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Been awhile - thought you guys would like to see a what we found when we took the cover off of the diff unit in my 65 (which went BOOM and then rocks in a blender and then locked up at the driveshaft)
(weak stomachs looks away!)
Thankfully, I live within an easy drive from Gary R - man what great guy, I learned a ton just listening to him for 30 minutes while he opened up the unit - and I've already seen the top notch, well-documented work he does. I'm in good hands
Ooooohhhh! was my gut reaction....did not expect it to be THAT grenaded! And, like T.K Simmons, I've seen a few things.
Blow up at slow speed. Notice the hole in the Posi case.....we could not save the unit or carrier . I replaced it with a 79 unit with Gary completely rebuilding it with new gears, spindles, bearings and 40 hrs of machining and tuning....it will out last me and the car....
so one must know what type of driving and how sticky of rear tires where you using to cause this. there doesn't look to have any savable parts left inside
so one must know what type of driving and how sticky of rear tires where you using to cause this. there doesn't look to have any savable parts left inside
...looks like the differential case broke, which can happen usually from a surface flaw at the "window", which then turns into a crack and propagates until it goes poof!
That's why the Chevrolet Power Manuals recommend polishing and shot peening the edge of the window.
When my SWC had no more than about 30K miles in '65 the drive pinion snapped in two, probably from the same mechanism. A flaw at the section change developed into a crack that propagated and went poof one day when I got on it hard. Section changes are always stress concentrations and need a generous fillet. The early ring and pinion was a weak design, but it was later improved beginning about '65. You can buy a complete loaded Positraction case and hopefully the ring and pinion is okay.
so one must know what type of driving and how sticky of rear tires where you using to cause this. there doesn't look to have any savable parts left inside
I was simply putting the car to its intended use 😁
doesn't everyone leave two dark stripes at every stop sign?
Upon dis-assembly of my 65 rear end, I found the crack that is common to the 65 and newer carriers. It's caused by a casting flaw. Luckily, my big block didn't grenade it. I put in a new posi unit and everything else but kept the original ring and pinion. They're a ticking time bomb. The more HP/TQ you have, the shorter the fuse on that bomb.
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What a mess. I still have the original rear end in my 65. It's the only part of my car that hasn't been apart. Over 300,000 miles. I change the fluid every 3 years. No hole shots, but spirited driving once I'm under way.
Duke, can you show a pic of the "window" you refer to? Dennis
I don't have a digital photo, but look at your service literature, and I think there's a photo in the Chevrolet Power Manuals. You can kind of see it in Jack's photo, but most of the surrounding material is gone. The window is there in order to load the Positraction clutch packs/differential gears into the case. It's rectangular with generous corner radii. Some case designs are two piece that bolt together. I'm not sure if either one is inherently superior. I think it comes down to the detail design.
I recall when I overhauled my SWC's axle in the mid-sixties I disassembled the case, had it Magnaflux inspected, and there was a crack in the window edge, so I bought a new loaded case from GM, which wasn't much more expensive than just buying the Positraction clutch packs, which needed replacement due to wear. Once I got the axle assembled the differential gear end play was in spec and the side yoke play was 5 and 7 thou. I thought about removing/disassembling the case to swap out a Positraction shim (between the last clutch disk and case) to get the 7 thou end play back to 5 or less as recommended by the Chevrolet Power Manual, but decided to leave well enough alone.
Upon dis-assembly of my 65 rear end, I found the crack that is common to the 65 and newer carriers. It's caused by a casting flaw. Luckily, my big block didn't grenade it. I put in a new posi unit and everything else but kept the original ring and pinion. They're a ticking time bomb. The more HP/TQ you have, the shorter the fuse on that bomb.
You mean the case, not the carrier. The differential case is what the ring gear bolts to and contains the Positraction clutches and differential gears. The differential carrier is what the case is mounted to, and when you bolt the cover to the carrier you have a complete axle. A lot of guys confuse these terms.
It's interesting that you can actually see the crack with magnification. Some cracks can only be seem via Magnaflux inspection.
When overhauling an axle the Positraction clutches are usually worn, which increases differential gear backlash an side yoke end play. Given that the case is subject to fatigue failure the best idea is to buy a new loaded case and, of course, new bearings/seals, so the only original part left in the axle may be the ring and pinion.
Your photo also shows how rough the window edge is. That's why the Chevrolet Power Manuals recommend (assuming it passes Mag inspection) grinding the edge smooth and having it shotpeened, but given all the work involved, for a road car, it's less expensive to just replace and then limit the number of times you sidestep the clutch at 5000 revs.
I was simply putting the car to its intended use ��
doesn't everyone leave two dark stripes at every stop sign?
I know I do!!!! That's normal right?
LOL
I have to admit.. I was standing on both the gas and the brake...at the beginning.. then I just let her eat.. Needless to say those black stripes were there for a WHILE..
I have to admit.. I was standing on both the gas and the brake...at the beginning.. then I just let her eat.. Needless to say those black stripes were there for a WHILE..
By the way, for those who did not recognize my reference to "Gary R" (in my first post) as the one who is doing the work on this diff, that's CF member GTR1999 - talk about an expert who has a true passion for his craft and "doing it right" !
Gary is the real deal and he most certainly does the polishing / clean-up work Duke described in his informative posts above. I'll post some pics of Gary's work on my diff unit once he embarks on that job.
09-01-2018, 04:10 PM
Well That Explains It (65 Diff Grenaded)
That will NOT buff out!
Dennis
perfect
