Can someone explain when Buick used 28 spline rear ends and when they used 30. I thought I was begining to understand but I came across an application chart from Eaton that got me confused again. What did the 72 Skylark come with?
I believe all the stock 8.5 that came in the 71-72 skylark/GS, and the GN's have 28 spline axles. 30 spline is an upgrade. My 1971 GS rear was rebuilt with Moser 30 spline axles and matching Eaton Posi.
Larry, Is is correct that the 72-81 Z-28s and Firebirds were also 28s? What GM cars were 30s ? Why were the 30s considered an upgrade ? Were they stronger or smoother running ? Sorry for all the questions but I'd like to know a little more about the posi units.
I'm not sure if there were stock GM 8.5 cars with 30's. More splines means more contact and stronger axles. The larger spline count axles should also be a bit larger. I believe 8.5's came with 28 spline axles. Monzaz will know for sure.
i think the only factory vehicles that came with the 30 splines where infact the 8.6 rears...same as 8.5 minus different carrier bearing as mentioned before monzaz will know
I would say the 30 spline axles are larger. Mine are Mosers, so I know they are stronger than stock. Spline count must match between axle and posi carrier. Can't be converted to my knowledge.
normally WHEN YOU INCREASE AXLE SPLINE COUNT YOU INCREASE AXLE DIAMETER. usually...lol. -28 spline axles are stock in GM 8.5 till 1989. Grand National was one of the last performance 28 spline Rwd vehicles ... -1990-1998 8.5 10 bolt were 30 spline c-clip rears -1999-2009 8.6 were 30 spline axles and had larger carrier bearings (same size as the 12 bolt chevy of old.) A36 bearing set. SOME eaton posi units can be converted to 30 spline from 28 BUT the carrier case where the axle slides into the side gear through needs to be machined larger...AND since they already build 30 spline units this would really be redundant in a way...definitely NOT cost effective. 30 spline is as big as the 71 72 BUICK 8.5 rear can be made with the bearing A9 712146 seal. But if we used the A10 bearing and matching seal we could build a 33 spline wagon rear...that would be cool and stealthy...anyone want to front some money for that fun build... :beer So with increased spline count in a fine spline the diameter increases and the strength usually comes along with it. BIGGER is better to a point then the axle gets too darn heavy and will actually cause power loss and fatigue to the internal ring and pinion and spider gears...this is the reason for GUN DRILLING , less mass to rotate a 40 spline axle shaft is VERY heavy!!! Hope I got all the questions ...if I did not I am sure you will let me know...lol. Jim
Hope I got all the questions ...if I did not I am sure you will let me know...lol. Jim[/quote] Thanks Monzaz. Somewhere along the way I got the idea that Buicks had 28 spline axles up until 1970 and then went to 30 in 1971 and 1972. I don;t know where I got that idea now but thanks for clearing things up.
Well we do alot of 30 spline MOSER custom axles in the 71 72 buick axles and it works really great for super street and track use. PLus the posi unit is the same price as the 30 spline so it really makes no sense to rebuild a 28 spline rear with Custom moser 28 spline axles when it will cost the same for 30 . JIm Take care and good luck on the hunt. Jim
Thanks for all the information. I feel like I know a lot more than I did two days ago and I'm a little better prepared to start looking for parts.
