10s

As mentioned, the reverse cut gears are stronger in a front axle, but if you're going to "top out" at 31", the front ring gear strength isn't going to be an issue. 31" tires only need 2" or 3" of lift, so your front drive shaft angle isn't going to become an issue either. You don't really need to do the swap, unless you want to, or find a really cheap axle.

Yeah, that's why I've been debating doing the swap in the first place... I have no immediate plans to go larger, but we all know how that can change.

I've been trying to justify the swap from the standpoint of being able to do a bench build of the new axle, as well as have a reason to finally join the local TechShop (thereby allowing me to have access to all the tools I could possibly need to do a complete build correctly, including media blasting and soon a paint booth). I can source a HP D30 for less than $200, and then build it up correctly over a few days or weeks (doing a complete overhaul/rebuild at the same time). This would also allow me to do the WJ front brake swap in a much easier and more timely fashion.

Most of my projects end up being pretty horrendous due to poor planning and giving myself an extremely limited window of time in which to complete them. Doing a bench build might be the wisest thing for me to do

In having chosen 4.10s over 3.91s, do you have any remorse? I'm afraid of losing some fuel economy and highway manners (in terms of higher cruising engine speed).

I think you're way over-thinking this entire operation.

anthrax323 said:

In having chosen 4.10s over 3.91s, do you have any remorse? I'm afraid of losing some fuel economy and highway manners (in terms of higher cruising engine speed).

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'Never made it on the highway with that configuration! :rof::roflmao::rof: Remember the comment about plans changing?
The "current" build plan includes no lift, heavy anti-roll bars, 4.56 gears, and 29" gravel tires.

tbburg said:

'Never made it on the highway with that configuration! :rof::roflmao::rof: Remember the comment about plans changing?
The "current" build plan includes no lift, heavy anti-roll bars, 4.56 gears, and 29" gravel tires.

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Planning for a rally there buddy? Sounds like it'd be a fun vehicle.

anthrax323 said:

Planning for a rally there buddy? Sounds like it'd be a fun vehicle.

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Did ya see WRC is coming to DiscoveryHD next month???party1: We like them rally cars.....:cheers:

anthrax323 said:

Planning for a rally there buddy? Sounds like it'd be a fun vehicle.

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As a matter of fact,...