Another 8 3/4" diff question.

[VIOLENT\6]

On Summit's site they list different ring & pinion sets for the 8 3/4" Chrysler Differential.

They list a 489 casting & a 742 casting. I have a few questions.

What is the difference?

Is one more desirable than the other?

What are the different applications/car/truck models for each?

How do I tell them apart when they are in/out of the vehicle?

 

[VIOLENT\6]

Bump!

Come on guys, I was led astray by SB Chevies (I did have a 340 4-speed Dart Swinger in "72") I'm a bit green on the Mopars, trying to learn.

As soon as I get the "06" Daytona Charger in the mid 12s, My son & I are going to attack that "65" Valiant of his.

 

[ValiantMike]

Check here for good info on 8 3/4 rears. I do beleive that the 489 is the better of the three types, but others may disagree. You can also use a 8 1/4 if you keep HP at or below 400, as a rule of thumb. Mike
http://www.moparts.com/Tech/Archive/axle/21.html

 

[66dartman]

The 489 uses a crush sleeve to set pinion bearing preload while the 742 uses shims. The 489 is a 1-7/8 pinion shaft while the 742 is a 1-3/4 pinion shaft. I like the 742 better, once you crush the crush sleeve on a 489 it's done. With an a body, I think the difference in pinion shaft size is minimal.

 

[VIOLENT\6]

Thanks guys. Anyone have any opinions on aftermarket lockers? http://www.forabodiesonly.com/mopar/showthread.php?t=19027

 

[fishy68]

The 489 and 742 cases are different. A gear set for a 489 case won't fit in a 742 case and vise-versa. Kinda like a Chevy 10 bolt is different from a Pontiac 10 bolt. The case casting is stamped on the drivers side close to the bottom. The last 3 numbers is what we all go by. Which one is better is a long debate. Each one has it's own good points. Now you can buy a solid spacer and shims to replace the crush sleeve in the 489 case. That might give it an edge.

 

[VIOLENT\6]

The 489 and 742 cases are different. A gear set for a 489 case won't fit in a 742 case and vise-versa. Kinda like a Chevy 10 bolt is different from a Pontiac 10 bolt. The case casting is stamped on the drivers side close to the bottom. The last 3 numbers is what we all go by. Which one is better is a long debate. Each one has it's own good points. Now you can buy a solid spacer and shims to replace the crush sleeve in the 489 case. That might give it an edge.

Any links to a source for the spacer/shims?

 

[340mopar]

I would add that although the pinion is smaller at the gear end on the 742 the spline end shaft diameter is the same as the 489 so this is were it would break if it it did. The 742 is stronger because the inner bearing is larger that the 489.

Chuck

 

[fishy68]

Any links to a source for the spacer/shims?

Sorry but I don't remember exactly where I saw them at. I think it might have been on E-bay. I don't usually do much differential work so I didn't save the link.

 

[demon seed]

Yukons got overhaul kits. http://www.yukongear.com/Default.aspx


Terry