When ab 8 3/4 breaks................????????

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JBurch

JBurch

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Like the title says, when an 8 3/4 breaks, regardless of what housing it is, what is the failure point?
 
I have never broke one, my friend broke a set of Richmond gears. Put in a set of Motive gears and been fine.
 
JBurch said:
Like the title says, when an 8 3/4 breaks, regardless of what housing it is, what is the failure point?
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The driveline. :D

Just kidding, it's usually the gears themselves like Marco said.
 
image.jpeg
Yes the factory cast caps are a weak point.
 
stuff breaks when there is slop, when I recently rebuilt my 742, the main carrier bores were .002" larger than the carrier race OD. that allows the carrier to dance around-will cause the cap to break. I sanded down the cap face .002"-.003"
 
twisted two housing...broke 4 ring gears...and one cap...

cars will update to Dana 60s ...one down and two to go....second one in January..
 
So it's pretty much broken caps and/or shelled teeth off the ring gear..........
 
JBurch said:
So it's pretty much broken caps and/or shelled teeth off the ring gear..........
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back in the day-----5:13, and 5:38`s, got to blowing one every other week end. stripped the gears off. went to a dana 60 , problem over.
 
Broke axle, up graded, broke spider gears, installed upgraded ones, broke those, installed spool, broke ring and pinion, swapped in Dana 60 no more worries. This was on a potent 4 spd small block car with sticky street tires. A solid hook was the killer for me. The car hooked as well on the street as the track. Some things I broke at the track, some on the street. Oddly enough, never broke a cap.
 
famous bob said:
5:13, and 5:38`s, got to blowing one every other week end. stripped the gears off.
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Lol, every other weekend? One in a season could be devastating "back in the day" for some.
5:13 here that never got fixed .................
Broke513.jpg
 
I have broken/seen broken hundreds of rearends over 35+ years of doing this. most common is broken gears. they are expendables ie they do not last forever. second broken main caps/bolts. my car in pic ran 8 sec 1/4 3000/bs gearset would last between 150-200 passes. 8 3/4 with strange axles and spool. us gear 4:56 ratio. billet steel cap on lh side. usually lh breaks first and takes out rh side. you either need a billet cap or the new nodular cases that I/doctor diff/moser carry. make sure it has the heavier 9" style caps not the original looking 8 3/4 caps. had the best luck with us gear, and motive gears, but us gear is going to all gear sets being 2 cut as opposed to the odler 5 cut system, questions in my mind about durabilty??? stay away from chinese junk gears/beaings/spools. had a new spool from name mail order company the ran out by .012 acceptable is .001-.0015. lots more to it but limited space.paul
 
The original 489 case 3:23 cone sure grip in my '69 Super Bee 440 4 speed blew out the pinion bearing after the crush sleeve failed.
Lots of burnouts with L-60-15s and a good Mcleod clutch didn't help............
Installed a 3:54 Dana 60 out of a rolled '68 GTX, problem solved!
 
Dartnut said:
The original 489 case 3:23 cone sure grip in my '69 Super Bee 440 4 speed blew out the pinion bearing after the crush sleeve failed.
Lots of burnouts with L-60-15s and a good Mcleod clutch didn't help............
Installed a 3:54 Dana 60 out of a rolled '68 GTX, problem solved!
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Probably a front pinion bearing went first causing end play. then crunch. front bearing is the same as 12 bolt.ford 9" but not as heavy as the 742 cases.sometimes pinion nut backs of from driveline vibrations or reusing nut after seal change( seen lots of those in all rearends).paul
 
I'll add this....I think the crush sleeve in the 489 housing was a STUPID idea on Chrysler's part........it just keeps collapsing over time!
 
Yes you need to use a solid sleeve to replace the crush sleeve and shim it. Under hard acceleration the pinion gets pushed forward that's why the 742 case is stronger, the bearing is larger, and the carrier bearings are smaller so the cap thickness is thicker. In theory the crush sleeve should not have a effect on it unless you do burnouts in reverse, or hard downshifts.
 
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