Saturday, August 11, 2018

1966 Barracuda 8-3/4" Differential Adjustment

My Barracuda had a strange rubbing noise coming from the differential when I drove it home the day I bought the car. I wondered if one of the tires was low and causing the Sure Grip to make noise. Nope, wasn't it. I then checked the axles for end play. That wasn't it either. I checked the axles for excessive run-out on the lathe (the photo below shows measuring in the middle of the axle but I checked bearing and spline ends too). Still not the problem.

Well what could it be? The next logical course of action was to delve deeper and pull the center section of the rear differential.

Fortunately I found the problem without too much difficulty. There was about .030" of side-to-side movement between the differential case and carrier. (Notice the cone-type Sure Grip, denoted by the spring showing near the ring gear). While not the better clutch-type Sure Grip, it's hands-down better than an open differential.

I tightened up the side adjusters...

... then adjusted the bearings until I got good side-to-side case positioning in the carrier, a good contact pattern on the ring gear teeth, and about .008" backlash between the ring and pinion gear.

The differential in the car now is from a 1969 model year car (ring gear dated 1 6 69). When my brother bought the car it had an open (non Sure Grip) 7-1/4 differential, however the car was ordered with Sure Grip, a $37.60 option, in late 1965 so the open 7-1/4 wasn't original to the car. It makes one wonder what happened to the original differential, although chances are pretty good that it broke when someone dumped the clutch. Brings back memories of how I broke the 7-1/4 in my '65 Barracuda in the early '80s.... back then I'd replaced that with an 8-3/4 too.

Ain't it purdy?... An 8-3/4" rear axle is so much nicer looking than the wimpy 7-1/4" that came with most of these older A-bodies.

The center section in the car is a "741" casting, which is the smallest pinion shaft diameter of the three types available in the 8-3/4 axle ("741", "742" and "489" are the three types, known by the last three numbers of the respective Chrysler part number). I don't mind a "741" in my car as it is mated to the lowly hi-po 273 V-8, and I've read that these diffs hold up well even with high horsepower engines.

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