Hello, Does anybody know for sure what rear end would be in my 1972 Skylark with a 350? It has 2.73 gears, but I would like to know if it is the 8.2" or 8.5" ring gear and how many splines it would have so that I can start looking for a posi unit for it. Thanks
It is an 8.5 rear with 28 splines if it is the original rear. You can contact Monzaz and he can set you up with a good posi unit. He rebuilt me a rear for my car and was way more than fair and honest...
It can also be a 12 bolt if the car was built in Canada. Count the cover bolts. If you have a 10 bolt, it is most likely the 8.5. The 8.5 10 bolt is the standaed axle on the 71-72 cars.
Thanks guys. It is a 10 bolt but I was unsure whether it was an 8.2 or 8.5. I presume that it will have bolt in axles? I have only had the car for a couple of weeks and am having too much fun driving it to even take a brake drum off and have a look....
Look around the center section where the axle tubes go into it. If it's smooth, then it's an 8.2. But if there are four "bumps" around there at the 12,3,6,9 positions, it's an 8.5. Plus if there are "ears" on the bottom of the center section, that's a good sign of it being an 8.5.
Both the 8.2 and 8.5 used bolt in axles. In addition to the 2 things Phil mentioned about the 8.5, the rear yoke on the 8.5 will retain the u-joint with straps and bolts, the 8.2 will have u-bolts with nuts.
I just looked and all indications are that I have the 8-1/2" 10 bolt. Now my next question: Will this unit stand up to a mildly built 455, or do I need to look for a 12 bolt? Thanks for all the help so far.
The 8.5 10 bolt will easily stand up to your 455, especially if you equip it with aftermarket axles and posi. Aftermarket support is excellent also, unlike the 8.2 axle. It has bolt in axles which are better than the c clips in the 12 bolt. I would say it will hold up to street use with a mildly built 455. Lots of torque + a heavy car + perfect traction = most stress on a rear. I would say the 8.5 is more than up to the task.
Is the stock GM posi an acceptable posi if I can find one or am I better off to go with an Eaton unit?
I would go with a new posi. The Yukon Posi is an exact copy of the Eaton unit for less money. I would have used it instead of my Eaton had i known at the time. http://www.yukongear.com/Positractions.aspx
Thanks Now when I go to install my new posi unit, can I get away with just setting the backlash to the same as it is now by shimming the carrier, or will I need to adjust the pinion too? It seems logical that If the pinion is not disturbed, it should remain in the correct position relative to the carrier and ring gear. I may be just trying to take a shortcut that will get me in trouble later, but the quicker I can get this job done, the sooner I can start on other upgrades.
