posi unit for 66 - Pontiac GTO Forum
User Tag List

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 18 (permalink) Old 10-31-2015, 10:47 AM Thread Starter
 
Join Date: Aug 2013
Posts: 58
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
posi unit for 66

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.

Last edited by tonyli; 10-31-2015 at 12:46 PM. Reason: spelling error
tonyli is offline  
Sponsored Links
Advertisement
 
post #2 of 18 (permalink) Old 10-31-2015, 12:43 PM
 
1968gto421's Avatar
 
Join Date: Mar 2014
Location: Travelers Rest, South Carolina
Posts: 765
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 72 Post(s)
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.
1968gto421 is offline  
post #3 of 18 (permalink) Old 10-31-2015, 05:32 PM
Administrator
 
05GTO's Avatar
 
Join Date: Oct 2004
Location: Deliverance, GA
Posts: 5,139
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
I believe the carrier breaks are;
1 series 2.56-2.73,
2 series 2.93-3.36,
3 series 3.55 and up

Randy


05GTO is online now  
 
post #4 of 18 (permalink) Old 10-31-2015, 07:26 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,714
Mentioned: 1 Post(s)
Tagged: 1 Thread(s)
Quoted: 401 Post(s)
Garage
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.

PontiacJim is offline  
post #5 of 18 (permalink) Old 10-31-2015, 11:00 PM Thread Starter
 
Join Date: Aug 2013
Posts: 58
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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?
tonyli is offline  
post #6 of 18 (permalink) Old 11-01-2015, 09:09 PM
 
Join Date: Jan 2015
Location: Injun Territory, 'Merica!
Posts: 1,611
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 121 Post(s)
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.
Pinion head is offline  
post #7 of 18 (permalink) Old 11-02-2015, 08:49 AM Thread Starter
 
Join Date: Aug 2013
Posts: 58
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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
tonyli is offline  
post #8 of 18 (permalink) Old 11-02-2015, 09:20 PM
 
Join Date: Jan 2015
Location: Injun Territory, 'Merica!
Posts: 1,611
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 121 Post(s)
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.
Pinion head is offline  
post #9 of 18 (permalink) Old 11-03-2015, 10:34 AM
64-67 Expert
 
geeteeohguy's Avatar
 
Join Date: Feb 2008
Location: Fresno, California
Posts: 8,558
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 119 Post(s)
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!
geeteeohguy is offline  
post #10 of 18 (permalink) Old 11-03-2015, 03:22 PM
Former Super Moderator
 
Rukee's Avatar
 
Join Date: Feb 2007
Location: South Central Wisconsin
Posts: 9,919
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
You have to keep fresh fuel in those out board carbs!!
Rukee is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Noise From Auburn Posi Unit 68Resto-mod 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes. 9 04-10-2015 11:09 PM
will a 8.2 10 bolt posi unit out of a chevy fit in a bop 8.2 rear? danthepontiacman 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions. 8 09-04-2012 02:08 PM
posi Topkat 1964-1974 Tempest, Lemans & GTO General Discussion 9 11-29-2011 10:08 AM
69 GTO 10 bolt non-posi convert to 12 bolt posi AzStateFan 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions. 0 09-12-2009 05:34 PM
Posi? THEHERDER 2004-2006 GTO General Discussion 16 02-24-2007 03:45 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome