Sold 4.10 COPO gears

[jeremy clark]

Real deal, original COPO specific matched gear set. 4.10 ratio, dated 2-69. Ring gear number 3916226, pinion gear number 3916228 -I believe the original part number for the set was 3917971. Gears are in good shape, no spun bearings, chipped teeth, cracks, threads are excellent.


I lucked out at an estate sale the other day and bought a 72 Chevelle 12 bolt and these gears were in it. No, it didn't have a COPO specific posi carrier, axles or any other COPO specific parts -just this set of gears


Before I removed the gears I cleaned everything up and applied gear marking compound and checked out the pattern then I checked the backlash which was .0105. Next I removed the carrier and checked the pinion depth with a proper pinion depth gauge from TD machine products -the measured pinion depth was 2.758 there was a .026 shim between the bearing and pinion head.


As you can see, the pattern on the "coast" side of the teeth is pretty darn good, it is a nice wide, even pattern. The contact at the "toe" of the teeth (toward the center of the ring) is definitely more pronounced as evidenced by the shiny metal showing through the marking compound but keep in mind that under load the contact pattern will tend to move toward the "heel" slightly. This indicates a pretty good pattern to me -especially on a used gear set. I have not cleaned them with anything other than parts washer solvent or used any sort of abrasive.


The pattern on the "drive" side of the teeth is also wide at the "toe" but tapers to a point, the wide point of the pattern being at the "root" of the tooth -if I were setting up a new gear set this would indicate that the pinion was set too high in the housing but this is typical of used gears as the pattern will move slightly when under load. This is a pretty darn good pattern IMO I am fairly experienced with building differentials (done maybe 30 of them) but I definitely don't consider myself an expert -I encourage you to get a second opinion- I think they'll agree this is as nice a gear set as you could hope to find.


$1,750