Rear Differential Cover Cracks

Javier · 06-05-2020, 01:03 AM

Hello All,
Like you I'm turning my 2009 old diff. into a backup LSD. I have a class 3 NDT classification, for those that do not know what (NDT) stands for id non-destructive testing which I perform daily at my job. I decide to clean all my diff. parts and inspect them before I put a $1200.00 LSD in it. I found that the old diff. that I subjected to penetration inspection with black light was cracked in at least a dozen places. Also the old hardware is not reusable due to the lock washer that comes installed with the bolts is worn to the point that it does lock anything cause the spring tension on the washer is gone. Also that lock washer also created a groove in the soft aluminum and the stress not having any place to go creates cracks. My differential as yours probably the rear mount factory bushing blew out how long ago I do not know. As a suggestion and you do what you want, I suggest placing a thin steel washer first then install the new hardware. This will prevent damage to the new rear cove. I have attached pictures of my rear cover showing all the cracks and pictures of the worn lock washer on the factory bolt. Replacing the rear cover was my only solution and buying new hardware, believe me these are not forging marks. Will it crack apart eventually maybe, I do not have a crystal ball but I rather be safe than sorry.

Rusty · 06-05-2020, 02:13 AM

Polish out the cracks and retest. Maybe surface imperfections. The raise metal around the bolt holes are from the lock washers biting in. See that all the time in soft metal. Some of the things you are seeing is found in castings. It's a sand casted piece. The mold wasn't up to temp when they poured the aluminum. So you are seeing incomplete filling of the mold. It shows up as voids and folds in the webbing on the inside. It does look like cracking on the inside of the cover around the stud hole. That's where most of the covers break at. Interested in the area around the plug hole. Looks like crack, but stops before the machined area around the threads.

Degrees in welding engineering and mechanical engineering. Have done NDT testing myself.

06-05-2020, 02:13 AM	#2 (permalink)
Rusty Ronin Samurai - Assassin Join Date: Dec 2011 Location: Fayettenam,Pennsyltucky Age: 68 Posts: 34,865 Drives: 2011 Nismo GM 6M Rep Power: 2684436	Polish out the cracks and retest. Maybe surface imperfections. The raise metal around the bolt holes are from the lock washers biting in. See that all the time in soft metal. Some of the things you are seeing is found in castings. It's a sand casted piece. The mold wasn't up to temp when they poured the aluminum. So you are seeing incomplete filling of the mold. It shows up as voids and folds in the webbing on the inside. It does look like cracking on the inside of the cover around the stud hole. That's where most of the covers break at. Interested in the area around the plug hole. Looks like crack, but stops before the machined area around the threads. Degrees in welding engineering and mechanical engineering. Have done NDT testing myself. __________________ 浪人 - 殺し屋 "The Difficult Anytime, The Impossible By Appointment Only" http://www.the370z.com/members-370z-...o-journal.html

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