10 bolt 8.5 carrier interchange question - Chevy Nova Forum
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Old 13th-August-2007, 07:18 PM   #1
68_RATPOISN
 
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10 bolt 8.5 carrier interchange question

Will a 8.5 carrier from any year made fit any other year 8.5???? (an '80's carrier fit a '73 8.5) I am thinking qn 8.5 is an 8.5, but have questions since I see on Ebay that they are list to fit different years.
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Old 13th-August-2007, 08:10 PM   #2
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i think they are the same the only difference is the newer trucks that have a sensor on the pinion.
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Old 13th-August-2007, 08:37 PM   #3
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Axle spline count changed to 30 in the eighties. I can't remember the years but early 8.5" axles are 28 spline.
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Old 14th-August-2007, 01:29 AM   #4
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Yep, in the (late?) 80's the spline count changed from 28 to 30 splines.
Also, when ABS came out the pinion gear was changed slightly.

All parts are interchangeable with each other. Using a factory 30spline unit in a housing for a 28 spline unit *may* require special bearings...but any local diff. shop or even napa carries them. Also not you'd need the corresponding 30 spline axles if using the 30spline carrier.

I'm using a posi unit out of an 80 (IIRC) camaro in my '72 nova (8.5") with no issues.

I've seen those ads on ebay as well...many of them don't list novas on them at all. Others say their 8.5" gears work on 70-up cars and truck...but the 8.5 didn't start until '72. When in doubt, ask--or find a better seller.
Remember, a LOT of parts on ebay are "seconds" or "blems" that may or may not be in top condition, or even useable...so make sure you're buying from an authorized dealer and/or know exactly what you are buying.

Last edited by Bscman; 14th-August-2007 at 01:32 AM.
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Old 14th-August-2007, 01:39 AM   #5
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As mentioned, spline count is important.

Also, ratio. 2.73 and up (I think to 3.73, or maybe even 4.10) will interchange, but 2.56 will NOT fit anything but 2.56.

As well, do NOT buy a governor style posi. They will not hold up.
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Old 14th-August-2007, 02:07 AM   #6
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Quote:
Originally Posted by Carl Stevenson View Post
As mentioned, spline count is important.

Also, ratio. 2.73 and up (I think to 3.73, or maybe even 4.10) will interchange, but 2.56 will NOT fit anything but 2.56.

As well, do NOT buy a governor style posi. They will not hold up.
Good point. The "series two" carriers are for gear set numerically lower than 2.73. Series three carriers are 2.73's and numerically higher.
The "Gov-Lock" type factory units are grenades waiting to go off...google "gov-lock" and see for yourself. There are a few guys on the forum that own/work in differential shops that can attest to all the rear ends DESTROYED by these units failing.
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Old 14th-August-2007, 12:28 PM   #7
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I will NOT use a GovLoc in my Nova. I have seen 8.5 10 bolt Posi units with 28 spline listed, but from a late '80's GM. Would this fit or up to what year is safe to look for, used on Ebay.
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Old 14th-August-2007, 01:15 PM   #8
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If it's from an 8.5 and it's 28 spline it should work, period. I believe the 28 spline rear went up to about '88.

Keep in mind, though, the factory "S-spring" type posi units do not have as much preload on the clutches as an Eaton or similar aftermarket unit. This means the clutches are more easily disengaged, and allow each wheel to spin freely whereas many of the aftermarket units are a lot stiffer and will keep the rear axles better locked together.
Stiffer is better to a degree, but at some point you'll start getting clutch chatter (depending one preload, vehicle weight, etc).

Since the S-spring type units don't have as much preload one the clutches, and it's easier to disengage the clutches and allow the wheels to spin independantly, it's also a lot easier to burn 'em up. Many of the used units you'll find are in serious need of a rebuild.

Over time, as the springs weaken and the clutches wear, the amount of friction in those clutch packs decreases...if the posi unit has lead a hard life (i.e. iroc camaro doing a lot of burnouts) it's very likely the clutch disks are completely shot and it's pretty much going to act like an open diff.

How does that work? Obviously as wear increases, the friction decreases...now let's say the previous owner has a lead-foot and liked his burnouts. As the friction in the clutch packs decrease, the wheels are more likely to spin independently of each other--so if the previous owner does many burnouts when the posi is slipping (i.e. one tire fire) those clutch disks will be slipping at a high rate of speed, creating a lot of heat, and glazing over...
Then, VOILA! You have a posi unit that is no better than an open diff!

The reason I'm telling you this, is because those factory posi units are selling for an insane amount of money on eBay these days...I've seen several selling for $200+ in used condition. If you're lucky, it'll still be "decent" enough to just use...but there have been very few I've come across in that type of condition. More that likely, you can plan on it needing a rebuild.

A rebuild kit is $120-150 for new clutches, and a clutch shim pack--definitely get a kit with the clutch shim pack. Shim it as tight as possible *barely* being able to reassemble it. This will increase preload and make for a MUCH stiffer posi!
Figure anoth $20ish for a new S-spring, and another $40ish for new carrier bearings...now you've got nearly $400 into your "stock" posi unit--and it isn't as strong as an aftermarket unit you could have bought for $450.

Of the three used "s-spring" posi units I've dealt with, only ONE would work like it was supposed to...but it was still disapointing how easily the clutches could be over-ridden (by no means as strong as any of the aftermarket types).
One of the others was so weak that if one person held the brake drum in place, you could spin the other side freely...the other was tight enough that the tires had to be on (more leverage) before you could do the same thing--i.e. it was still VERY weak.

Again, my point is don't expect a used posi to perform as well as a new aftermarket unit...and go into the purchase assuming the factory unit needs rebuilt, as *MOST* of the time they do. If you can't buy the unit, purchase a rebuild kit, and get new bearings for a combined cost of less that about $300 don't waste your money--you'd be much happier with a stronger aftermarket unit.

FWIW, the most I paid for any of the above posi units was $75--and that was only because it came with the entire rear end. .

Just my $0.02

---EDIT----
Just in case, this is what I mean when I refer to an "S spring" type posi unit.

Last edited by Bscman; 15th-August-2007 at 01:55 PM.
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Old 14th-August-2007, 07:04 PM   #9
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Just be careful because late 80's posi units from trucks and vans are govlocks.

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Old 14th-August-2007, 08:23 PM   #10
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Quote:
Originally Posted by 68_RATPOISN View Post
Will a 8.5 carrier from any year made fit any other year 8.5???? (an '80's carrier fit a '73 8.5) I am thinking qn 8.5 is an 8.5, but have questions since I see on Ebay that they are list to fit different years.
I have a 28 spline 8.5 10 bolt s-spring posi unit. I think I have gears too.(410) I sent you a PM.

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Old 14th-August-2007, 09:59 PM   #11
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Rat poison, if you are talking about the 8.5 I sold you, it is a 72 if that makes a difference.
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Old 15th-August-2007, 06:42 AM   #12
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Bscman you are the Posi Guru...Thanks for your Input.

Big Fran...Replied to your PM

hardcore72nova....yes and no it does not make a difference
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Last edited by 68_RATPOISN; 15th-August-2007 at 06:47 AM.
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Old 15th-August-2007, 11:42 AM   #13
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Bscman you are the Posi Guru...Thanks for your Input.
Far from it...
but thanks!
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Old 15th-August-2007, 01:32 PM   #14
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posi info

Shim it as light as possible *barely* being able to reassemble it. This will increase preload and make for a MUCH stiffer posi!
Is this statement correct? You want to shim it fairly thick. Not too much as to wear out your spiders. about 110 with new clutches and 115 with used stuff. Never really had much trouble with the s spring units.

Another trick too you can take regular 12 bolt /8.5 aftermarket springs and cages from a EATON unit and install them in your factory 8.5. now you will have the grip you need.

More info for you.

1971-1989 are all 28 spline rear axle shaft rears 1990 and up changed to 30 spline.

Gov lock units are not a bad design at all. The mechanical lock and unlock. They serve a purpose, better gas mileage when unlocked and good grip lock-up when they are engaged. They are designed for low rpm work. Mud, snow, slippery road condition. They are for your normal everyday driver that gets stuck etc. They are clutch design so they are rebuildable( even though i have NEVER seen one wear out...lol. ONLY explode...lol Usually if you find a used one in one piece, it will work fine.

The Unit we want in our muscle cars are called or classified as a PERFORMANCE LSD (limited slip differential) They are on or energized all the time clutch or cone type. PERIOD.

Now on to the other things. BURN outs DO NOT hurt the clutches in the posi. AT LEAST STRAIGHT burn outs...lol. Oh and if you do a burn out, do it do not spin the tires slow and work you way into speed....This is what puts great stress on the drive line, axles, spider gears and yes clutches if the road conditions are not equal in surface conditions (smooth or rough patches) etc. EVERY time you turn a corner the posi is wearing out. Nothing you can do about that, except for do not drive the car.... NOT gonna happen here....lol. I'm DRIVING .

So if you do deside to tighten up that posi unit clutch pack your gonna end up wearing the clutches out sooner. THIS is why GM and most factory units seems (and are in most ways) to be inferior to the aftermarket. The Factory always goes with the happy medium ...give them as much hook up as we can with the most durability it can provide (which usually is not ever enough).

So again we have to make a choice ...do you want monster grip and more wear or a little less grip and longer life on the clutches..... OR you can get the best of both world and go with the new e LOCKERS OUT THERE FOR 600- 1000 DOLLARS.....

Well that is my spare change on that thread. Hope it adds

somemore to the thread good or bad. But it is facts.

Oh and the 450 for the new unit does not include bearings , so add your 40 dollars for bearings on to that too 490.00 oh what about shipping??? just being real. It is true you really have to watch your ebay sellers and others too. Some guys say the tear down these posis and check them etc. they look like they just cleaned them with brake cleaner and put them up...most likely they did! Your right on the prices, I can not believe the 8.5 used units sell for 250.00 (used) with out anything done and I recondition mine for 20 dollars more then them. But at least my stuff works and I do not have them coming to get me when it does not work. Good luck out hrer you guys have a fun fall . Jim
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Old 15th-August-2007, 02:10 PM   #15
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Quote:
Originally Posted by monzaz View Post
Shim it as light as possible *barely* being able to reassemble it. This will increase preload and make for a MUCH stiffer posi!
Is this statement correct? You want to shim it fairly thick. Not too much as to wear out your spiders. about 110 with new clutches and 115 with used stuff. Never really had much trouble with the s spring units.
Sorry, I edited the post. I meant to say as TIGHTLY as possible...apparent later with my "*barely* being able to reassemble it" remark.
The tighter you get it, the more preload on the clutches, and the harder it is to over-come the friction and spin independantly.

Quote:
Originally Posted by monzaz View Post
Now on to the other things. BURN outs DO NOT hurt the clutches in the posi. AT LEAST STRAIGHT burn outs...lol.
My comment about burnout burning up the clutches was in regards to a a burnout when only one wheel is spinning (i.e. weak posi unit on uneven surfaces, etc).

The result of a such a burnout is the same as slipping the clutch for an extended period of time in a manual transmission car...it'll glaze 'em over and burn 'em up.

If both wheels are spinning, as you mentioned, that's not going to happen.

Quote:
Originally Posted by monzaz View Post
So if you do deside to tighten up that posi unit clutch pack your gonna end up wearing the clutches out sooner. THIS is why GM and most factory units seems (and are in most ways) to be inferior to the aftermarket. The Factory always goes with the happy medium ...give them as much hook up as we can with the most durability it can provide (which usually is not ever enough).
Yes, the heavier the preload the more rapidly it is going to wear when those clutches slip. How much faster? I'm really not sure...but I haven't had any issues with mine (shimmed as tightly as possible to reassemble) in the thousands of miles it's been in my '72 (daily driver).
Another reason GM was a little lax in this area was safety and comfort. A TIGHT posi unit will occasionally chatter around tight/slow speed turns--obviously something *most* people don't want to deal with. A tight posi unit is also more likely to put your sideways in a corner.


Quote:
Originally Posted by monzaz View Post
Oh and the 450 for the new unit does not include bearings , so add your 40 dollars for bearings on to that too 490.00 oh what about shipping??? just being real.
If you watch for deals you can geat new units for about $400.Occasionally, summit and others will run specials and will include a basic install kit free with a the purchase of a carrier. Generally, however, you are correct--and the prices just keep going UP as well

Thanks for adding the info, and pointing out my mistake!
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