8 3/4” rear end

[Moparman2]

Hi, I am putting a 3:91 gear in my 65 Coronet 500. I currently have a 741 case with a ( I think) 2:76. I bought a 742 case with a 3:91. Does anyone know if the 741 & 742 cases are the same length? Just wondering if I have to shorten the driveshaft. Thanks in advance.

 

[Red63440]

Yes they are although IMO the 742 is stronger due to the tapered pinion. Are the yokes the same size?

 

[Jerry Hall]

To answer the question, it's a bolt in swap, if the yoke size is the same.
The tapered pinion came with the 489 case.
The 742 is a 10 spline pinion. Both are much better than the 741 case. All are strong rear ends.

 

[Fran Blacker]

Picture of both yokes. The 741 probably a 7260 u-joint. The 742 could have 4 different maybe more. Three most likely yokes 7260, 1330 and 7290. 7260 will measure 3.25"appox outside cup to cup. 1330 and 7290 will measure 3.75"outside cup to cup. To tell the difference between 1330 and 7290 yokes is the 1330 has a small tab to hold cups in and cup diameter of 1.0625". 7290 has no tabs but inside of yoke is machined flat so clips on u-joint cups hold cups in place. Cup diameter is 1.125" on 7290. Combination u-joints are available for them. First 2 pictures 7260 pictures 3 and 4 are 7290. No picture of 1330.

 

[Fran Blacker]

Found a picture of the 1330 tab.

 

[Moparman2]

Yes they are although IMO the 742 is stronger due to the tapered pinion. Are the yokes the same size?

I don’t know, I haven’t taken it apart yet. So what you are saying is that I will have to take it apart to know for sure.

 

[Red63440]

No just saying you have a stronger set up now based on the case number.

 

[TN Mopar]

It's an easy swap
just be careful you dont lose the button that the ends of the axles butt up against otherwise you wont be able to set the axle end play
(note if your axles have green bearings you wont have this button)
lastly when its all together if the U-joint doesnt fit in the pinion yoke its much easier to change the U-joint then it is the yoke

 

[Fran Blacker]

As TN Mopar said you'll need to change the u-joint. Your driveshaft probably has a 7260 u-joint you'll need a combination u-joint. Post a picture of driveshaft u-joint with a tape measure visible. Also picture of yoke in 742 with tape measure.

 

[beanhead]

Hi, I am putting a 3:91 gear in my 65 Coronet 500. I currently have a 741 case with a ( I think) 2:76. I bought a 742 case with a 3:91. Does anyone know if the 741 & 742 cases are the same length? Just wondering if I have to shorten the driveshaft. Thanks in advance.

741 case with 7260 yoke is approx. 9.5" from mounting flange to the bottom of the U-joint cup
742 with 7290 yoke is approx. 10.25" from flange to cup
Both cases 8.25" OAL

So, depending on your power level and what you're trying to do you'll either need to:

---Replace or shorten the driveshaft. You then have to decide if you wanted to upgrade the shaft yoke at one or both ends to use the larger U-joint series...and replace the trans slip yoke to also use a bigger U-joint. This would add some cost but be the best option. If not and you elected to just have it shortened, then you'd use that combo U-joint at the rear mentioned above and the existing parts up front.
---Swap the small pinion yoke over to the 742 (assuming both are the same spline count) This is not the easiest job but you'd be able to re-install your existing driveline. You would then be using small-series yokes and joints throughout which really isn't the best idea if you're making even stock big-block power.

Around here, a freshly-made 3" steel shaft with 7290 yokes on both ends, balanced and painted, runs about $300. Trans slip yoke, another maybe $100 or you could get the fancy billet one for more $$.

 

[Tragistro]

Hi, I am putting a 3:91 gear in my 65 Coronet 500. I currently have a 741 case with a ( I think) 2:76. I bought a 742 case with a 3:91. Does anyone know if the 741 & 742 cases are the same length? Just wondering if I have to shorten the driveshaft. Thanks in advance.

I think they are not the same length even though you can adapt all of that I think.

 

[Cranky]

The 41 isn't exactly a weak kneed weakling.....I've never broke one anyways and just about everything I've owned got terrorized. What is weak is any street type ring and pinion because it has hardened gears for longevity and don't like shock loads so drag racing them with a 10 second car can shave teeth off of the ring gear especially if you have a stick in front of it. All of them have a weak point at the front of the pinion where the splines are just in front of the front bearing. If a pinion shaft is going to break, they usually break in that area.

I've yet to see a gear head broken off any pinion but did see a Ford 8" (baby 9) with the whole pinion broken out from the 3rd member/case. A buddy did that with a 289 and 3 speed no less! He thought he slung the drive shaft and upon walking back to get it, he saw something not quite right. The pinion at the u-joint was still bolted to the shaft and included both bearings and a good chunk of the front of the 3rd member. Never saw anything like it lol

 

[khryslerkid]

I did this very swap. 741 case to a 742 case. Plug and play. No U joint change or driveshaft alteration. (Where did you guys get your info?)

 

[dadsbee]

My 741 with 2:94's is out of a '67 Charger that probably already had a 80K on it. I put it in the Bee in 1978 and I tell yah I've done my damnedest to bust it in 43 years and 60+ thousand miles more, but I haven't managed yet.

 

[beanhead]

I did this very swap. 741 case to a 742 case. Plug and play. No U joint change or driveshaft alteration. (Where did you guys get your info?)

Tape measure and two units on the garage floor?
As measurements showed, the yokes were what made the difference in length.

 

[beanhead]

The 741 is fine. It's having the 7260 stuff that can cause a bad day if you're making any steam.
But like the two guys gambling in Stephen King's "Cats's Eye" said...."anyone can do anything they want!"

 

[1967coronet]

If you do not have a factory service manual or a Chilton's manual we can help you with the axle end play adjustment.
Pickup a housing gasket and axle seals.
Also there is a flange seal kit you will want to have on hand.
Also once you have the axles out and all nuts off the center chunk take one nut and thread it back onto one of the top studs a few turns.
That is just for while your draining the 90 weight, prop the bottom open and go have a cold one.

 

[Cranky]

That is just for while your draining the 90 weight, prop the bottom open and go have a cold one.

Or two. There's been times when I let them drain over night even.....

 

[Mark Barnes]

"Around here, a freshly-made 3" steel shaft with 7290 yokes on both ends, balanced and painted, runs about $300. Trans slip yoke, another maybe $100 or you could get the fancy billet one for more $$."
This^^.
Just had this exact thing done, and Beanhead hit the numbers dead nuts. Apparently the costs run pretty close, even between CA and MI.

 

[old guys rule]

Picture of both yokes. The 741 probably a 7260 u-joint. The 742 could have 4 different maybe more. Three most likely yokes 7260, 1330 and 7290. 7260 will measure 3.25"appox outside cup to cup. 1330 and 7290 will measure 3.75"outside cup to cup. To tell the difference between 1330 and 7290 yokes is the 1330 has a small tab to hold cups in and cup diameter of 1.0625". 7290 has no tabs but inside of yoke is machined flat so clips on u-joint cups hold cups in place. Cup diameter is 1.125" on 7290. Combination u-joints are available for them. First 2 pictures 7260 pictures 3 and 4 are 7290. No picture of 1330.

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Canby confusing at times. Will a 1350 fit a 741 case? What about