Let hear the opinons and theories on why 8 3/4 rears fail in drag applications. I'm thinking housing twist and flex is the biggest killer, then main cap failures.

I have seen so few fail that it is hard to tell, and the ones I have seen go took out teeth on the ring and pinion.

Like Don1 says, setup correctly they take a beating. How fast ya gonna go? I know they are good down into 10 second zone. And in the past chevy racers took the 12 bolt out-put the 8 3/4 in. Not sure how long they last in say a 4500 pound racecar with 500 cubes, 700 hp and 538 gears, slicks, 4500 stall and a trans brake launches???

Crush sleeves are the biggest culprit. When the end play gets loose the teeth of the ring and pinion dont mesh up properly and its just a matter of time. Solid spacer and good caps make them last a good long time.

i say age is the biggest killer 90% of the pumkins on the road/track are over 30 years old
cone/clutches just dont age well

If you have a backbrace and pro gears (only available in a 4.86 for the 742) you can make them live. We got 365 transbrake passes on our last set of gears. We have since added the MW caps, but we never had a failure with the stock caps. Our best 60' is 1.2576.

I blew 2 of them out until I changed to a Dana 60. I was using a power lock sure grip in a 742 case. Every time it would take out the cross shafts (even after market ones without the holes for the buttons). I came to the conclusion that big torque and heavy cars don't mix.

I think you can make it live if you use a spool and billet caps, or better yet, the aluminum pumpkin, but for that money you can build a bullet proof dana.

I already have a spool and Moser axles. I've been thinking of adding the back brace and the billet caps. If i was building this rear all at once, I'd just go with a Dana for sure.

Greg, I've not had personal experience w/an 8 3/4 failure. However most everyone I've talked too said the loss was due to cap failure.

Personally, I have broken a wheel barrow full of r&p's, never once did I have a cap failure, I had a backbraced housing in the car, used a spool, and good axles, maintenance on it was replace the r&p, every 200 runs, and that for me was getting on the edge, after I built my newest engine 3 years ago, I went thru 3 r&p's in one season, but this was in a heavy car 3400lbs, but off the foot brake, I finally got tired of working on the rearend, and trans, all the time, went the dana route, and have been very pleased, 2 seasons, and 285 runs, and it still looks like new, I am not condeming the 8 3/4, they are very good rears, I ran them for a bunch of years, just got to the point, it was not feasible to use it anymore.

Dave

Greg,
Some good points have been brought up, like Foggy's example of just plain asking to much of it. I've never experienced cap failure, always teeth, but I did some things this last time around that so far seem to be working. personally, I think the #1 reason for failure in a car that is not OVER powered for an 8 3/4 is incorrect set up, by that I mean, as someone pointed out, with one exception, there are no "good" gears available for them, so we get steel gears and set them up to the manufacturer's specs...WHICH WONT WORK for very long. Those specs are for a stock, daily driver, not a race car. Every set I've ruined were set up stock, and had tooth failure because under load you can see that the wear pattern ran right off the edge of the teeth, eventually breaking them off.
Heres what I did, First: had a new set of gears shot peened for added strength (forgiveness), Second, deberred the interior of the case where the bearings & caps go to get correct tork, Third, corrected the bore alignment...it was way off, Fourth, Installed main stud in place of bolts and shot peened the caps, Fifth, set up the gears favoring the toe about 5 thou more than they called for. Now its got a good pattern on it even with the stroker motor and has about 150 runs with all its teeth where they belong. You can check the numbers in my sig. Has all this been the key? Dont know, but its finally living.

seen one pop and it was due to a main cap failure. loud pop it was too.

What Gary said, makes good mechanical sense to me. It would also explain Strokerposts symptoms of his rear pinion gear pattern running off the side of the ring gear before breaking some gear teeth. It seems most are breaking the gears and not the caps. This post is important to me because I still run the 8.25 but have a 8.75 489 on standby, next up. mike

I still have the 8&3/4 under the valiant, with who know's how many passas, this year I'm going to start beating on it hard with the trans break. I have beefed up the caps, and installed some moly bolts in them, and still have the crush sleave, the housing has a backbrace and the ladder bar mounts are tied in to the shockmounts and backbrace, the housing is the problem for me, I have bent the housing more then anything else.
I have the 489 case with a spool and moser axels, and 4.30 street gears.

i've been running a 8 3/4 rear in my 70 dart 440 ,600 hp this year and no trouble yet. i changed from 4.89, to richmond 4.30 r&p. i put the rear together myself. car runs 11.0- 11.30 at 122 mph. foot brake only car and is lite weight but still around 3000- 3300 lbs. i don't abuse the rear and leave the line at 2500 and shift at 6400 rpm. the car has 10 1/2 in mt,s and they break loose alittle easing the strain on the rear somewhat. bashing off the line at 5500 on a trans- break, with 13 in or so tires hooked to the max, i don't think it would hold up. i don't race every weekend either. i have a complete dana 60 ready to put in, if i want, but i don't need it now. in fact it is for sale on ,diff- on this forum. heli301@comcast.net..........RON.

now we are getting somewhere! Great info guys.

Mark Williams cap on driver's side. 489 housing. Solid pinion spacer. 4.56 ring and pinion, less than 200 miles, around 100 passes. Like new except for one tooth missing from ring gear...



I had to put one of my 4.10's back in.

I was surprised. 400HP maybe, auto, no-transbrake, 3300-3400 pounds.

Didn't the factory engineers specify Dana 60 rear ends for cars approaching 500 ft/lbs torque , such as the six barrel cars ? . That would be the breaking point for the 8 3/4 setups, I would imagine.

No breakage here yet (489 case 8 3/4, 4.10) over 50 passes - another "advantage" of the smallblock - something to cheer about in one respect, I guess.

What's the opinion on the MW caps? One, both ?