Jarrid; There is quite a big difference between hypod and spiral bevel
final drive gears.
The spiral bevel has its pinion gear positioned "exactly" on the centerline
of the ring gear. The teeth are straight cut spur gear type but of course
are tapered towards a common center point. This form of drive gear permits
input power to be turned 90 deg. (as we require in a axle housing) and does
this job with the lowest power loss. It has three drawbacks.
1. noise is higher than hypoid gears
2. strength is lower than hypoid
3. drive shaft must ride higher under the floor pan, causing a floor hump
which is higher than a hypoid.
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Hypoid (originally perfected by Gleason Gear Co about 1927) has its pinion
gear located quite a bit below the centerline of the ring gear.
The teeth on both gears are cut with a curve shape which allows this low
mounted pinion to "slide" as it engages and also this action provides a
much larger area of tooth engagement which in turn gives this design the
ability to handle larger power transmission than a spiral bevel could.
One disadvantage is that due to the sliding tooth motion, a very special
lubricant MUST be used, or the gear will self destroy. These lubricants
have high EP additives and are generically called "Hypoid Oils".
A hypoid oil will also protect a spiral bevel gear set but is technically
not required. The API rates gear lubes as GL1 thru 5. The GL 1,2 and 3 are
better for spiral bevel as it contains less severe additives which in
certain cases may corrode bronze spacers found in the diff. housing. The
usual recommendation is to use the GL3 because it has some needed anti-foam
and anti-corrision properties which are helpful. High rated motor oil will
also protect spiral bevel just fine.
Hypoid advantages are:
1. Lower drive shaft location
2. Higher strength and power transmission
3. Very quiet operating sounds
A dissadvantage would be that the hypoid absorbs more HP due to its sliding
rather than rolling motion. For very small HP vehicles, this loss is
considered important but for normally larger engine vehicles, the slight
loss is overlooked in favor of the hypoid advantages.
In a Rootes size car, I would guess the amount of hp loss between the two
types would be approx. 3-4 hp at near top speeds and perhaps 1 hp loss
diff. at city driving speeds.
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I have no recollection re. the dana Spicer rear axles used. This firm in
Indiana, made rear axle units for Volvo going back to the immediate postwar
era. At that time we found that Studebaker (and others) used the same diff.
housings and gears from many other small size US cars would fit the volvo
just fine. Likely, some old junk yard interchange books would shed light
on this subject but I have lost all memory and cannot advise further.
Dick T.
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