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Old 10-01-05, 10:39 AM   #1
Drunken Chicken
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Torque wrench important when installing disc brakes?

Next week my new wheelset should arrive and then I'll install my front Avid Juicy 5. The thing is, I want to do it myself, but in the installation manual I keep seeing how much torque to put here and there and, well, I wanted to ask: Is a torque wrench important when installing disc brakes? If so, how much is a decent one?

Thanks,
-DC
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Old 10-01-05, 09:01 PM   #2
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[QUOTE=Drunken Chicken: Is a torque wrench important when installing disc brakes? If so, how much is a decent one?

Thanks,
-DC[/QUOTE]


The short answer, yes proper torque on any fastener is important. The installation torque creates a preload in the joint that allows friction to secure the parts from sliding, and proper preload prevents the fastener from vibrating loose. Torquing to specification ensures you don't strip the threads during installation of the fastener, yet it won't be loose as to slip during use.

That said, I am sure some (if not most) bicycle shops do not use torque wrenches. I think the most important torque requirement for installing disc brakes is fastening of the disc rotor to the hub. When attaching the rotor, two parameters are very important: 1) torque sequence and 2) torque consistency.

1. Torque sequence is usually in a cross or star pattern. This pattern ensures the rotor is flat against the hub and helps prevent any warping. Also, it is important to tighen all fasteners a little at a time. Better to tighten all to 2 ft-lb, then tighten all to 5 ft-lb and finally 7 ft-lb.

2. Torque consistency is important too. Torque on all fasterners should be the same. In this case, I believe torque consistency is more important than the actual torque value. For example, it is better to have all fasterners torqued to 7 ft-lb, rather than have a range of torque values (5, 7, 9, 10, 4 ft-lb).

I've seen cheap torque wrenches at $20 and good ones $250. If you want a decent torque wrench, Sears Craftsman wrenches are in the $70 range (depending on features). I use my torque wrench on my automotive and bicycle work.


(Note, the above torque values are for illustration purposes).
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Old 10-01-05, 09:20 PM   #3
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I was asking the same question as you earlier in the summer. I ended up buying a very cheap quality torque wrench on eBay, for about $30 shipped.

Unfortunately, due to the very crude construction of the wrench, i don't entirely trust it's torque dial. I stripped some bolts (luckily just the heads, not the threads) when installing my Avid discs, i think because the torque wrench wasn't clicking when it should have. If i had been doing it by hand, that would never have happened.

In the end, though, I think that all the torque specifications are partly there because the manufacturers are covering their asses. If somebody installs a part too loose, and it falls out and they get hurt, they could sue the company for not telling them how tight to fasten the part. So now companies go overboard, telling you how many Newton meters to torque your water bottle cage bolts, or whatever.

If you've been working on your bike for a while, you probably already have a good feel for what is a suitable torque, keeping in mind what materials you are dealing with. Steel into aluminum, aluminum into aluminum, steel into steel, ti into aluminum, etc.
Using a bit of beeswax or loctite will insure that the bolt won't come loose as long as it's installed reasonably tightly.

Disc brake rotors obviously are vital to you stopping, so you don't want them coming off, but there are 6 bolts, and the force on them is perpendicular to their shafts. In other words, the only danger is that they might vibrate loose, and even then, more than a few of them would have to come out before you'd have a serious situation. Loctite is good for peace of mind, but just keep an eye on them and periodically check that they're tight, and you should be fine.

People will always say 'OMG it's your brakes! You're going to die if they're not just right!' but with some common sense, you probably don't need a torque wrench.
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Old 10-02-05, 03:35 AM   #4
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Awesome, thanks to both of you for the informative replies. One question: Loctite is a liquid which you place on (for example) a bolt, and it dries and secures it into place, not letting it come loose? How easy is it to get off afterwards (for example, if I wanted to swap my brakes over to another bike)?

Thanks again

PS: Assuming I didn't use a torque wrench, would tightening all the bolts and bits&pieces to, say, 12 turns of the bolt, mean more or less the same torque on all of them?
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Old 10-02-05, 06:57 AM   #5
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Quote:
Originally Posted by Drunken Chicken
Awesome, thanks to both of you for the informative replies. One question: Loctite is a liquid which you place on (for example) a bolt, and it dries and secures it into place, not letting it come loose? How easy is it to get off afterwards (for example, if I wanted to swap my brakes over to another bike)?

Thanks again

PS: Assuming I didn't use a torque wrench, would tightening all the bolts and bits&pieces to, say, 12 turns of the bolt, mean more or less the same torque on all of them?
Hi. I have the same thing with my aerobars , to buy a new torque wench to install them or not. I decided not to buy one and try to estimate the torque myself. I did the same thing as you stated , counting the no. of times i turn the bolt , but i found out that the torques would not be the same , even if i started turning every bolts from the same position. So i would not recommand counting the turns.
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Old 10-02-05, 01:27 PM   #6
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In one of the old Beechcraft Aircraft manuals the military method for achieving a propellor torque of 800 ft-lbs was a 200lb man hanging on a 4 ft wrench. Then to seat it, another guy would tap the wrench with a mallet.
It is a novel way to write a manual, but the principle does cross over. If you want (for discussion sake) 4 ft-lbs, you could use a 1-ft wrench and 4lbs of force. If you only have a 6 inch wrench, then you would use 8 lbs of force.
Thus, If you need to achieve 7 ft-lbs and dont want to strip out or use a metering wrench(which is still the best way), you could use 14 lbs force on a 6 inch wrench(i.e. an L-handle torx wrench). There are many ways to achieve the same end in this instance, but that is the simplest one I have seen.
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Old 10-02-05, 01:45 PM   #7
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Quote:
Originally Posted by Drunken Chicken
One question: Loctite is a liquid which you place on (for example) a bolt, and it dries and secures it into place, not letting it come loose? How easy is it to get off afterwards (for example, if I wanted to swap my brakes over to another bike)?
Loctite is a trade name for a thread locking compound. There are various grades of Loctite. I prefer to use the "Blue #242", which is a medium strength and is considered serviceable - in other words, you can remove the fastener, but it won't vibrate loose by itself. It's easy to remove, and you may need to use a little more torque than is typically required for a fastener that size. Initially, it's hard to break the bond.

They make a high strength version too, but I don't recommend it.
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Old 10-02-05, 02:41 PM   #8
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Unless you are in constant touch with hardware (IE:, like mtnbikerinpa, I'm also an aircraft mechanic) and after many years, I can quite accurately torque a bolt/nut without the use of a Tq wrench but in some cases I will use one because of the component, like a propeller nut as an example. I doubt many on here (just by some of the questions on this forum) can guesstimate the torque of a bolt/nut. There is a TQ for all hardware and it's not put there by the manufacturers for the fun of it. Too loose, you know what happens, too tight, your now stretching the bolt and may strip/break it. Loctite seems to be the "magical solution" for alot of folks on here. I do not use it on my bikes though I don't do the off-road thing as much anymore. Loctite, though used in the aviation field is used more for hardware that is not all to accessable and even then at times not. Of course we use locknuts, bolts that have nylon inserts and so on. But most screws (leading edge, fuel tank panels as an example) are torqued in place and a plane (esp a prop jobby) shakes, rattles and rolls more than a bike does. Saying that, can you borrow a TQ wrench from someone? Maybe a buddy, your dad's buddy....and if you can, TQ all your hardware to the specs and then with your wrench/allen keys/sockets, play with the hardware to get a feel of what 70" lbs is like, what 350" lbs is like and so on. A properly Tq'd nut/bolt should remain in place. But if you want to feel "safer" by all means use 242 on bolts that are not greased.
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Old 10-02-05, 05:05 PM   #9
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-DC[/QUOTE]The short answer, yes proper torque on any fastener is important. I use my torque wrench on my automotive and bicycle work.[/QUOTE]

This is the correct answer. Just for fun I went through the BBI mechanics course (loved it) and learned what a useful and important tool a torque wrench is. Although it does not apply in your case, they are especially important when getting anywhere near carbon fiber parts. If I go into a bike shop and don't see a torque wrench hanging up on the wall, I will probably walk out. I once went into a high end bike shop and saw a mech working on a CF Pinarello TT bike (probably worth over $10,000). He was securing the seat post collar with out a torque wrench. It made my stomach turn. Sure hope he did not crack the seat post.
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Old 10-02-05, 06:36 PM   #10
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I still feel that for most bicycle components, it is quite possible to install them properly without a torque wrench. That doesn't mean that if you have NO IDEA how much to torque them that it will be fine, or that loctite will be the magic elixir. If you are asking how many turns to tighten a bolt, you probably don't know how to judge the tightness.. In order to tighten bolts consistently, you have to feel how hard you are torquing the wrench with your hand, and stop turning when you get to the same point with each one.
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Old 10-02-05, 07:39 PM   #11
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Let me give you some advise as a mechanic....... I work on aallllllllot of disc brakes.... in fact some days I stick of brake fluid when i get out to ride.

You do not need a torque wrench to work on them. for one, a good one is expensive. cheap ones arent accurate at all. Companies list torque settings on parts and on paper to cover their ass when you break one off in a hub and try to warranty a bolt. HAHAHAHA

Make sure their snuged up and go 1/8th past. Avid jucy's have dry loc on the bolts witch helps alot.

So take it from a racer and wrench who hates nothing more than removing a rotor bolt with no face left.
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Old 10-02-05, 08:04 PM   #12
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Quote:
Originally Posted by RockyMtnMerlin
-DC
The short answer, yes proper torque on any fastener is important. I use my torque wrench on my automotive and bicycle work.[/QUOTE]

This is the correct answer. Just for fun I went through the BBI mechanics course (loved it) and learned what a useful and important tool a torque wrench is. Although it does not apply in your case, they are especially important when getting anywhere near carbon fiber parts. If I go into a bike shop and don't see a torque wrench hanging up on the wall, I will probably walk out. I once went into a high end bike shop and saw a mech working on a CF Pinarello TT bike (probably worth over $10,000). He was securing the seat post collar with out a torque wrench. It made my stomach turn. Sure hope he did not crack the seat post.[/QUOTE]

I hope this doesent sound too ignorant, first time on a forum. I agree with the point made about the necessity of proper torque on all fasteners. my question is, where does one find the ever important specs? Of all the books on bicycle repair I have looked at, I don't recall one that told the torque specs; same to be said for parts that were purchased. Many thanks Rev. Scott
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Old 10-02-05, 08:49 PM   #13
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All Shimano components and several other competent component companies will give a data sheet in the shipping box of the component.
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Old 10-02-05, 08:57 PM   #14
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Originally Posted by Rev. Scott
my question is, where does one find the ever important specs? Of all the books on bicycle repair I have looked at, I don't recall one that told the torque specs; same to be said for parts that were purchased. Many thanks Rev. Scott
Park Tool lists torque specs, see:http://www.parktool.com/repair/readhowto.asp?id=88
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Old 10-03-05, 08:57 AM   #15
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OK, thanks to everyone for posting, all the post were very useful!
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