Caliper Mounting Bolt Torque

[BeerBudgetRacing]

Looking for a reference for torque spec on caliper mounting bolts on an RF01 with standard VD uprights.

Can't seem to find one anywhere.

Thanks.

[DaveW]

What thread & size bolts, how many threads are engaged, and what material (aluminum or steel) are you mounting them to?

I could give you a good estimate if I knew that.

[BeerBudgetRacing]

3/8-16 going into alum.
Engaged about 3/8-1/2.
The ear on the upright is about .55 in thick.

[BeerBudgetRacing]

When I removed the caliper I tested and the wrench was set at 45lbft before it loosened without clicking.
But it's been on there for years.

[DaveW]

3/8-16 going into alum.
Engaged about 3/8-1/2.
The ear on the upright is about .55 in thick.

IMO, if you have at least 3/8" of threads engaged, 25-30 lb-ft would be safe, and use blue Loctite. This is a place w/o much stress, but you don't want them to come loose.

[Garey Guzman]

I always safety wire them so I have a quick visual of any movement.

https://www.aircraftspruce.com/catal...All%20Products

[EACIII]

I had a bolt come out on a rear caliper at Pocono a number of years ago. Not as much fun as you would think. Check them often now.

Ed

[sccadsr31]

Not intending any disrespect but I would not use my good torque wrench to remove a bolt, first it is only used to torque to put bolts on and the "break away" torque does not reflect the torque required to tighten the bolt. I have great heart ache when I have to torque a left hand thread and am most likely to get out the beam torque wrench.
If you Google Bolt Torque Charts you can find some useful images.

[DaveW]

Not intending any disrespect but I would not use my good torque wrench to remove a bolt, first it is only used to torque to put bolts on and the "break away" torque does not reflect the torque required to tighten the bolt. I have great heart ache when I have to torque a left hand thread and am most likely to get out the beam torque wrench.
If you Google Bolt Torque Charts you can find some useful images.

Loosening, as above, should always be done with a non-ratcheting breaker bar to avoid breaking or compromising either a ratchet or torque wrench. The initial breakaway torque could be an order of magnitude greater than the fastener's tightening torque due to corrosion, etc. Winter road wheels (salt) are the most likely to have the worst issues, but any fastener that has been stationary and not lubricated properly for a while could require enough loosening torque to damage a torque wrench or ratchet.

Even on the racecar, I never use a ratchet or torque wrench to loosen anything that requires much torque.

[BeerBudgetRacing]

Not intending any disrespect but I would not use my good torque wrench to remove a bolt, first it is only used to torque to put bolts on and the "break away" torque does not reflect the torque required to tighten the bolt. I have great heart ache when I have to torque a left hand thread and am most likely to get out the beam torque wrench.
If you Google Bolt Torque Charts you can find some useful images.

Loosening, as above, should always be done with a non-ratcheting breaker bar to avoid breaking or compromising either a ratchet or torque wrench. The initial breakaway torque could be an order of magnitude greater than the fastener's tightening torque due to corrosion, etc. Winter road wheels (salt) are the most likely to have the worst issues, but any fastener that has been stationary and not lubricated properly for a while could require enough loosening torque to damage a torque wrench or ratchet.

Even on the racecar, I never use a ratchet or torque wrench to loosen anything that requires much torque.

I know you're talking about me

I was mostly curious as to the consistency of the values. I did say they had been on there for years.

I treat the $15 Harbor Freight torque wrench as a breaker bar. I figure it's been accurate within 20%.

I have 4 different CDI torque wrenches in different ranges for snugging stuff up.

I haven't found a comprehensive chart covering type of material as well.

[Lyngengr]

3/8-16 going into alum.
Engaged about 3/8-1/2.
The ear on the upright is about .55 in thick.

I would be very careful with the torque value you use. The aluminum uprights are castings, so the tensile strength is very low. I had one of my rear bolt holes strip last year (from overzealous torqueing) and had to helicoil it. From that experience, the shear strength of the aluminum casting is the limiting factor. I'll run some numbers and post it, but it will not be very much torque, maybe 15 - 20 ft-lbf at most. You're really not trying to keep the joint tight, as is the use for most bolted joints, you're just trying to keep the caliper in place. Using the prop bolts or even drilled head AN bolts and safety-wiring is a good idea.

[mark elder]

I think the real issue with alloy uprights is that that are typically cast out of cheese. Then the caliper bolts get tightened to the 'text book torque' multiple times over decades. Eventually the threads say enough. To make it worse, sometimes the bolt is not using the full thread in the upright (because we shimmed the caliper or put a 'nice thick washer' on etc).

I think you are saying the bolt was loosened with disturbing ease. I would be looking very carefully at the threads. Any doubt and I would be heli-coiling the upright. Oh, and I have seen heli-coils pull out of uprights too. Then it is time-sert or big-sert time. When you tighten the bolt, it should snug up then go tight. Again, if your hands are saying cheese when tightening the bolt, take it all apart and fix it. These are brakes.