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79 - Rear end differential cover cracked
I was leaking a lot of fluid and it seemed to have been getting worse. I thought it was a gasket and was trying to postpone this job. I finally put it up in the lift, removed the spare tire carrier and inspected - differential cover is cracked. Son of uh......
The whole rear end needs a serious refresh so I may take this opportunity and just start working on this big job. Would welcome any words of wisdom from those who tackled this job. https://cimg6.ibsrv.net/gimg/www.cor...31891ce2df.jpg |
It is pretty easy to replace the cover. All these years and I never broke my rear end cover. This last rear end replacement I went for a HD rear end cover. They aren't that much more than the standard. It uses much bigger diameter spring bolts and a HD spring plate. You should also look into the aluminum disks that hold the diff x-member in place.
This is the stock cover as I was starting to remove the diff. https://s26.postimg.cc/70ld6gixl/diff_E.jpg |
Muskegon Brake sells the H.D. cover for just over $100. Then you will need the gasket, two bottles of GM Lube and one small bottle of GM Posi modifier.
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The gasket isn't necessary. Just black permatex. It makes it easier to clean up the next time you have it apart.
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https://cimg2.ibsrv.net/gimg/www.cor...ba9542b274.jpg
Exhaust is out - next is the rear spring set - it is old, soaked with differential fluid and the laminates between the steel plates is half gone. May be a new spring set.... |
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What a coincidence. I just replaced my cracked differential cover today. Took me about 4 hours. As far as advice, disconnecting the strut rods from the center bracket makes it a ton easier getting the half shafts off and reinstalled on the diff since it gives the arms lateral movement.
https://cimg1.ibsrv.net/gimg/www.cor...92fac1cbac.jpg |
Originally Posted by Cool95vette
(Post 1597774677)
What a coincidence. I just replaced my cracked differential cover today. Took me about 4 hours. As far as advice, disconnecting the strut rods from the center bracket makes it a ton easier getting the half shafts off and reinstalled on the diff since it gives the arms lateral movement.
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I was really lucky with the differential crossmember removal this morning - two bolts and a gentle tug with my 2' pry bar and it came off.
The pumpkin is on the engine stand - time to open it up and see what kinds of surprises await me!!! https://cimg0.ibsrv.net/gimg/www.cor...c1a7430b4c.jpg https://cimg7.ibsrv.net/gimg/www.cor...6c2eab9cf8.jpg https://cimg6.ibsrv.net/gimg/www.cor...7ced547018.jpg https://cimg9.ibsrv.net/gimg/www.cor...a48861f3d4.jpg |
Differential is toast
The differential is toast just like I suspected. What would cause such a catastrophic failure?????
I am open to suggestions as to my options - I have never rebuilt a differential but I do have the knack and tools for something like that. I did rebuild an engine and transfer case. Where is the best place to source parts? If I decide to just go with a rebuilt unit, what are your recommendations for vendors? Thank you! https://cimg4.ibsrv.net/gimg/www.cor...460604c78c.jpg https://cimg3.ibsrv.net/gimg/www.cor...75535c72c9.jpg https://cimg1.ibsrv.net/gimg/www.cor...d00a0e9a1e.jpg |
My differential was rebuilt last year, all my parts came from Tom's Differentials. He also has some videos on Youtube. This is his web site address https://www.tomsdifferentials.com
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Tom passed away last January. His wife JoAnn is still running the business and will have the parts you need. The ring gear bolts backed out, locked up and sheared. Common enough issue with the 77-79's. If the posi case isn't too bad you might be able to reuse it. Use Loctite #271 on the new bolts if you rebuild it. Looks like you have a nice shop there so if you have the time and tools you might be able to rebuild it there. All depends on what your plans are for the car, street use or hard use.
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Originally Posted by GTR1999
(Post 1597780154)
Tom passed away last January. His wife JoAnn is still running the business and will have the parts you need. The ring gear bolts backed out, locked up and sheared. Common enough issue with the 77-79's. If the posi case isn't too bad you might be able to reuse it. Use Loctite #271 on the new bolts if you rebuild it. Looks like you have a nice shop there so if you have the time and tools you might be able to rebuild it there. All depends on what your plans are for the car, street use or hard use.
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While the problem you have is not uncommon, breaking the cover is. Is there an impact spot on the inside of the cover from a bolt shooting into it? Covers break at the ears from improper spring loading or a heavy hit.
For your application you can build a strong diff at home without a lot of machine work, if you have access to a lathe, mill, or surface grinder even better. If you have questions on rebuilding the diff you can contact me directly and I will go over it with you. |
Originally Posted by GTR1999
(Post 1597781965)
While the problem you have is not uncommon, breaking the cover is. Is there an impact spot on the inside of the cover from a bolt shooting into it? Covers break at the ears from improper spring loading or a heavy hit.
For your application you can build a strong diff at home without a lot of machine work, if you have access to a lathe, mill, or surface grinder even better. If you have questions on rebuilding the diff you can contact me directly and I will go over it with you. There is a scrape in the insight of the cover corresponding to the crack plus an internal section of the cover broke off (ear?). I shall post some pictures shortly.. |
Is the case salvageable?
Posting pictures below of the empty diff case. I had it cleaned in an aqueous hot bath (industrial parts washer). There are definitely some issues but with the judicial use of a grinding store to get rid of any sharp edges I may be able to reuse. The cover is toast and will post pictures next
https://cimg0.ibsrv.net/gimg/www.cor...e4f420a54b.jpg https://cimg2.ibsrv.net/gimg/www.cor...de33505eae.jpg https://cimg3.ibsrv.net/gimg/www.cor...07dbf23aa0.jpg |
Differential cover
A couple of pictures showing the damage on the cover
https://cimg2.ibsrv.net/gimg/www.cor...7aff27e891.jpg https://cimg3.ibsrv.net/gimg/www.cor...e0efd19d1d.jpg https://cimg4.ibsrv.net/gimg/www.cor...142c984e2a.jpg |
I could not find any issues with the ring gear itself (ignore the bolt head stuck between the carrier and the ring :ack:). The pinion gear had a couple of issues shown with red arrows. The carrier itself had a couple of "bruises" but nothing serious (or so I think)
I will be disassembling the carrier next to take a look at the clutch pack and planetary gears. https://cimg3.ibsrv.net/gimg/www.cor...18da044378.jpg One bolt got loose and caused 6 out of the remaining bolt heads to be sheared off. https://cimg5.ibsrv.net/gimg/www.cor...5bd1e76a30.jpg Could not find anything wrong. Ran my bear fingers on the edges of the teeth and detected no problems https://cimg9.ibsrv.net/gimg/www.cor...4e71e10a78.jpg Chipped teeth on the pinion gear https://cimg0.ibsrv.net/gimg/www.cor...36a73d8ffb.jpg Chipped tooth on the pinion gear https://cimg1.ibsrv.net/gimg/www.cor...aac0f66fc5.jpg Surface "bruises". Note that the bearing on top was destroyed https://cimg2.ibsrv.net/gimg/www.cor...57193d9495.jpg https://cimg4.ibsrv.net/gimg/www.cor...cc96f05368.jpg |
Your pictures didn't show on my screen.
I can see them now, that took a good hit inside. The left hand damage is common and usually can be dressed with a die grinder and some time. Look for cracking at the pad holes. If you find any replace the housing, in fact just get a good core and rebuild it. The RH pad damage is not common but really must have locked up and broke loose like a cannon shot. Check the posi case close for cracks, check the ring gear holes for being egg shaped- if found again replace the part. The clutches used in these were not good and should not be reused, the spiders were 10-17's and were good. Mark the position of the pinion to side gears so they go back in the same way in this case or another. If there are no chips in them they are probably good- but check them. The axles, if original, are soft faced which is no good. If they are not worn but just soft they can be hardened and reused but that rarely is the case with 73-79 axles. Do not reuse the ring & pinion. They took an impact and if there is a fine crack in the tooth base you don't want them coming apart again. Market value on a complete used 73 -79 diff core, out of the car is $300- $400 that's it, sorry those asking more for a core either don't know or care. When you go looking for correct dated and stamped cores the price skyrockets, only because there is a buyer looking. Rarely does this apply to 73-79's due to lower resale value of the car. Rebuilders pay less then that. That might be your best option given what I see. If you want to use yours for training go for it, back in the day we would build what we had or just bolt in a core and go. |
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