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Unread 12-28-2013, 11:56 AM   #1
Colt44
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Quick question - reverse ring and pinion? (Nothing is ever easy)

Just a quick question about yet another Jeep parts variation.

I got a 3.54 R&P to replace the original 2.73 in the AMC 20 rear of my '83 CJ7, and was about to order a set for the front (Dana 30).

I went onto the 4WD.com website and put in the model info, etc., and lo and behold one of the options was "reverse ring & pinion."

I'd never heard of that, which is a fairly common experience when looking for Jeep mechanical parts. A little Googling reveals that the reverse R&P seems to be for certain YJs.

Is this something I need to check for, or just another case of weak search filters on the 4WD website?

One other consideration: Got G2 for the rear because Dana/Spicer doesn't make those any more. But they do make R&P sets for the 30. Should I get the Dana parts, or be consistent and stay with the G2?

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Unread 12-28-2013, 12:56 PM   #2
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Reverse rotation is kinda a wrong and misleading term....in sort, those gear sets are for high pinion diffs. Yours is a regular low pinion so just get the regular gears for a Dana 30 CJ years.
Its not as important to match brands front to rear in a CJ because with your lockout hubs, the front ONLY spins when in 4WD, so the front set will only have a fraction of the wear that the rear gets over the lifespan. Yes, I would stick with the Spicer/Dana sets.
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Unread 12-28-2013, 07:50 PM   #3
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I have a set of original 3:54 gears from my Dana 30 in my 79 that you can have with the carrier if you want to cover the shipping?
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Unread 12-29-2013, 02:24 PM   #4
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Originally Posted by GB3440 View Post
I have a set of original 3:54 gears from my Dana 30 in my 79 that you can have with the carrier if you want to cover the shipping?
PM sent. This is for the front, correct?
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Unread 12-29-2013, 05:29 PM   #5
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Quote:
Originally Posted by Colt44 View Post
Just a quick question about yet another Jeep parts variation.

I got a 3.54 R&P to replace the original 2.73 in the AMC 20 rear of my '83 CJ7, and was about to order a set for the front (Dana 30).

I went onto the 4WD.com website and put in the model info, etc., and lo and behold one of the options was "reverse ring & pinion."

I'd never heard of that, which is a fairly common experience when looking for Jeep mechanical parts. A little Googling reveals that the reverse R&P seems to be for certain YJs.

Is this something I need to check for, or just another case of weak search filters on the 4WD website?

One other consideration: Got G2 for the rear because Dana/Spicer doesn't make those any more. But they do make R&P sets for the 30. Should I get the Dana parts, or be consistent and stay with the G2?
Look at the location of the axis of the pinion shaft, relative to the axis of the halfshafts.

You can have a "high pinion" front (pinion shaft ABOVE halfshafts) or "low pinion" front (pinion shaft BELOW halfshafts.)

If you have a "low pinion," you may use standard gears. If you have a "high pinion," you have to use reverse spiral gears (the hypoid spiral was reversed to allow the pinion to enter above the halfshaft centerline.) This has nothing to do with the actual direction the gears turn - merely the "hand" of the spiral formed by the gear teeth.
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Unread 12-29-2013, 05:39 PM   #6
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Look at the location of the axis of the pinion shaft, relative to the axis of the halfshafts.

You can have a "high pinion" front (pinion shaft ABOVE halfshafts) or "low pinion" front (pinion shaft BELOW halfshafts.)

If you have a "low pinion," you may use standard gears. If you have a "high pinion," you have to use reverse spiral gears (the hypoid spiral was reversed to allow the pinion to enter above the halfshaft centerline.) This has nothing to do with the actual direction the gears turn - merely the "hand" of the spiral formed by the gear teeth.


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Unread 12-30-2013, 09:52 AM   #7
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Okay, checked mine and it's the low type. That's what I was talking about; seems there's never just one part for any given model and year.
Did AMC just go to their vendors and literally buy whatever happened to be laying around in the warehouse on any given day?
Sure seems like it sometimes.
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Unread 12-30-2013, 04:33 PM   #8
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Originally Posted by Colt44 View Post
Okay, checked mine and it's the low type. That's what I was talking about; seems there's never just one part for any given model and year.
Did AMC just go to their vendors and literally buy whatever happened to be laying around in the warehouse on any given day?
Sure seems like it sometimes.
AMC...
People are fond of saying 'A Mixture of Cars' is what AMC stands for.

Personally, I say they went Dumpster Diving and came up with whatever they could buy cheap...
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Unread 12-30-2013, 06:57 PM   #9
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AMC...
People are fond of saying 'A Mixture of Cars' is what AMC stands for.

Personally, I say they went Dumpster Diving and came up with whatever they could buy cheap...
J-just
E-everybody
E-else's
P-parts

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Unread 12-30-2013, 07:22 PM   #10
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Originally Posted by Colt44 View Post
Okay, checked mine and it's the low type. That's what I was talking about; seems there's never just one part for any given model and year.
Did AMC just go to their vendors and literally buy whatever happened to be laying around in the warehouse on any given day?
Sure seems like it sometimes.
AMC - All Makes Compatible.

My RENIX has a Bendix control computer, a distributor with a Ford OEM #, and most of the sensors are GM parts. Connectors are a mix of Delphi Weatherpack and Deustch. AMC engine, Toyota transmission (which replaced the fifth wretched damned Peugeot transmission!)

Confused yet?

It's actually not that bad when you get used to the idea.

The quirk of front axles is that, by using a low pinion entry, they can standardize parts to simplify logistics. However, there are cases where manufacturers say logistics be damned - they want to do the best that they can do.

Thus, the high pinion axle. You gain something like 3-4" ground clearance under the pinion knuckle, and that can make a difference in some cases!

However, it's the nature of hypoid gears (look 'em up, you're better off reading it for yourself than having me try to explain it...) that changing the relative entry of the pinion requires significant alteration to the gearsets. Why? Because a hypoid gearset represents a combination of a common spur-cut bevel gear and a helically-cut spur gear. This is an advantage (if it weren't, it wouldn't be done. Both bevel gears and helical gears are far cheaper to make than hypoids, but the hypoid type is significantly stronger in this application,) but a hypoid gearset does carry its own peculiar disadvantages in exchange:
- Pinion Entry Offset: This allows an elevation (rear axle, sometimes front) of 1.375"-3" of the pinion axis relative to the centreline of the axle. This usually results in increased ground clearance, and less interference with the pinion and objects on the ground.
- Hypoid Loss: Due to the spiral contact (constant mesh,) and the slight difficulty encountered in getting the gears to move (increased friction,) the power loss through a hypoid gearset is nominally greater than most other gearsets. Given the advantage of a hypoid gearset, it's been decided that we can just live with the power loss (I can.) Nota bene This is why Ford stopped making their Hell-for-strong 9" rear axle - the 9" had a hypoid offset of close to 3", which increased the hypoid spiral and power loss through the geartrain. It was eventually decided that this loss was unacceptable, and the 9" was ditched as an OEM axle in light of federal CAFE (Corporate Average Fuel Economy) regulations. It was replaced with the 8.8" axle in cars some 6-8 years before its final full replacement in production (it held on in light trucks for a bit.)
- Pinion Flexion: Again, this is due to the hypoid spiral tooth profile. The pinion shaft is typically forced away from the face of the ring gear, which can be dealt with in one of two ways:
-- Most commonly, they use a solid pinion shaft with enough material to reduce/eliminate flex, and a rigid housing & bearing setup (this is why the cast snouts are so thick.)
-- Less common, a third pinion bearing is used, on the nose. Typically referred to as a "pilot" bearing, this is a fairly heavy needle bearing that rides on a reduced diameter (typically 1" or so) and is situated inside the ring gear. This turns the pinion from a "beam" to a "bridge" for purposes of flexion. This is also more expensive to manufacture, which is why you typically only find it on heavy axles (Ford 9", GM 14-bolt 9.5" and 10.5", and I think the bigger AAM axles.) This can typically be spotted straight away through inspecting the pinion entry, the pinion and the two large bearings may be removed as a unit, without disassembling the axle.

As far as the "weird" ratios you see (2.73:1, 3.07:1, 4.54:1, ...) there's really a simple reason for it: Equalizing wear. The ratio is such that every tooth on one gear will make contact with every tooth on the other gear within a fixed number of revolutions, which prevents gear teeth taking a set to each other. This is a common principle in geartrain design, and not at all unique to hypoid gearing (you'll find it in any geartrain designed for major power transmission.)

Probably more than you wanted to know, but I'm sure others are curious (even if you are not. )
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