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1957 Plynouth Axle Identification - Center Section ID #425093 07/31/09 09:04 PM 07/31/09 09:04 PM
Joined: Jan 2003 Posts: 42,714 Spokane Washington ScottSmith_Harms OP Mr Wizzard
ScottSmith_Harms OP Mr Wizzard Joined: Jan 2003 Posts: 42,714 Spokane Washington	My wagon has what appears to be an 8.75 rear end, but the center section casting number is weird: #1684983, anyone know anything about these?

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #425094 07/31/09 09:56 PM 07/31/09 09:56 PM
Joined: Jan 2004 Posts: 27,347 Today? Who Knows? 1_WILD_RT Management Trainee
1_WILD_RT Management Trainee Joined: Jan 2004 Posts: 27,347 Today? Who Knows?	It predates 8.75, I think the earlist 8.75 casting # is 657... & showed up around 59-60 ... Lookin for Dr Diff..

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: 1_WILD_RT] #425095 07/31/09 10:27 PM 07/31/09 10:27 PM
Joined: Jan 2003 Posts: 42,714 Spokane Washington ScottSmith_Harms OP Mr Wizzard
ScottSmith_Harms OP Mr Wizzard Joined: Jan 2003 Posts: 42,714 Spokane Washington	Right, Here's the history on the 8.75" that I am already aware of, Quote: The Chrysler 8-3/4" rear axle assembly was introduced in 1957. 1-3/8" small stem pinion... (aka. '741')... Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972). 1-3/4" large stem pinion... (aka. '742')... Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969). 1-7/8" tapered stem pinion... (aka. '489')... Carrier casting numbers: 2881488, 2881489 (1969-1974). Notice there's no mention of my casting number? I think I may have an 8.25" unit, really weird that they'd build such a dead ringer for an 8.75" in a smaller unit.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #425096 07/31/09 11:06 PM 07/31/09 11:06 PM
Joined: Oct 2004 Posts: 6,293 Northeast, Alpine, NY 9 9 Sec Phill On a road near you
9 Sec Phill On a road near you 9 Joined: Oct 2004 Posts: 6,293 Northeast, Alpine, NY	Im still thinking its an 83/4 rear Scott...Phill

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: 9 Sec Phill] #425097 07/31/09 11:48 PM 07/31/09 11:48 PM
Joined: Jan 2003 Posts: 4,588 St. John's Newfoundland 440newport master
440newport master Joined: Jan 2003 Posts: 4,588 St. John's Newfoundland	How many nuts are holding the center section to the housing? The old 8 1/4's have 11...8 3/4's have 10.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #425098 08/01/09 12:37 AM 08/01/09 12:37 AM
Joined: Jan 2003 Posts: 8,016 Polson, MT DoctorDiff master
DoctorDiff master Joined: Jan 2003 Posts: 8,016 Polson, MT	If I remember correctly, the 983 casting is the odd ball 8 3/4" third-member with the 741 style gears and the 742 front pinion bearing and seal. Is there a big "X" cast into the side of the case? Contact info

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: DoctorDiff] #425099 08/01/09 02:01 AM 08/01/09 02:01 AM
Joined: Jan 2003 Posts: 42,714 Spokane Washington ScottSmith_Harms OP Mr Wizzard
ScottSmith_Harms OP Mr Wizzard Joined: Jan 2003 Posts: 42,714 Spokane Washington	Cass, there's no "X" that I can see (pretty grimey) where would it be? Seems there is nothing on the drivers side anyway.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #425100 08/01/09 03:27 PM 08/01/09 03:27 PM
Joined: Jan 2003 Posts: 25,796 Rio Linda, CA John_Kunkel Too Many Posts
John_Kunkel Too Many Posts Joined: Jan 2003 Posts: 25,796 Rio Linda, CA	Quote: My wagon has what appears to be an 8.75 rear end, but the center section casting number is weird: #1684983, anyone know anything about these? Take a closer look, the number is probably 1634985, this is the early equivalent of the later 742. Reportedly the difference is that the early housings are cast steel and the later are cast iron. The INTERNET, the MISinformation superhighway

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: John_Kunkel] #425101 08/01/09 04:18 PM 08/01/09 04:18 PM
Joined: Jan 2003 Posts: 42,714 Spokane Washington ScottSmith_Harms OP Mr Wizzard
ScottSmith_Harms OP Mr Wizzard Joined: Jan 2003 Posts: 42,714 Spokane Washington	I'll have a look John, thanks, hopefully you are right, would save me allot of parts hunting. So, if it turns out to be what you think it is will the tapered axles I have fit into a new 742 assembly ok if I swap it out? I had a BAD axle seal leak that looks like it went on for a long time, I'm guessing the current gears may be toast from lack of fluid.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #425102 08/01/09 06:20 PM 08/01/09 06:20 PM
Joined: Jan 2003 Posts: 25,796 Rio Linda, CA John_Kunkel Too Many Posts
John_Kunkel Too Many Posts Joined: Jan 2003 Posts: 25,796 Rio Linda, CA	All 8 3/4" axles are 30-spline, in pre-'64 units the axles are different length for Sure-Grip and open differential so, if the original has an open differential and you want to swap in a Sure-Grip, you'll need to trim 1/8" from each axle shaft. The INTERNET, the MISinformation superhighway

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: John_Kunkel] #425103 08/01/09 06:29 PM 08/01/09 06:29 PM
Joined: Jan 2003 Posts: 42,714 Spokane Washington ScottSmith_Harms OP Mr Wizzard
ScottSmith_Harms OP Mr Wizzard Joined: Jan 2003 Posts: 42,714 Spokane Washington	It's an open dif now and I plan on using another open one for now.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471631 03/25/18 01:45 AM 03/25/18 01:45 AM
Joined: Mar 2018 Posts: 3 Ohio C CMcKnight member
CMcKnight member C Joined: Mar 2018 Posts: 3 Ohio	I know that this is an old thread, but I have this same exact third member with this weird casting number. It has 10 bolts, no "X" on the side and the brake backing plates on the axle are an odd size. I would appreciate any updates as to what was found out as I am trying to buy a new carrier and ring and pinion for this rear end. Thank you.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471632 03/25/18 01:52 AM 03/25/18 01:52 AM
Joined: Jan 2003 Posts: 42,714 Spokane Washington ScottSmith_Harms OP Mr Wizzard
ScottSmith_Harms OP Mr Wizzard Joined: Jan 2003 Posts: 42,714 Spokane Washington	I still have the car/rear, and have picked up another axle assembly, I'll have a look at it in the morning and post what I can.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471660 03/25/18 03:31 AM 03/25/18 03:31 AM
Joined: Dec 2003 Posts: 4,951 northwest USA N NANKET master
NANKET master N Joined: Dec 2003 Posts: 4,951 northwest USA	If you swap in a 1965 and newer open differential you still need to remove 1/8" from each axle shaft. Here is a pic of the 1965 and later centering block with open space around the block. The second photo is 1964 and earlier is an actual block that fills all the area between the spider gears and side gears. Both are open differentials.

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471679 03/25/18 09:29 AM 03/25/18 09:29 AM
Joined: Apr 2007 Posts: 905 SD Z zrxkawboy super stock
zrxkawboy super stock Z Joined: Apr 2007 Posts: 905 SD	I don't know specifically about the casting #, but I know that in '57/58, the 6-cyl cars got an 8.25" diff while the V8 cars got the 8.75". It's Swifty! Swifty, you toad sucker!

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471748 03/25/18 12:36 PM 03/25/18 12:36 PM
Joined: Mar 2018 Posts: 3 Ohio C CMcKnight member
CMcKnight member C Joined: Mar 2018 Posts: 3 Ohio	What I am trying to do is buy an Auburn limited-slip and a new 3:73 ring and pinion. The Auburn carrier specifies that it is for 1964 and newer. So, I guess what you guys are saying is that I can use this set-up if I shorten my axles by 1/8"?

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471876 03/25/18 04:40 PM 03/25/18 04:40 PM
Joined: Dec 2003 Posts: 4,951 northwest USA N NANKET master
NANKET master N Joined: Dec 2003 Posts: 4,951 northwest USA	Yes

Re: 1957 Plynouth Axle Identification - Center Section ID [Re: ScottSmith_Harms] #2471895 03/25/18 05:14 PM 03/25/18 05:14 PM
Joined: Mar 2018 Posts: 3 Ohio C CMcKnight member
CMcKnight member C Joined: Mar 2018 Posts: 3 Ohio	Good to know. I just hope the new carrier will fit in my 1957ish third member housing.

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