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Technical Positraction vs limited slip?

Discussion in 'The Hokey Ass Message Board' started by Master Brian, May 1, 2019.

  1. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    Can someone clear this up for me for once and for all?

    My understanding is that positraction was the term GM used to describe their limited slip rear diffs.

    I think this confuses me because some definitions seem to say limited slip sends more power top the slipping wheel but not equal so tires won't chirp around a turn. They then say posi sends equal power to both and thus will chirp on corners.

    Are they confusing posi for a locking diff?

    My 60 suburban has posi. My 95 Yukon has a G80 Positraction/ limited slip diff....unless its the heavy duty one line my 12 Yukon xl. My 03 burb has a locking diff, I believe. My 12 Yukon xl Denali has a heavy duty g80, which I understand to be locking and not locking.

    What gives here?
     
  2. :p
     
    Last edited: May 2, 2019
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  3. khead47
    Joined: Mar 29, 2010
    Posts: 1,536

    khead47
    Member

    Yes. They are confusing posi with locking.
     
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  4. squirrel
    Joined: Sep 23, 2004
    Posts: 42,977

    squirrel
    Member

    The gov lock is still a limited slip though, isn't it? it has clutches, not a mechanical locking mechanism. It just increases the friction in the clutches (by increasing the pressure on them), depending on the difference in speed between the axles.

    At least that's my understanding...
     
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  5. Casey Riley
    Joined: Jun 27, 2018
    Posts: 374

    Casey Riley

    G80 "Gov Bomb" lock is mechanical lock/unlock.
     
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  6. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    Ok, but this is the typical description....
    ****What's the difference between Limited Slip and Posi? Posi means that both of the drive wheels always spin at the same speed all the time. Limited slip allows one wheel to spin fast than the other for better turning, but if it detects one wheel spinning much fast than the other it makes them both lock up and spin.****

    That is my understanding of the old school posi. Maybe I'm wrong in this.... maybe that's the 'welded gear's posi.

    I've attached two pics. One is the posi rear diff in my 1960 suburban. The other is a non posi rear diff I have from a 1962 c10 pickup. Is the 62 an open diff?
     

    Attached Files:

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  7. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    The description on the g80 locking diff is that it's open when not locked.
     
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  8. squirrel
    Joined: Sep 23, 2004
    Posts: 42,977

    squirrel
    Member

    Why do you believe the 1960 rear is a Posi?
     
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  9. Truckdoctor Andy
    Joined: Jan 13, 2017
    Posts: 744

    Truckdoctor Andy
    Member

    Positraction was Chevrolet’s trade name for their limited slip differential.


    Sent from my iPhone using The H.A.M.B. mobile app
     
  10. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    The G80 is a specialized differential designed by Eaton to work as a low-speed traction aid, offering full lockup during its operation. When in normal conditions, the unit acts as an open differential, letting the rear tires spin independently of each other, with the outside wheel spinning faster during turns. However, when one tire spins 120 rpm faster than the other, the G80 locker kicks into action.
     
  11. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    Has discs and have been told it is by anyone who has seen it. Did you see the differences in the pics above? Here is a picture of the disc on one side. 'Unfortunately missing a guide, which I can't find'
     

    Attached Files:

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  12. Smokeybear
    Joined: Apr 20, 2011
    Posts: 299

    Smokeybear
    Member

    Hey! How exactly is a rainbow made? How exactly does a sun set? How exactly does a posi-trac rear-end on a Plymouth work? It just does.
     
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  13. Oldioron
    Joined: Dec 12, 2018
    Posts: 792

    Oldioron
    Member

    Ford called its clutched diff a LD or locking differential . To me a locking differanshal is a Detroit locker........
     
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  14. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    The main thing that led me to ask this is trying to make sense of what I have so I can get the correct fluids. I used royal purple 75w-90 on my 03 suburban several years ago when I changed fluid. I need to change it on my 12 Yukon xl Denali AWD. I need to top off my 60 suburban as it has a small leak. And in looking at these g80 truck axles I see they say no additives, per GM. I specifically recall seeing an invoice on the 95 Yukon where a shop added posi additive to it when they changed it several years ago when my brother owned it. I have 2 quarts of BG 75w-90, but it says additive in it.

    I'm curious if the BG full synth is ok for the posi in the 60 or if I need a different weight lube and/or if I should go conventional on it.

    I also wonder if I should drain the 95 and replace with something else. I know Amsoil doesn't have additive, I haven't confirmed on the royal purple yet.
     
  15. squirrel
    Joined: Sep 23, 2004
    Posts: 42,977

    squirrel
    Member

    Late model stuff...do what the owners manual says.

    I didn't realize they made a posi version of that 55-62 rear end. I have a 59 chevy pickup rear that's posi, it's a Dana 40, and also has clutch plates, and no springs.

    Thanks for the pic showing the clutches, that makes sense now.
     
  16. Master Brian
    Joined: Apr 10, 2017
    Posts: 142

    Master Brian

    My understanding is it's super rare. Most 'experts' I've talked with in trying to get info on it, as i mentioned missing clutch disc guides, say they've heard of never seen.

    Just got off phone with royal purple and their tech said their 75w90 is fine in everything I have and does have the additive in it, but no issue for the g80 locking rear.
     
  17. oldtom69
    Joined: Dec 6, 2009
    Posts: 383

    oldtom69
    Member
    from grandin nd

    I remember a 1958 Impala with a"positraction' emblem on the glove compartment door-from the factory-that would be the 55 to 64 passenger car rear end
     
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  18. dan c
    Joined: Jan 30, 2012
    Posts: 1,876

    dan c
    ALLIANCE MEMBER

    i think studebaker called theirs "twin-traction." everybody had a pet name for it.
     
  19. Heavy Old Steel
    Joined: Feb 1, 2019
    Posts: 50

    Heavy Old Steel
    Member
    from Virginia

    Yes, marketing term.
     
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  20. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,325

    Boneyard51
    Member

    There are many “ urban legends “ on traction enhancing differentials. Some pretty comical. As stated there are two main kinds of traction enhanced rear ends. The clutch type and the mechanical locker. There are several versions of both. Marketed under a variety of factory names. The most common are the clutch type , as they help with traction and have little bad habits.... usually. Most clutch type enhancers depend on the angle of the gear teeth, to compress the clutches. The more power applied, the more “ locking” action. But the problem with this is ,with more power , more locking action is needed! The angle of the gears is rather steep, in order to maintain strength, so the clamping action is compromised
    Dana solved this problem with their version , by the utilization of a two piece spider gear shafts, for four spider gears, anchored on a approximately 45 degree slope, there by applying a lot more clamping action than the approximately 60 to 70 degree angle of the teeth on the gears.

    So with this version you get better traction and no bad habits.





    Bones
     
    Last edited: May 1, 2019
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  21. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,325

    Boneyard51
    Member

    With a clutch type traction enhancer, resistance is needed on both axles to activate the clutches.With no resistance, there is no force trying to separate the spider gears, therefore no force to apply the clutches. There is a spring in most , to apply some pressure.

    My point being, you take a perfectly good clutch type traction enhanced rear end, put one tire on wet grass, the other on dry pavement..... give it the gas...... one wheel will spin! Nothing wrong with the rear end.

    With these rear ends, it is imperative that you have somewhat equal traction , before it will operate. I repeat... somewhat!




    Bones
     
  22. G80 does not identify any particular style of limited slip differential. It is a GM RPO (Regular Production Option) code and the GM parts catalogs describe it as "AXLE,REAR,POSITRACTION,LIMITED SLIP".

    Over the years there's been models with different clutch and spring set-ups in them supplied by different vendors as well as the governor & ratchet design. In GM's eyes all of them use the same RPO code, G80.
     
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  23. squirrel
    Joined: Sep 23, 2004
    Posts: 42,977

    squirrel
    Member

    3776936 for 60-early 61, or 3789939 for late 61 or 62.

    That's the GM part number for the GUIDE, clutch plate, for the Chevy half ton truck rear end.
     
  24. Ford offered three types of 'posi-traction' rear axles. They were a bit sloppy as to assigning names in their sales literature...

    The 'base' unit is referred to as 'limited slip' in service manuals, was a conventional clutch-type and used a large Belleville washer to apply pre-load. These were a 2-pinion design.

    The next step up is referred to as 'Traction-Lok', is again a clutch type but uses more clutch area, uses four springs to apply pre-load, and featured four pinions for increased strength. This was the most commonly used unit in the performance models, but could be optioned on most models.

    The primary difference is the limited-slip only required 40 ft-lbs to overcome the clutches, while the Traction-Lok was higher at 75 ft-lbs.

    Lastly, the famous 'Detroit Locker', a true 'locking' differential. More commonly seen in trucks, Ford didn't like to install these in cars due to their sometimes-harsh and noisy operation, generally limiting these to drag racing packages, but again it could be special-ordered.
     
  25. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,325

    Boneyard51
    Member

    Ford also offered the Dana’s traction enhancer, in the truck line. I had one in a 59 and in a 68. I think it was marketed as a “ equal lock” or something like that.

    In the Trucks, the Detroit locker, was marketed as a “ No-spin” had one in a 1959 ton and a half. It was very harsh.


    Bones
     
  26. Oldioron
    Joined: Dec 12, 2018
    Posts: 792

    Oldioron
    Member

    The 8.8 had the designation of an TL traction lock on both the tag and owners manual and when buying service parts. It has a large S spring loading clutches.

    My Fairlane has a Detroit locker in it and it's a quirky diff to drive. With the slightest power applied on a slow turn it will snap and pop click in with a faint tire squeal.
     
  27. big john d
    Joined: Nov 24, 2011
    Posts: 85

    big john d
    Member
    from ma

    if it has a detroit locker in it , it will take you and two buddies to push it around a corner
     
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  28. Beanscoot
    Joined: May 14, 2008
    Posts: 985

    Beanscoot
    Member

    Ford made the Equa-Lok from the late 50s to 1967. It made the Traction-Lok from 1968 up, according to the info I've been able to dredge up. Both were plate style.
    The Equal-Lok used one large Belleville spring whereas the Traction-Lok used several smaller coil springs.
    They were available in 8" and 9" differentials.
     
  29. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,152

    sunbeam
    Member

    A pretty good explanation
     
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