10 vs 29 Spline 8 3/4 Yoke, Is One Better/Stronger Than The Other?

[Road_Runner]

I'm starting to put together a stronger center section for the Roadrunner's 8 3/4 rear and see there are two different splines available 10 & 29.  Mine is a 70 so from what I read probably has the 10 spline.  Since I'm building this up from scratch I assume I can use either one with my all new parts.  Is one type of spline better than the other?  So far I've purchased a nodular 489 carrier, looking at picking up a Powerloc differential, Dr Diff's HD axles, and a new ring & pinion: brand & ratio TBD.  Figure this should hold up fine for my purposes and keeps the original rear housing in the car.  Personal experiences and advice appreciated.

Later, Jim

[7212Mopar]

I thought 489 case use 29 spines but I suppose you can change to match your axles. Sorry I don't know which is stronger but interested in learning the various choices and differences between Ture Trac, Power Loc etc.

I will be dropping mine down in the next few weeks for clean up and paint. It works fine now, no noise and put down two stripes.

[burdar]

I "think" more = better.  Guys that drag race talk about upgrading to 35 spline axles.  I would think the same thing is true for the yoke.  More splines= more contact area.  I'm interested to hear what other say.

[GoodysGotaCuda]

More splines are stronger.


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[mopar jack]

I have raced 741 and 489 case gears for years in a  mild 440 E-body and never had a problem. I think the 29 spline is stronger. I attached a useful link for 8 3/4 part numbers and specs. http://www.planethoustonamx.com/main/chrysler_8_34_rearends.htm

[jhaag]

Just to be clear guys, he is talking about pinion splines not axle splines. Yes typically mores splines would equal more strength. Having said that, always found it interesting that the famed hemi 4 speed had an 18 spline input and the "regular" 4 speed is 23 splines?

[Road_Runner]

I have raced 741 and 489 case gears for years in a  mild 440 E-body and never had a problem. I think the 29 spline is stronger. I attached a useful link for 8 3/4 part numbers and specs. http://www.planethoustonamx.com/main/chrysler_8_34_rearends.htm

My 8 3/4 is going behind either a 450 or 488 stroker that should be a 500+ motor and 727 auto so hopefully a built rear will hold up.  I tried your link but got an error.  Thanks, Jim

[mopar jack]

Sorry about the link, I tried it and I also get an error but it I cut and paste it to the search bar it opens. Maybe one of the other more computer savvy members can fix it.

[dodj]

Just to be clear guys, he is talking about pinion splines not axle splines. Yes typically mores splines would equal more strength. Having said that, always found it interesting that the famed hemi 4 speed had an 18 spline input and the "regular" 4 speed is 23 splines?

Ya! I always thought the hemi 18 spline must be the weaker input shaft. 

I "think" more = better.  Guys that drag race talk about upgrading to 35 spline axles.  I would think the same thing is true for the yoke.  More splines= more contact area.  I'm interested to hear what other say.

More splines = more contact area= stronger

[mopar jack]

Please try the link again, I think it will work now.

[Aracer]

When I got new 4.30 Zoom gears for the 489 housing it came with 10 spline pinion. The original 2.76 has 29 fine splines, so my vote 10 splines is stronger since they are thicker and may have a tighter grip on the pinion. I think my Richmond 5.12 is 10 spline also. Both are on spools. 
     My 3.90 gears on a 1968 tracloc clutch has 29 splines from the factory in a 741 carrier. The quietest of them all. It confirmed that my new drive shaft balancing is perfect past 6500. With those low gears the harmonics usually get noticed at high speed. If they're tight and need a .010 pinion shim or are too close to the ring gear they buzz and run slow.

[Road_Runner]

When I got new 4.30 Zoom gears for the 489 housing it came with 10 spline pinion. The original 2.76 has 29 fine splines, so my vote 10 splines is stronger since they are thicker and may have a tighter grip on the pinion. I think my Richmond 5.12 is 10 spline also. Both are on spools. 
     My 3.90 gears on a 1968 tracloc clutch has 29 splines from the factory in a 741 carrier. The quietest of them all. It confirmed that my new drive shaft balancing is perfect past 6500. With those low gears the harmonics usually get noticed at high speed. If they're tight and need a .010 pinion shim or are too close to the ring gear they buzz and run slow.

You would think more drag oriented gears would use the strongest pinion design.  I'm going to ask a few vendors and I'll post back here what they say.

Thanks, Jim

[brads70]

I took Neil's advice and bought a new Dana from Cass .... before I owned 2 8 3/4's....

[Road_Runner]

I took Neil's advice and bought a new Dana from Cass .... before I owned 2 8 3/4's....

Did you break the 8.75's and if so were yours beefed up at all?  What broke?  For me not to keep the original 8.75 rear throws into question keeping the rest of the drive train original.   I've been planning on swapping it to a 4 speed forever, especially since its originally a column shift auto, so if I deviate from that I'll probably start thinking about the 4 speed all over again, its  either original or its not, kind of binary for me.  That said I don't want to wipe out the car breaking an axle etc. that could put me off the road / against the wall.

Thanks, Jim

[HP_Cuda]

I don't think the 8 3/4's are that easy to break.

Remember when going to the Dana you don't have the variety of gears to put in there that the 8 3/4 does.