aside from the number of bolts holding the reas cover on,
whats the big difference bewteen how many bolts? Spline axels?
do certain rears have posi with certain bolts? I have a 10 bolt and only 1 drive tire i was wondering if it was bad to have 10 bolts..i really want a posi soon though

 

well, the bolts are an easy wasy to identify them. The 10 bolt is the smallest and weakest (I thin around 7.5inch). The 9bolt is bigger and stronger ( i think around 7.75 in.) . The 12 bolt is biggest and strongest, (I think around 8.5in.). If you make huge power you need a 12. If you don't a 9 bolt will be good till 11's, and it's 1/10 of the cost. $300 vs $3000. The 10 bolt is just crap. All can be made posi. get an austrailian 9 bolt

 

there are two 10 bolt rears, the newer 7.5 and the older 8.3 (i think) 12 bolts are 8 7/8" plus with the larger the ring gear the larger the axles and everything else. there is also a dana 44 for thirdgen f body cars and aftermarket 9" rears.

 

There are actually 3 10 bolts. Third gens use a 7.5". Older GM 10 bolts were 8.5" and 8.2". The 8.2" isn't very common.

A 12 bolt is 8 7/8".

There are a lot of differences between the different differentials other than ring gear size.

 

thanx for all the info... i knew i had the worst one unfortunately.. its from an 88 lo3 TBI one day i'll get posi

 

Also for correction there are 4 10 bolts.

7.5" 82-84 fbody's and all 78-87 gbody's (expect GN's and 442's), 26 spline
7.625" (85+ fbody's) (26 spline till 87)
8.2" don't know but there around
8.5" - standard on all 70-81 F-Bodys (30spline?)


12 bolts - 2 different spline counts I think one for cars one for wagons/HiPo cars.

8.875" (30 and 31 spline IIRC)


9 bolts - australian (hard to find parts only around from 86-89)

7.75"

I think that covers the "traditional" rears, not including any Dana's

 

there is no differance in the 7.5 and 7.62 ten bolts. one in the same. gm just wanted to confuse us a little by changeing how they IDed the rear.

 

well, the point here is that you are right, you have the **** one, but you are not alone. I got my austrailain 9 bolt for $300. One can definately be had for less than $600 easily, and you will get limited slip positraction with it. They also usually come with 3.27 or a nice 3.45 gears, and you can get a 3.70 gear for them. 3.45 is probably the best choice. Open the cover and count the teeth on each gear and divide the larger # byt the smaller #. That'll give you the ratio. Try to get a 3.45 because I think it's good for many street applications, obviosly somewhat depending on your setup. But in genderal I think 3.45 is a good street gear, for gas milage, highway, hooking up and decent acceleraition. later

 

check out www.9bolt.com they have an excerpt from an article that says the 9 bolt is stronger than a dana 44. All disc brake 9 bolts are posi and the few drum brake 9 bolts out there are non posi. My 89 iroc has the 9 bolt disc rear end but it only has the 2.77 gears. I am getting rid of it for a 9 inch that was given to me...

 

Well, i'm not sure about that. But i have beat the **** outta mine, and it's fine. That article must be real old, they even said it has 3.73's. I thought 9 bolts had 3.70's. cool though

 

I think the 8.2 inch that was referred to is the one also commonly called the BOP (Buic Olds Pontiac) rear, and it only had one real claim to fame - bolt in axles rather than c-clips. Other than that it was worth about whatever you'd pay for a boat anchor. Gear sets were/are impossible to come by, and the MUCH more common 8.5 inch "corporate" rear was a better (stronger, cheaper, more parts) rear in all respects save the stupid c-clips - and you can get replacement kits for those, too, if you really need to. These rear ends are identifiable first of all, by the kind of vehicle they appear in, and second of all, the rear cover appears to have "scallops" taken out of both sides, so it's more of a "figure of 8" kind of shape (really obvious once you've seen one).

All this is a LITTLE moot, given the topic, but just wanted to add my $0.02. Neither the 8.2 or the corporate 8.5 will directly bolt under the third gen, so look for the 9 bolt Borg Warner, or the Dana 44. Most people seem to like the BW 9 bolt better, but parts are pricey. Great advice on this board though!

Jonathan

 

Ive got a fresh-rebuilt 3.45 nine bolt, believe me, if you want all new hardware it isnt that cheap. The used rear was $200, new posi/carrier & install kit were $820, and labor for setting up the gears was $200. Im happy with my choice of gears though, 3.45s are great street gears. They totally recouped my low-end loss caused by the HSR, the car pulls like mad up top and will still smoke the tires if punched @ 25-30mph.

 

The 12 bolt is thhe best axle.. its up there with the Ford 9" and the Mopar 8.75".

Its what was used in all the Hi-performance cars back in the day... SS396/427/454, Z28, etc etc

 

just do a chrysler 8 3/4 like me, custom make it yourself , and its better than a 12 bolt.