9" 3rd member from yard w/ good ratio?

Side gears can not always be swapped between 28 &31 as the hole for the axel in the traction loc is to small to allow the 31's to fit. Also do do go swapping pinion supports from one carrier to the next with out knowing what you are doing. It sets the pinion depth into the ring gear. This is controlled by a set of shims that are specific to the carrier and pinion support. New gear sets will come with a marking on the pinion gear that will tell you how much to add or subtract from the shim pack with the new gears. If you loose the original shims or try and put a pinion support from another carrier you are on your own. This normally takes a differential specialist to get set up correctly.

65FBE2 said:

Side gears can not always be swapped between 28 &31 as the hole for the axel in the traction loc is to small to allow the 31's to fit. Also do do go swapping pinion supports from one carrier to the next with out knowing what you are doing. It sets the pinion depth into the ring gear. This is controlled by a set of shims that are specific to the carrier and pinion support. New gear sets will come with a marking on the pinion gear that will tell you how much to add or subtract from the shim pack with the new gears. If you loose the original shims or try and put a pinion support from another carrier you are on your own. This normally takes a differential specialist to get set up correctly.

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He's talking about going from 31 to 28. Not an issue here. Changing the side gears wouldn't affect the pinion depth, I'd be more fearful the wear on the pinion gears wouldn't be compatible with the new gears. He'll need to reset the gear contact patch using the bearing preload nuts, that only takes attention to what you're looking at, no special tools needed there, only some good sticky grease.

Last year for a 9-inch being installed in a Ford car was 1980. Last year for a 9-inch being installed in a Ford pickup was 1986.

All 9-inch 3rd members will fit any 9-inch rear end housing. The only catch is the differential's spline count has to match the axle's spline count.

Cars will typically have high ratios [low numerically], good for gas mileage, bad for performance.

Ford half ton pickups from '67-up will have the better ratios ...3.25, 3.50, 3.70, etc.

All early Broncos ['66-'77] had 28-spline axles/differenitals, but not all had Limited-Slip differential. Broncos from '73-'79 had 31-splines.

Most trucks prior to '73 had 28-spline axles. Most trucks from '73-'86 came with 31-spline axles.

If you are putting a 9-inch rear in an early Mustang, the companion flange on the pickups are shorter than the ones that came on the 9-inch passenger car 3rd members. The pickup companion flange is better suited to the stock early Mustang drive shaft length.

Finding a 9-inch 3rd member with a Traction-Lok differential in the wrecking yards is not easy these days. A 28-spline differential is even harder to find than a 31-spline.

Third Member I.D. Codes