IRS Rear End to frame correct torque values?

[cc2Arider]

Hey Y'all,

I thought I was squared away on my IRS install...

Then I noticed a discrepancy in the torque values documented in the MkIV build manual. On the page where it instructs me to torque the front and rear IRS unit mounts to the frame, it mentions 100lb-ft...a few pages later in the build manual, it says 129lb-ft (I think) :confused:

Which is actually correct? Is 100lb-ft sufficient? I noticed similar values for all other similarly-sized chassis fasteners...

Appreciate the feedback!

Craig C

[FDLWproject]

Good question Craig - I think I saw this same question come up recently in another thread (and in the one below) and the guidance from the gurus was that yes there is a discrepancy in the manual but just aim for something in between (115-ish).

https://thefactoryfiveforum.com/showthread.php?46837-Torque-specs-for-center-section-Contradiction

[M22_COBRA]

What grade bolts are going into the housing / what numbers are on the hex head? Is the rear gear steel threaded, or aluminum with heli-coils?

[cc2Arider]

Thanks Russell for the reply and link :)

Apologies for not searching better on my own :o

I think I'll stick to 100lb-ft for now...

Craig C

[cc2Arider]

What grade bolts are going into the housing / what numbers are on the hex head? Is the rear gear steel threaded, or aluminum with heli-coils?

Thanks for the reply, and I think I know where you're going for this...that I could learn for myself what the standard torque values are for the grade and size of fastener. I considered that, but then the limiting factor of the clamping force to me seems to be the spacer collar between the nut and bolt. I figure that would probably deform before the bolt would...

But yes, the other thing that had me worried was threading into the aluminum housing with too much torque...

Craig C

[M22_COBRA]

Thanks for the reply, and I think I know where you're going for this...that I could learn for myself what the standard torque values are for the grade and size of fastener. I considered that, but then the limiting factor of the clamping force to me seems to be the spacer collar between the nut and bolt. I figure that would probably deform before the bolt would...

But yes, the other thing that had me worried was threading into the aluminum housing with too much torque...

Craig C

I kind of do this for a living and have the tools available to be able to check the provided values against what it should be quickly without burning up my calculator. Or at least look and say this is the applied clamp load per the provided spec. I just don't have my FFR kit ordered yet so I don't have all the provided items and documents in hand to go look at. Ford calls out 129ftlbs for the diff to sub frame FWIW

It would be nice as I am going thru my build to evaluate all the torques and create a list of what the clamp load actual is per the provided spec and make changes as necessary. It would highlight clamp loads that are lighter which would help us understand how close we are to potential back off at load. The end goal would be to have a document of torques for new builders and current owners to reference to ensure we get proper clamp, and less worry about is this gonna back off. You could have a FFR "as provided" list; and a list that is checked per fastener engineering standards highlighting any recommended adjustments.
Maybe they wont be that different but given the track record on conflicting info (elephant in the room).... In God I trust, everybody else show me your data.

[rich grsc]

OMG, this isn't a spacecraft on a mission to mars, nor is it brain surgery. None of the torque values or loads are even close to failure rates. If it say 110 one place but 120 another, pick one. or chose in the middle. IT"S NOT a life or death decision 10# one way or the other.

[M22_COBRA]

For example I'm assuming M16x2 6g thread, thread engagement of 1.3" ( 2x diameter ), bare to a black oxide coating interface, a class 8.8 material....

Torqued to 129ftlb = 12289 lb clamp, 61% of the tensile yield which is 20220 lbs, (75% is maximum limit)

Torqued to 100ftlb = 9526 lb clamp, 47% of the tensile yield which is obviously unchanged @ 20220 lbs

[M22_COBRA]

OMG, this isn't a spacecraft on a mission to mars, nor is it brain surgery. None of the torque values or loads are even close to failure rates. If it say 110 one place but 120 another, pick one. or chose in the middle. IT"S NOT a life or death decision 10# one way or the other.

Fastener backs out of your car and kills you, YEAH it kinda is life and death.

[gbranham]

Fastener backs out of your car and kills you, YEAH it kinda is life and death.

True, but it's not going to back out if you torque to 100 and the manual says 120. I appreciate the desire to follow the manual to the letter, and also understand questions when discrepancies in the manual arise, but 'close enough is good enough' when we're working with torque values this high.

On my first build, I had a crappy torque wrench that probably wasn't even remotely accurate. For most suspension bolts, I simply followed the 'TTYF' concept...Torque Till You Fart...hah! For other small bolts, I may have used the torque wrench in some cases, and in others, I just snugged em up good. That car was built in 2005, and is still on the road with no failures to my knowledge.