8 3/4 identification

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DartVadar

DartVadar

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I just picked up a third member today, really good price and it's in great shape (so I think anyways) spins real nice, and is nice and clean. 4.10 gears and a sure grip, come type I think as I can see the springs?

My question is the case, I believe it's a 742 case, but I don't find the casting number anywhere. The number is 1634983. It's definitely a 3 at the end, not a 5, that's what's confusing me. Here's a picture to confirm lol.
 

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Mopar had a rear end before the 8 3/4 that looked VERY similar, but is not a 8 3/4.....I think that's what you might have. If so, to me, IMO.......pretty much useless
 
replicaracer43 said:
Mopar had a rear end before the 8 3/4 that looked VERY similar, but is not a 8 3/4.....I think that's what you might have. If so, to me, IMO.......pretty much useless
Click to expand...

.....That is a 10 bolt pattern its definitely a 8 3/4...if its 11 bolts its a 8 1/4....ya I know, if it is 11 bolt pattern it will positively say 8 1/4 above 1 of the bearing caps.....kim........
 
its definitely an 8 3/4 says so right on it, and looks identical to the others I have that are 741, except there are no X stampings on it. Soo it's useless then?
 
fishy68 said:
Not if it's an early 8-3/4 unit, which it is. You can see the date on the side saying it was made in 57. That's before the 741/, 489, or 742 casting numbers were used
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So when were the later cases after 64? something like that
 
Wow that is pretty old, so being that it's an early one what does that mean? Can I still use it? That's really my main concern, hopefully so, I've got three of these things now lol
 
I was steering him to look at the driver side. That unit looks identical to the 741, and is the unit in my 56' savoy. The difference between the two is the axles shafts.
I can't Install a newer 741 in my 56'. I saw the numbers, but I blame totally my not seeing them on my shitty glasses.(I'm hoping you all believe that) I am dumping it all, and Installing a 67' 8 3/4 in the Savoy. No more crappy axles with nuts on them, and better brakes.
 
Being an older style 741 case does that change anything? Does that cause issues with axle shafts or fitting in the housings? What exactly is the difference between the old and new style cases.
 
That may be an odd ball early 8.75" third-member that came with 741 gears and a 742 front pinion bearing and seal.

Does it have the bolt pattern for a pinion snubber?
 
DartVadar said:
Being an older style 741 case does that change anything? Does that cause issues with axle shafts or fitting in the housings? What exactly is the difference between the old and new style cases.
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The 1957 to 1964 8 3/4 rear ends are ok to use but the axles and pumpkin are not interchangable with the1965 and up 8 3/4s.
 
Here's a good read from BigBlock.com
http://www.bigblockdart.com/techpages/875axle.shtml

A Chrysler 8-3/4" Rear Axle Guide, Part II

Section 1: Thrust Block Variations

There was a difference in thrust blocks prior to 1964 that make center section interchange, as well as axle interchange problematic. The thrust block, or "axle shaft thrust spacer", it thr block that both left and right axles butt up against inside the center of the differential. Prior to 1964, all open differentials used a thrust block was approximately 1/8" to 1/4" thicker than units made after 1964. The Sure Grip thrust block prior to 1964, however, was indentical to all 1964 and later Sure Grips and open differentials. In 1964, the thrust block width was changed to match the Sure Grip thrust block width.

Since the unit you have has a suregrip it should work with later axles. Check if there is a production date stamped on the suregrip carrier.
This difference in thrust blocks between Sure Grip differentials and open differentials required that two different axles be produced for each 8-3/4" housing manufactured. This is true of all 1959-1963 cars with 8-3/4"s.

A 1964 and later differential, or any Sure Grip differential, cannot be used with 1959-1963 rearends and axles originally equipped with an open differential. The original axles must be machined or original Sure Grip length axles must be used.
 
DartVadar said:
I just picked up a third member today, really good price and it's in great shape (so I think anyways) spins real nice, and is nice and clean. 4.10 gears and a sure grip, come type I think as I can see the springs?

My question is the case, I believe it's a 742 case, but I don't find the casting number anywhere. The number is 1634983. It's definitely a 3 at the end, not a 5, that's what's confusing me. Here's a picture to confirm lol.
Click to expand...

By the date code it looks like a 1957 chunk. My book goes back to 57 and lists a #1634985 so a 983 would be earlier. 1 3/8" small pinion. A 4:10 gear probably came out of a pick up.
 
DoctorDiff said:
That may be an odd ball early 8.75" third-member that came with 741 gears and a 742 front pinion bearing and seal.

Does it have the bolt pattern for a pinion snubber?
Click to expand...

It has a pinion snubber already on it, and from what I can tell it looks identical to the other late 60s third members that I have.
 
Magiver said:
The 1957 to 1964 8 3/4 rear ends are ok to use but the axles and pumpkin are not interchangable with the1965 and up 8 3/4s.
Click to expand...

Thanks for the link, and I have to buy axle shafts anyways so I wouldnt be re-using any parts anyways, as long as it will still fit into a housing.

mderoy340 said:
Here's a good read from BigBlock.com
http://www.bigblockdart.com/techpages/875axle.shtml

A Chrysler 8-3/4" Rear Axle Guide, Part II

Section 1: Thrust Block Variations

There was a difference in thrust blocks prior to 1964 that make center section interchange, as well as axle interchange problematic. The thrust block, or "axle shaft thrust spacer", it thr block that both left and right axles butt up against inside the center of the differential. Prior to 1964, all open differentials used a thrust block was approximately 1/8" to 1/4" thicker than units made after 1964. The Sure Grip thrust block prior to 1964, however, was indentical to all 1964 and later Sure Grips and open differentials. In 1964, the thrust block width was changed to match the Sure Grip thrust block width.

Since the unit you have has a suregrip it should work with later axles. Check if there is a production date stamped on the suregrip carrier.
This difference in thrust blocks between Sure Grip differentials and open differentials required that two different axles be produced for each 8-3/4" housing manufactured. This is true of all 1959-1963 cars with 8-3/4"s.

A 1964 and later differential, or any Sure Grip differential, cannot be used with 1959-1963 rearends and axles originally equipped with an open differential. The original axles must be machined or original Sure Grip length axles must be used.
Click to expand...

Never knew that there were little changes like that to consider. and the date on the housing is 1957, so it would be one of the earlier ones, but because I need new axle shafts anyways I shouldnt have to worry about the axle shaft differences I wouldnt think.
 
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