Differentials: 4-series vs. 3-series
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,438
Likes: 2
From: Melrose Florida
Differentials: 4-series vs. 3-series
I have a differential with a casting number of 3899143, code of FC 6 22 67, cast date of F 7 7.
It looks like a '67 (or early '68) BB 4.56 posi unit by the code.
My current question is about the carrier casting number (3899143), was this the same for 4-series and 3-series? I've heard about shimming 3-series gears to go in a 4-series carrier or something like that.
Someone suggested that the casting for the 4-series should be EDB-30175, but I haven't found any numbers like that.
In the absence of the "FC" code, are there any external (or easily visible internal, rear cover off) differences between the 4-series and the 3-series differential carriers?
I'm debating rebuilding this one, if I can absolutely verify that it is BB HD Posi 4-series, because my car currently has a SB posi 3-series that is leaking at the pinion seal...and the car is a 427/435.
Thanks in advance,
Steve
It looks like a '67 (or early '68) BB 4.56 posi unit by the code.
My current question is about the carrier casting number (3899143), was this the same for 4-series and 3-series? I've heard about shimming 3-series gears to go in a 4-series carrier or something like that.
Someone suggested that the casting for the 4-series should be EDB-30175, but I haven't found any numbers like that.
In the absence of the "FC" code, are there any external (or easily visible internal, rear cover off) differences between the 4-series and the 3-series differential carriers?
I'm debating rebuilding this one, if I can absolutely verify that it is BB HD Posi 4-series, because my car currently has a SB posi 3-series that is leaking at the pinion seal...and the car is a 427/435.
Thanks in advance,
Steve
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
It is the other way around. You need to shim a 4 series gear to fit on a 3 series carrier. A 3 series gear will not fit on a 4 series carrier. I would not use a shim. They now have thick 4 series gears so they will fit a 3 series carrier without a shim. I blew up a rear using a shim. Do not use a shim!
Last edited by Gordonm; Dec 20, 2006 at 02:12 PM.
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
I will agree with Gordonm 100% and add...you can`t tell from the outside the housings will accept a 3 series or a 4 series posi. the difference in the posi is the thickeness where the ring gear bolts up...the 4 series is thicker...
...redvetracr
PS: if anyone NOT concerned with the price of gasoline is interested I have a freshly rebuilt (ready to bolt in) 4:10 I would like to sell. e-mail direct!!
...redvetracr
PS: if anyone NOT concerned with the price of gasoline is interested I have a freshly rebuilt (ready to bolt in) 4:10 I would like to sell. e-mail direct!!
