Ford SuperDuty Recall 21S31

[DebiM]

Originally Posted by 4x4ord

That really does suck. Was there any sign of shaking or vibration before you brought your truck in or did you just bring it in to be checked? If the parts are not yet available for those who need axle replacements I think holding off bringing my truck in is definitely the thing for me to do. Back in 2011 I had a turbo acting up on my new truck. I brought it in and Ford determined the turbo needed replacing but head office told the service department “don’t use a replacement turbo from parts … we will send you a new modified turbo”. In my case I was able to use the truck till the new turbo came in.

We had a trip planned for months and so thought taking it in would hasten the fix. Once truck was checked they said do not drive. Ours had started separate so still at dealership and don’t know if we will make our trip or not. Very disappointing!

[Jack Klompus]

Originally Posted by 4x4ord

You mean the Dana axle … and I agree the recall is likely to be expanded to include other trucks using that axle. It seems to me that hard braking could be just as, if not more stressful on the axle than hard acceleration. The 7.3 F350 has a higher payload rating than the 6.7 and the same braking ability.

Oof. Yes Dana.

And yes, we agree. A loaded 7.3 F series will have some significant stress on it. I have had one rather serious stop already and have about 10,000 towed miles on it

[SGhost]

I believe the payload is a little higher on the 7.3 gas based on the engine weight variable. That said, I would think you could still spin that axle based not only on the torque applied but more seriously on the braking power applied which can also spin the axle if the tubes are crushed. Seems no ones talking about that possibility......

[bross]

So this recall only affects 20-21 trucks. Can someone with a 2019 or prior F-350 take a pic of their axle / spring perch to see if it's welded all the way around? Obviously Ford changed suppliers or the supplier changed something in the 2020 model year???

[4x4ord]

Originally Posted by DebiM

We had a trip planned for months and so thought taking it in would hasten the fix. Once truck was checked they said do not drive. Ours had started separate so still at dealership and don’t know if we will make our trip or not. Very disappointing!

If it was just requiring the welding, the dealer would be in control and could certainly get it done in little time. When they are waiting for new parts to be shipped it is understandably much more difficult and I doubt there's a thing you can do to hasten the process. I hope they get it fixed for you in time that you can enjoy your vacation.

[77Travco]

Originally Posted by bross

So this recall only affects 20-21 trucks. Can someone with a 2019 or prior F-350 take a pic of their axle / spring perch to see if it's welded all the way around? Obviously Ford changed suppliers or the supplier changed something in the 2020 model year???

The newer axle has thinner wall axle tubes than previous version. Probably saved the manufacturer a few cents.

[bross]

Originally Posted by 77Travco

The newer axle has thinner wall axle tubes than previous version. Probably saved the manufacturer a few cents.

Wow, f#cking bean counters, what a stupid place to try to save a few pennies on a heavy duty truck. Cheaper fabric or speakers etc. sure, but bloody structural running gear.

[4x4ord]

I think if something is going to crush these axles it’s going to be the u bolts clamping the axle to the spring. I looked up the clamping force of a 1/2 grade 8 bolt tightened to 90 ft lbs….. 14,400 lbs. So 8 bolts per axle …… 115,200 lbs plus the 3500 lbs for the rear axle truck weight. Whether an additional 2500 lbs or 5000 lbs is placed on the pin is kind of a insignificant factor.

[Jerry Burks]

Originally Posted by 4x4ord

I think if something is going to crush these axles it’s going to be the u bolts clamping the axle to the spring. I looked up the clamping force of a 1/2 grade 8 bolt tightened to 90 ft lbs….. 14,400 lbs. So 8 bolts per axle …… 115,200 lbs plus the 3500 lbs for the rear axle truck weight. Whether an additional 2500 lbs or 5000 lbs is placed on the pin is kind of a insignificant factor.

Yes and no...actually the U-bolts are M16 and the prescribed torque is (AFAIK) 185 ft-lbs. Assuming typical friction that will come out to about 70,000 lbs per spring perch. But you are pretty close.

However, this does not contribute much to the overall axle stress because it is applied only locally from the top down (perch) and compensated bottom up (saddle) so the only deformation is to make the tube a little bit oval around the U-bolts, not much effect on the weld beads. The payload and acceleration forces on the other hand will bow the entire axle as a beam.

The biggest stressor is however the acceleration torque in low gear as well as the braking torque. Both are limited by the ability of the wheel to stick to the pavement but can probably result in several 3000-4000 ft-lbs torque at the axle that have to be held by the perch weld beads with the stress concentrated at the ends of the crescent shaped beads. I guess that may be the reason for Ford to hope that the 360 degree welds help a little.

I agree with other people here that the use of the weakened axle for the 7.3 l gas engine is similarly questionable.

[4x4ord]

Originally Posted by Jerry Burks

Yes and no...actually the U-bolts are M16 and the prescribed torque is (AFAIK) 185 ft-lbs. Assuming typical friction that will come out to about 70,000 lbs per spring perch. But you are pretty close.

However, this does not contribute much to the overall axle stress because it is applied only locally from the top down (perch) and compensated bottom up (saddle) so the only deformation is to make the tube a little bit oval around the U-bolts, not much effect on the weld beads. The payload and acceleration forces on the other hand will bow the entire axle as a beam.

The biggest stressor is however the acceleration torque in low gear as well as the braking torque. Both are limited by the ability of the wheel to stick to the pavement but can probably result in several 3000-4000 ft-lbs torque at the axle that have to be held by the perch weld beads with the stress concentrated at the ends of the crescent shaped beads. I guess that may be the reason for Ford to hope that the 360 degree welds help a little.

I agree with other people here that the use of the weakened axle for the 7.3 l gas engine is similarly questionable.

From the pictures of the failed axles it looks to me as though the axle failing as a beam is not the issue but rather the perch crushing into the top of the axle tube ... that's why I'm suggesting the clamping force of the bolts as a factor. Once you have enough weight on the truck to achieve good traction would additional weight play much of a factor in the perch crushing into the tube or the perch welds letting go?

[Jerry Burks]

Originally Posted by 4x4ord

From the pictures of the failed axles it looks to me as though the axle failing as a beam is not the issue but rather the perch crushing into the top of the axle tube ... that's why I'm suggesting the clamping force of the bolts as a factor. Once you have enough weight on the truck to achieve good traction would additional weight play much of a factor in the perch crushing into the tube or the perch welds letting go?

It is hard to separate the individual contributors to the failure. But I agree that the static load by the truck and cargo weight on the axle is only a minor one.
It does have an indirect effect, since with higher load the tires can develop more accelerating or braking forces before they spin or skid. Example: if you have a load of 6800 lbs and assume a coefficient of friction of 0.9 for dry road you could get max. 6120 lbs of accelerating or braking force (2-wheel drive) or 3060 lbs per tire. Given the tire radius of 16 inches this makes for a max. torque of 4080 ft-lbs.

I modeled the axle in CAD and did an FEA calculation using all known load conditions that I posted on another forum. That does show the highest stresses at the ends of the perch welds. While the U-bolt clamping forces look indeed very high, they just compress the tube and this is quite resilient to such deformation (see the light blue strips at the bottom of the tube). But no doubt, this also contributes.

If you want more information about this calculation, send me a PM.

[SGhost]

Excellent analysis Jerry! I think this only reinforces the concern that the welds are not the answer only a bandaid fix for what many feel is a serious problem. I for one would never feel completely safe loading my truck and then navigating the kinds of roads (horrible condition) I just traversed from Florida to Colorado and back. Thank goodness for the Moryde pin box damper system which absorbed some of those impacts.

I'm going to get with a friend who's a lawyer and take closer look at the Florida lemon law applicability based on this flaw. While I'm not anywhere near the full payload capability of the truck (as designed) it now has a potential weakness that may effect its value and resale not to mention its usability for the use intended. I believe Ford is hoping most people will go along with the fix and think its sufficient. I think they underestimate the type of buyer that uses these trucks.

[4x4ord]

Originally Posted by SGhost

Excellent analysis Jerry! I think this only reinforces the concern that the welds are not the answer only a bandaid fix for what many feel is a serious problem. I for one would never feel completely safe loading my truck and then navigating the kinds of roads (horrible condition) I just traversed from Florida to Colorado and back. Thank goodness for the Moryde pin box damper system which absorbed some of those impacts.

I'm going to get with a friend who's a lawyer and take closer look at the Florida lemon law applicability based on this flaw. While I'm not anywhere near the full payload capability of the truck (as designed) it now has a potential weakness that may effect its value and resale not to mention its usability for the use intended. I believe Ford is hoping most people will go along with the fix and think its sufficient. I think they underestimate the type of buyer that uses these trucks.

If you're talking to a lawyer, I think knowing if a recalled axle has been "fixed" and then fails 10 years down the road is Ford still liable for the failure?

[4x4ord]

Originally Posted by Jerry Burks

It is hard to separate the individual contributors to the failure. But I agree that the static load by the truck and cargo weight on the axle is only a minor one.
It does have an indirect effect, since with higher load the tires can develop more accelerating or braking forces before they spin or skid. Example: if you have a load of 6800 lbs and assume a coefficient of friction of 0.9 for dry road you could get max. 6120 lbs of accelerating or braking force (2-wheel drive) or 3060 lbs per tire. Given the tire radius of 16 inches this makes for a max. torque of 4080 ft-lbs.

I modeled the axle in CAD and did an FEA calculation using all known load conditions that I posted on another forum. That does show the highest stresses at the ends of the perch welds. While the U-bolt clamping forces look indeed very high, they just compress the tube and this is quite resilient to such deformation (see the light blue strips at the bottom of the tube). But no doubt, this also contributes.

If you want more information about this calculation, send me a PM.

Thanks Jerry for your analysis. I do not have the training to fully understand your diagram but after looking at it with an untrained eye, it seems reasonable to expect Ford's solution to be adequate. What would your diagram look like if you ran the numbers again with the axle perch welded all the way around?