Differential Question

[maz72]

I have a factory 8 3/4 rear with a 489 case. Suregrip with 3:23 gears. Looking to change the chunk with a swap for another case. Its the factory unit the car came with. Is this considered a small yoke? How many splines would this be? Fine or course? Assuming this is a cone type as well. Correct? Getting educated on Mopars as I have been in another manufacturers camp for a while. Expand my knowledge guys. Thanks.

 

[70aarcuda]

if you swapping out the complete third member/chunk/plg...the axle splines are all basically the same 30 splines ...the yoke on the 3rd member will dictated by the splines on the pinion gear....10 splines or 29 splines...

there is a conversion u joint to from the same 7260 yoke to the larger 7290 yoke or 7290 to 7260...it goes both ways..

 

[jerry6]

I have a factory 8 3/4 rear with a 489 case. Suregrip with 3:23 gears. Looking to change the chunk with a swap for another case. Its the factory unit the car came with. Is this considered a small yoke? How many splines would this be? Fine or course? Assumeing this is a cone type as well. Correct? Getting educated on Mopars as I have been in another manufacturers camp for a while. Expand my knowledge guys. Thanks.

Think the factory unit is clutches , at least mine were , not sure on yoke size but think 489 is large , but don' take my word

 

[maz72]

Would have been beneficial to state that my car is a 72 340 Duster. Duh....

 

[fishy68]

If I'm not mistaken all A-body small block cars used the small yoke (known as the 7260 yoke). In 69 the 489 case debuted and they started switching to the cone type sure grip and at first the splines (10 count) were coarse. btw: the books say 68 was the last yr. for a clutch type but some were left over and used in early 69 so it's entirely possible to have a 69 489 case with a clutch type SG. I believe it was around 71 that they started using the fine spline (29 count) yoke so if yours is an original 72 A-body 3rd member it's most likely a small yoke fine spline unit. It's easy to identify what spline pinion it is by the size of the yoke retention not. If a 1-1/8" socket fits it's a coarse spline. If it's larger (1-1/4" I believe) it's a fine spline. As Tony said all the factory axle splines are the same 30 spline.