8 3/4 axle splines

[dodj]

I'm lining up what I need to buy to rebuild my 8 3/4 centre section. I see diffs listed as 29, 30, 31 and 35 spline. Do I have to pull my axles to know the factory stock spline count?

[70CUDA4SPEED]

All factory are 30 splines.

[dodj]

Thank you 

[dodj]

https://www.summitracing.com/int/parts/dtl-913a572/reviews/

Summit just states for 8 3/4 rear. It doesn't specifically state, but will it fit a 489 case?

[70CUDA4SPEED]

yes that's the correct one, it fits all houses 741, 742 and 489, I have bought two from them.

[dodj]

Thanks again 70CUDA! 
Now to pick out a gear set from somebody.  Probably 3.23. Maybe 3.55. Not sure yet.

[dodj]

yes that's the correct one, it fits all houses 741, 742 and 489, I have bought two from them.

Did you buy one of the installation kits as well? If you did, which one did you go with?
Yukon is $219
Motive is $119
Not sure why the big difference in price? Do different diffs (ie open, sure grip, trutrak) use different carrier bearings?
Edit: With a little more research, I see that the sure grip does use different bearings from an open diff or trutrak.

[jimynick]

Thanks again 70CUDA! 
Now to pick out a gear set from somebody.  Probably 3.23. Maybe 3.55. Not sure yet.

The 3:23's in my 4 spd (shouldn't make a difference) turn the engine about 3200 rpm at around 65-70 mph. If I remember correctly, yours is a big block isn't it? With a good supply of lower rpm torque and unless you're going for acceleration, and presuming neither you nor your Dad own a gas station, I'd be tempted to even go into the 2's. But then, that's just my  worth. 

[70CUDA4SPEED]

Did you buy one of the installation kits as well? If you did, which one did you go with?
Yukon is $219
Motive is $119
Not sure why the big difference in price? Do different diffs (ie open, sure grip, trutrak) use different carrier bearings?
Edit: With a little more research, I see that the sure grip does use different bearings from an open diff or trutrak.

I found two new sets Richmond at ebay and bought them, this is kopied from Cass "doctor diff" page, ""Powr-lok" (clutch-type) sure-grip or pre 1969 open differentials use 1.8" inside diameter carrier bearings. Spools, Auburn cone sure-grip, Eaton True-Trac, Detroit Locker or post 1968 open differentials use 2" inside diameter carrier bearings."

[70CUDA4SPEED]

And bearing kit, those did I buy from Summit, I think Ratech for the 489, https://www.summitracing.com/int/parts/rat-302k/overview/ 742 https://www.summitracing.com/int/parts/rat-301ka/overview/ just check so you get the right carrier bearings.

[dodj]

The 3:23's in my 4 spd (shouldn't make a difference) turn the engine about 3200 rpm at around 65-70 mph. If I remember correctly, yours is a big block isn't it? With a good supply of lower rpm torque and unless you're going for acceleration, and presuming neither you nor your Dad own a gas station, I'd be tempted to even go into the 2's. But then, that's just my  worth. 

Ya, I hear ya. I have a 2.76 open in the car now. Great for distance runs.

[Rdchallenger12]

I found this thread just as I needed it since I will be changing my open diff to a sure grip and adding 3.23 gears. Mine will have a 340 and is an automatic. I was thinking 3.55 but in case I decide to take it on a long trip I think I'd rather have the 3.23 for highway speeds

[dodj]

I'm going 3.23 as well. I decided, in my mind,  the 3.55 is kind of a goofy ratio. Not great for the highway, not great for the drag strip.