Finding diff lash in an unexpected place

So, here ya go.

Diff lash

The gears look pretty good if not almost unharmed. I can ferret out some slop in the spider gear shims. Other than that, I’m not sure what I’m gonna do about this yet. I would like to find a way to tighten this up.

Bolt failure on the crown wheel is not unknown.
As I recall they increased the diameter around '54 or '55.
This is from a '53 car.


    November 30

Bolt failure on the crown wheel is not unknown.
As I recall they increased the diameter around '54 or '55.
This is from a '53 car.

Based on my experience, I would call ring gear bolt failure common in the early 4ha differentials. The fix is new bolts of the highest quality and stuff I normally don’t like to use, Locktite. ARP makes good bolts. I’ll have to do some checking, but I believe that Ford motorsports flywheel and/or 9" differential ring gear bolts will work.

The Ford bolts are 7/16" and the early 4HA bolts are 3/8". In engineering parlance, the Ford bolts are called “place bolts”. Place bolts are designed to survive in high load, high vibration, environments. The Ford bolts come with a locking compound pre-applied. The Ford place bolt is on the right.

As others have said, bigger, hi-quality shoulder bolts and retread rethread the crown wheel.

Damn autocorrect!

I did a little poking around last night and roughly spot-checked this. I can nail it once it’s on the bench and get a fuller sample pool: The bolts have a shoulder diameter of about .371". The hole in the carrier is about .392".

Holy crap, what where they thinking? Seriously. It’s not moving because it’s worn.

They’re 3/8-24 1" shoulder. I’ll try a few bolts (I’ve got lots of time) before chucking it and starting over. McMaster, here I come.

That’s funny. … Rethread.

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If not worn, perhaps McMaster may be about to supply proper shoulder bolts to fit the holes, w/o retreading… I mean, rethreading.


I’d rather spend my time doing something on my car that people see.

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I have always been biased against the soft iron straps and tabs. I’ve never seen them provide any benefit. You can see the impression of the bolt heads where they plasticized and crept. If you are using conventional bolts, I can’t imagine why you would not use a hardened steel washer in their place.

It’s why I always pitched those soft, butter metal lock tabs.

Agreed: hardened washers, proper torque, and Loctite.

They WONT come loose.

When you think about all the places where we DON’T find those locking tabs, you have to wonder why they were used at all. If the tab couldn’t be made to fit on the ring gear… what then? Lock washers!

Of course, we’re dealing with 70 year old technology, state of the art at the time. Old designers stick to their old ways.

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A fellow restorer posted this on Face Book. Obviously a PO had issues also, hence the wire.

…Gives one pause…

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LOL straps AND wire! I don’t recognize those as anyone’s ring gear bolts. Three radial lines on the bolt head = SAE Grade 5. At least he saved the bolt heads.

“At least he saved the bolt heads.” Imagine if he hadn’t wired them :scream:

He went through all that trouble and fell a few hash marks short of his goal.

He prolly torqued the beejeebers out of them and did most of the damage before the tires even hit the ground.

Grade 8 wouldn’t have popped.

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Exhibit A in “Where do you thing he got those drilled head Grade 5 bolts?”

You can’t know that. Let’s not post negatives here without proof. He could have gone to any supplier for all we know.

There was a flood of reports of bad fasteners a few years ago. There’s nothing in this photo to show the failure was anything other than operator error with a torque wrench (or lack of one) or a poor choice of tensile strength.

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Sorry, I wasn’t clear. I’m not saying that there was any fault with the fasteners at all. I buys LOADS of fasteners from McM-C. Sometimes, every day. And I have never once in more than 20 years been disappointed with the quality of any of it. My point is that someone made an ill-conceived decision to buy a wholly inappropriate, inadequate bolt for the task at hand. This was not the fault of the bolt or the vendor.

I mean, look at that dismal attempt at safety wire. Somewhere, there is a bale of hay missing it’s belt.

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