The 489 obsession

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Sounds like we're all on the same page here. The pinion is not the weakest link on any of the three cases. So I'm thinking the biggest problem with the 741 is the lack of available ratios these days.
 
The case nonsense is another of the Mopar red herrings.

Ring gear deflection is the biggest weakness. How much does the size/strength of pinion play into that... about ZERO.
 
Not to mention the 657, which is the precursor to the 741. Yep, the same 657 responsible for all those neutral drops from the push button automatic max wedge cars. And, say what you will, but the keywayed drums of the early cars were a pretty stout unit as well. Of course, most passenger cars were so crusty that you needed a drum puller to get them off. But if you can survive several hundred neutral drops, I’d say it’s a good unto.
 
I had an open rear 741 case years ago, the bolt either came out or broke and the slide pin fell out, it made horrible noise driving and I swapped in my cone clutch 489 with 3.91s. I called a reputable shop who I shall not name and the guy on the phone told me "the 741 is junk" I took his word for it and scrapped it. Wish I wouldnt have . I would have liked to at least still have the case and put new guts in it.
 
IIRC- 741 in everything utill mid year '68, then 742 for a brief stretch, and by '71/'72- 489 in everything.

3.55 741 extremely common in A series vans and trucks with 225 engine.

My research suggests 742 actually has the most difficult to find gear selection.
 
I ran a lot of 742's even with slicks and hemi's and never broke one and most of them were limited slip. But everytime I upgraded it was with dana's. Never broke one of them either. lol
 
Case in point right here! Cruising the classifieds this morning and saw this. Considering his other ads the seller obviously knows Mopar stuff, and he wants more for the 3.23 489 than he does for the 3.55 741.

Dodge plymouth 8 3/4 8.75 differentials | Tires & Rims | Truro | Kijiji

2023-01-21_124432.jpg
 
Darter6 said:
Found a 741 sure grip 3.91 in a 67 Dodge 100 van. :)
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That’s what I had in mine, a 741 open 3.55 that someone before replaced a 3.91 SG with (likely a 741 case as well) I put some 3.73 gears in it as that’s all I could find before passing it on. There is an article by one of the better known differential specialists comparing the three cases. The gist of the article was that there’s nothing wrong with the 741, it’s plenty strong obviously to a point just like the others.
 
Are they rebuildable to a Sure grip if you buy an open rear? I scrapped an open rear years back I would have kept it but an expert told me it was junk.
 
a70duster said:
Open 8 3/4 diffs going for at least $500? I bought a decent one last year for $50 (742). Geesh!
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That's $500 CAD, so about $50 USD
:rofl:
Just kidding, it's about $375. I've recently seen a 2.94 ratio for $150 CAD, so $500 might be over valued for a 3.55. I guess it depends on how badly someone wants it.
 
I was contemplating changing gears from 3:23 to 3:55, but not sure if there would be much "gain".
autopar3000 said:
That's $500 CAD, so about $50 USD
:rofl:
Just kidding, it's about $375. I've recently seen a 2.94 ratio for $150 CAD, so $500 might be over valued for a 3.55. I guess it depends on how badly someone wants it.
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The original 741 in my car went well over 100k miles and I beat the hell out of it. I took the cone sure grip out of the original 741 and put it in a 489 case 391 center and eventually the cones wore out. But the original 741 bearings, gears, housing I still have in storage and are in pristine perfect condition no signs of wear on any of the parts.
 
340sFastback said:
The original 741 in my car went well over 100k miles and I beat the hell out of it. I took the cone sure grip out of the original 741 and put it in a 489 case 391 center and eventually the cones wore out. But the original 741 bearings, gears, housing I still have in storage and are in pristine perfect condition no signs of wear on any of the parts.
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I have 400,000 miles on a 741 3:23 Clutch Sure grip. Original 67 Barracuda.
 
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489 case is like the 906 or 915 HP heads, it ain't special it's just the stuff that was on the most popular Mopars, I honestly prefer the 742 and the 452 heads though lol.
There's probably dozens of Mopar wives tales, thin bore late casting blocks, BS. I can't think of any others now because I need to go to sleep
 
I have a 742 open with 3.23 that I couldn't give away on craigslist last year. Sitting in a bucket taking up space.
 
a70duster said:
Open 8 3/4 diffs going for at least $500? I bought a decent one last year for $50 (742). Geesh!
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About 10-12 years ago I had 6 open 741 rears of various ratios for $25 each.
Not sold a one...
 
IMO in drag racing applications, regardless of the housing/casting numbers, the weakest point of an 8 3/4" are the ring & pinion teeth. #2 are the caps. #3 are OEM yokes & cheap u-joints. I believe numerically lower gears tend to be stronger because there are less teeth and they are bigger. 741 isn't as popular because of less ratios to choose from.

Over the years the only things I ever broke in an 8 3/4 was the ring & pinion teeth and I switched to billet steel 7620 yokes and solid Spicer u-joints after a particularly scary break when an old OEM yoke spread a bit and the u-joint hammered out. 3,540+ lbs, wheels up and 1.47 60' best while footbraking. I preferred the 742 case because there wasn't a crush sleeve or spacer to fiddle with.
 
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