Torque- Socket vs Clawfoot

[Eric F.]

I'm getting my 75 convertible ready for the Northwest Regional and in the process I am tightening various bolts and nuts per factory specifications. The problem I've run into is the inability to place a socket over some of the nuts/bolts because of space constraints. However I am able to get a clawfoot into the area and onto the nut/bolts. Will the torque wrench deliver the same torque to the nut/bolt using the clawfoot? I ask because the clawfoot is offset compared to the center of the socket, which is identical to the center of the nut/bolt.

In case I'm misusing the term "Clawfoot" I will describe it. It is tool similar in shape and size to the open end of an open end wrench. It attaches to a standard 3/8 drive ratchet.

[Phil P.]

Re: Torque- Socket vs Clawfoot

personal experience with a claw foot is that it is going where nothing else would fit,therefore,torque is not an issue---tighten it untill it feels like the the open end wrench will spread and then quit---not to be rude but that style of wrench is usually used on very large bolt/nuts not common the automotive industy---i could be wrong---phil

[Joe L.]

Re: Torque- Socket vs Clawfoot

Eric-----

The tool you describe is usually called a Crowfoot wrench. When these are used in conjunction with a torque wrench there does need to be a correction factor applied for torque value. I've forgotten how to calculate it, though. However, since there is actually a torque RANGE for most applications, I would just set the torque to the bottom of the range and disregard any correction factor.

[Wayne W.]

Re: Torque- Socket vs Clawfoot

The torque difference would be negligible. If you figure most torque wrenches are like 14-16 inches long, one more inch offset would make little difference. In the case of a of a 16 inch wrench, it would 1/16 less than actual.

[Richard K.]

Re: Torque- Socket vs Clawfoot

Eric,

I've never used an extension on a torque wrench but do remember that it does affect the applied torque. From an old Sear's torque wrench owners manual:

"Drive Extensions"

There are two types of drive extensions. Concentric extensions extend directly along the centerline of the drive and as such do not effect the torque readings. Other extensions and attachments extend to points away from the centerline of the drive and the torque applied with them is different from the torque set on the wrench. Use the following formulas to calculate the correct torque:

E - Effective length of extension - measured along the centerline of the torque wrench (added by me: from centerline of torque wrench head to centerline of extensions grip)

L - Lever length of the wrench - center of grip to center of drive

T(W) - Torque set on the wrench

T(E) - Torque applied at the extension

So, Eric, where, T(E) = T(W) x (L + E /L)

or, [("lever length" plus "effective length")divided by "lever length"] times "torque set at the wrench" equals "torque applied at the extension"

So, yes you're crowfoot extension will affect the torque set at the wrench. Just doing a quick calculation with my own torque wrench and a one inch crowfoot extension, the effective torque is increased by almost 20% by that short extension!

I've done my best to describe what the manual's drawing and text show. If clarification is needed, I'll do my best to answer your questions. Just keep in mind, I'm DEFINATELY NOT a mathmatician or scientist........lol

[Chuck S.]

Re: Torque- Socket vs Clawfoot

Rich, I'm wondering if the formula shouldn't be T(E)=T(W) X (L+E)/L.

Sometimes printers and proofreaders without a mathmatical background don't give enough attention to the proper sequence of mathematical operations. A little slip like that and you'll get a totally different, and erroneous result.

The formula as I show it above makes more sense than the way they appear to have printed it...it increases the torque setting by the ratio of lever length plus extension divided by the lever length. For a one inch extension, this torque increase would be minimal in the context of a 16" lever length...one sixteenth more torque as Wayne said above.

In any event, I consider a crows foot wrench a jerry-rig tool, and wouldn't use one to apply more than about 20 ft-lb. There's not enough gripping surface, and what you have is poorly distributed; one slip and you'll bugger the corners of your hex nuts. The judges aren't going to check the torque of your fasteners anyway...unless the can see they are about two threads from being finger tight.

[Chuck S.]

For Example...

If I am correct about the formula, without the crows foot wrench, say you are applying the 20 ft-lb setting. Then, assuming a 16" torque wrench, when the crow foot is added, the corrected torque would 20 ft-b X (16"+1")/16", or 20 ft-lb X 1.0625 = 21.25 ft-lb.

[Eric F.]

Re: Torque- Socket vs Clawfoot

Joe,

I knew you'd offer some good information. And thanks for correcting my terminology. For as long as I can remember I refer to those wrenches as "clawfoot" and I'm always reminded that they are "crowfoot" wrenches.

Eric

[Eric F.]

Re: Torque- Socket vs Clawfoot

Rich,

Thanks for the information, it definately answers my question. Math has never been my strong suit but I expected there would be a difference when using a crowsfoot (extension). I will keep the formula for future use.

Eric

[Harmon C.]

Re: Torque- Socket vs Clawfoot

Eric
I have not seen an engine judge with a torque wrench but if you have not cleaned the area of the block on the rear flange or the stamp pad the judge will be happy if it is clean.
Good luck

Lyle

[Michael W.]

Crowfoot adapters

are used extensively in the aircraft engine industry in circumstances that do not allow a conventional socket to be fitted over the nut flanges- such as a pipe fittings.

The OP is doing the right thing by asking how to correctly compensate the setting on his torque wrench.

[Joe L.]

Re: Torque- Socket vs Clawfoot

Lyle-----

I don't think that torque is checked for judging purposes, either. However, every-now-and-then folks are interested in functionality rather than or in addition to originality. Proper torque is primarily an issue of functionality. If it wasn't important in that regard, GM would not have gone to the trouble of specifying torque information to the assembly line OR the expense of purchasing torque-specific or adjustable equipment to the assembly line.

Notwithstanding the above, the error produced by the use of the crowfoot wrench in conjunction with a torque wrench is small. As I previously mentioned, if one applies torque at the lowest end of the specified torque range for a particular fastener, one will virtually always have a final torque within the specified torque range without bothering to apply any correction factor.

[Joe L.]

Re: Torque- Socket vs Clawfoot

Eric-----

By the way, as others have mentioned, a crowfoot wrench is usually not a suitable tool for applying torque in instances in which the torque specification for the fastener is high (e.g. above 25 lb/ft, or so). There are also other functional limitations to the use of crowfoot wrenches.

For dealing with situations in which one must apply a specific torque to a fastener which can't be accessed with a socket, there are available tools called "torque adapters". These are wrenches which have a box end on one end and a square drive on the other. The square drive is attached to the torque wrench and the box end to the bolt or nut. These wrenches are much longer than a crowsfoot wrench and a torque correction factor must be applied. Sometimes, the correction factor is embossed on the torque adapter wrench.

VERY few amateur mechanics have torque adapter sets in their toolbox. In fact, many professionals probably don't.

[Richard K.]

Re: For Example...

Eric,

Chucks calc is correct. I re-looked at my math (should have done that before posting!) and there was an error. With a very short extension, there is not much effect on the torque set at the wrench.

An important thing to remember though is that the longer the extension, the greater the effective torque will be, and the calculation should be done.

[Eric F.]

Re: Torque- Socket vs Clawfoot

Joe,

You responded to Lyle before I could. You are correct that I was using the torque wrench for functionality while inspecting the car for judging purposes too. The main reason came up when I took the car in for an alignment. I noticed the local "reputable" shop mechanics tightened everything but never used a torque wrench. When they were done I drove the car home and put it on my lift and discovered some of the fasteners were well below torque specifications; and some not more than hand tight.

Thanks again to everyone for your assitance. I always like it when I learn something new and useful.