Class 8.8 bolts strong enough?

asand1 · Dec 3, 2015

A while ago I swapped 6th generation front brakes onto my 4th generation Maxima. The '96 torque member bolts were 12mm while the 6th gen are 14mx1.5.

Initially I sourced 14mx1.5 bolts from Mazda control arms, but had to stack washers due to the long shoulders.

Today I picked up new 8.8 14mx1.5x35 bolts with grade 8 9/16" split lock washers

After some internet searching, I have read endless opinions that 10.9-12.9. I have also read that Porsche only uses 8.8 in their 911 for various reasons.

What do you all think, am I OK? should I pay alot more for higher class bolts?

eljefino · Dec 3, 2015

Why can't you just cut the mazda bolts shorter?

Kool1 · Dec 3, 2015

Those look like brake caliper bracket mounting bolts. I remember swapping over a 1968 Camaro from front drum brakes to disc brakes. I used grade 5 SAE bolts to hold the caliper bracket to the steering knuckle. They are nowhere near as strong as grade 8 and I never had a problem with the bolts or front brakes. I drove the car for a few years and sold it.

asand1 · Dec 3, 2015

Originally Posted By: eljefino
Why can't you just cut the mazda bolts shorter?
Its the shoulder thats too long.

asand1 · Dec 3, 2015

Originally Posted By: Kool1
Those look like brake caliper bracket mounting bolts. I remember swapping over a 1968 Camaro from front drum brakes to disc brakes. I used grade 5 SAE bolts to hold the caliper bracket to the steering knuckle. They are nowhere near as strong as grade 8 and I never had a problem with the bolts or front brakes. I drove the car for a few years and sold it.

Thats one "good enough" from personal experience then. Thank you.

Donald · Dec 3, 2015

I would be class 5 is good enough. Class 8 is certainly good enough.

Ramblejam · Dec 3, 2015

Whether OE (4th gen), or retrofit (6th gen), 10.9 is proper fitment.

Do the right thing.

CarbonSteel · Dec 3, 2015

8.8 is the equivalent of a Grade 5 and 10.9 is the equivalent of Grade 8. Here is a comparison chart. Bolt size could be the reason why 10.9 is specified over 8.8--a larger bolt may be OK in 8.8, but a smaller one requires more tensile strength (in regards to your Porsche reference).

The real question is what is your safety worth? I have to think it is worth more than a few dollars for some bolts.

eljefino · Dec 3, 2015

You can find tensile strength formulas for both grades, and multiply by area.

The question is, is a weaker 14mm bolt as good as a stronger 12?

Merkava_4 · Dec 3, 2015

Are saying you don't need the shoulders ?

Do you want the bolts threaded all the way to the head ?

asand1 · Dec 3, 2015

Originally Posted By: Merkava_4
Are saying you don't need the shoulders ?
Yes

Quote:
Do you want the bolts threaded all the way to the head ?

I don't "need" shoulders, in fact I can only have ~10mm shoulders. Problem is the current shoulders are ~20mm.

JHZR2 · Dec 3, 2015

I would think that if you knew:

-Rotor mass
-Rotor diameter
-Tire circumference

Then you could figure the rotor tip speed at 100 MPH or so, coupled with mass and deceleration rate at lockup, and determine the force on those bolts once the ever arm was considered.

Then apply a safety factor of 2 and get your answer.

You might need to determine cross-sectional area of the bolts.

Regardless its easier to buy the strongest you can find and call it a day...

Unless there's some other tradeoff with the stronger ones...

JimPghPA · Dec 3, 2015

McMaster-Carr has a great selection of bolts.

buck91 · Dec 3, 2015

I saw a lot of 10.9 working on the Mustang as well as my truck. I can't remember what the caliper bracket bolts were, though. I'd bet 8.8 is sufficient but I'm not sure if I'd bet somebody's life on it. Whats the cost difference for you?

Merkava_4 · Dec 3, 2015

Is 14mm the hex size or bolt diameter size ?

Ramblejam · Dec 3, 2015

Originally Posted By: JHZR2
Regardless its easier to buy the strongest you can find and call it a day.

No need to source anything crazy here.
No need to save a few bucks on inappropriate bolts, either.

There's a happy medium...

Proper class
Proper coating

What we see in the picture doesn't adhere to either of these criteria.

asand1 · Dec 3, 2015

Originally Posted By: Merkava_4
Is 14mm the hex size or bolt diameter size ?

14mm is the thread diameter.

dlundblad · Dec 3, 2015

Originally Posted By: Ramblejam
Originally Posted By: JHZR2
Regardless its easier to buy the strongest you can find and call it a day.

No need to source anything crazy here.
No need to save a few bucks on inappropriate bolts, either.

There's a happy medium...

Proper class
Proper coating

What we see in the picture doesn't adhere to either of these criteria.

What kind of coating should they have?

bdcardinal · Dec 4, 2015

FWIW ARP sells bolts based on dimensions. I ordered random stuff just to be fun on my 95. I now have 12pt ARP bolts for the ABS sensors on my 95 Mustang.

meborder · Dec 4, 2015

I would look up the proper torque spec for the appropriate year and choose the right bolt grade based on that. From experience, caliper bolts are usually torqued in the 100-150 lb-ft range, which would make the 8.8 look marginal being good for only 89lb-ft.
http://www.engineershandbook.com/Tables/torque1.htm

Ditch the lock washers too. I've never seen them in an OEM application. While controversial, there are some conditions in which lock washers quicken self loosening rather than hasten it.

Class 8.8 bolts strong enough?

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