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Rear Brake Torque Specs

chris_keller

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I will be replacing rear calipers since the rear dust boots melted from track days. Does anyone have the following torque specs:

Brake line to caliper torque spec
Caliper Mounting Bracket torque spec (18mm bolt)
Caliper to mounting bracket torque spec (14mm bolt)
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ronemca

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I would be grateful to learn this as well. All I have found is the bracket -> hub spec (85 ft/lbs) I'd like to verify the slider pin spec as well, please.

And is there any difference <-> front & rear?

* * EDIT * *
In my continuing search I came across this thread: https://www.mustang6g.com/forums/threads/diy-for-rotor-replacement.89411/#post-1982878 but I think there's an error. It shows the front brackets @ 85 ft/lbs - okay - but one hundred & twenty nine foot pounds for the rear??! That's a suspicious coincidence with rear subframe bolts...not to mention hellishly tight for bolts of this caliber/purpose. I'm also skeptical that the rears would be 50% higher than the fronts.

And the apparent discrepancy causes ALL of the values to be suspect (like a clock that chimes thirteen times)

Any verification, gentlemen?
 
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gtorpedo

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Rear brake line to caliper: 35 lb/ft (47.5 Nm) - replace brass washers
Rear caliper mounting bracket (18mm bolt): 129 lb/ft (175 Nm) - blue loctite
Rear caliper to mounting bracket (14mm bolt): 24 lb/ft (32 Nm)
 

NightmareMoon

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Rear brake line to caliper: 35 lb/ft (47.5 Nm) - replace brass washers
Rear caliper mounting bracket (18mm bolt): 129 lb/ft (175 Nm) - blue loctite
Rear caliper to mounting bracket (14mm bolt): 24 lb/ft (32 Nm)
Somebody post those numbers to in the sticky thread for torque specs at the top of this Suspension and Brakes subforum!
 

ronemca

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Rear brake line to caliper: 35 lb/ft (47.5 Nm) - replace brass washers
Rear caliper mounting bracket (18mm bolt): 129 lb/ft (175 Nm) - blue loctite
Rear caliper to mounting bracket (14mm bolt): 24 lb/ft (32 Nm)
Thank you.

But there remain two things that trouble me:
1) why is the mounting torque (force) on the front caliper -- which is substantially larger/heavier AND subjected to greater stresses AND a higher workload AND more heat -- nearly half that of the rear??
2) isn't 129 lb/ft perilously high for a bolt of this size?

I have no doubt that these numbers have been gleaned from a manual, but am I the only one that is skeptical? because I know that manuals sometimes contain incorrect info.
 
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gtorpedo

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Thank you.

But there remain two things that trouble me:
1) why is the mounting torque (force) on the front caliper -- which is substantially larger/heavier AND subjected to greater stresses AND a higher workload AND more heat -- roughly half that of the rear??
2) isn't 129 lb/ft perilously high for a bolt of this size?

I have no doubt that these numbers have been gleaned from a manual, but am I the only one that is skeptical? because I know that manuals sometimes contain incorrect info.
Your doubts will be overcome when you actually look at the front vs rear bolts themselves. Its no coincidence the rear caliper bolts have the same torque spec as the cradle bolts...they are both 10.9 grade 14mm bolts.
 

ronemca

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Ah! :like: But what's the theory behind that? Why are the rears (by comparison) so robust? (Why are the fronts less robust?) :frown:
 

NightmareMoon

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Its normal torque for that kind of 18mm bolt.

People tend to overestimate the torque for little bolts (and break them) and underestimate the torque for big ones.
 

ronemca

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Well - I now agree that once you're under there and actually turning the 18mm rear carrier bolts...129 ft/lbs seems acceptable/reasonable. But this very subjective opinion is based purely on the caliber of the bolt relative to other 18mm bolts of the same caliber. i.e.: I'm not as apprehensive about leaning on it as I was before I did the job. However...

I think it's silly -- not to mention counter-intuitive -- for the Chassis engineers to set the rears at 129 but the fronts at 85. The amount of threaded material is the same (although the fronts use a smaller bolt, which is ALSO counter-intuitive) but the fronts probably do 60% more work and get hotter than the rears.

<scratches pointy head>
 

NightmareMoon

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I'm at a computer, not under the car, but are you talking apples to apples here? Isn't the rear caliper-to-bracket bolt less than the front caliper-to-bracket bolt? The big 18mm bolt in the rear just holds the the bracket to hub, no?

Either way, my brakes haven't fallen off yet, so I'm going with "Ford knows what its doing".
 

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Norm Peterson

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I think it's silly -- not to mention counter-intuitive -- for the Chassis engineers to set the rears at 129 but the fronts at 85. The amount of threaded material is the same (although the fronts use a smaller bolt, which is ALSO counter-intuitive) but the fronts probably do 60% more work and get hotter than the rears.
Not sure what you're trying to say here. If the front bolts are of a smaller diameter than the rear bolts, and both bolts are of the same grade, it makes sense that the front bolts would be installed to a lower torque spec.

Bolt size is determined by the loads on the bolts, which depends on the geometry of the bolting arrangement and in this case how the braking loads resolve into loads at those bolt locations.


Norm
 

ronemca

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I'm smiling as I write - and not trying to be confrontational and/or obstinate. :angel:

Isn't the rear caliper-to-bracket bolt less than the front caliper-to-bracket bolt?
The front caliper does not use a bracket.
The big 18mm bolt in the rear just holds the the bracket to hub, no?
Correct.

I am comparing the two bolts that affix the front caliper to the hub with the two bolts that affix the rear bracket to the hub.

Yes - the fronts are smaller.

And I acknowledge & understand that torque specs correlate with fastener size, fastener material, material being fastened, thread pitch, load, temperature, shear, number of fasteners, Barbie's bra size, etc. etc. etc. A number of factors. Agreed. Therefore - since the fronts are smaller - they have a lower torque spec. Yes. But WHY are they smaller??

I'm not arguing; - I am musing. Out loud. In an attempt to grasp the logic of what SEEMS TO BE an anomalous design. We all know that:

* the front brakes contribute 55% or 65% or 71% of the total braking force. (The exact ratio is irrelevant - but it's greater than the rear)
* the front calipers are dramatically heavier and larger than the rears.
* the front pads are bigger, and are therefore presenting a larger surface area against the rotor (which could increase the stress on them)
* the forces introduced upon the front wheels during high-speed steering inputs would presumably add some sort/amount of stress on the caliper attachment (via the pads via the rotors)

In light of these factors, it SEEMS as if the front calipers would be the ones that demand (or should receive) the larger fasteners and/or more fasteners.

It's just an opinion. An observation. A chance to learn something. I had hoped for a logical explanation as to WHY the discrepancy exists.
 

Norm Peterson

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Therefore - since the fronts are smaller - they have a lower torque spec. Yes. But WHY are they smaller??
With nothing to look at, I would have to assume that the load-carrying details (caliper to bracket) are somewhat different front vs rear.


Norm
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