Banjo Fracture

[apbright]

Hi folks,

My Banjo Housing has fractured. Mercifully, my local parts store, All Ford Parts, had a NOS replacement available (for the price of a family dinner at a fancy restaurant), to get me back on the road quickly.

But, my question: How in Texan Tarnation does this happen?

Thanks in advance, Andrew

[updraught]

https://i.imgur.com/rrXmjZb.gif?1

[updraught]

delete

[Synchro909]

I've seen and welded up cracks in that area but never seen one break right through like that. It was a weakness in the original design which Ford made stronger in later production. Then, of course, there is the matter of about 90 years worth of fatigue.

[J Franklin]

Jack rabbit starts!

[rotorwrench]

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They definitely needed the rib in there.

[Purdy Swoft]

The 28 banjo was the weakest .

[100IH]

Do you have the mushroom footrest next to the mushroom gas pedal. Do you use it? The foot should touch both and twist the foot to avoid breaking the banjo. Also the first castings broke easier and gussets were added at some time, its in the service bulletins.Looks like you have the reinforced one.

[Tom Endy]

One possibility is if the car had just come off a rear axle assembly overhaul where the two nuts on the pinion sleeve were not adjusted for a pinion bearing pre-load and were way over tightened. Usually in this case Henry's 40 horses will break it loose by spinning the double race in the banjo. However, if they were extremely tight something has to give and it could damage the banjo.

The damaged banjo in the photo is a 30\31 with support gussets at the torque tube flange. The very early banjos did not have these support gussets and were prone to cracking in this area.

Tom Endy

[Tom Wesenberg]

Originally Posted by J Franklin

Jack rabbit starts!

Yep, also spinning tires on snow, ice, or mud, then the tire suddenly grips dry pavement and something gives. I've never seen the housing that broken though.

[100IH]

Going airborne over RR tracks can be a culprit.

[Tom Endy]

Originally Posted by 100IH

Going airborne over RR tracks can be a culprit.

That usually cleans the teeth off the pinion gear. Happened to a friend when we were teenagers.

Tom Endy

[apbright]

Thanks for the comments folks.

This differential underwent a mild re-build about one year and 10,000 miles ago (it was really just to swap the ring-and-pinion gear, to a 1:3.54 ratio).

The pinion nuts were set by a local machinist who, indeed, may have not known what he was doing. That said, it did turn freely when installed, and when recently disassembled. Also, I see no visual signs of the race having rotated inside the banjo (although, admittedly, I'm not exactly sure I would know what to look for).

Re car setup: Engine is std. bore, 'touring cam,' 6:1 head, oversize intake valves, sometimes Weber, sometimes Modal B carb, 26% Mitchell O.D. Over 50% of mileage is 65-75mph highway. (Sorry, I know, for many that's too fast, by on California freeways, IMHO that is most death-proof speed). Average zero donuts/year.

Another possible clue: On the opposite of the banjo from the primary fracture can be seen a hairline fracture ('B,' in photo below). I don't know if this changes any opinions but thought worth sharing. Umm... also, I might have used standard thread, 18-8 stainless steel 3/8 x 24 bolts, to fasten the axle housings to the banjo; don't know if that matters (???).

[Tom Endy]

The area of the two cracks in your photo is where the early banjos that did not have support gussets would crack. Most every early banjo I have seen had a hairline crack at all four banjo holes, two on each side near the torque tube flange. I do a lot of overhauls for a local restoration shop, when a job comes in with an early banjo we switch it out for a later one with support gussets. I have done some that were for 28 blue ribbon cars and the owners wanted the early banjo. Even these had slight hairline cracks at the four holes.

Banjos are not hard to come by at swap meets here in Southern California and they are not costly. The thing to check out is that the double race is still there and is tight and none of the bolt holes are stripped out.

Tom Endy

[CT Jack]

Many probable causes for the banjo failure have been sited in the previous threads. A fundalmental problem when using a cast metal for this type of application is the fact that cast metals in general are very low in ductility, meaning they are basically very brittle. Installing tapped holes can cause micro cracks to develop during a regular machining. The material thickness between the inside diameter of the banjo and the outside diameter of the tapped hole is very small. The combination of over tightening fasteners and applying high impact levels of torque will definitely limit the life of the banjo. These conditions cause the initial micro cracks to rapidly grow into visible cracks as shown the photo.