What is the true rear diff cover torque spec?

[Kevin Scarbel]

One Ford documents says 20 Nm (14.75 lb ft).
(https://www.bronco6g.com/forum/thre...rb-m220-cover-looking-for-torque-specs.73980/)

But the Ford performance cover's installation instruction says 40 Nm (29.5 lb ft).
(Page 6 - https://performanceparts.ford.com/download/instructionsheets/IS_M-4033-BR_050423.PDF)

Dana says 20-25 lb ft, which is way above 20 Nm and people have broken bolts.

I'm guessing 20 Nm is correct but does anyone have the latest info from Ford?

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[Ducati1098]

The easiest way to avoid potentially broken bolts is to make sure that the threads are clean, dry and that there is nothing in the holes prior to torquing the bolts. Usually people wont do this, and that's where the problems start.

This is from the workshop manual.

 

[evilletruck]

The Ford Performance cover comes with its own bolts, and is heavier which is why it has a different torque spec then the OEM non performance one.

 

[Kevin Scarbel]

The Ford Performance cover comes with its own bolts, and is heavier which is why it has a different torque spec then the OEM non performance one.

That makes zero sense.
It doesn't matter if the cover is heavier.
And I'll add it doesn't matter that it comes with longer bolts as they're the same size and extend the same distance into the axle housing (the clamping effect is the same).

 

[Kevin Scarbel]

The easiest way to avoid potentially broken bolts is to make sure that the threads are clean, dry and that there is nothing in the holes prior to torquing the bolts. Usually people wont do this, and that's where the problems start.

This is from the workshop manual.

Thank you Ducati. I appreciate your assistance.

I don't get the 25 degree instruction. Give me a torque spec and a torque wrench and I'll stop when it clicks.

 

[WarthogJr]

I used the specs on the paperwork that came with it. Nothing bad happened. No leaks after 1.5 years and several Starbucks visits (12k miles).

 

[ssls6]

General guidelines...bolt strength also matters.

 

[Fastmc25]

What they’re saying is the performance cover is heavy cast or billet and can handle a higher torque clamping pressure than the stamped steel cover. If the stamped one is over torqued it can deform the bolt holes and not give as much clamping force. With the right sealant it won’t matter much.

 

[Kevin Scarbel]

What they’re saying is the performance cover is heavy cast or billet and can handle a higher torque clamping pressure than the stamped steel cover. If the stamped one is over torqued it can deform the bolt holes and not give as much clamping force. With the right sealant it won’t matter much.

That doesn't matter. It's the fastener that has the torque limitations. And the bolt is the same size for both (length does not matter as the amount of bolt within the diff housing is the same).

 

[Fastmc25]

Nevermind

 

[Fastmc25]

The performance cover is thicker and can handle a higher torque. The bolt stretch is a constant but if the cover is thin it can be deformed by using the max torque that the bolt/stud is rated so the thin cover has a lower crush torque rating. It always depends on what you’re fastening as to the required torque.

 

[Ducati1098]

The performance cover is thicker and can handle a higher torque. The bolt stretch is a constant but if the cover is thin it can be deformed by using the max torque that the bolt/stud is rated so the thin cover has a lower crush torque rating. It always depends on what you’re fastening as to the required torque.

The factory gasket prevents this from happening. It doesn’t use silicone.

 

[evilletruck]

That makes zero sense.
It doesn't matter if the cover is heavier.
And I'll add it doesn't matter that it comes with longer bolts as they're the same size and extend the same distance into the axle housing (the clamping effect is the same).

Makes perfect sense to me, if you are installing the stamped cover follow the specs that are meant for that part and hardware, if you are installing a completely different part with different hardware and its own set of specs then use those.

Being heavier is an oversimplification, its different material, different thickness completely different product, you asked which spec is correct, they both are but for their respective part.

 

[Brian_B]

I don't get the 25 degree instruction. Give me a torque spec and a torque wrench and I'll stop when it clicks.

Torque all bolts until you click (step 1)
Then go another round on the bolts another 25 degrees (about half a flat) (step 2)

But speaking realistically - this isn’t carrying a load beyond the weight of the cover, it’s just gotta be tight enough to seal the gasket. So the torque isn’t super critical… and the bigger danger is in over torque rather than under…. If you are under, it drips and you just tighten a bit more…. If you are over, you risk stripping out the housing, breaking off bolts and/or damaging the reusable gasket.

Not something that requires being overthunk. The torque spec is just there because Ford and Dana have to say something other than “Well, tight enough to not leak but don’t break it”. Not surprised there are differing specs - it isn’t super critical

 

[swamp2]

It's not inconceivable that for the same size bolt with a different cover and more importantly different seal could result in a doubling of the torque spec. One thing to note is that the torque spec isn't solely based on the fastener size. Sure, if the intent of the Design Engineer was simply to take the fastener to yield, then yes, the torque would be the same for both covers and both seals. It seems here that wasn't the intent. Given his much thicker and stiffer the FP cover and FP gasket are, any minor missalignnent would need much more torque to insure a seal. No idea if that type of consideration actually drove through FP spec, just hypothesizing...

What diameter are the bolts?

IIRC, I used the factory gasket (looked way higher tech and better sealing) with the FP cover along with the 40 Nm plus 25° torque spec. It isn't leaking.

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