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.

1 Like

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.

1 Like

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.

1 Like