Posted By: ScottSmith_Harms
1957 Plynouth Axle Identification - Center Section ID - 08/01/09 01:04 AM
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?
Posted By: 1_WILD_RT
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 01:56 AM
It predates 8.75, I think the earlist 8.75 casting # is 657... & showed up around 59-60 ...
Lookin for Dr Diff..
Posted By: ScottSmith_Harms
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 02:27 AM
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.
Posted By: 9 Sec Phill
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 03:06 AM
Im still thinking its an 83/4 rear Scott...Phill
Posted By: 440newport
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 03:48 AM
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.
Posted By: DoctorDiff
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 04:37 AM
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?
Posted By: ScottSmith_Harms
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 06:01 AM
Cass, there's no "X" that I can see (pretty grimey) where would it be? Seems there is nothing on the drivers side anyway.
Posted By: ScottSmith_Harms
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 08:18 PM
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.
Posted By: John_Kunkel
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 10:20 PM
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.
Posted By: ScottSmith_Harms
Re: 1957 Plynouth Axle Identification - Center Section ID - 08/01/09 10:29 PM
It's an open dif now and I plan on using another open one for now.
Posted By: CMcKnight
Re: 1957 Plynouth Axle Identification - Center Section ID - 03/25/18 05:45 AM
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.
Posted By: ScottSmith_Harms
Re: 1957 Plynouth Axle Identification - Center Section ID - 03/25/18 05:52 AM
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.
Posted By: NANKET
Re: 1957 Plynouth Axle Identification - Center Section ID - 03/25/18 07:31 AM
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.
Posted By: zrxkawboy
Re: 1957 Plynouth Axle Identification - Center Section ID - 03/25/18 01:29 PM
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".
Posted By: CMcKnight
Re: 1957 Plynouth Axle Identification - Center Section ID - 03/25/18 04:36 PM
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"?
Posted By: CMcKnight
Re: 1957 Plynouth Axle Identification - Center Section ID - 03/25/18 09:14 PM
Good to know. I just hope the new carrier will fit in my 1957ish third member housing.