Hey guys, I'm in the market for a new Eaton posi and Richmond 3.73 gears. Now I'm a little confussed when the posi says its for 28-spline but the Richmond 3.73 gears (for 71-81 Camaros) has 30-spline. Will the 30-spline work for my 78? I dont want to buy something and have an installer say it doesnt fit. Any help on this topic would be great! I'm trying to learn more about rear ends...car rear ends that is:P Thanks!!

 

To answer your question about the Richmond gear 30-spline, no it won't work.
Providing you have a stock unchanged rearend, you have 28 spline axles.
Starting in 1971, GM went to a standardized "10 bolt" that had slightly larger diameter ring & pinion gears as compared to 1970 and older.
1971-1981 specs:
Ring gear diameter, 8.5". Pinion diameter, 1.625"
The old 12 bolt rears came with 30 spline axles, not the 10 bolts.
In order for the Richmond unit to work, you would have to upgrade to 30 spline axles.

 

ohhh ok. See, I've even asked technical support at summit and an ebayer who is selling richmond gears and they both said they'd work. I'm glad I didnt buy them So, lets say I do purchase an eaton posi, keep my 28 spline axles, what kind of ring and pinion will work (Brand wise)? And Do you think I should upgarde my axles since I'm getting a new posi and gears? I'd appreciate yourhelp 69

 

Just a source Ive had good luck with...http://www.ringpinion.com/Default.aspx Also when you buy your posi search for the lowest price(I think randys was good) I got a price from an ebay store and Summit matched it saved about $80+ from the normal Summit price, but I bought it off Randys Summit just matched it and Randys is very helpfull and knowledgeable. .

 

*UPDATE* Just purchased a new Eaton posithe GM 10 bolt 8.5" axle with28 splines for $250 off of ebay Apparently the highest bidder cancelled his bid and I won! Anywho, since I'm stuck with 28-spline what ring and pinion will work? I've looked EVERYWHERE and no luck...

 

did you look here?
http://store.summitracing.com/partde...p;autoview=sku

 

Hey got3. Yes, I looked at Richmond gears but what does it mean when it says the pinion spline count is 30? I though I need a pinion spline count of 28 since my posi unit is 28 spline...right?? I'm soooo confused...

 

The pinion is the gear that the yoke for your drivshaft bolts to the spline count of the yoke must match the spline count of the pinion( 30 vrs 30) The posi needs to be a 28 spline count so your 28 spline axels can slide in (they shoud be 28 but the can be 30). The other issue with the posi you need to know if you are buying gears is the series posi it is, a 2 series is 2:43 and down and a 3 series is 2:73 and up to I believe 4:56...

 

You're mixing two different things up. Your factory axles have 28 splines at the end. Those splines slide into the posi carrier. The ring gear (the big round one) bolts to the carrier. The pinion gear rides on the ring gear at a right angle, andthe rear of the driveshaft attaches to that. The pinion gear shaft also has splines at the end, and the rear u-joint yoke slides onto that and is heldin placewith a big nut. The thing I don't know is how many splines you have on the pinion gear. It might be safest to pop off the rear yoke and count them. Clear as mud now?

 

Ditto!!
Both axles and pinion should be a 28 spline. If you have a 10 bolt rear end, (most likely itis)when you drop the drive shaft and remove the yoke you should be able to count 28 splines. Use a sharpie pen to mark one spline and count around to your mark. Then youll know, and can get the right ring/pinion gears.