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Old 03-02-2010, 09:56 PM
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what is inside my dif?

I've got a 1980 camaro z28 with a factory th350 trans. I'm in the process of figuring out what my differential assembly contains. Does anybody know what these came with? It has a 10 bolt cover......but would this be an 8.5"? Did these cars come with factory posi assemblies? What ratio gears would I most likely have? I can pull the cover to take a look but to identify the size I must measure the diameter of the ring gear, correct? Also if it is a posi how would one tell from looking in the cover?

Thanks for any help with these questions.
Keith
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Old 03-02-2010, 10:14 PM
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Car will have an 8.5" 10-bolt, if it is an actual Z28 it should have positraction, there will be a metal strip tag 5/8" wide x 1-1/4" long on one of the rear cover bolts that is stamped with "USE LIMITED SLIP LUBE ONLY". This tag is often tore off/rotted off or left off at a service of the rear fluid.

Gears could be 3.08, 3.23, 3.42. I think 3.42 was only with a 4-speed but not sure.

Pull the cover and find out, it is likely the fluid needs changed anyway. Factory posi unit will have a big flat folded S-spring in the center around the center pin, pressing out on each side axle spider gear

Try www.nastyz28.com

Edit: Nasty z28 says the 350ci th350 Automatic got the 3.42 ratio, the deepest offered that year. Stick cars and 305 auto got only 3.08's.

Last edited by ericnova72; 03-02-2010 at 10:21 PM. Reason: more info
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Old 03-03-2010, 07:04 AM
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All '71 to '81 Camaros and Firebirds got the 8.5 10 bolt rear end. I looked at a '80 Z28 rear end yesterday that had 3.42 gears and a standard differential. Not all Z28s got the posi rear end. The only way to know is to remove the cover and look inside.
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Old 03-03-2010, 07:35 PM
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Hey guys thanks for the info. So I took the cover off today and managed to read the production number stamped on the passenger side axle tube. The number (from what I can tell) is 2 PE G333 2 spaced just like that. From what I found at nastyz28.com the PE means it has 3.42 gears non locking. Inside the carrier I found no such "S-spring" either just 4 spider gears. I am removing the entire dif. to do some suspension upgrades and I plan on throwing in some higher gears into it while it's out. Is this dif. worth beefing up? Since it is the 8.5" 10 bolt non-posi would I be able to make it a posi by replacing the carrier with one from Eaton or another manufacturer that makes posi units? I am really gonna need a posi in this car once it is all done because those tires are gonna smoke pretty easy, espeically once I install a taller gear. If I can not install a posi unit into this dif. then I will have to search for a dif. with a posi.

Thanks for any help here,
Keith
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Old 03-04-2010, 07:12 AM
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Read this. http://www.nastyz28.com/forum/showth...ht=change+posi
The 8.5 is a very good rear end, and you can add a new Eaton Posi with no problems. Do you really want to change the gears? The 3.42 is a very good street/strip gear, especially if you drive the car a lot. Changing gears is a lot more work that installing a posi requires more specail tools and you must know how to set the pinion depth, bearing preload and backlash.
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Old 03-04-2010, 05:12 PM
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^^^ What BigGearHead said, the 8.5" is a stout piece and the 3.42 is a nice gear if you are going to cruise it much. If you are thinking of changing to 3.73 it would be a waste of time, you will barely notice a difference, you would need to change to something like 4.10-4.56 to see a big difference.

Bummer, a Z without posi - what was the factory thinking?? Feel the same way every time I see a Monte SS without it, which is really common....What were they thinking ,.... you can't find a Mustang GT 5.0 without traction lock.
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Old 03-04-2010, 07:58 PM
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Thanks for the replies guys, you guys definately know your stuff. I gave that link you posted a read and I am now considering installing a powertrax Lockright. From what I have read about these units they are very easy to install and do you a good job of locking the wheels. Would you recommend I go this route and if so what is involved in installing one. I got my whole dif. out today leafs attached and all so it is easily accessible. How much more work would it be to install an Eaton posi unit? Would I need to remove all the internals?
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Old 03-05-2010, 09:44 AM
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I have had a Lock Right in my work truck for about 13 years and I have put about 140,000 miles onit. I like teh way it works in a truck, but it might not be what you are looking for. It locks up very well and works great, but it is jerky and pops from time to time. It's not as smooth as the Eaton. The Lock Right installs easily with comon tools and you don't remove the differential to install it.

The Eaton can be installed by folowing the instructions in the link that I posted. You will need a dial indicator with a magnetic base, a torque wrench and a good shim set. You can do this job in a few hours, but be patient and do it right. You will have to install and remove it a few times to get the backlash and bearing preload set right.
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