8.5 10 Bolt Question

Discussion in 'Got gears?' started by MNBelv57, Mar 9, 2020.

  1. MNBelv57

    MNBelv57 Well-Known Member

    Hello all. I just read a letter to one of the journalists in the latest "Hemmings Muscle Machines" issue. It was in the "Swap Meet" section I think. The person was asking how he could add a posi unit and numerically higher gears to his car which was a 1975 Hurst Olds. He said it had the 8.5 10 bolt with 28 spline axle shafts and that the letters AH on the axle tube mean't that it had 2.56 gears from the factory. He said he wanted to go to 3.42 gears with a posi unit. He also said that his present carrier was only able to accept 3.08's and no larger. The journalist agreed with him and went on to give him different options. Here's my question. I had the same situation some years back with my rear end. It had the same AH and 2.56 gears and was an open, non posi unit though my car is a 75' Regal rather than a 75' Olds. My service manual seemed to confirm that my carrier could only go up to a 3.08 but my mechanic was able to put in 3.73 gears though at the time I did not put the posi in. The car runs great but I still don't understand why he was able to put those larger gears in and will I have a problem if I upgrade to a posi unit. According to the adds in Summit's catalog it doesn't seem to be a problem. Can anyone straighten out this confusion ?

    Thanks, Mario.
     
  2. DasRottweiler

    DasRottweiler -BuickAddict-

    You mechanic probably utilized a spacer with the 2 series open carrier to move the gear within spec.
    It works , but you would want a 3 series posi carrier if looking to upgrade from the open carrier. Jim
     
  3. Bens99gtp

    Bens99gtp Well-Known Member

    I put 4.1 gears on a 2 series open carrier with mini spool in it early on. It was just shimmer way over to 1 side making it hard to select correct shims. Not highly recommend
     
  4. monzaz

    monzaz Jim

    LOL. Yah NO with c-clip rear you didn't...lol
    10 bolt 8.5 1971 - 1999
    2.41 -2.56 are 2 series
    2.73- 5.57 are 3 series carrier
    10 bolt 8.2 chevy (which is what they were getting mixed up with)
    2.56 - 2.73 2 series
    3.08 - 5.13 3 series
    B 1964 - 1967 and P 1964 - 1972 10 bolt 8.2
    2.56-2.78 2S
    2.93 3.08 3.23 3S
    3.36 - 5.13 4S
    BUICK 8.25 10 BOLT
    2.56 1S
    2.73-2.93 2S
    3.23 - 3.42 3S
    3.64 - 5.00 4S
    12 BOLT OLDS 12 COVER 10 BOLT RING
    2.56- 2.78 2S
    3.08 - 3.23 3S
    3.42 - 5.00 4S
    12 BOLT CHEVY
    2.56- 2.73 2S
    3.07 -3.73 3S
    4.10 - 6.14 4S
    3.90 COULD BE ON 3 OR 4 SERIES CARRIER DEPENDING ON MANUFACTURE.

    JIM
    JD RACE
     
  5. Bens99gtp

    Bens99gtp Well-Known Member

    I assumed since mine where 2.73 gears they were on a 2 series carrier.......and bolt in axles on a 72....
    I know the op has a newer housing more likely no bolt in axles
     
  6. MNBelv57

    MNBelv57 Well-Known Member

    You know Jim come to think of it I believe he did use a spacer. It was so many years ago I had forgotten. That being said, do you think there would be a problem with me installing a "Lunch Box Locker" in that type of carrier ?
    Mario.
     
  7. monzaz

    monzaz Jim

    NO Problem if you can deal with some clicking in turns...and be sure you install it correctly , they work great. Jim
     
  8. MNBelv57

    MNBelv57 Well-Known Member

    Thanks Jim, will do. Mario.
     
  9. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I just put a lunch box locker in the dana 44 in my 09 wrangler. It works great.
     
  10. No Lift

    No Lift Platinum Level Contributor

    Apparently you are not beating too much on that setup with a spacer and your power level. They never lasted long when I tried it with 4.10's on a 3 series 12 bolt with a 455 pushing it. Later on I did run one of those "lunch box" setups from Lock-Rite, I believe, and while it worked good for off the line acceleration locking up both wheels most of the time with no problem out on the street is where it sometimes got shaky. With some HP in front of it you had to watch going around slow curves on a damp road at an easy rate and if you tried to give it a little too much gas the rear would still be locked up and the back side would try to come around. Just something to remember out in wet weather.

    If it was me I'd look around for a used 3 series posi on E-Bay or even a new one and have it installed. Shouldn't cost much to have it installed because all they have to do is reset the backlash to whatever it was before they pulled the non-posi carrier out. Plus from what I'm seeing those "lockers" aren't too much cheaper than a new posi at Summit.
     
  11. monzaz

    monzaz Jim

    Lunch box lockers we consider them WEEKEND WARRIOR posi unit for sure. THEY ARE NOT for road racing by any means... They are built for mostly straight line accel and cruising through town showing off.
    I would never take these units on long freeway drives or going through mountain roads etc. Just not designed for that stuff. They fill a need for MUSCLE CARS for sure.
     
  12. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Funny enough I daily drive the wrangler nearly 80 miles a day.. Literally through the mountains and on the highway. True its not a "posi" (probably the most misused term in the hobby), its a locker. It works great and didn't change or hurt drivability in anyway. It's been installed for about 8k miles. No odd tire wear either. I bought it specifically to drive in the snow. Out here in the boondocks the town roads do not get plowed at night. Couple that with the mountains, traction becomes top priority.
     
    Last edited: Mar 22, 2020

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