I posted over in Engines&Drivetrain that my posi came completely apart. Pieces of posi are everywhere. What a mess! So, its rebuild time and I have a few questions.

Here's one:

Two kinds of Eaton Posi: one good for 3.08-3.73 and one good for 3.73+.

If I get the 3.08-3.73 posi, Summit shows gears up to 4.88 that will work with it. But, is this a good idea? What's the issues with running more than 3.73 with the posi that is supposedly only good up to 3.73. Is it weaker? More chance to whine? Or... no problem?

Thanks

Not being a differential expert at all, but I think if you run a gear that is bigger numerically (4.10, 4.56, 4.88 for example) on a carrier meant for numerically lower gears, you need to use a spacer between the ring gear and the carrier. This is inherently weaker than bolting the ring gear directly to the carrier. Some will say that they have successfully run ring gear spacers without problems, and that's great. There are also "thick" ring gears that make the spacer unnecessary, but I think they are harder to find and more $$$. If you're starting from scratch, get the carrier that matches your gearset.

Buy the 3.08-3.73 carrier as they are built to the exact same strength standards as the 4 series unit.. Also, the gears in the 4+ range that run on the 3 series carrier are built thicker so you do no have to use the ring gear spacer. Get it, the 4 series gear is even thicker than the 3 series gears making them in my mind extrememly strong..

You want the 3.08-3.73-or commonly known as the 3 series unit..

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1969 Camaro SS 350-383ci., T-56, 12 bolt, Eaton posi, 3.31 gears, 4 wheel disc, Deluxe black houndstooth interior, rear window defogger, tilt steering, console w/AutoMeter gauge package, center mntd. clock, Tach.

Rogue68
I am currently looking for some internal parts for a posi unit that I am putting together. If any of your parts are still useable, please contact me as I would be interested in buying them from you..

Please contact me at poolstuff@juno.com and let me know if anything is still useable, and how much you want for it.. Thank you!

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1969 Camaro SS 350-383ci., T-56, 12 bolt, Eaton posi, 3.31 gears, 4 wheel disc, Deluxe black houndstooth interior, rear window defogger, tilt steering, console w/AutoMeter gauge package, center mntd. clock, Tach.

[This message has been edited by Go69 (edited 01-16-2003).]

If I may respectfully disagree, I don't think the thick ring gear setup is any stronger that the standard setup. If it IS stronger, it's in an area that seldom fails anyway, the body of the ring gear. Where these things are prone to failure is in the teeth, and in the bolts that hold the ring gear to the carrier. I have never heard of the bolts pulling out of the threads, but have heard plenty of stories of the bolts breaking at the junction between the carrier flange and the gear, due to the fact the stress placed on the bolt is in "shear". That is at least partially why ring gear spacers are undesireable...it creates an additional shear point on the bolt.

The only reason a fastner would fail is if it were istalled incorrectly, or the fastner itself was streched from re-use or over tightening. I have been in the drivetrain engineering (specifically differential) business for more than 10 years and have only seen MAYBE two fastner related failures and they were both in 9" Ford third members.

There is NO strength advantage/dis-advantage to using a thick or thin gear set. But ring gear spacers are never an advised product, unless you have no other recourse but to use one....like in a chassis that hasnt been built for 40 something years and you have no other choise. And you then park the car for the rest of its life.

If you think that you may want to change to a higher ratio later you still can if you purchase a 3.08-3.73 carrier.

If your really worried about noise and gear whine, I wouldnt recommend Richmond either. US and Precision are about the best that your money can buy......

I would suggest getting the 3 series posi so you will have a larger selection of gear ratios. I feel that there is a slight strength advantage to the thick gears, but only because it will not flex as much as a thin gear. The bad side to the thick gear is the increase rotating mass, which can slightly slow accelleration.

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'69 RS/SS396 pro street
427/4spd/9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead (http://www.lubedealer.com/biggearhead)

Thanks for the replies.

So, a 3-series it is.

Go69 - I will probably rebuild this posi. I hope you are able to find the parts you need. Thank you for asking.

Go69- What parts are you looking for I may have some/them laying around the shop.....