8 3/4 identification help

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Johnny Mac

Johnny Mac

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Hey all,

Pulled a 8.75 from a 75 roadrunner parts car today. It has none of the common identification numbers that I'm used to seeing. My dart has them on the driver snout..this has nothing there.

It does have pinion snubber holes. HUGE drums. Same width as the 8.25 that also came from a late B body.

Is this perhaps a really early one? No gear ratio tags either. Going to need a sure grip, but Idk if the case is even usable, or what it is.

Thanks for any help.

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The 2 on a 742 tells you it is a 742 pumpkin.

The 657 or whatever that number is one of the early number used for 8 3/4.

1-3/8" small stem pinion... (aka. '741')...
Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972). This assembly was typically used in low weight/low horsepower applications through low weight/medium horsepower and high weight/low horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

1-3/4" large stem pinion... (aka. '742')...
Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion starting in the 1969 model year. 1970 RW (Plymouth and Dodge mid-size) were the last models to use the 1-3/4" which appeared in a 2881489 case. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

1-7/8" tapered stem pinion... (aka. '489')...
Carrier casting numbers: 2881488, 2881489 (1969-1974). This assembly was introduced in 1969 and was phased-in to relace the 1-3/4" unit through 1970. Note: the 1-3/4" pinion also appeared in some '489' carriers during this period. By 1973, the '489' was the only unit available in passenger car applications. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth is set with shims, preload is set with a crush sleeve. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

All 8-3/4" carrier assemblies can be identified externally by the casting numbers. Additionally, the '741' commonly has a large X cast on the left side, the '742' may have a large 2 cast on the left side, and the '489' has a large 9 cast on the left side. Through 1965, the factory ratio was stamped on the identification boss, followed by an 'S' if Sure Grip equipped. After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio. If Sure Grip equipped, an additional Sure Grip lube tag was sometimes affixed; later years sometimes had the filler plug painted orange.
 
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Looks like the early 657 case to me. Came before the 741. It doesn't have the axle nut correct?
 
my5thmopar said:
Looks like the early 657 case to me. Came before the 741. It doesn't have the axle nut correct?
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Have not even had the wheels off it...can you clarify what you mean please and thank you?

You are disagreeing that the "2" above means 742?
 
Jadaharabi said:
The 2 on a 742 tells you it is a 742 pumpkin.

The 657 or whatever that number is one of the early number used for 8 3/4.

1-3/8" small stem pinion... (aka. '741')...
Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972). This assembly was typically used in low weight/low horsepower applications through low weight/medium horsepower and high weight/low horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

1-3/4" large stem pinion... (aka. '742')...
Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion starting in the 1969 model year. 1970 RW (Plymouth and Dodge mid-size) were the last models to use the 1-3/4" which appeared in a 2881489 case. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

1-7/8" tapered stem pinion... (aka. '489')...
Carrier casting numbers: 2881488, 2881489 (1969-1974). This assembly was introduced in 1969 and was phased-in to relace the 1-3/4" unit through 1970. Note: the 1-3/4" pinion also appeared in some '489' carriers during this period. By 1973, the '489' was the only unit available in passenger car applications. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth is set with shims, preload is set with a crush sleeve. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

All 8-3/4" carrier assemblies can be identified externally by the casting numbers. Additionally, the '741' commonly has a large X cast on the left side, the '742' may have a large 2 cast on the left side, and the '489' has a large 9 cast on the left side. Through 1965, the factory ratio was stamped on the identification boss, followed by an 'S' if Sure Grip equipped. After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio. If Sure Grip equipped, an additional Sure Grip lube tag was sometimes affixed; later years sometimes had the filler plug painted orange.
Click to expand...

Thanks so much. I could find the definitions, but it was so different from my darts rear I was lost. What designates the clone or clutch? Or do I just need to tear it apart? It's either an open diff or broken.
 
Johnny Mac said:
Have not even had the wheels off it...can you clarify what you mean please and thank you?

You are disagreeing that the "2" above means 742?
Click to expand...

Looking at the outside of the wheels, he's talking about a large nut that screws onto the axle end that holds the axle flange on. That's how some of the earlier 8 3/4 rears were. they has tapered axles that the axle flange slipped on, had a key and keyway and a large nut held them on. You'll know it if it's there.

I think fruitcake up there is right. It's a 742.
 
Your pumpkin is a 57-64, 1 3/8 pinion. Early version of the 741.
It has a 2 cast on it where all 742 housings has a 2 cast on it also.
 
Jadaharabi said:
Your pumpkin is a 57-64, 1 3/8 pinion. Early version of the 741.
It has a 2 cast on it where all 742 housings has a 2 cast on it also.
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Cool, then you were.......wrong? Say it aint so. lol

If you need some more help in bein wrong, I give lessons. LMAO
 
To add to this....."I thought" I read somewhere that all the early versions of the 8 3/4 were the 741 case......I cannot remember where I saw that. OR if it was right.
 
RustyRatRod said:
Cool, then you were.......wrong? Say it aint so. lol

If you need some more help in bein wrong, I give lessons. LMAO
Click to expand...

Wrong about what? He has a 657 carrier which is a early 741. It has a 2 cast on it as do all 742 housing but it is not a 742 it is a early 741.
 
1820657 I see it now fellas. Thanks!!!

So usable for a new sure grip build? Or does the entire Center section need to go, and just the housing is worth anything?
 
Jadaharabi said:
Wrong about what? He has a 657 carrier which is a early 741. It has a 2 cast on it as do all 742 housing but it is not a 742 it is a early 741.
Click to expand...

you said at first it was a 742.
 
Johnny Mac said:
1820657 I see it now fellas. Thanks!!!

So usable for a new sure grip build? Or does the entire Center section need to go, and just the housing is worth anything?
Click to expand...

Naw, nothing wrong with a 741. Although for your green car, "I" would use one of the others for the larger pinion shaft. A 10 second car might find the difference. lol
 
Jadaharabi said:
Wrong about what? He has a 657 carrier which is a early 741. It has a 2 cast on it as do all 742 housing but it is not a 742 it is a early 741.
Click to expand...
I misread it the first time. It's a 741 based on casting numbers. But 742 ALSO had a "2" I get it now. It's late lol.
 
Johnny Mac said:
Thanks so much. I could find the definitions, but it was so different from my darts rear I was lost. What designates the clone or clutch? Or do I just need to tear it apart? It's either an open diff or broken.
Click to expand...

If original it would be a clutch type Sure Grip unit known as a Dana power lock I believe. The cone type Sure Grip did not come into heavy use until 1969 or thereabouts

If you read post number two you will see that the 1 3/8 and the 1 and 3/4 and the 1 7/8 we're all use from 57 up. They just had different numbers for the housings.
 
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Johnny Mac said:
I misread it the first time. It's a 741 based on casting numbers. But 742 ALSO had a "2" I get it now. It's late lol.
Click to expand...

Right. He said the same thing I was thinkin. Usually, when there's a large single number like a 2 or a 9, that's what it is. A 742 or a 489 respectively. Course there's always them danged exceptions. lol
 
RustyRatRod said:
Naw, nothing wrong with a 741. Although for your green car, "I" would use one of the others for the larger pinion shaft. A 10 second car might find the difference. lol
Click to expand...
The green car has a 742. I could put it in the blue tank, and do a 9 inch for the green one. Would only need to move the perches. This donor was just an easy bolt in. Was praying it had a sure grip. No dice.
 
Jadaharabi said:
Please forgive me for correcting myself after I saw the 657 number on the side of the housing. I humbly beg your forgiveness. The two on the side of the housing threw me off temporarily.
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Calm down Francis. I was jokin around. That's twice you got your panties all wadded up recently over me jokin around. Do I just need to stop interacting with you altogether?
 
Johnny Mac said:
1820657 I see it now fellas. Thanks!!!

So usable for a new sure grip build? Or does the entire Center section need to go, and just the housing is worth anything?
Click to expand...

I have sold the early housing at swap meets to guys wanting the correct pumpkin for their year car.
741s came in 383 & 440 cars.
I personally prefer the 742 as it has the largest inner pinion bearing and no crush sleave.

What ratio is your 657?
 
RustyRatRod said:
Calm down Francis. I was jokin around. That's twice you got your panties all wadded up recently over me jokin around. Do I just need to stop interacting with you altogether?
Click to expand...

Now you're calling me a mule and I wear panties? You have hurt me deeply. I don't know if I'll ever recover.



By the way that 657 pumpkin could have a set of 336 gears in it. or 3.73s
 
Jadaharabi said:
By the way that 657 pumpkin could have a set of 336 gears in it. or 3.73s
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I don't know. I will have to look tomorrow.
Where is the "identification pad"? Hopefully I can see it on this 60 year old rear.
 
More info. It will be interesting to see what axles you have in that rearend.

Interchange Notes:
Any 8-3/4" center section may be interchanged for another as an entire assembly, with the exception of center sections manufactured prior to model year 1964 (See Part II, Section 1: "Thrust Block Variations").

Sure Grip
Sure Grip is the Chrysler name for a limited slip differential. It was optional on the 8-3/4" axles, 1958-1974. Two styles were used.

Dana Power-Lok
1958-1969 used the Dana Power-Lok (# 2881487). This unit utilized clutches for the differential locking action. The Power-Lok can be rebuilt using kit # 2070845 ( Mopar Performance [MP] # P4529484 ). In this assembly, axle driveshaft end thrust is taken by the thrust block assembly (replacement # 2881313). This Sure Grip appeared in the '741' and '742' assemblies. The axle bearings are: 25590 (Timken cone), and 25520 (Timken cup), (Chrysler numbers 1790523 and 696403). The Dana Power-Lok can be recognized by its bolt-together assembly, bolts around the side opposite the ring gear, and multiple openings exposing the cross shafts.

Borg Warner Spin Resistant
1969-1974 used the Borg Warner Spin Resistant (# 2881343). This unit utilized a spring-preloaded cone friction arrangement for the locking action. Axle end thrust is taken by the cross shaft. This Sure Grip appeared in '489' assemblies and 70 and later '741'/'742' assemblies. The differential axle bearings are: LM 104912 (Timken cone), and LM 104949 (Timken cup), (Chrysler numbers 2852729 and 2852728). The Borg Warner Spin Resistant unit can be recognized by its lack of bolts on the side opposite the ring gear (like the Dana), and two openings exposing the preload springs. Borg Warner sold this design to Auburn Gear who currently offers the replacement Sure Grip assemblies.

Non-Sure Grip differentials can be identified by the large openings in the differential exposing the differential (aka. spider) gears. There are no springs or clutches.
 
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