What is next best 8 3/4 case under the 489

[moparjohnny]

Thanks to everyone.

 

[69RRberkeley]

ive been told the 742 is nearly a strong, while the 741 not so much

 

[1970GTX]

742

 

[Cranky]

I'll take a 42 over the 89 unless I'm building the 89 with a solid spacer....and how many broken 41's have you seen? I've seen more broken 89's than the other two combined.

 

[PettyBlue72]

IMO the 742 case is stronger than the 489 because the pinion does not taper down at the yoke end like the 489 does which I think makes the 742 stronger than the 489. The power Lok clutch type Suregrip unit in the 742 is far superior to the cone type Auburn unit in the 489 and the clutch type is easily rebuildable.

Joe

 

[Hemi Rebel]

Pettyblue72 is right. And you see more broken 89's because that's what most rears are. So odds are if you come across a broken one that's what it is. Show of hands, how many here have broken a rear? I never have.

 

[BIGSHCLUNK]

Run a 89 in my HEMI car... never broke yet. But I have heard lots of good thing about 42's..........

 

[Cranky]

A buddy and I were racing Super Street in the very early 80's with a 3000 lb road runner, big block and 4 speed. We were tearing them up quite often. I guess they didn't like 6k launches but we were mainly running gears that were built by someone else. What usually failed was the ring gear. Never ever broke the pinion but we shaved the teeth off lots of rings. This started happening went the car was still running low 11 second brackets but when we made the car faster, a Dana 60 went in and all that stopped. We also learned how to set up our own rear ends. That Dana was my first gear change experience and since there were not many around that knew how to set up gears, and there was no internet so we had to learn it on our own. And as far as most gears being 89's......I've have plenty of all of them. Right now I only have one 89 case sitting here vs several 41's and a few 42's.

 

[Budnicks]

allot more readily available gear selection for the 489 gear case/carrier VS either of the 741 or 742, but if you search well enough, you can get almost any gear ratios you want, my personal preference is the stronger 68 & prior 742 case, or the new MP Aluminum 742 version/copy of it... like mentioned above it has a stronger/larger non tappered pinion section, that's why they use it in their Aluminum versions also, there were way more 489's made than 742's they are easier to find thou.... Also IMHO if your not making more than 500hp to the rear axle, or running a 4/5/6 speed manual trans & dumping the clutch with sticky *** tires or slicks, or 5000-6000rpm trans-brake launches @ the race track/drag-strip, it doesn't really matter which one you choose really...

 

[RustyRatRod]

They are all almost equal. Arguin about which one is strongest is pointless.

 

[lewtot184]

They are all almost equal. Arguin about which one is strongest is pointless.

probably a lot of truth in this statement. the average guy probably won't know the difference between the '42 and '89. but, if i was looking to squeeze the most out an 8 3/4 i'd do the '89. an '89 with a solid spacer, the larger inner pinion bearing that controls the pinion movement better, and a tapered shaft without any steps would by my choice. i'm not a fan of hot rodding a '41 in a big block, especially with a tall gear. a tall gear '41 has a large pinion head, small inner bearing. using a lower gear in a '41 in a small block a-body automatic may work well. just my opinons.

 

[benno440]

dont know why all over the internet it says the 489 is strongest because it has the biggest pinion.

wish i knew this before i sold my 741 non sure grip and bought a 489 with eaton true trac in it .

 

[RustyRatRod]

Generally the 489 IS the strongest because of the pinion diameter, but the differences between all three are very minimal. Now, as lew mentioned, when you install a crush sleeve eliminator in a 489, then it becomes the strongest by a little more of a margin, but it's still not a huge amount. When people start this arguement, I always ask this question: How many broken 741 pinions have you seen? I've never seen any. I have seen a few broken 489 pinions and I think it was due to crush sleeve failure. Most people who answer that question honestly will either say they've seen very few if any broken 741 pinions. Look at it this way. The 741 pinion has a bigger stem than any Ford 9 inch.

 

[daredevil]

I broke teeth off the ring gearin my 742 in my bracket car but I wasnt running the softer race gears. I had street gears in it and I believe the pinion flexed and then it broke the ring gear teeth

 

[lewtot184]

the size of the inner timken pinion bearing will help control the thrust that wants to spit the pinion out the front of the case and the '489 has an edge. crush sleeves are a weak link because they are made to collapse. anyhow, after you get good control of the pinion then the caps break, and so on and so on. i really think people expect too much out of an 8 3/4. back in the day when we really didn't make that much power and there wasn't good tires we got by. nowadays with good heads, good intakes, strokers i wouldn't consider an 8 3/4 for serious work. and this is coming from a guy who loves the 8 3/4!

 

[RustyRatRod]

Right. A good rule of thumb is, if you think you're gonna stress an 8 3/4, look for a Dana.

 

[benno440]

answer me this is a mopar 8 3/4 stronger than a foprd 9 inch, i continually have this arguement with my mate. i say only reason people use them is they are cheap and plentiful. but the 8 3/4 is stronger

 

[RustyRatRod]

I don't think it is. The phord has front pinion support, where the 8 3/4 does not.

 

[lewtot184]

two things about the ford that i think is an advantage, the pinion support, and the coarser teeth (larger teeth with a bigger root). the disadvantage of the ford is that the pinion is too low and isn't very efficient (takes more power to drive it). also i don't know of any good clutch type p-tracks. seems like it's either a detroit locker or spool. the real advantage the ford has is parts and the universal acceptance as "the rear end". if it where me and i was busting 8 3/4's regularly, i'd head directly to the dana 60.

 

[1970GTX]

Here is an interesting article on the 8 3/4
http://www.carcraft.com/techarticles/ccrp_1210_sure_grip_chrysler_differential_swap/