I have a C1 posi unit with the marking cast into it of C-3074 and CHEV and XN Seems to be a good unit . I would like to put it into my 61 to replace my cracked one. Will this work? Jerry
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Re: C1 Posi Unit need help with identifying
Jerry
Does it say Arma Steel on the top? A three series has the numbers C-30743 and the four series is C-30751. Can you post some pictures? I'm sure one of the rear end guys will also chime in.
Terry -
Re: C1 Posi Unit need help with identifying
The numbers C-70745 are on one of the flanges. There is no ARMA that I can see. I'll take a shot at posting a photo.Comment
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Re: C1 Posi Unit need help with identifying
There were TWO versions of the early posi units (used 57-62 Vettes and 57-64 pass cars).
The early version is 57-59, the late version is 60-64, plus, there is a 3-series and a 4-series posi in both the early and late version.
WITHOUT question, that picture is the later (and better) posi unit. Also, it APPEARS to be a 3-series posi unit (can only be POSITIVE with a measurement).
Sooooooooooooooooooo, if you plan to use this with any 3.08 through 3.70 gear, it will be a direct fit (based on it being a 3-series posi). If you plan to use it with a 4-series gear, such as a 4.11, 4.56, etc, then you will need to use a ring gear spacer.
BUUUUUUUUUUUUT, if it is a 4-series posi, it can ONLY be used with a 4-(or 5-) series ring gear (a 3-series ring gear CANNOT be used with a 4-series posi).
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Re: C1 Posi Unit need help with identifying
What measurements should I take?? I'm planning on using a 3.70 gearComment
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Re: C1 Posi Unit need help with identifying
Jerry,
Place the posi unit (as you have it in the picture above) on a flat surface. Measure from the flat surface to the flat surface of ring gear flange. The dimension may vary SLIGHTLY from unit to unit. But, it will be APPROXIMATELY 2 5/16in for a 3-series. If it is a 4-series, the dimension will be APPROXIMATELY 1/4in closer to the center line of the unit (or about 2 9/16in).
Below is a comparrison of a 3- (left) and 4-series (right) NON-posi differential. REGARDLESS of whether the differential is posi or non-posi, the dimension will still be the same for the ring gear flange. As you can see, the difference between the position of the flange for a 3- and 4-series is noticeable.
This is a comparrison between a factory 4-series posi and an aftermarket Eaton 3-series posi unit. Again, the difference between the position of a 3- and 4-series flange is noticeable.
This is a comparrison between an early (57-59 left) and late (60-64 right) factory posi units. IMMEDIATELY, notice the difference in the V angles for the cross shafts between the two. UNMISTAKEABLE!
One last thing to look for (and I don't have a good picture to post). USUALLY, the outer edge of the ring gear flange on 3-series posi units has a bevel to it, as opposed to flat like the 4-series units above. I cannot see the edge of the flange in your picture, but it kind of looks as if it MAY be beveled on the outside edge of the flange.Comment
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Re: C1 Posi Unit need help with identifying
Mine measures 2 1/4 so it's a three series. Thank you for your help. You are really good at illustrating the differences. Much appreciated. Now all I need to do is put a new clutch pack in it and go.Comment
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Re: C1 Posi Unit need help with identifying
Since that is a 60-64 posi unit, did you know that the bolts are LEFT hand thread?
Also, If you buy a clutch pack, and it does not have 2 thin plates, then you MUST re-use the old thin plates (if they are worn, just flip them over).Comment
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