torque spec, caliper to mount

[yohy]

Can anyone give me the torque spec for the caliper body to the caliper support. '09 Legacy SE non-turbo. I am working on my son's car and don't have a service manual for this specific car. I have one for the '93, '97, '03 and the '04, but not this one. I have cross referenced to what I have but they seem to vary between 27.5 and 19.5 ft lbs., I would just like to get it right.

 

Thanks.

[GeneralDisorder]

It's not a critical fastener that needs a specific torque. Just make it tight with a box wrench and you'll be good to go.

 

Mechanic's don't torque stuff like that - they would waste their entire day if they bothered with every single bolt. As my old boss used to say "half a turn before it breaks". Specifc torque values are used when gasket crush or clamping force need to be very accurate - head gaskets - etc, or for fasteners that are part of an assembly that experiences high speed movement or especially rotational forces - axle nuts, crank bolts, pulley bolts, etc. If it doesn't move or hold something that needs a specific clamping force then the torque value given by the book is going to come simply from a table in a machinists guide that lists reccomended torque by size and grade of the fastener.

 

In other words - "hand tight". Just don't break it .

 

GD

[yohy]

GD,

Thank you for your reply, insight and suggestions. My dad, a Georgia Tech graduate who holds a PE license, contends that lack of confidence or understanding tends to lead one to overbuilding or over engineering. With that, as a shade tree mechanic versus yourself, a professional, I tend to over compensate for my lack of experience by being as precise (or anal) as I can. With that, I stress over things like torque specs, while you would just tighten to a known range and be done, I search for the elusive specification. I guess I just have to have more confidence.

 

Thanks again.

[Qman]

It is not wrong to want to do the job correctly. Torque specs are important. It will stop a bolt or fastener from being over-stressed. Your caliper bolt is best between the numbers you gave. Shoot for the mid and you'll be fine. You can add a little blue lock-tite if you are concerned of it coming loose.

[GeneralDisorder]

I completely understand - getting a "feel" for the torque of fastener sizes takes years - though it was entirely transparent to me as I began wrenching from a very young age. But I have worked with very intelligent people that have no sense at all for this - a friend of mine (software engineer - no dummy to be sure) misread the torque spec in the manual for his car and torqued an 8mm threaded nut to about 60 ft/lbs..... or tried anyway. It snapped right off of course. Fortunately it was an easy fix but it was clear that he had no idea what 60 ft/lbs should feel like and if that was even reasonable for the size of nut he was working on.

 

Here's what you should do - find a chart online of reccomended torque values for different thread sizes and bolt grades - then take out your torque wrench and see what those values feel like with a nut/bolt in a vise.

 

GD

[StructEngineer]

Are any connections in brake work slip critical?

[Qman]

I completely understand - getting a "feel" for the torque of fastener sizes takes years - though it was entirely transparent to me as I began wrenching from a very young age. But I have worked with very intelligent people that have no sense at all for this - a friend of mine (software engineer - no dummy to be sure) misread the torque spec in the manual for his car and torqued an 8mm threaded nut to about 60 ft/lbs..... or tried anyway. It snapped right off of course. Fortunately it was an easy fix but it was clear that he had no idea what 60 ft/lbs should feel like and if that was even reasonable for the size of nut he was working on.

 

Here's what you should do - find a chart online of reccomended torque values for different thread sizes and bolt grades - then take out your torque wrench and see what those values feel like with a nut/bolt in a vise.

 

GD

 

Or...

 

 

 

 

 

 

 

 

 

 

you could do it on the car and actually accomplish something...

[Fairtax4me]

Or break something.

 

 

Caliper bolts generally just have to be tight.

 

Not entirely sure what you mean by "slip critical". The caliper slides on the bolts regardless of how tight they are, so I guess the answer is.... no?

[StructEngineer]

Nah, you're a bit off on that. Slip critical means something else. I'd be interested to hear from "torque it by eye" folks.

[Qman]

Or break something.

 

 

Caliper bolts generally just have to be tight.

 

Not entirely sure what you mean by "slip critical". The caliper slides on the bolts regardless of how tight they are, so I guess the answer is.... no?

 

Every bolt has a specific torque value. The guys who subscribe to the thought that just make it tight are the ones I blame when bolts don't come loose without using extreme force. And tight enough explains why I see wheels seperate from cars going down the road.

 

And thanks for showing your ignorance...

 

Generally speaking, there really isn't a reason for slip critical joints or bolts in an automotive application. I guess bushings would sort of fall into that catagory but not bolts.

Edited April 12, 2010 by Qman

[Setright]

Getting back on track:

 

 

I have used a smidgen of copper grease on the threads, and 80Nm on the caliper support brackets. This is near the top of the range according to the Subaru service manual. Using these values, on many Subarus, including friends, and my own - which get a good thrashing on trackdays - I have not had problem. Nothing loose, nothing not able to be opened come the next brake service.

 

I register close to 300,000 miles of happy driving behind the wheels of my own cars.

 

Add in the extra mileage on the car's I have helped with, and I think my method has stood the test of time.

[StructEngineer]

Every bolt has a specific torque value. The guys who subscribe to the thought that just make it tight are the ones I blame when bolts don't come loose without using extreme force. And tight enough explains why I see wheels seperate from cars going down the road.

 

And thanks for showing your ignorance...

 

Generally speaking, there really isn't a reason for slip critical joints or bolts in an automotive application. I guess bushings would sort of fall into that catagory but not bolts.

 

I would venture to say that the caliper bracket to knuckle connection is a perfect example of a slip critical connection. If it were designed as a bearing connection every time you'd brake the bracket would slip from the play in the bolt holes.

 

yohy, I am also a PE and tend to agree with your dad.

[Fairtax4me]

And thanks for showing your ignorance...

 

 

 

Well thanks for 'splainin' it to a "po' dunk country boy".

 

Now that I went and looked it up (verified my initial thought). I'll still say no, it's not a slip critical connection. The bolts don't bear any substantial load when braking force is applied because of the design of the bracket that the caliper rides in. Even if it does slip there is no chance of failure because the caliper simply can't move far enough to break the bolt.

 

What could break the caliper slide bolt would be over tightening, which is where "tight" comes into play. Everybody has their own definition and feel of what's "tight". So it comes down to personal preference, but basically if you're using a standard size 3/8" ratchet, you won't get a bolt that size tight enough to break without really trying to break it.

[Qman]

Well thanks for 'splainin' it to a "po' dunk country boy".

 

Now that I went and looked it up (verified my initial thought). I'll still say no, it's not a slip critical connection. The bolts don't bear any substantial load when braking force is applied because of the design of the bracket that the caliper rides in. Even if it does slip there is no chance of failure because the caliper simply can't move far enough to break the bolt.

 

What could break the caliper slide bolt would be over tightening, which is where "tight" comes into play. Everybody has their own definition and feel of what's "tight". So it comes down to personal preference, but basically if you're using a standard size 3/8" ratchet, you won't get a bolt that size tight enough to break without really trying to break it.

 

Sorry, bad form.

 

I think he is refering to the mounting bolt rather than the slider. My initial thought was the same as slip critical meaning that the joint was designed to slip under pressure. Those are not.

 

Over tightening is what my comments were directed at more than anything. Torque by feel will generate more over torqued bolts. Which will result in more "stretched" or over torqued bolts. Both of which will cause more grief than good. Using a torque wrench on the car with the proper torque specs will not only not break bolts but it will give the OP the true feel for the torque value specified. "Feel" takes years to get and that still is not fool-proof. In the end only torquing bolts with a torque wrench can ensure that they are correct.

 

Now, before this arguement starts,. I do not torque every bolt myself. I have, however, been doing this for over 30yrs and know the difference and when torquing is required. I use 1/4", 3/8" and 1/2" ratchets depending on bolt size to avoid over-torqueing whenever possible.

 

Ken

[StructEngineer]

Yes, I'm referring to the bracket mount. Not the bolt that connects the caliper to the slider pin.

 

All I was getting at is if you take the approach of eyeballing torque on every bolt other than those in the head and engine block you may be missing this issue. Albeit difficult, just trying to inspire some thinking.

[yohy]

To all who have responded. I am grateful to the folks who are active contributors to this forum, I know when I am stuck, there will be a good hearted soul who is willing to take the time to respond. Oh and I also love the "exchange" of ideas. Thanks again to all.

[Qman]

Yes, I'm referring to the bracket mount. Not the bolt that connects the caliper to the slider pin.

 

All I was getting at is if you take the approach of eyeballing torque on every bolt other than those in the head and engine block you may be missing this issue. Albeit difficult, just trying to inspire some thinking.

 

That is where a factory manual is very handy to have. It will tell you the torque value for every bolt in the car. Re-engineering the car after the fact may be time better spent elsewhere.

[Fairtax4me]

I agree and understand there are many places that a torque wrench should be used rather than just going by "feel". Lug nuts (probably the most commonly over/under tightened fastener on the car), head bolts, flywheel, even valve covers and oil pans should be torqued to proper spec to avoid warping and prevent leakage, just to name a few.

 

But even with a torque wrench you still have a risk of stripping threads or breaking bolts, especially ones that are 15-20 years old and have been torqued and re-torqued several times throughout the life of the car. Metal fatigues with time and repeated heating, cooling, and other environmental variables that the assorted fasteners on a car are exposed to.

[GeneralDisorder]

My torque wrench comes out for lug nuts (avoids warping rotors), head bolts, and EJ series axle nuts.

 

I have not experienced the need for one on any other Subaru fasteners. Nor have I ever broken one (except twisting them off when trying to remove a rusty fastener - which I try to avoid but am not 100% succesful at) or over tightened them..... or had a part fall off or come seriously loose for that matter.

 

That's 10's of thousands of fasteners - without a single too tight/too loose failure.

 

Of course - don't attempt it if you aren't sure you can feel it.

 

If this were NASA I would be walking around in a white smock with a torque wrench in either hand. And I would be charging $10,000 for a clutch job - and it wouldn't be ready for 6 months.

 

GD