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Hot Rods Rear end woe's, again!

Discussion in 'The Hokey Ass Message Board' started by Joe Romano, Feb 1, 2016.

  1. I need a GM 8.5" 10 bolt rear that measures 54 1/4" form back plate to back plate.
    Anyone know what car's GM used this size rear in.
    I have some clues from the old rear....
    Stamped on the on the r/s case is GM69 , on the left side of the case is 3969340NF.
    on the r/s tube is stamped O(I think, it's not very clear)then, OC 0706G1
    I know that it's a 2:73 rear.
    Thanks, Joe
    Last edited: Feb 2, 2016
  2. Outside
    Year Model
    54.25 1983-2004 Chevy S10 2WD, GMC S15 2WD
    57.75 1962-1964 Chevy II/Nova
    57.75 1965-1967 Chevy II/Nova
    58.00 1978-1988 Chevy Malibu, Monte Carlo
    59.50 1968-1982 Corvette
    60.00 1955-1964 Chevy Car
    60.00 1967-1969 Camaro
    60.25 1968-1979 Chevy II/Nova
    60.50 1984-1995 Corvette
    60.50 1964-1967 Chevelle
    62.00 1955-1959 Chevy Pickup
    62.50 1968-1972 Chevelle
    62.50 1970-1981 Camaro/Firebird
  3. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248


    Whats the width from Wheel Mounting Surface (WMS) to WMS?
    Backing plate measurements are erratic and misleading due to variations in brake shoe width requiring some backing plates to be countersunk more than others.
    gimpyshotrods likes this.
  4. junkman8888
    Joined: Jan 28, 2009
    Posts: 606


    Have to second Hackerbilt, a backing plate to backing plate measurement will tell you nothing, if its roughly 58" from axle face to axle face, it's probably 79-85 G-body chevy. And pictures always help.
    gimpyshotrods likes this.

  5. 4thhorseman
    Joined: Feb 14, 2014
    Posts: 261

    from SW Desert

    S-10's had the 10 bolt 7.5" rear ends I believe. They grenade easily under stress. Ask me how I know... :oops:
  6. KevKo
    Joined: Jun 25, 2009
    Posts: 575

    from Motown

    IIRC, S10's with V6 manual trans had the 8.5" rear.
  7. I need to find out how to measure. I thought I was doing it right.
    In the mean time a friend, has a friend that rebulids rears, mine has 2 missing teeth in one of the gears and the ring gear has some minor chips at the edges. So.... I'm going to get a price on a rebuild in the mean time.....Joe.
    Last edited: Feb 2, 2016
  8. indyjps
    Joined: Feb 21, 2007
    Posts: 4,161


    Takes the rear wheels off and measure from the wheel mounting surfaces.
    Pics will help, looking for cut off brackets etc. If it's on leaf springs measure the center of the leaf spring mounting pad, see if they look like factory mounting pads or added later on.
  9. sawbuck
    Joined: Oct 14, 2006
    Posts: 1,890

    from 06492 ct

    2.37 ratio ?
  10. TYPO....2.73
  11. Nothing on this car is factory except the From the ground up it's all retro.The chasis is even after market.
  12. indyjps
    Joined: Feb 21, 2007
    Posts: 4,161


    Understand, the rear end came from something, we will try to help you identify it. Could have been a G body with mounts cut off and leaf spring pads welded on, or a leaf spring rear with pads cut off and coil over mounts welded on. I've done it a few times.

    If you want to rebuild it, that's fine, gear, posi, bearings, it adds up. If you wanna see what it came from and try to find a replacement, we'll help.
  13. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547


    indy is right on the mounts , a g body rear would have cast ears on the upper portion of the center section , and you could see if they were cut off , a leaf spring car would have signs of brackets near the end of the axle on the bottom side and the weld undercuts s or grind marks should show it also on the 8.5 there is a cast date on the center which would help to place what year range for decoding .
  14. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248


    The 4.3 versions had a bigger rearend than the 7.5 and its pretty strong...and as Kevko says, apparently some even came with the 8.5.
  15. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,131


    I'd say you are looking at a mid 70's Nova / Camaro / Firebird rear axle. A good replacement would be far less expensive than having the gears replaced in yours.
    That's adding 3-1/2 to 4 inches a side for the mount surface to back of backing plate distance.
    31Vicky with a hemi likes this.
  16. I get the GM69 from the case, on the ring gear itself I get o6 70, the tube is stamped O OC so I'm thinking it's from an Old's but I don't know friend said it looks like it came off a G body. The leaf spring pads are welded on, but I don't see any sign of anything being ground down or cut off. I will double check that tomorrow. I'd don't know if only the broken gear could be replaced. I like most am strapped for cash, so, I'm looking to get out of this without being hammered to hard. Social security only goes so far..
  17. What gear broke? That makes a difference.

    G body rear would have had those Mickey Mouse type big ears on top. Someone may have cut them off

    Attached Files:

  18. cavman
    Joined: Mar 23, 2005
    Posts: 646


    4.3 S-10's with the ZR-2 option had 8.5", but they are wide. The other 4.3 S-10's had 8.2". The one I have is out of a '94 4x4 and is 54.5 inches wide backing plate to backing plate. Factory 3:73 with a locker. The outer axle bearings are the weak link.
  19. Looks nothing like that...I'll try to find a picture.
  20. I counted the teeth on the gears and it is a 2.73 10 bolt 8.5 inch. 54 1/4in backing plate to backing plate.
    A replacement rear needs to be the same size due to the off set of the rim's. We measured for a narrower one but there is no room, either tire would rub the frame or the fender.
  21. one of the carrier gears, the one on the L/S side, it's missing 2 teeth, one just sheered off and the other was just ground up.
  22. Spider gears- easy swap.
    Or cheaper yet Pull the pieces out and weld the spider gears together, Aka Lincoln locker

    No one measures and records a rear by backing plate- so you'll not get any help from that.
    You might get somewhere with the housing flange, but the most bestest way is wheel mounting surface to WMS. Pull the rear wheels and measure that.

    No ears or evidence of them then you can forget the G body thing.
    I'm with mr 48 chevy on probability
  23. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,133


    Lots of folks do. It is just a useless measurement.
  24. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248


    Pop the wheels off.
    Use two straight edges against the axle flange surfaces, one on either side, measure the distance between them.
    You need the measurement of the complete rearend assembly and axles, minus the lugs and the center rings that align the wheels. WMS to WMS.
    Slow down likes this.
  25. Now this I understand, Thanks. Joe
    Hackerbilt likes this.

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