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!)
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.