8 3/4 rear casting 1820657

[67DART340]

My 67 Dart 340 hybrid has 8 3/4 rear, type 1820657 (58-64). It acts like a non-Sure Grip (wheels don't spin in the same direction when off the ground). The gear ratio on these units is stamped into the case toward the back, on the opposite side of the casting numbers. The numbers stamped appear to be 3.58 (no "S" for Sure Grip). As far as I can tell from what I've read and known about, this ratio does not exist. It probably would be a 43/12 gear set, but I haven't taken it apart yet. Does any have knowledge of such a ratio?
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[Mrmopartech]

Your rear center section is a C body unit only.YES some one installed it from a big C car to replace some gear set that went south.Now you need to check out some of the gear set that you could get from 58-64 in imperials,new yorkers,300,etc to find the ratio,s that could be in there.Or just lift the car,block one wheel and a freind with some brains,turn the drive as many times as needed to turn the wheel once,making note of how many times the drive shaft turned to complete the wheel turning once,your ratio,mrmopartech

 

[demon seed]

When the 657 first came out and for years later it had keyed tapered end axles. The brake drum was fit over the taper and held on with a nut. Hopefully someone retrofitted your rear end with flanged end axles and it's easy enough to check.

Terry

 

[375inStroke]

I'm sure he doesn't have the entire C-body differential. Just the center section. A worn out Sure-Grip could spin one tire, but both will still spin the same direction when off the ground. If an open diff, you need to keep one wheel from turning, turn the other wheel for 2 revolutions, and count the number of times the driveshaft turns. That number will be your gear ratio. The reason you turn the wheel 2 times is that the spider gears are walking around the side gear of the fixed wheel.

 

[67DART340]

Thanks for the info. Since it's an open rear (non posi), what I did was turn the drive shaft and watch the wheel turn one rotation, but because it's an open rear and the other tire does not move, I rotated the wheel twice or 2 turns because of the spider gears multiplying it times 2 with one wheel not moving. The ratio that I came up with was about 3.6:1, which would be pretty close to the 3.58 that's stamped on the carrier. The only thing is the listed ratios I found are: 2.76, 2.93, 3.15, 3.19, 3.23, 3.31, 3.36, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57. The earlier rears were the only ones stamped with the ratio (no tag).

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[67DART340]

Thanks for the feedback. This car appears to have an A body housing at about 50.3" brake plate flange to flange, or so . I looked for numbers on the housing, but couldn't find any. I suspected it just has spider gears, no posi, but I was only 98% sure about my logic for the 2 wheel turns with an open (spider gear) rear off the ground. It doesn't have tappered axles like my 63 Newport, it has flanged type axles and has a 4.5" bolt pattern and not the normal 4.0" that should have been. It has all RH threaded studs, too. The brakes look like maybe 10" X 1.5", I'm going to try to measure it today.