So we grenaded the 8.75 in our belvedere and replaced it with the aftermarket case from doctor diff.

If you are interested in more details check out the video on YouTube - 8.75 Video

You really can't beat doctor diff. Great stuff.

I would have stolen an old school trick used on Connecting rods, and polished out those casting striations on the upgraded 489 caps.
With the OP's initial failure of ring broken teeth, it would matter little in the final outcome once a broken tooth gets wedged between the R&P however since something has to give/break.
Breaking on a by run?

Spool , crush sleeve, cast caps and stock axles , that thing was definitely on borrowed time.

And a gear dated 1969.

We were hoping to get through the year and upgrade over the winter.

Photos are of three different cases ... who makes what ???

The new case worked pretty good in its debut.

Windy Hollow Garage Mopar Nats

Monte preached to us long ago about the 8.75 . I remember when Mopar closed these out for CHEAP!

Closed what out cheap, R&P? which failure of caused the carnage pictured?

Looks to me like the case cracked and probably flexed, which caused the issue with the ring & pinion that finished off the case. If you look at the broken edge, there are several places where the break appears to be not as fresh (more dull in brightness) as other places. Those places that are not as bright have been cracked or broken longer then the bright places.

Not the way I see it, if case cracked first under very high load conditions, I suspect the R&P would break contact extremely fast with a few broken teeth as that occurred. If the R&P became locked solid with a broken tooth leading to more broken teeth and quickly escalating. I can visualize force building enough to destroy the pictured or any case. I don't fault the case here based on what I see any more than I would blame an Alum KB block destroyed/windowed by a cheap over revved failed con rod.

edit, under very loads causing any initial crack in the case, that would be the end of any case flexing and failure would be immediate.

Mopar performance in the mid 90’s discontinued the aluminum center section and liquidated them. Think we got them at work for something like $200 at cost. I never used them and sold them off.

Pinion relationship to the ring gear and no pinion support….. lifting of the left cap has been a thing with the 8.75 forever. I think with the aluminum center it was the cap through design saying “I got this”, and physics saying “hold my beer”.

The thru bolt upgrade in this case evidently solved that cap lifting issue shortcoming mentioned and moved the failure to next weakest point when overloaded or suffering a jammed R&P tooth failure IMO.

Regarding these Alum cases, Summit was selling them for approx $650 in 2004, and $1087 in 2008. In past few years I have seen them on ebay new for $2800.

The aluminum one looks like the discontinued Mopar performance (center)
Gold Iridate (Bottom) is something I've never seen on a diff, like it was a display model or something for pics?
(top) diff looks super beefy and looks like it's pretty sturdy, which is different from what the OP has in his video.
Would love to know which case that top one was from.

Mark Williams, long out of production, a 742 Style

Thank you. Now I just have to hope one shows up or figure out if Doc’s is just as strong. If the new diff is good to 600hp/lbs of torque, I would buy a couple over buying a new Dana 60 rearend.

I'll add you to my will.

Why?!

Get a full floater Dana 60 for cheap out of a pickup, cut the ends off your 8 3/4 (or use aftermarket), use your existing backing plates/brakes and get axles from Dr. Diff.

Cheaper and stronger.

I have just under $1k in my Dana after dealing with trying to get an 8 3/4 to live behind a 600 hp stroker. We're over 850 HP now with a heavy car and so far no issues with the Dana.

I am running 10.40’s at almost 3400 pounds. I bought a nodular case 8.75 from Moser, after a 50 year old case failed..Billet adjusters, all grade 8 hardware, very nice piece. But I footbrake. Wouldn’t use a brake. This is a 4 inch stroke deal that makes plenty of torque

I built an 8 3/4 with one of those Yukon cases for a 10 second foot brake Duster and it held up very well. Casting was a little rough but it was thick where it needed to be.

If I had a regular bracket car it would have an aftermarket 9" under it. Using NO factory Ford parts.

Gus