8 3/4 chunk question

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rusty

rusty

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what is the difference in casting # ie 489 741 and so on,strength,gears available or what? Found a complete rear end from a 69 dart w/741 case and a 69 dart is what i am putting it in.Thanks.Todd
 
Basically it's all about the pinion diameter. The 741 is the smallest, the 742 the next size up but and a machined cut on it, and the 489 is the biggest but has a tapered end on it and uses a crush sleeve but you can now over come this by using a solid sleeve on it which will make the 489 even stronger. Best bet would be to get your hands on the 742 or 489 (these two have the best selection of gears for them).
 
741 will do just fine even though it is the smallest/weakest of the three. It has survived behind many a big block car for years.
 
GET IT. I have way too much money into mine due to starting with a bare housing. (489 case rearend going in the duster)

In my other (project) car, I have no second thoughts putting my spare 741 pumpkin in it and it will see a lot of track time. They may be the "weakest" of the three cases, but they're still plenty strong.
 
741= 1 3/8" pinion shaft dia.... 742= 1 3/4" pinion shaft... 489= 1 7/8" tapered shaft. Difference in a typical 69 Dart...nada!!! Get it and worry about building your optimum center section after it's installed, you can do all that on the bench and swap it under the car!!! Geof
 
thanks guys I appreciate the help,now to see what i can get it for.And find out ratio and if posi or not!
 
741 will be fine, although you will be somewhat limited in gear choice. To see if it a "suregrip", posi is for chebbies, raise both rear wheels of the ground and turn one tire if the other side rotates in the same direction it is a suregrip, if it rotates in the opposite direction it is open. To check your ratio, put a mark on the tire at the bottom and lay something on the ground to line up with the mark. Put another mark on the drive shaft. Count the revolutions of the drive shaft to "one" revolution of the tire. 1 revolution of the axle and 2 3/4 revolutions of the shaft would suggest 2.76 to 1 ratio. I'm betting that's what it is.

You can also look for a tag on the rear, there might be one on one of the bolts around the pig that will tell you what the ratio is.
 
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