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Old 09-14-2006, 08:42 PM   #1 (permalink)
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reverse cut gears and high pinions?

I thought that reverse cut gears were good because they were stringer. When I was talking to a buddy of mine today who knows more tech stuff than I do, he said that reverse cut gears are weaker because there is less contact area for the gears to mesh. What is the truth? My other question is if you have a high pinion axle does that mean that the gears are reverse cut?
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Old 09-14-2006, 09:03 PM   #2 (permalink)
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Reverse cut gears are used on some front axles. Standard cut gears in a front differential will be driven on the coast side when you are going forward. Reverse cut gears in a front diff will be driven on the drive side when going forward which is a stronger setup. So standard cut gears are stronger in the rear and reverse cut are stronger in the front. The only reasons that they use standard cut gears in front axles is cost and simplicity.

I don't believe all high pinion axles are necessarily reverse cut (hi-pinion 9's?).
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Old 09-14-2006, 09:26 PM   #3 (permalink)
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if it is a high pinion dana axle it will be reverse cut.
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Old 09-14-2006, 09:29 PM   #4 (permalink)
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all high pinion gears are reverse cut even high 9
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Old 09-14-2006, 10:27 PM   #5 (permalink)
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so that means that a standard front ring and pinion are not cut different from the rear they just run on the other side of the cut. and reverse cut in the front would than run on the same side of the cut as the rear?
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Old 09-14-2006, 10:33 PM   #6 (permalink)
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so a reverse cut front and a standard cut rear are a good thing and are the strongest set up as far as the way the gears are cut is concerned
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Old 09-14-2006, 11:32 PM   #7 (permalink)
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A reverse cut high pinion gear in the front is stronger for a couple reasons, the biggest is that the pinion head is pulled into the ring gear under load. This is why you see hi pin diffs from the OE only in front applications.

If you were to run a hi pin in the rear, the ring gear pushes the pinion away. This is one of the reasons you see more hi pin failures in the rear.

A standard cut lo pin is stronger in the rear 'cause the ring gear pulls the pinion in, but when used in a front application, the pinion is pushed away from the ring gear.
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Old 09-15-2006, 05:26 AM   #8 (permalink)
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To play devils advocate. On average, the most force a front axle will ever be subjected to is backing up a hill. Almost all of the weight is on the front axle. In this instance, a standard rotation ring and pinion which is running on the drive side is strongest in the front.

I run a high pinion up front. I am just saying this so it isn't overlooked in the discussion.
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Old 09-15-2006, 07:41 AM   #9 (permalink)
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Technically, the word "cut" in "reverse cut" is a misnomar - it has nothing to do with the way the gears are "cut".

Dana's term is actually "reverse spiral". I find that a little confusing as we're likely to be throwing the word reverse around in the discusion to mean other things.

If I ruled the world (when?) we'd call gears by "leaft" and "right" spiral. i.e. lay - the ring gear down, teeth up. Hold your fist over the centre, thumb extended and pointing up. If you use your right hand, your fingers will be curving to the left. If the curve of the gear teeth match the curve of your fingers, you have a "Left hand spiral gear" - i.e. what we know as "reverse cut" or "high pinion"

If you use your left hand, and the curve of your fingers matches the curve of the gears you habve a right hand spiral gear (low pinion).

In other words, Thumb up, match curve, the gears spiral is the opposite of the hand you're using.

If your fingers curve left on your left hand with your thumb pointing up you're
fawked.

I may not be adding much tech to this - perhaps I drank too much cough syruo this am??

But seriously - this would make it simpler to identify gears on sight, and to talk about hwat Tim;s saying in detail. i.e. what he says is correct, and we could also discuss whether the gears tend to increase or decrease backlash under torque, where decresaing can be bad as it can lead to tooth jambing and breakage - but it depends on whether we're talking left or right spiral gears, upside down or right side up, front or rear axle, going forwards or in reverse, and I suppose which way round the engine is mounted too (driveshaft rotation) - in rear engine apps.
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Old 09-15-2006, 09:31 AM   #10 (permalink)
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Quote:
Originally Posted by Tech Tim
A reverse cut high pinion gear in the front is stronger for a couple reasons, the biggest is that the pinion head is pulled into the ring gear under load. This is why you see hi pin diffs from the OE only in front applications.

If you were to run a hi pin in the rear, the ring gear pushes the pinion away. This is one of the reasons you see more hi pin failures in the rear.

A standard cut lo pin is stronger in the rear 'cause the ring gear pulls the pinion in, but when used in a front application, the pinion is pushed away from the ring gear.
My mental image of this, completely contradicts what you've just explained.

I'll see if I can draw a pic. brb
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Old 09-15-2006, 09:55 AM   #11 (permalink)
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REAR AXLE

the red arrows illistrate the force on the pinion.

A high pinion would have to pull the ring gear,

vs low pinion would be pushing the ring gear.


I always suspected the strength of a 9" was primarily due to 2 differences.

1. the pinion being so low on the ring gear, the teeth were conciderably longer. ie..greater contact area of the teeth

2. the force on the pinion is closer to parralel to the pinion as opposed to a 90* force

I'm just thinking out loud here so, please correct me.
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Old 09-15-2006, 10:19 AM   #12 (permalink)
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Quote:
Originally Posted by BillaVista
Technically, the word "cut" in "reverse cut" is a misnomar - it has nothing to do with the way the gears are "cut".

Dana's term is actually "reverse spiral". I find that a little confusing as we're likely to be throwing the word reverse around in the discusion to mean other things.

If I ruled the world (when?) we'd call gears by "leaft" and "right" spiral. i.e. lay - the ring gear down, teeth up. Hold your fist over the centre, thumb extended and pointing up. If you use your right hand, your fingers will be curving to the left. If the curve of the gear teeth match the curve of your fingers, you have a "Left hand spiral gear" - i.e. what we know as "reverse cut" or "high pinion"

If you use your left hand, and the curve of your fingers matches the curve of the gears you habve a right hand spiral gear (low pinion).

In other words, Thumb up, match curve, the gears spiral is the opposite of the hand you're using.

If your fingers curve left on your left hand with your thumb pointing up you're
fawked.

I may not be adding much tech to this - perhaps I drank too much cough syruo this am??

But seriously - this would make it simpler to identify gears on sight, and to talk about hwat Tim;s saying in detail. i.e. what he says is correct, and we could also discuss whether the gears tend to increase or decrease backlash under torque, where decresaing can be bad as it can lead to tooth jambing and breakage - but it depends on whether we're talking left or right spiral gears, upside down or right side up, front or rear axle, going forwards or in reverse, and I suppose which way round the engine is mounted too (driveshaft rotation) - in rear engine apps.

Correct on the spiral, but there are two parts to the way the gear is cut- the spiral and the angle of the coast and drive sides.

The direction of the spiral has to do with the location of the pinion (high or low). The angle of the tooth cut determines which direction the tooth is strongest in.

High pinion diffs are both reverse-spiral and reverse-"cut".

Running on the coast side is weaker because the angle of the face of the tooth wants to force the gears apart (like Tim said), causing misalignment which leads to breakage. Running on the drive side doesn't force the gears apart nearly as badly since there is very little angle, and is therefore stronger.

It would be possible to machine a gear set that was reverse-spiral but standard-cut (had the tooth angle cut so that it was strongest when run forward in a rear diff), but AFAIK it has never been done yet.
And I'm kind of surprised that it hasn't...
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Last edited by ErikB; 09-15-2006 at 10:27 AM.
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Old 09-15-2006, 10:41 AM   #13 (permalink)
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you guys have good tech on the gear teeth, but also another thing as you probably all know is the way a HP case or housing is oiled compared to a standard. if you were to take a standard housing and reverse it, oiling/cooling would also be a failure point no? unless you machine a scoop or something of the sort to oil your pinion bearings.

It's off topic, but on as well. Which case is better at keeping the bearings oiled and cooled?

flame away!
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Old 09-15-2006, 07:24 PM   #14 (permalink)
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Quote:
Originally Posted by ErikB
Correct on the spiral, but there are two parts to the way the gear is cut- the spiral and the angle of the coast and drive sides.

The direction of the spiral has to do with the location of the pinion (high or low). The angle of the tooth cut determines which direction the tooth is strongest in.

High pinion diffs are both reverse-spiral and reverse-"cut".

Running on the coast side is weaker because the angle of the face of the tooth wants to force the gears apart (like Tim said), causing misalignment which leads to breakage. Running on the drive side doesn't force the gears apart nearly as badly since there is very little angle, and is therefore stronger.

It would be possible to machine a gear set that was reverse-spiral but standard-cut (had the tooth angle cut so that it was strongest when run forward in a rear diff), but AFAIK it has never been done yet.
And I'm kind of surprised that it hasn't...
Well said

The reason no one has built gears that way, is they would have to build a new gear cutting machine to do it.
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Old 09-17-2006, 11:53 AM   #15 (permalink)
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[QUOTE=Tech Tim]A reverse cut high pinion gear in the front is stronger for a couple reasons, the biggest is that the pinion head is pulled into the ring gear under load.

How is the pinion head "pulled into the ring gear" ?

When looking at ring gear teeth both the drive and coast sides of the teeth have some amount of deflection causing angle to them. This is especially noticable on the D60 as far as the drive side goes.
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Old 09-17-2006, 05:42 PM   #16 (permalink)
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so if you were to use a HP 60 in the rear of a vehicle, it would be weaker because the driving force would be displaced on the coast side of the teeth? im having a mental picture block going on....

EDIT: lubricating pinnion bearing issues aside.
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Old 09-17-2006, 06:03 PM   #17 (permalink)
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Quote:
Originally Posted by crusty1007
so if you were to use a HP 60 in the rear of a vehicle, it would be weaker because the driving force would be displaced on the coast side of the teeth? im having a mental picture block going on....

EDIT: lubricating pinnion bearing issues aside.
Exactly.
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Old 09-17-2006, 09:16 PM   #18 (permalink)
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It looks like a need a cell phone that takes better pictures, but here's a dana 60 tooth profile
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Old 09-17-2006, 09:17 PM   #19 (permalink)
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and a 9" tooth profile
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Old 09-17-2006, 09:17 PM   #20 (permalink)
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alright crappy sketch on a crappy pic. Imagine the circle is the pinion and the two arrows are the reaction forces on the pinion resulting from either driving on the coast side or driving on the drive side.

The nearly horizontal arrow is for the drive side. The angled one is for driving on the coast side.

Hopefully you can see when you drive on the coast side it tries to force the pinion away from the ring gear, as well as the pinion tries to "climb" the ring gear. When you drive on the drive side the pinion just tries to climb the ring gear.

So the tooth profile is a good reason to pick a dana axle over a 9in in the front, but the 9in has the 3rd bearing to pretty much stop pinion deflection.
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Old 09-18-2006, 10:53 AM   #21 (permalink)
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So the tooth profile is a good reason to pick a dana axle over a 9in in the front, but the 9in has the 3rd bearing to pretty much stop pinion deflection.[Gordon/QUOTE]



Yes, or at least when low pinion in front, depending on if a person is going forward or backward. Wouldn't a person then agree that a LP 9 would be better in the rear based on that tooth angle?
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Old 09-18-2006, 11:08 AM   #22 (permalink)
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Quote:
Originally Posted by truehi9
Wouldn't a person then agree that a LP 9 would be better in the rear based on that tooth angle?
Well, maybe, until this happens and screws the deal.





I believe that one can be chalked up to 'ring gear deflection', caused by the destruction of this bearing cap.



That was #2 ford 9" that I blew up. The first one I blew the back off a LSD carrier which I understand isn't all that uncommon...then this one happened a few weeks later. Bronco w/stock 302 and 5-speed plowing snow, 3.55 gears.

Might just be me, but I've moved on to other things since then. Never had any problems with the Dana axles I've ran.
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Old 09-18-2006, 11:39 AM   #23 (permalink)
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I wasn't trying to start a Ford 9 vs. D60 debate. I was just pointing out the fact that maybe there's more going on than that one angle.

I should have just answered the original question. HP and LP (left hand or right hand spiral) gears are the same strength. They are the same size and made from the same material from a given manufacturer.

The thing that makes one better in a certain situation are the forces acting on them and the deflection (the gears being pushed apart) that is caused from the driveshaft turning different directions (forward or reverse).

Overall gear tooth strength is determined by the size of the gear teeth themselves and the contact between the teeth. The more teeth overlapping from the design of the gears is one contact factor.

The other contact factor of the teeth is that since the teeth are triangle shaped from the root to the tip, when load is applied deflection occurs. The more angle the more deflection. When this deflection (the gears being pushed apart) occurs the load is put more at the tip of the tooth where there is less material because the tooth is thinner there making it easier to break the tooth.

I hope this helps answer some questions.
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Old 09-18-2006, 12:12 PM   #24 (permalink)
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Quote:
Originally Posted by truehi9
I wasn't trying to start a Ford 9 vs. D60 debate. I was just pointing out the fact that maybe there's more going on than that one angle.
Yeah, me neither. I realize that my 9" experiences have been somewhat...abnormal I guess. Although if you have any thoughts on what the culprit was in the above pictures I'd like to hear them.

FWIW I've wheeled a few rigs with the Hi-9 setup and haven't broken it. And a bunch of guys I know that run in comps all run the Hi-9 too and they swear by it. I think maybe I cursed out that Bronco a bit too much and it just felt like getting back at me (never been a ford guy...).
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Old 09-18-2006, 02:22 PM   #25 (permalink)
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In your pic I think the cap broke first. I pulled one at a junkyard that had a cracked cap and slightly wierd wear on the ring gear.
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