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66 diff leak

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Old 02-17-2017, 01:14 PM   #1
sugg60
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Default 66 diff leak

I'm changing out the rear spring on my 66 coupe(HD 3:36). I removed the 4 bolts and plate that hold the spring to the diff and I now notice a few drops of gear lube coming out of one of the bolt holes. I left the bolt out for several days and it has not stopped. Is this normal or is my diff cracked? What say you.
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Old 02-17-2017, 01:40 PM   #2
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I'm changing out the rear spring on my 66 coupe(HD 3:36). I removed the 4 bolts and plate that hold the spring to the diff and I now notice a few drops of gear lube coming out of one of the bolt holes. I left the bolt out for several days and it has not stopped. Is this normal or is my diff cracked? What say you.
No it's not normal, the problem probably is from someone putting a longer bolt in that hole than original. It's a blind hole and a longer bolt will break thru the casing , causing the leak. This can be fixed from the inside using JB weld , or replace the casting. You know how I know this... Hope this helps Jeff
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Old 02-17-2017, 01:54 PM   #3
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No it's not normal, the problem probably is from someone putting a longer bolt in that hole than original. It's a blind hole and a longer bolt will break thru the casing , causing the leak. This can be fixed from the inside using JB weld , or replace the casting. You know how I know this... Hope this helps Jeff
Broken/cracked rear cover. Just went thru this with a good friend and his 1969 Corvette. Fortunately, he worked for a large New Orleans machining company and had the shop welders fix it for him. Pre and post weld heating required in addition to the weld itself. Now it is as good as new.

You might get by for awhile just using a thread sealant on the bolt. Heavy duty replacement rear covers are available from Muskegon Brake.........and also used originals are also out there if you search. But you may never find/get the original codes..........if that matters to you.

Larry
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Old 02-18-2017, 08:54 AM   #4
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You could try cleaning the threads with brakleen and installing a new clean bolt with sealant...worth a try.
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Old 02-18-2017, 09:38 AM   #5
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Just wondering...are all four bolts for mounting originally the same length or are two of them that go into the cover shorter? In other words, can you mix up the original bolts on an install and break the cover? Dave
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Old 02-18-2017, 11:04 AM   #6
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Just wondering...are all four bolts for mounting originally the same length or are two of them that go into the cover shorter? In other words, can you mix up the original bolts on an install and break the cover? Dave
They SHOULD all be the same length..............but you never know on a 50 year old car what is/was installed in the past.

The two bolts that thread into blind holes are the critical ones that require checking.........the other two don't really matter as long as they go thru all the rear cover threads.

Reproduction springs and reproduction spring liners are a different thickness than originals, so any changes/replacements to them will also affect the required/needed bolt length. Do not just assume that all is well.

Larry
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Old 02-18-2017, 11:31 AM   #7
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They SHOULD all be the same length..............but you never know on a 50 year old car what is/was installed in the past.

The two bolts that thread into blind holes are the critical ones that require checking.........the other two don't really matter as long as they go thru all the rear cover threads.

Reproduction springs and reproduction spring liners are a different thickness than originals, so any changes/replacements to them will also affect the required/needed bolt length. Do not just assume that all is well.

Larry
Thanks Larry, The reason I asked was that I replaced my rear spring with an Eaton a few years back and the bolts were all the same length. I put weight on the car before final tightening of the bolts. Months later I had the car on a lift and noticed some seeping from one of the cover spring bolts. I removed it and a bit more flowed out. I put a bunch of permatex on the bolt and replaced it but still have a very little seep but no drip. I wipe the spring base every six months or so.
I've wondered since how that could have happened. The bolts may have been replaced before since the spring I replaced wasn't original. Thanks for the info. Dave

Last edited by dkleather; 02-18-2017 at 11:32 AM.
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Old 02-18-2017, 11:47 AM   #8
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Originally Posted by sugg60 View Post
I'm changing out the rear spring on my 66 coupe(HD 3:36). I removed the 4 bolts and plate that hold the spring to the diff and I now notice a few drops of gear lube coming out of one of the bolt holes. I left the bolt out for several days and it has not stopped. Is this normal or is my diff cracked? What say you.
Thanks for all the replies, very helpful. I think I'm going to put thread sealer on the threads and see what happens.
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