What is the difference in a 741 and a 742 8 3/4 case?

[66383]

difference??

 

[1967coronet440]

Pinion size

 

[gkent]

Biggest (and probably the only) difference is the size of the pinion shaft. The 741 is the smallest of the three and the 742 is the largest. The 489 sits in the middle.

In the tech archives on Moparts there's a comparison photo of all the popular rear ends including the Dana, GM 12 bolt and the 9" Ford.

 

[1967coronet440]

Biggest (and probably the only) difference is the size of the pinion shaft. The 741 is the smallest of the three and the 742 is the largest. The 489 sits in the middle.

In the tech archives on Moparts there's a comparison photo of all the popular rear ends including the Dana, GM 12 bolt and the 9" Ford.

489 pinion is tapered and considered the strongest, correct?

 

[YellowDodge67]

Biggest (and probably the only) difference is the size of the pinion shaft. The 741 is the smallest of the three and the 742 is the largest. The 489 sits in the middle.

In the tech archives on Moparts there's a comparison photo of all the popular rear ends including the Dana, GM 12 bolt and the 9" Ford.

I thought the 489 was the largest at 1-7/8IN, 742 at 1-3/4 and 741 being the smallest at 1-3/8?

 

[khryslerkid]

http://www.mymopar.com/Mopar8_75RearEndGuide.htm

 

[Cranky]

And have you ever seen a 741 with a broken pinion shaft? Very rare.....and the splines where the yoke fits are all the same size with only the difference being fine and course.

 

[PurpleBeeper]

And have you ever seen a 741 with a broken pinion shaft? Very rare.....and the splines where the yoke fits are all the same size with only the difference being fine and course.

Hey Cranky, can you elaborate on the fine/coarse splines on the pinion/yoke? I just learned that there was 2 different splines about a month ago. Is one considered stronger? (coarse?) What cars got fine? Which ones got coarse? Any other related information we should know?

THANK YOU!

 

[big_shmoop]

Cass has some good info here: Doctor Diff

TLDR...it's not as big a difference as many make it out to be.

 

[Cranky]

Hey Cranky, can you elaborate on the fine/coarse splines on the pinion/yoke? I just learned that there was 2 different splines about a month ago. Is one considered stronger? (coarse?) What cars got fine? Which ones got coarse? Any other related information we should know?

THANK YOU!

Read below! A buddy and I ran a 4 speed roadrunner in the Super Street wars (10.90 index) in the early 80's and before we even got the car into the SS ranks, we started shaving ring gear teeth with the 8 3/4. Pinion deflection or....??? It didn't matter what rear we used as all of them did it. We used the 89 figuring the 42 wasn't strong enough but it failed just as fast. Lousy setup? Who knows as we weren't doing the setups at that time but we swapped to a Dana and all that went away. It was about that time when we started doing our own setups.....

Cass has some good info here: Doctor Diff

TLDR...it's not as big a difference as many make it out to be.

Cool beans! I ran across a similar site stating the differences but couldn't find it. Didn't even think about looking on Cass's site. Thanks!

 

[moes]

many 383 cars came with the 741 behind them, I'm sure the factory would have not used them if they thought they would not hold up the the torque of the 383 motor.

 

[moparmarks]

I thought the 489 was the largest at 1-7/8IN, 742 at 1-3/4 and 741 being the smallest at 1-3/8?

741 is 1-5/8" correct on the others.
489 crush sleve
741-2 shimms
489 cone SG
741-2 clutch SG

 

[moparmarks]

many 383 cars came with the 741 behind them, I'm sure the factory would have not used them if they thought they would not hold up the the torque of the 383 motor.

My 65 Satellite 383HP 4-spd had a 741 SG

 

[gkent]

many 383 cars came with the 741 behind them, I'm sure the factory would have not used them if they thought they would not hold up the the torque of the 383 motor.

Skinny street tires that would spin like crazy were no threat but if you stepped up the gear ratio and added slicks it was a whole different story.

 

[moes]

I ran 275/60/R15 with my 1970 383, 741 SG - 3.55 gears and a 4 speed for 10 years and I pounded the gears, I never had a problem and my 383 was not stock. That car would leave black stripes all day long. I'm sure slicks would be different situation.

 

[Bee1971]

So are parts available to rebuild a 741 Case 3:91 Suregrip that I pulled out of a van many moons ago ?

Resides in my 71 Bee now for the last 25 years

Factory 489 Case 3:23 Suregrip is long gone

 

[moparmarks]

Dr Diff probably has what you need for your 741.

 

[JimKueneman]

The 741 has the least choices in gear ratios available though. Like 2.

 

[threewood]

So are parts available to rebuild a 741 Case 3:91 Suregrip that I pulled out of a van many moons ago ?

Resides in my 71 Bee now for the last 25 years

Factory 489 Case 3:23 Suregrip is long gone

They are but make sure to do the research and call to ask. Cass should have the parts but I remember when I had my 741 built up that the pinion shims shipped with the rebuild kit were the wrong i.d. twice before I had my local shop find some. Also as has been mentioned gear ratio selection is lacking.

 

[YellowDodge67]

741 is 1-5/8" correct on the others.
489 crush sleve
741-2 shimms
489 cone SG
741-2 clutch SG

Everywhere I've read has the 741 @ 1.375in (1-3/8)