The gears are custom
made in the U.S.A. for
us by Strange.
They are reverse cut 9"
These are identical in
size and shape to
standard 9" gears, just
cut for high pinion
9" gears utilize a "pocket
bearing" for extra support
and virtually zero pinion
The ring gear is also
supported by a thrust
block anti deflection
device in the case.
4.11 in stock (works with
4.07's to 4.15's)
4.57 in stock (works with
4.53's to 4.61's)
4.86 in stock (works with
4.82's to 4.90's)
5.14 in stock (works with
5.09's to 5.19's)
5.38 in stock (works with
5.33's to 5.43's)
These gears will NOT work
in stock Ford 9" gear cases.
|Click picture for enlarged view.
GM 10 bolt 4.88
Ford 8.8 and
GM 12 bolt Dana 60 4.88 Ford 9" 4.86 Dana 80 4.10
GM 10 bolt 4.88 Dana 60 4.88 Ford 9" 4.86 Dana 80 4.10
Ford 8.8 and
GM 12 bolt
Pinion shaft with third bearing
Pinion shaft with
Some questions & answers about gears:
1. What is the benefit or disadvantage of a larger pinion vertical offset?
(distance measured in inches where the pinion meets the ring gear vertically in relationship to the
ring gears' centerline.)
Examples: Ford 9" 2.25" is a large offset Dana 60 1.125" is a small offset
A. The larger offset creates more pinion to ring gear tooth overlap.
What this means is that if a Ford 9" and a Dana 60 both had the same ring and pinion tooth count,
like 5.38s, the Ford 9" has 3 COMPLETE teeth in contact with each other at all times where as the
Dana 60 has less than 2. The teeth are the same size but there are more overlapping with the Ford
9". But in the case of a 4.88 ratio there would be so much overlap that Ford went to a 4.86 that has
1 less tooth on the pinion but still has equal tooth overlap to the Dana 60 only the teeth on the Ford
9" are .040" thicker at the tip and .090" thicker in the center of the teeth where the load is applied.
B. Why are Ford 9" gears sometimes off a little in gear ratios like 4.57 compared to a 4.56 of
others? All gear manufacturers choose the tooth count that gives them the best overall strength
combination between tooth overlap and tooth thickness.
2. What is the benefit or disadvantage of a larger/smaller ring gear?
A. A larger ring gear allows the same number of teeth to be larger. This means that if you have 40
teeth spread out on a 10.5 circle they will be larger than if they were spread out in an 8 inch circle.
That is why a GM 10.5 14 bolt has such huge teeth with very little pinion offset. BUT the Ford 9"
already has larger teeth than a Dana 60 so there is no advantage to the Dana 60s' 9.75" ring gear vs
the Fords' 9" ring gear.
B. Ground clearance. The advantage now lies with the Ford 9" due to better ground clearance.
3. There has been some questions as to why the Fords' pinion teeth look more angled than other
pinions. The Fords' pinion teeth (because of the larger pinion offset) can be angled more (in
relationship to the pinion stem) which is what creates more tooth engagement. The Ford 9" pinions
act/look somewhat more like a screw or worm gear than other pinions.
4. Pinion shaft size. Factory and cheaper aftermarket Ford 9" gears have a reduced diameter area
just after the splines toward the pinion head which weakens the pinion shaft. Richmond gears do
NOT have this reduced/weakened area. The smallest diameter on the Ford 9" of ours from
Richmond and the Dana 60 lies in the minor diameter of the splines which is 1.120 on the Ford and
1.160 on the Dana. So the Dana 60 is .040" larger at the splines. Some NON-Richmond Ford 9"
pinions have broken off at the reduced area on stock or lesser quality gear sets (usually from the
truck being dropped on the yoke on a rock which would be pretty tough with a Hi9) but Richmond
has very rarely seen a pinion twisted off on their pinions.
5. Running on the coast side. Why? Because we have no choice. No gear manufacturers have a
machine set up to cut them the other way. The reason Gleason (the folks who build gear building
machines) don't build them the other way is that when under drive side conditions the pinion is
being pushed away (forward when low pinion in the rear) and under coast side conditions the ring
gear is being pushed away. They believe if neither of the gears are being pushed away (high pinion
rear on drive side situation) the gears will "jump" each other causing instant destruction. Can it be
done? Possibly, but the cost of building the machine that may cause more problems than it solves
may not be worth building.
6. Are all high pinion rears running on the coast side of the gears? Yes. Is running on the coast side
weaker? NOT when deflection is controlled. Why are other manufacturers HP diffs weaker?
Because deflection is not controlled. Running on the more angle side of the tooth pushes the ring
gear and pinion apart under load. This causes the ring and pinion teeth to separate and run tooth tip
to tooth tip instead of center of tooth to center of tooth. Can we control these separation forces?
Sure. Just think of holding the pinion head on both ends of it with a 3rd bearing compared to
holding it with just 2 bearings when these separation forces are at work. Now try to control the ring
gear forces 3 inches away from where they are occuring instead of with a thrustblock like heavy
duty rearends use including the monster trucks you see jumping and landing throttled up. I've had
monster truck 3rd members in my shop and believe me they have a thrustbolt. People have called
me with busted high pinion rear Dana 60's that have two distinct wear patterns on the teeth, one
where they normally run and one where they run when they are under a load which is at the tooth
tips where there is less material. The thrustblock in our differential virtually eliminates this ring gear
deflection. Add that to the fact that a Dana 60 starts out with either less tooth thickness or less
overall tooth contact and which do you think is going to break first?
7. Why didn't anybody build a Hi9 before? Simple. No gears. Increased cost of getting them cut
and less profit.
8. Will the pinion blow out the front of the case like on a stock low pinion Ford 9"? That would be
pretty tough because the ring and pinion are pulling themselves together when in a high pinion
configuration in the rear as compared to pushing themselves apart front to back in a low pinion
application. Plus the nodular iron is considerably stronger than the grey iron used in stock gear
9. Will the pinions 3rd bearing support in the housing break like in a low pinion Ford stock gear
case? That is also pretty tough because if you look at how a low pinion 3rd bearing is supported
when the pinion tries to "climb" the ring gear there isn't much support above it. Now look at the
Hi9 and you will see that when the pinion tries to "climb" the ring gear there is a tremendous
amount of material supporting the bearing. Plus it is thicker all around the bearing and with less
material machined out of the center and with better material than stock it would seem to be pretty
strong. Also if a stock Ford 9" breaks that area out trying to control the pinion head from moving,
think about how much a Dana 60 pinion head moves around.
10. All the information above is fact. These are the reasons why we believe we easily have the
strongest high pinion differential available. Plus with the driveshaft higher and the u-joint closer to
the rear end for a longer driveshaft ( less angle yet ); this high pinion differential is hard to beat.
11. High pinion rear = coast side of gears Low pinion rear = drive side of gears
High pinion front = drive side of gears Low pinion front = coast side of gears
The following statements are when moving forward.
Here are some interesting numbers concerning the tooth size and differences between our ratios and
two Dana 60 ratios. I only have 4.88 and 5.13 Dana 60 gears at this time to measure.
Ring gear tooth dimensions
Hi9 4.11 4.57 4.86 5.14 5.38 5.40 D60 4.88 5.13
Thickness (pattern center) .300 .315 .315 .265 .240 .400 .250 .270
Length (pattern center) 1.475 1.495 1.540 1.655 1.660 1.600 1.600 1.750
Overlap (engagement) 2.305 2.135 2.265 2.375 3.204 2.00 1.25 1.500
Thickness cubed x length x overlap
(this number is representative of overall strength)
The higher the better .092 .098 .109 .073 .074 .205 .031 .052
Here are some more interesting numbers concerning the pinion head diameter.
A larger number means less force applied to the ring gear teeth for a given torque input.
A smaller number means its easier for the pinion to break the ring gear.
Pinion Head Hi9 4.11 4.57 4.86 5.14 5.38 D60 4.88 5.13
Major O.D. 3.98 3.87 3.62 3.74 3.48 3.13 2.95
Minor O.D. 2.72 2.67 2.52 2.95 2.78 2.20 2.06
Average O.D. 3.35 3.27 3.07 3.35 3.13 2.67 2.51
Radius from pinion center to
center of pattern 1.505 1.465 1.365 1.598 1.415 1.185 1.105
What this means is that with a motor torque output of 350 ft. lbs., a low gear tranny ratio of 4.0 to
1 and a 5.0 to 1 low range t-case ratio thats 7000 ft. lbs. of torque going into the pinion.
With that 7000 ft. lb. number and the pinion radius number we can calculate the force applied to (or
trying to break) the engaged ring gear teeth.
Hi9 4.11 4.57 4.86 5.14 5.38 D60 4.88 5.13
55,814 57,338 61,538 52,566 59,364 70,886 76,018
Gear size & strength info:
What does all this tooth talk mean? Well a picture is worth 1000 words.
The first pic is a Hi9 5.14, second pic is a HPD60 5.13.
In both photos the bottom pinion tooth (tooth with the dot) is just at the point of leaving contact with
the ring gear.
On the Hi9 the next tooth to the right is in full contact with the fattest part of the ring gear tooth, tooth
2 is in contact with the center part of the ring gear tooth and the 3rd tooth is starting to grab the first
1/4 of the ring gear tooth.
On the HPD60 the first tooth is in contact 3/4 up the ring gear tooth and the 2nd tooth is starting to
grab the first 1/4 of the ring gear tooth.
So you basically have 1 more tooth carrying the load on the Hi9 5.14
Hi9 5.14 Dana 60 HP 5.13