8 1/4 or 8 3/4 rear end in my Duster 340?

Transmission and Drivetrain Tech

  1. spence340

    spence340 Well-Known Member

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    I was at a big cruise meet at Gillette stadium the other night because I am selling my '73 Duster 340. It recieved a lot of attention with people crawling all over and under the car and one thing that came up was the rear end. From the old days I remember the 8 3/4 rearend being the smooth on the back front mount pumpkin type. I think they were called hotchkiss while the 8 1/4 was the rear cover plate style called salisbury. Well my matching numbers 340 appears to have a 8 1/4 in it but the 1973 sales brochure clearly states that the 340 package came with an 8 3/4 axle. Did they ever make a rear load 8 3/4 set up. Did they run out of 8 3/4 rear ends the day my car was being built and just threw in the 8 1/4? Any ideas out there?
     
  2. stansblue72

    stansblue72 one of one 1953 ME! Legendary Member

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    Thought I read some where that the 8.75 was used through the 1972 model year. After that it was the 8.25. I'm not a 100% on this though.
     
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    • stansblue72

      stansblue72 one of one 1953 ME! Legendary Member

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      Found it. This says it was in 73s

      Chrysler 8 3/4" Rear Axle & Swap Information

      Chrysler Corporation's 8.75" rear axle assembly first appeared in 1957. The measurement refers to the 8-3/4" diameter ring gear. This gear, which is turned by the pinion gear, changes the direction of the power being transmitted to it. The pinion gear is turned by the driveshaft. It is a banjo-type (Hotchkiss) axle. The term "banjo" means that the differential is contained in a removable carrier (or center section) assembly. When the carrier is removed, the empty housing resembles a banjo. The carrier is removed from the front of the housing, and is retained by 10 nuts on studs in the housing. The rear of the housing is smooth with a non-removable rear cover that is welded onto the main housing. The housing and axle tubes are made from stamped and welded steel.

      The 8-3/4" axle was the primary axle assembly used in most non-compact car lines through 1972. It was also used in some high performance compact cars. Of the many axle types that Chrysler used since 1960, it was also the only axle assembly developed by Chrysler. It was phased out because it was more expensive to manufacture than using the outsourced Spicer 7.25", 8.25" and 9.25" units.

      There are three basic types of 8.75" carriers available, which are distinguished by their drive pinion stem diameter. The choice of axle pinion assembly was determined based on a combination of vehicle horsepower and weight. Below are the 8.75" axle carrier types.

      8.75" Axle Carrier Types and Years of Production

      ''741' Casting - 1 3/8" (1.375") Small Stem Pinion.
      Carrier casting numbers were 1820657 (1957-1964) and 2070741 (1964-1972). This unit was usually used in low weight/medium horsepower and high weight/low horsepower applications. Although it is the weakest of the 8.75" units, it is still a stout unit, and is stronger than the Spicer-built Chrysler 8.25" rear. The 1 3/8" pinion is also larger than the pinion in the Ford 9" rear.
      ''742' Casting - 1 3/4" (1.75") Large Stem Pinion.Carrier casting numbers were 1634985 (1957-1964) and 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion '489' casting starting in the 1969 model year. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Although not generally considered to be stronger then the '489' carrier, the '742' carrier is extremely stout, and is favored by many Mopar enthusiasts because they are easier to set up. Noted Mopar enthusiast John Kunkel mentioned that the biggest advantage of the 742 carrier is that it has the largest rear pinion bearing of all the 8 3/4" carriers. The larger bearing helps to prevent pinion deflection better under a load than the others.
      '489' Casting - 1-7/8" (1.875") Tapered Stem Pinion Carrier casting numbers were 2881488 or 2881489 (1969-1974). This assembly was introduced in 1969 and was phased-in to relace the 1-3/4" pinion '742' 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, and was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. This carrier is considered to be the strongest by some Mopar enthusiasts. Because it requires a crush sleeve to set bearing preload, some Mopar enthusiasts prefer the '742' casting. This is not really an issue now because there are now parts available to eliminate the crush sleeve.

      Carrier Identification:
      All 8-3/4" carrier assemblies can be identified externally by the casting numbers. The casting numbers are cast onto an ID pad on the driver's side of the carrier just behind the 'snout' of the case where the yoke attaches to the pinion. In addition to the casting numbers:

      The '741' will usually have a large 'X' cast on the left side
      The '742' will usually have a large '2' cast on the left side
      The '489' will have a large '9' cast on the left side.
       
    • spence340

      spence340 Well-Known Member

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      Wow, your good Green but it still leaves some question as to when they stopped using them in the Duster 340. The Duster was definetly not considered a "high weight" application. I'm sure the '73 brochure was printed in late summer or early fall of 1972 so maybe that's why they still stated the 340 comes with a 8 3/4 axle. Anybody out there with a '73 340 who can verify this question?
       
    • jimmyray

      jimmyray Well-Known Member

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      My #'s matching 73 340 had the 8.25. I thought they all did after 72. No reference data, though...
       
    • demon seed

      demon seed The Original Demon Seed

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      I suspect, but don't quote me, that the reason Mopar went away from the 8 3/4" in 73 was because by then they were dropping significant horsepower and torque off these and all the other engines. In short the 73 didn't need the 8 3/4".
       
    • pettybludart

      pettybludart Well-Known Member

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      My 73 Dart Sport 340 4 speed came stock with 8 1/4 with 3.23,s,I changed mine to 8 3/4 after adding more horsepower.
       
    • caferacerx

      caferacerx BAND MEMBER

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      the a body 8 3/4 was only available in 5X4" small bolt circle from the factory, the 8 1/4 a body rear was only available in 5X4.5" big bolt circle, if your car came with big bolt single piston front disk brakes it would be supplied with the 8 1/4 rear ( 7 1/4 was available in both big and small bolt circle)
       
    • spence340

      spence340 Well-Known Member

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      Cafe are you saying the 8 1/4 in '73 was somewhat heavy duty? What size rear end would a '73 slant six have come with and as far as the disc brakes my car has them but I don't know anything about a big bolt set up. Demon seed I agree would you that in '73 not only was it not a "heavy weight application" but it wasn't really a high horsepower application either.
       
    • alsdemon

      alsdemon Well-Known Member

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      71/72 was last year for the small 4on5 bolt patern or wheel. with the single piston front brake they have the 5/5.25 or /5.5 bolt/wheel patern.
       
    • spence340

      spence340 Well-Known Member

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      Oh. I see, you are talking about the small bolt pattern on the earlier Dusters. Anyway it looks like I am OK with my '73 having the 8 1/4 even though the sales lit. says 8 3/4.
       
    • Gryzynx

      Gryzynx Senior Moment

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      Sure would like to see this sales brochure that mentions the 8 3/4 in '73.

      Parted a '73 340 4 spd Dart years ago and the rear was an 8 1/4. All
      Chrysler literature that I've seen says the 8 1/4 replaced the 8 3/4 in '73 A bodies. As such, it was the heavy duty rear end in '73 and later. As mentioned before, there were no LBP A body 8 3/4's.
       
    • crackedback

      crackedback FABO Gold Member FABO Gold Member

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      What sales lit says Dusters got 8.75's in 1973? I'd love to see something that says that.

      73 was the transition year from 8.75's in 72 to the 8.25 in 73
       
    • juris340

      juris340 Member

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      my 1973 dart sport 340 and my 1973 duster 340 have the 8.25.
       
    • 67valiant 100

      67valiant 100 go fast or go home

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      So your saying that if you got drums all the way around then they would be sbp thous using the 8 3/4 because it only came in sbp while the 8 1/4 came only in lbp which would be use with disc brake equipped cars?:dontknow:
       
    • oldkimmer

      oldkimmer FABO Gold Member FABO Gold Member

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      .........A 73 340 car will have discs, 8.25 rear and big bolt pattern.......if u have drums all around u have small bolt pattern........no 340 cars had drums all the way around and small bolt pattern for 73 up..........kim........
       
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