Hi vs Lo

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[jps4jeep]

Is there a huge difference in strength of a Hi pinion versus a low pinion? this question pertains to all type of axles.

I ask because I was reading an article regarding a Hi-pinion third member as opposed to a low pinion third member and one of the arguments for keeping the low pinion was that in the manufacturing process of a Reverse cut versus a standard cut gear pattern, the material is simply not as strong.  Honestly I am a little baffled... I have also heard from other people the exact opposite when in regards to a Dana style axle that the reverse cut is better strength wise than the standard cut.

Is this due to the fact that one is a third member and the other is not, that in the design of the carrier, the gears are just not as stong..

Or is this all smoke up my arse..

Just wondering.


To add.... has anybody else seen the 40 spline 9" spools yet... very sexy!

[jeeptech]

You should check out the True Hi-9. http://www.truehi9.com/index.html  The one currie builds is not a real HP-9", It's a flipped LP 9" with modifications made to lubricate the pinion bearings.  All gear sets are stronger in one direction because of the mesh of the gear, more surface contact area.  The 9" gear set is stronger than most because it has more teeth meshing at the same time, unlike other gear sets.  Hi-9 controls ring gear deflection which makes it super strong.   

[jps4jeep]

Thanks. I was somewhat baffled, I believe that perhaps the Currie unit was the piece that was being discussed at the time.

[bobnoxious]

High pinion, or reverse cut gears, are specifically designed for front applications. High pinion gear sets are actually using the weak side of the gear set when used in a rear application. The "True Hi-9" is strong enough to get away with running in the rear because it has the 3rd pinion bearing and ring gear thrust block...essentially forcing the gears to resist deflection forced on them due to running on the weak side of the gear. The Currie Hi-9 always had problems when used in the rear due to the fact that it was essentially a Rev. 8.8 gear set (as found in the front of an F150, no extra pinion support bearing) in a custom 3rd member (it couldn't just be a "flipped" 9" 3rd...the rotation would be incorrect).

Every helical gear set has a "strong side" of the R&P, and a "weak side". Standard low pinion gear sets are designed to run in the rear, and their direction of rotation has them running on the strong side of the gear set (they're not trying to push away from each other). When a low pinion is run in a front application, it's now running in "reverse", making the gears run on the weak side of the gear set (ring and pinion are constantly pushing away from each other). The solution was to cut the gears in the opposite direction, so they would be on the strong side of the gears when run in the front. In order to do this, the pinion had to be moved up in relation to the ring gear (high pinion was a by-product of making stronger front gears).

[Twisty]

Good explanation Bob!

[jps4jeep]

Both of you, Great! about freaking time we get some cool tech in here..

If I play devil advocate... keep it coming!



what is the difference between the "stong side" and the "Weak side" versus the coast and drive side of gears.


to add, I am by no way a gear expert, in fact I am the beginer at best, I set up my own gears for the first time and the have not blown up after a couple wheeling trips and about 600 miles so I am liking the learning!

[Twisty]

Both of you, Great! about freaking time we get some cool tech in here..

This isnt good tech?
http://newenglandjeepz.org/forum/index.php?topic=654.0





j/k

I also want to know about coast/drive.  I've heard that if you are pulling somone in reverse with an HP front axle, you risk breaking a ring gear more than pulling them while going forwards.

[ayoung]

I also want to know about coast/drive.  I've heard that if you are pulling somone in reverse with an HP front axle, you risk breaking a ring gear more than pulling them while going forwards.

yes you do risk breaking things more when you are going in reverse...I think dan gray knows that from first hand experience

[bobnoxious]

It's easier to explain if I could show you with a set of gears in my hand, but I'll try...

Basically, the "drive side" is the "strong side"...when we're talking about a rear diff driving forward. It has to do with how the gears are cut.

Sorry about the size of these pics, but I need to show them full size so you can see what I'm talking about.

This is a low pin D44 (it's an XJ rear D44). Notice how one side of each tooth has a severe angle, and one side is fairly squared off? The squared off side is the drive side, the strong side (this diff drives from bottom to top...it's the back of the rig). The gears aren't trying to push away from each other (at least not as badly as they do when in reverse, or if they were in the front and therefore always running in "reverse"...front differentials run in the opposite direction from the rear differentials).



This is a high pinion (or reverse rotation) D30, in the front of an XJ. Notice that the helical cut and orientation of the squared side of the tooth vs. the angled side of the tooth? This diff drives from top to bottom as seen here.



See how each diff is out of it's element when forced to run backwards from it's original design?

[jps4jeep]

Nice, lets take this a notch up, I know one member on here was considering a hybrid 9" with D60 inner C's D60 kinpin knucle, etc.. Is it possible to take a D60 rear, cut to desired width and weld on the inner C's from a front axle? what would be the effect on the oiling, the gear meshing so on so on?

for ease of discussion, this is regardless of hi pinion and lo pinion?

[Twisty]

Awesome Bob!  Thanks for that post!

[jps4jeep]

Awesome Bob!  Thanks for that post!

X10

[bobnoxious]

Nice, lets take this a notch up, I know one member on here was considering a hybrid 9" with D60 inner C's D60 kinpin knucle, etc.. Is it possible to take a D60 rear, cut to desired width and weld on the inner C's from a front axle? what would be the effect on the oiling, the gear meshing so on so on?

for ease of discussion, this is regardless of hi pinion and lo pinion?

Yes.

A low pinion front differential (Waggy, Chevy and Dodge trucks, Scouts, etc.) is a rear differential...running in reverse. The effect on oiling is that it isn't an issue. The effect on gear mesh is that they're forced to "drive" on the "coast" side of the gears.

A high pinion rear differential is a front differential...running in reverse (from it's intended helical cut).  It's forced to "drive" on the "coast" side of the gears when run like this (in the rear).

[jps4jeep]

so in theory a Hi pinion rear D60 could be easily converted to a front axle.. with the Inner C's welded on?

[bobnoxious]

so in theory a Hi pinion rear D60 could be easily converted to a front axle.. with the Inner C's welded on?

A HP D60 already is a front axle...converted to rear use