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So I'm doing a little digging underneath my '77 and find an alarming crack. There's a decent sized split along the arms of the spring mount in the rear. I don't want to just jump on it with a welding torch since it's tight under the gas tank, but also don't want to drive on something that could dislocate my spring. Anybody know the best way to repair this?
Thanks! The crack on the spring mount
Common problem and difficult to weld. Get a Heavy Duty Diff cover. Hopefully someone can chime in with details for a supplier, I put mine on like 30 years ago. Muskigan (excuse the spelling). I think was the brand. sorry, a long time ago. these are beefed up in the spring mount area.
Oh, and be prepared. This is a big job. might want to goggle How to threads on removing your Diff.
Difficult, but possible.... but not something we would try at home. And mind you, we`ve rebuilt most of our 71 ourselves, including engine, trans, & rear end.
I would find a welding shop familiar with welding cast iron. As a side note, Willcox Corvette told me when you mount the spring, don`t tighten the bolts all the way until you put the car on the ground. Then tighten them to torque specs under load. Failure to do it that way could bust the case.....quite like what you have there, I`d imagine.
Also make sure you use the proper torque spec. I wish I remembered,,,, but I do remember there was a big difference between different covers. A new cover would go a long way for peace of mind.
I've seen anywhere from 40 ft/lbs to 100 ft/lbs. I think 100 is way to much.
Welding cast iron could be a nightmare. Why bother? It could fail again on the passenger side.
Like 4-vettes said, Muskegon Brake in Michigan. Last I checked the cover was around $125. Super Heavy Duty.
Then order your gasket, 2 bottles of GM Lube and a sm bottle of GM Posi modifier.
Update: Muskegon Brake is $139.95
But not a very user friendly web site. Click on suspension parts or use the search feature.
And by the way, I did manage to remove the cover without dropping the entire diff. if you support the diff with a floor jack once your car is up on jack stands. it is possible to remove the two bolts going into the top of the diff cover. A real pain in the ***, and you will need a good selection of tools. But it defiantly can be done. Most on here will tell you to drop the entire diff. I've done this a couple times, as about 25 years ago I also replaced the stub axles with hardened ones.
Removing the rear end is not difficult but it is labour intensive. I would forgo the welding route and get the heavy duty cover. Maybe a fiberglass spring too while your at it!
sometimes if you are lucky you can weld a crack in cast iron well enough for coolant to stay on one side and oil on the other. but most cracked blocks are scrapped cuz it is too iffy. this is beyond what is doable. PLUS, you would have to remove it to attempt the weld. replace it. even with a stock diff cover.
My 75 had two cracked corners, with a machine shop at my disposal at work, three machinists, that's 3, they said replace it.
That's the way it works, don't cheap out, life is to sort.
Stop digging underneath your 77 and just pull the body, you will have full access to replace the rear end cover.
Seriously, for a small stack of Benjamin's and your own labor you can have a clean rolling chassis. Not so long ago a fully restored rolling 65 chassis cost me about $3K in parts and that was with all new hardware, rotors, calipers, shields, brake & fuel lines etc. You could shave about $500 or more off that reusing a lot of the existing hardware. Restoring a rolling chassis is more about labor than cost of parts. While the body is off you have full access to the underside to clean as well.
Is it a lot of work, yes but the upside is your one and done after the body is put back on and never have to worry about the underside.
04-27-2021, 06:10 PM
Welding the rear spring mount?
💯%,,,and I'm a welder, and would replace NOT repair this,,,
