# posi unit for 66



## tonyli (Aug 14, 2013)

I currently have a peg leg rear end with 3:08. I just installed a 200r4 so next thing to change is the gear ratio and get a posi unit. I located a 1966 Safe t Trac post unit locally. It may have 3:36 gear ratio in it. My question is can I change the gears to 3:55 or 3:73 in this rear? What should I inspect beside the gears. Can this rear be rebuilt if necessary? Or should I look for a 12 bolt instead.
My car has the original 389 with mild cam other then that it has all stock components.


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## 1968gto421 (Mar 28, 2014)

You might want to PM PinionHead as in my opinion he is the most knowledgeable person around when it comes to rearends. I'm just now learning all the variations and intricacies of them.


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## 05GTO (Oct 6, 2004)

I believe the carrier breaks are;
1 series 2.56-2.73,
2 series 2.93-3.36, 
3 series 3.55 and up


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## PontiacJim (Dec 29, 2012)

Pinion head will be the expert on this. I am sure he will suggest the 8.5 over the '66 factory 8.2. The 12-bolt will cost and really isn't needed for what you have. The 8.2 will of course work, but for long term use and possibly easier to get parts, the 8.5 may be a better pick.

An acquaintance through my work races a '71 Nova and '74 Nova in the 1/8 mile. The '71 is a 454 bored to 467 and his '74 has a 496CI big-block stroker, both with powerglides, both running 6.30's in the 1/8 mile (9.95 seconds in the 1/4 mile). He has run them for years using the 8.5 rear end. Said they are just as tough as the 12-bolt and he doesn't baby them. He said the only thing he has to change on them is the ring & pinion every 2-3 years because they don't sell a competition type gear. He said many other racers also use them with no problems as well.

:thumbsup:


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## tonyli (Aug 14, 2013)

Thank for your responses. How do I determine which carrier is series 1,2 or 3. Also would a grand national 8.5 rear fit my a- body car with out major modifications?


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## Pinion head (Jan 3, 2015)

the GN 8.5 rear won't work, the upper control arm perch portion of the center housing are positioned with a different spread, the shocks & coil springs are also mounted differently. Another big problem w the G body rear, it is significantly narrower and the axles are c clip retention, not a bolt in tapered bearing axle. I've modded early 8.5 A body rears to go in G body's, it's considerable work.

On any Pontiac vehicle considering a posi traction addition/gear change with a non posi gray iron 8.2 Pontiac rear, I usually ask the following questions:

-how much torque do you plan on throwing at the rear? Stick or automatic? 10 sec car leaving on a trans brake?
- vehicle weight...if something really oddball
-if the A body is being built as a driver, are there plans for serious handling improvements being made, wider and larger tire/wheel combinations/ spindle changes/ ect.
-trailered relatively stock car built for very stringent points judged car shows, minimal driving, minimal drag strip use on sticky steet tires or slicks at the stock HO / torque level?

If the last question is YES, then upgrading the original Pontiac 8.2 rear makes sense. 
For anything else, usually go with building off the correct 8.5 A body housing for the build. Reasoning to go 8.5, more pinion support than a stock 12 bolt, stock tapered bearing axle retention, wide variety of affordable quality gears and posi units.

Hope this helps.


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## tonyli (Aug 14, 2013)

Pinion head, thank you for your response. Just two more question. What year, make and model of cars had the 8.5 posi rear that I am looking for? Also would it be a direct fit or is there modifications involved. Thanks again


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## Pinion head (Jan 3, 2015)

the 8.5 housing I build off of for early A body's is a '71-72 Old/Buick piece. At the very end of the '72 model year, a few actually made it into a few very late Fremont plant built ElCo's. To install in the place of any 8.2 rear, a type "O", or any 12 bolt, will need to shorten the stock length driveshaft 7/8".

Built from the factory with a posi, the early 8.5 A body rears are next to non existent. Since the early 90's, I've pulled well over four hundred of the early 8.5 A body rears, and only two were factory posi rears, plus another I picked up at '01 Norwalk (seller didnt know what it was). Another issue, is if you do stumble onto a factory 8.5 posi out of a '71, good chance its a cone type Warner Motive posi, and most likely, it will be worn out. I've had '71 original posi 8.5 A body rears in here from Cutlasses and 442's to Stage 1 GS's, and each one had a well warn 2 pinion cone posi. All through the '90's, I rebuilt the S spring 8.5 posi's, shimmed up with new clutch packs. Eventually, the price of the GM clutches more than doubled, then GM discontinued them. Today, there is a limited reproduction of the clutches, but at $200 a set, (unless one buys 20 sets), it hardly makes sense to rebuild the S spring posi carriers. Just makes a lot more sense to buy a new Eaton posi carrier. Behind something like a moderate performance 389 or 400, can stick with 28 spline carrier and run the stock tapered beating axles. The stock tapered bearing axles actually are quite strong, Having seen where both will twist and break, many of us would put them on par with the forged axles out of the HD Safe-t-track Pontiac rears (only avail with 3.90 and 4.33 HD STT rears). Running quicker than high 11's on slicks in a 3700 lb streetcar, ESP with manual trans, I'll build with new HD 30 spline Eaton carrier and matching axles from Moser or Dutchman. Will even go that route for extra insurance in a 12 sec car. Desiring to go even quicker, into the high tens, footbraked,, will build off an A10 tapered bearing end A body housing and fit a lh steel cap and a higher end spicer 1350 pinion flange.


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## geeteeohguy (Feb 2, 2008)

I'll add: if you drive the car normally and don't beat the snot out of it, you can simply bolt the entire 3.36 unit into your car and run it with the 200R4. It will be very nice, and geared just right. Most cars that came withe the 200R4 had 2.41-2.73 gears in the first place (emissions/fuel economy mandates). I would replace the rear wheel bearings and verify that there are no pinion seal leaks, and good to go. I pulled the 3.36 ten bolt out of my '67 GTO at 239,000 miles to install a freebie 2.56 posi, and the original 3.36 rear end is still like new inside. If you beat the heck out of your car and abuse it a lot though, you will want a better rear end. I think most GTO owners out there abuse their cars a lot less than they think they will after they spend all their time and money getting them on the road!


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## Rukee (Feb 8, 2007)

You have to keep fresh fuel in those out board carbs!! :thumbsup:


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## PontiacJim (Dec 29, 2012)

OK class, so what did we learn about our rear end? :blush2:

The 8.2 is OK for if you are planning on doing a 100% factory resto that will be judged at the Pebble Beach Concours d'Elegance. It is OK with a stock HP type engine UNLESS it is a Ram Air engine.

PERSONAL OPINION - Never blew one up and I beat my cars. Had automatics, 3-speed, & 4-speeds - ALL non posi and stock tires of the day. A friend blew up a factory 3.90 non-posi by doing a "roll back" down a hill with a '65 GTO convert. and dropped the clutch to make that nice "J" black mark on the pavement. Pinion gear busted and shot through the bottom of the case - big hole. Automatics are easier on the rear. Wide tires will put more rubber on the road and more traction creates more stress - things break if you beat you car like a wild banshee. Gets worse with a posi & wide tires if you like to do burn outs or dump the clutch at a red light to impress the chicks. But, the 8.2 could also last your lifetime after a good rebuild.

The 8.5 would be a better choice overall as it will hold up to more abuse and seems to be somewhat equivalent to the 12-bolt and can be upgraded to handle even more punishment. Problem is locating one. Appears the years needed for the A-body is 1971-'72. Chances of finding a posi may be like finding tits on a bull - I think they got 'em, but your going to have to look real hard and I ain't gonna do that with a bull. :nonod: So you will most likely have to buy an aftermarket posi, gears, and while at it, go with aftermarket axles to do it right.

The 8.5 GN will not fit.

In conclusion. The '66 8.2 posi you found may be the best solution, but you did not state price. It will hold up better with the automatic. Add wide tires with the posi, you are still probably OK as long as you don't plan on revving the engine to 4 grand and drop it in drive. Do some investigation into prices for a rebuild kit, labor, etc. plus your initial purchase price. 

The 8.5 would be better stock for stock as measured against the 8.2, but to get a posi you will have to spend more money for upgrades in addition to the rear end purchase price.

The next option, if you plan to keep the car forevvvvvver and never sell, would be to go with an all new aftermarket rear end assembly. You can go 12-bolt or Ford 9" (with all the mounting brackets made for the GM A-body for a direct fit). Pricey, but do it once and be done with it. :thumbsup:


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## geeteeohguy (Feb 2, 2008)

What JIm said! Although 8.2's are considered 'junk', they will work fine for all around driving if you make sure the wheel bearings are up to snuff. If you are drag racing the car a lot, time to upgrade. I've blown one up, out of many. My fault: chipped a tooth off a gear doing a huge burnout, which punched a pinhole in the rear cover. I _think_. Didn't hear or feel anything at all at the time. Parked the car for about 4 months, and next time I drove it, it had no gear oil in the rear end. But I didn't know that. The car had been parked in a dark garage over old carpet, and no oil was evident on the ground.200 miles later, it started to make noise, failing completely shortly after that. That's when I saw the tiny hole punched out of the cover. $938 later, it was back in the car fitted with 3.36 gears, as the 3.55's were burnt to a crisp, completely rebuilt. Been in there trouble free since 1990. Will probably still be in the car when my estate gets settled after I am gone.


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## Pinion head (Jan 3, 2015)

My own influences and opinion on sinking lots of $$$$ into an 8.2 anything gray iron 10 bolt come from hands on experience dealing with many, many, many owners whose 8.2 10 bolts, not just my own (with varied result experience) running the 8.2 Pontiac rear ends. 

Have first hand experience with multiple dozens of Pontiac 8.2's that.
- had blew up the spider gears and subsequently the ring and pinion was damaged
- knocked several teeth off their 3.90, 4.33, and 4.56 ring and pinion due to hsg flex in the pinion area...13 sec cars, guys, for a few, their first time with aticky tires on the street or trip down the strip. 
- had worn out cone type posi units, and desired to go to a different ratio. (minimum of rebuild posi, build differential with nice used gear set, small parts, plus labor. many times had to go with new carrier, and new Richmond Pontiac 8.2 ring and pinion...more hard earned money)
- had a sealed bearing axle that exited the vehicle while cornering and the resultant damage banged up their outer wheel well, wheel opening area, and tweaked the original 8.2 housing. Each time, there was a substantial bodywork bill. High quality bodywork and paint aren't cheap! One of my favorite keeper cars, the only reason I have it, it broke an axle and banged up the quarter panel nearly 40 years ago. 
- dealt with many dozens of owners that have hauled me blown up bolt in axle 8.2's, sometimes wanting a quote to fix them, occasionally just to show me the carnage. Also been granted many times while at other guys shops , to "pick the pile", if anything I could use from their scrapped 8.2 rear ends. 
-bought well in the 6 figures of $ in new parts to repair/ build GM muscle era rears for everything from 16 sec totally stock putt around cars, to footbraked 3700 lb street/strip A body's running down in the 10's in the 1/4 mile. Extreme uses, heavy car, leaving on a trans brake, am not building a HD GM rearend, if a car is at that level, it needs something other than an a proven well built GM street/strip rearend. There are plenty of builders out that can assemble an aftermarket nodular case built 9" center section and ship a fabricated Ford 9" housing. Price 'em with brakes and required adjustable upper control arms to get pinion angle correct...not cheap. Not at that level, never going to be at that level, there are much better choices and one can still have a GM rear under the car!

Other FACTS; a little history. 
All domestic automakers recognized the weaknesses in their first muscle car application differentials and gradually made changes as factory torque levels of their engines rose, and as wide tires/wheels became available. First Oldsmobile, realized that the Buick cast housing 8.2 rear ends they were using in their 442's weren't holding up. While the early Olds 442's bested both the handling of the early GTO's and the quickly thrown together GS's, it wasnt till the '65 4spd application 442's that the original usage Buick cast 8.2 hsg was stressed. In order to provide a stronger rearend and prevent warranty claims, Oldsmobile was able to source the intersecting rib Pontiac gray iron center hsg which was stronger than the single rib Buick cast hsg. 

For '67 models, Pontiac ditched the gray iron hsg for its highest performance 8.2 10 bolt applications, and began casting center housings out of nodular iron (Ford was doing similar along with increasing pinion bearing size in its performance 9"s)
The Pontiac 8.2 nodular center housings was for Safe-T-Track 8.2 rears with 3.55, 3.90, and 4.33 factory gearing. Occasionally will run across a 3.36 geared nodular '67 rear, but only ones I've built, came out of Firebirds.

By 1968, Olds and Buick had designed their own strengthened ten bolts, Olds the type "O" Olds 10 bolt (12 bolt smooth cover). Buick designed and cast their new '68-70 BUICK 8.2 center hsg with more pinion support and a left carrier bearing boss that took a larger diam carrier bearing/race. housing to match. Both of these improved rearends made it in positraction lower ratio form under each divions heavy performance A body offerings. By 1970, both such performance A bodys were being subjected to over 500 ft lbs of torque behind a manual transmission. During this tine, 70 series and 60 series tires began to become common . While Chysler had previous gone to tapered bearing axle bearings, with the advent of "handling" improvements, std rear sway bars, and 60 series tires, both GM and Ford "got with the program" and began using tapered axle bearing axles and matching hsg ends. Fact: sealed axle bearings were not designed for higher side loading forces and wider tire and wheel combo's. Another high water mark... Chevrolet in their highest horsepower '69 A and F body offerings (COPO 427 cars) installed in those cars, special rearends, in each one, a 4 series Eaton posi carrier built with special heat treated 10-16 side gear/spider gears, thicker plates, HD preload springs, special HD axles. Service package axles had been avail for some time over the counter and many street/ strip guys sourced new axles and HD 12 bolt posi units over the counter.

Why all this concern about rearend strength? Could it be the previous performance rears were not holding up???
Not the vaunted Chevrolet 12 bolt with its small brittle spider gears in a standard Eaton posi carrier (what a joke to believe it's strong). 
Not the gray iron Pontiac 8.2, or even in the highest performance version with nodular hsg HD forged axles...a version which was shelved for a McKinnon built 12 bolt to be factory installed in a 500 ft lb '70 Pontiac offering. Hmmmm..

The Hobby.
One thing a few of us also realise is there is a WIDE spectrum of Pontiac A body and F body owner/restorers out there. Having cut my teeth auto crossing and streetracing a late second Gen Bird, understand quite a bit about handling and braking. While I have no interest in building a ultimate money pit "Protouring" A-body, know enough that GM would have never built such a car that could pull near a full G on a slid pad, and then saddle it with a junk rearend with small sealed axle bearings. Can not relay how many times I've receieved emails, PM boxes clogged, phone calls, questions at swappers from young guys and for some crazy reason reason they are maxing out their credit cards on front end parts, big front disc kits, big tires and 40 series tires, really stupid stuff like 2" wheel spacers, all while not giving one thought to the sealed axle bearing rear bolted under the back of their car. Also, often on a car, that quality full reproduction 1/4 panels are not available. 

Also routinely deal with owners building the very high point restored car, or trying to maintain it. Nearly 15 years ago, rebuilt the original 3.55 STT in one of the eight '69 TA converts. Have gone through quite a few HD STT's. These vehicles owners needs are directly tied to maintaining total originality, most are not out thrashing them on the street, or at the strip.

Widest portion of the Pontiac spectrum, deal with many owners of many GM muscle era vehicles whose cars are of the performance street and street/strip variety. Gray iron 8.2's easily find their match in this growing segment, have for decades. The inherant weakness of the stock GM performance differentials is how several of us stumbled onto building the strongest factory 10 bolts and 12 bolts. On 10 bolts, a rearend that has a very strong center hsg, choice of two different sizes of tapered bearing axles, a wide variety of affordable aftermarket parts, and as a housing style was installed in nearly a million A body's over two years. Sorry, Jim, disagree the A9 housing end 8.5 A body rears are hard to find, I bought two more last weekend, and both were sourced cheap and neither I knew of a week before. Like other 30+ year old GM rearends, am not so naive that the thought would cross my mind that I'd find one that came fresh out of a parted car and it had a clutch type posi and the rear functioned perfectly. No, both were core single tracks rears, and both were bought to be built up. One I traded a 71 cutlass auto console for, a cheap console, that is now getting the shifter area cut out. The other, the owner sent me 2 pair of axles to press new bearings on to, he provided the axle bearings. 

The putt around crowd is another segment of the hobby. Unfortunately, it's also the segment of the hobby, I've actually witnessed first hand the most damage from departed sealed bearing axles. Honestly dont have time to read every post, and post warnings to new owners of '64-69 GM bolt in axle intermediates, '67-69 Firebirds, and '69 GP's. Warnings to immediately pull the bolt in axles, and ck to see if the original green phenolic sided axle bearings are still present. If so, have them pressed off and see if axles are chewed, have new axle bearings installed if the axles are good. So many times, the two hours of work is too much for the majority of these owners. Over the years, I bet I've pressed off two 55 gal barrels full of RW507C bearings and chunked well over 200 chewed up sealed bearing axles. Sealed axle bearings were designed for use in a time when 7.75x14" tires were mounted on narrow 5" and 6" wheels. the RW507C axle bearings eventually seize and chew up the axle. It's a poor design, a design from an era when the first v8's did not even come with an oil filter. No thanks, on either choice. Having been able to converse at length with many longtime dealership mechanics, early service writers, dealership principals, and having pulled tons of sealed bearing axles, and built muscle era GM rears for near 25 years, my thoughts on the early gray iron 8.2 10 bolts, and the affordability of the best alternative have deep and wide roots. 

8.2 Pontiac rebuild/ build pricing... a quality pair of new bolt in sealed axle bearing axles, Mosers, with new wheel studs, and those good ol RW507CR axle bearings! Just the loaded new Moser axles will set one back near $450. a new Auburn (uggh) cone type posi, another $400, or an Eaton 8.2 carrier, closer to $500. gears $250-350+ ship, price the small parts, a bench build charge, and a "performance" rear cover, the price is ridiculous! The result, in a gray iron 8.2, is a pig in a poke! geeteeohguy, fwiw, that $900 plus you spent near 25 years ago would have bought TWO pro built 8.5 A body rears from any of the three concerns building them in N Texas in the mid 90's. Prices have gone up, new posi carriers are now the norm, not rebuilts, but there are several of us still across the country that build a VERY strong 8.5 A body rear, and build it and ship it for well less than throwing $$$$ at a junk gray iron 8.2 rear. Many thousand others that have followed our lead, sourced the hsg cores theirselves, and had them built locally.


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## PontiacJim (Dec 29, 2012)

PH 

Your price, a ready to bolt in posi, and able to handle 500ft lbs of torque/10" wide rubber?


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## tonyli (Aug 14, 2013)

Pinion Head thank you for detailed reply. That is why I asked before I purchased. I would be interested in quote too. If you want to PM me quote that would be appreciated. The same specs PJ wanted would be more than enough. Thank You.


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## Pinion head (Jan 3, 2015)

PontiacJim said:


> PH
> 
> Your price, a ready to bolt in posi, and able to handle 500ft lbs of torque/10" wide rubber?


500 ft lbs...piece of cake. in the 90's was accomplishing this with boneyard 8.5 S spring posi carriers, pro rebuilt, shimmed up with $56 worth of new GM clutches. 
Unfortunately, can't do that today. the clutches are discoed from GM, also can't put core 8.5 A body rears together in a wheelbarrow in the Pick-N-Pulls with a core #8 posi carrier for $45... just to get them home to build off of.

prices fluctuate, a month ago, had a smokin deal on Eaton TruTracs. 
Today, market priced on new parts: $1179 with high quality 3.42 or 3.73 Strange/US Gear ring and pinion, new clutch type posi carrier, Timken bearings, National axle seals, stock axles (proven into the high 11's in 3750 lb GTO on slicks) all small parts, and pro buillt on clean Southwest sourced housing. With new custom 30 spline MOSER axles and 30 spline clutch type carrier, add $420.


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## PontiacJim (Dec 29, 2012)

Pinion head said:


> 500 ft lbs...piece of cake. in the 90's was accomplishing this with boneyard 8.5 S spring posi carriers, pro rebuilt, shimmed up with $56 worth of new GM clutches.
> Unfortunately, can't do that today. the clutches are discoed from GM, also can't put core 8.5 A body rears together in a wheelbarrow in the Pick-N-Pulls with a core #8 posi carrier for $45... just to get them home to build off of.
> 
> prices fluctuate, a month ago, had a smokin deal on Eaton TruTracs.
> Today, market priced on new parts: $1179 with high quality 3.42 or 3.73 Strange/US Gear ring and pinion, new clutch type posi carrier, Timken bearings, National axle seals, stock axles (proven into the high 11's in 3750 lb GTO on slicks) all small parts, and pro buillt on clean Southwest sourced housing. With new custom 30 spline MOSER axles and 30 spline clutch type carrier, add $420.



Good price on the stock 8.5 axle rear rebuild -just about the price for a bare Currie 12-bolt axle housing with various companies selling complete new 12-bolt posi's beginning around $2300 and going up depending on upgrades. Still reasonable with the better Moser axles and upgraded posi. :thumbsup:


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## geeteeohguy (Feb 2, 2008)

Pinionhead, excellent post, very, very informative, and I have to say, I am in agreement. I have had to deal with axle and bearing issues in ALL of my GTO's in the past 35+ years....as these components were failing regularly when the cars were less than 15 years old, but fitted with wide 50 and 60 series rubber. Just a lot more leverage to work against an already marginal bearing. Had another one going out on the '65 a couple of months back (I could hear it and I always check the endplay when on a lift) and installed an replacement axle and bearing before I looked out the rearview mirror and saw yet another rear wheel running 10 inches out past the wheel well! I agree that in this day and age, with current tire technology and the loads generated, the 8.2's only virtue is originality. If I were 20 years younger and drove my cars accordingly, I would upgrade.


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