Cast Iron Diff Housings don't just belong on Manual Trans Cars: Broken Aluminum Diff

I had a long weekend of breaking parts at the track this weekend at NMRA Bowling Green World Finals. :doh:

First pass off the trailer - heard a very loud snap right on the launch. I snapped the ears right off the diff housing, on the front side.

Hey, Kelly, didn't you know - more wheelspin will prevent that!
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GTP said:

Hey, Kelly, didn't you know - more wheelspin will prevent that!
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Here is the pass that it broke on. lol

Which diff bushings are on the car?

I have the BK054 Diff Lockouts.

I put a Cast Iron Diff in it at the track, and it held up the next 3 passes. (I did break other stuff though)

Send the broken one to Ford. See how long it takes for the ECO to get back to China, and then into production cars. :lol:

I am a little confused with regards to the title.

Especially as someone is who looking to swap out there cast iron dif on a manual car.

So you swapped in a Aluminum dif in a a Manual GT car; broke it. Then put a cast Iron one back in it held up for at least three passes; however you proceeded to break other stuff.

Is it possible the stock bushing allow for enough flex that it helped contribute to the failure? Curious if stiffer/solid bushing would help prevent this.

My feeling is the lockouts are the reason they failed. The iron housing should be fine, but the forces have to go somewhere and the bushing's ability to absorb that energy is quite compromised. This isn't a knock on your products at all...just the harsh reality of the mechanics and physics of the systems.

I am a mechanical engineer who has been working in the automotive industry, at OEMs

68fbjjz109 said:

I am a little confused with regards to the title.

Especially as someone is who looking to swap out there cast iron dif on a manual car.

So you swapped in a Aluminum dif in a a Manual GT car; broke it. Then put a cast Iron one back in it held up for at least three passes; however you proceeded to break other stuff.

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Title: Cast Iron Diff Housings don't just belong in manual trans cars

As in, they come in manual transmission cars, but do NOT come in Automatics.

I have an automatic, and I broke the stock aluminum diff housing.

In other words, I think cast iron diff housings belong in both manual and auto cars.

madweazl said:

Is it possible the stock bushing allow for enough flex that it helped contribute to the failure? Curious if stiffer/solid bushing would help prevent this.

Click to expand...

I have the BK054 Lockout Kit

BmacIL said:

My feeling is the lockouts are the reason they failed. The iron housing should be fine, but the forces have to go somewhere and the bushing's ability to absorb that energy is quite compromised. This isn't a knock on your products at all...just the harsh reality of the mechanics and physics of the systems.

I am a mechanical engineer who has been working in the automotive industry, at OEMs

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You could be right, or you could be wrong.

The issue with your theory is, you would need to test whether the "shock" to the ears is more when being solidified (not giving) OR when they bottom out of their cushioned travel after the initial hit. Many times, if you allow something to move - then it bottoms out, that harsh stop of movement can be worse than the elimination of the movement altogether.

To provide more data, I have had a customer actually shear the diff bolts.

So, it is of your opinion that the diff housing shears before the 14mm bolts do? If so, that is not very "good" IMO.

FRPP offers billet aluminum diff bushings for the S550 IRS system. The Ford components are tested rigorously before being released to the public. I am very curious to know if they tested them out on an aluminum diff, making bigger power. I do not think they did, but I could be wrong.

Somehow, some way, the aluminum version was proven inferior at Ford. The proof is that they put the cast iron in all of the manual trans cars, that make 435HP.

(I blame my issue on making over 2X the power that the part was tested for)

BMR Tech said:

You could be right, or you could be wrong.

The issue with your theory is, you would need to test whether the "shock" to the ears is more when being solidified (not giving) OR when they bottom out of their cushioned travel after the initial hit. Many times, if you allow something to move - then it bottoms out, that harsh stop of movement can be worse than the elimination of the movement altogether.

To provide more data, I have had a customer actually shear the diff bolts.

So, it is of your opinion that the diff housing shears before the 14mm bolts do? If so, that is not very "good" IMO.

FRPP offers billet aluminum diff bushings for the S550 IRS system. The Ford components are tested rigorously before being released to the public. I am very curious to know if they tested them out on an aluminum diff, making bigger power. I do not think they did, but I could be wrong.

Somehow, some way, the aluminum version was proven inferior at Ford. The proof is that they put the cast iron in all of the manual trans cars, that make 435HP.

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Indeed, that has some merit. Even so, the bushing will absorb energy as the diff bolt travels through it, even if it does bottom out, it's still hitting some bushing (the outer material). It really depends on whether or not the diff housing continues to accelerate as it works the bushings, or if the force input is just an impulse from initial loading. Sounds like it could be the former.

Fair point on the aluminum diff bushings by FRPP. I have a feeling it probably wasn't tested at 700+ HP. At that point, all bets are off and it's not unreasonable for stuff to be breaking. If everything was engineered for that level of power, it'd be quite a lot heavier.

You probably initiated cracks in the ears in previous runs, and finally got them to the point where they propagated enough to crack all the way through on the next pass.

Scary stuff...

Because the previous passes were made with much less power, and no BK054 kit. lol

Time will tell. I predict many failures of many different parts out back in the next year or so. People are finally getting these cars figured out, and there were some very fast ones at the event over the weekend.

BMR Tech said:

Scary stuff...

Because the previous passes were made with much less power, and no BK054 kit. lol

Time will tell. I predict many failures of many different parts out back in the next year or so. People are finally getting these cars figured out, and there were some very fast ones at the event over the weekend.

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Yikes!

The other possibility is that there was porosity in the casting, and it's much more difficult to get ears and pieces of the part that stick out far like that to fill up really well. Aluminum is more difficult than iron/steel as it cools quite a bit quicker.