3rd member identification

Engine, Transmission & Driveline

  1. ofb383

    ofb383 Member

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    Hey guys, second hit at this as I've found some more markings. I need to identify the 3rd member so I can get a new gear set(3.23 or 3.55 )
    I know it's a 8 3/4 rear end but the 3 common castings don't seem to match what I have, I don't have the usual 41 or 42 , can't remember the 3rd one.
    Please look at the photos ( yes oily and the wet is cleaning fluid ) does anyone know what the 3rd member is from the photos, cast numbers and the large 3 digits painted on, also the bottom is yellow ? TIA:thumbsup:
    Diff1.jpg Diff2.jpg Diff3.jpg Diff4.jpg Diff5.jpg
     
  2. Polara_500

    Polara_500 Senior Member FCBO Gold Member

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  3. 413

    413 Active Member

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    How many fasteners holding that into the rear end housing?

    What car is it in? Sure grip or open?

    Look at the different casting ribs and pinion snubber.

    Looks like a 1961 (ish) or older unit.
     
  4. ofb383

    ofb383 Member

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    3rd member would cost quite a bit and not that common to pop up in the UK.

    68 Fury lll, I'll count the bolts and let you know and it's open, not sure grip:rolleyes:
     
    Last edited: Jan 22, 2020
  5. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Just for laughs, I googled the number and found a couple other guys with '68 Newports with the same issue.

    carrier identification help : - Moparchat - Home of MOPAR enthusiasts worldwide!
    3rd member ??s - Moparchat - Home of MOPAR enthusiasts worldwide!

    So... at least you aren't alone.

    I think the only true way you are going to figure this out is when the rear end is apart. You may be able to pull the assembly out and check ring gear part numbers, but when it comes down to it, it's going to have to come apart to change the gears anyway. My money is on it being a straight shaft, but no idea on shaft size.

    If you are changing to a 3.55 ratio, it's my opinion that you would want to also change to a sure grip rear. In that case, you really might be ahead to change that whole center section and be done with it. As it stands now, if you have the small shaft, you are probably going to want change to the larger shaft anyway, or at least I would because it's a heavy car.
     
  6. ofb383

    ofb383 Member

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    Well that makes me feel much better knowing that I'm not the only one who has a odd rear set up :BangHead::rolleyes::D
     
  7. ofb383

    ofb383 Member

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    Are we saying, if I take the assembly out and measure the pinion shaft size, that would / should point towards what more common unit it's a variant of and then hopefully the ring and pinion set for that 3rd member will fit?
    I was hoping to go to3.23, just to wake the old girl up and that was the recommended ratio for the cam I have fitted.
     
  8. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Yes. Since you can't identify what gear set to use based on the casting number, and all we have is a little bit of "it might be this", then the only way to verify the pinion shaft size is to actually measure it.

    The variable in all this is the pinion shaft size and configuration. This link will explain the differences and show what matches up to the common casting numbers. Mopar Casting Numbers - MyMopar.com - Mopar Part Numners

    As I said, there is a chance you can do some homework with the part number (if there is one) stamped on the ring gear without actually pulling the carrier apart.

    Unless you've done rear end setup, I don't recommend that you disassemble anything more than pulling the axles and carrier out yourself. Once you get into pulling the carrier apart, setting the gears, getting backlash, pinion depth etc., you'll need some specialized tools and some decent knowledge of what you are doing. Not a process you can easily (if at all) be "walked through" on a forum.
     
  9. Kernel Sanders

    Kernel Sanders Member

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    I've had a couple with weird numbers over the years but not the same numbers as yours. I dont have them anymore so cant tell you the numbers but they were late 50's early 60's and ended up using the same pinion seals as a 741. I hadn't had to do bearings on them but if I had I would have assumed the same as 741's... I know this likely doesn't help.

    One other thing with original ones of them years, on open diffs they had a square thrust block in the centre instead of the newer rounded ones
     
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  10. ofb383

    ofb383 Member

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    I have no plan on stripping the carrier, I no it's not a straight forward job without know what you are doing.
    The large nut holding the UJ on the pinion, If I remove this, with this mess with torque setting/differential set up?
    I could center pop some match points to do it back up, with this off can I measure the pinion diameter ?
     
  11. ofb383

    ofb383 Member

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    Just found this, so If I take the yoke off and count splines it may offer some more info or eliminate the casting/internals being based on a 742

    "You cannot swap pinion gears between the 741 and 742 housings, there is a dramatic difference in the OD of the rear bearing race in the housing. (Visible to the naked eye)
    All 8 3/4" rear ends used the same 30 spline axle from '57-'74.
    The only splines that were different in the 8 3/4" were the pinion splines where the yoke mounts. There were 10 and 29 spline pinions, the 742 used only the 10 spline while the 741 and 489 could have either."
     
  12. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    If that should turn out to be a tapered pinion (probably not, but still unknown), taking the yoke nut off is going to affect the crush sleeve and you'll never get it back together correctly.

    I don't think that pulling the yoke is going to tell you much. Actually, just pulling the nut will tell you the spline count, but yes, according to what you have read, a fine spline yoke would probably only be on a 741, but they will also tell you that your casting number doesn't exist. Do you really want to take a chance?

    If you're gonna change the gears anyway, why not have the carrier pulled apart, order the correct gears and put it back together with the new gears?
     
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  13. ofb383

    ofb383 Member

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    True, not worth chancing it. This will have to wait 5 months, my guy who was going to build the diff up is having a knee operation and I'm looking to move house in a few months or so. It will keep :lol:
     
  14. Kernel Sanders

    Kernel Sanders Member

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    Found this which has some of the other casting numbers.... unfortunately not yours:

    Center Section Types
    The 8-3/4" axle was available in three basic types. The types are differentiated by the pinion stem diameter....1-3/8", 1-3/4", 1-7/8". The choice of axle pinion assembly was determined based on the application. Differential bearing setting (ie. backlash ) is set with threaded adjusters on all carriers. All 8-3/4" carrier assemblies can be identified externally by the casting numbers.

    1-3/8" small stem pinion (aka. '741')
    Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972).
    This assembly was typically used in low weight/low horsepower applications through low weight/medium horsepower and high weight/low horsepower applications.
    Pinion depth and bearing preload is set with shims.
    1-3/4" large stem pinion (aka. '742')
    Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969).
    This assembly was replaced by a phase-in of the 1-7/8" pinion starting in the 1969 model year. 1970 RW (Plymouth and Dodge mid-size) were the last models to use the 1-3/4" which appeared in a 2881489 case. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications.
    Pinion depth and bearing preload is set with shims.
    1-7/8" tapered stem pinion (aka. '489')
    Carrier casting numbers: 2881488, 2881489 (1969-1974).
    This assembly was introduced in 1969 and was phased-in to relace the 1-3/4" unit through 1970. Note: the 1-3/4" pinion also appeared in some '489' carriers during this period. By 1973, the '489' was the only unit available in passenger car applications. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications.
    Pinion depth is set with shims, preload is set with a crush sleeve.

    The '741' commonly has a large X cast on the left side, the '742' may have a large 2 cast on the left side, and the '489' has a large 9 cast on the left side. Through 1965, the factory ratio was stamped on the identification boss, followed by an 'S' if Sure Grip equipped. After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio. If Sure Grip equipped, an additional Sure Grip lube tag was sometimes affixed; later years sometimes had the filler plug painted orange.
    Gear ratios available on the 8-3/4" axle through the years include: 2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57. On OEM gear sets, the ratio is usually stamped on the ring gear edge. Ratio may be determined by the number of teeth on the ring gear divided by the number of teeth on the pinion gear or by counting the ratio of the number of turns of the pinion relative to one turn of the axle shaft. The 8-3/4" center section is removed from the front of the housing. To remove the center section, remove the wheels, brake drums, and drive shaft (note: pre- 65 units have a pressed-on brake hub...requires a puller for removal). Remove the axle shafts, 5 bolts on the backing plate flange on post 64 units, use puller for pressed-in pre-65 units. Remove the 10 nuts on the housing studs around the carrier perimeter. Remove the carrier...may require prying, fluid will drain when carrier gasket seal is broken.
     
  15. ofb383

    ofb383 Member

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    Good info but like you said " not for mine'