Motor Vehicle Maintenance & Repair Asked by x0a on December 18, 2020
I just broke two 3/8 in. extensions trying to crack an underdrive pulley loose (specs say the pulley is at 130 ft-lbs, but it feels much higher than that).
This begs the question: are there standard tolerances for tools of a given thickness (a maximum amount of torque for 1/2 in and 3/8 in tools)? If so, what are they?
Good question, while we probably can't just ring up a tool manufacturer and ask, we can derive it with some accuracy:
Maximum socket size I can find for 1/2" is 36mm, that translates to an M24 fixing: http://stainlessautomotivefastenings.co.uk/pdfs/HEXAGONHEADIDENTIFIER.pdf
Standard torque figures for an M24 using a 12.9 grade fixing (strongest grade) is 926 lb ft http://electronicfilters.tpub.com/TM-10-4330-237-13P/css/TM-10-4330-237-13P_105.htm
So I think it would reasonable to say that, even with a tiny factor of safety, a 1/2 drive extension should be able to handle 1000 lb ft
Applying the same logic to 3/8", that would be a 22mm (M14) fixing, which equates to 177 lb ft. So 130 lb ft plus seizure could well exceed the limit for 3/8" hardware.
Correct answer by KnowledgeQuest on December 18, 2020
I can't answer for 1/2" but I just bought a 1/2" to 3/8" coupler from Facom and stamped on the side it says "maxi 202 Nm", which equates to about 150 ft lbs. I think 150 ft lbs is about the most a 3/8 drive can safely withstand.
Answered by Ron Weasley on December 18, 2020
I tested this out accidentally while doing an axle nut. 150 ft-lbs will break a 3/8" drive usually and about 300 ft-lbs will break a 1/2" drive. These are on regular breaker bars that are partially hollow and have the little ball in the space of the head to hold the socket.
A SOLID 1/2" heat treated impact rated drive anvil will go up to about 1200 ft-lbs.
Answered by Benjamin08273 on December 18, 2020
A VERY GOOD 1/2" extension might get close to 500ft-lbs on an impact, but if you put 250 lbs on a 2 ft pull handle, it'll twist it off EVERY TIME
Answered by eddie daniel on December 18, 2020
If you assume a reasonable quality tool steel that can handle 100K psi, a 1/4" drive can take about 30 ft-lb, 3/8" about 100 ft-lbs, 1/2" about 230 ft-lbs, and 3/4" about 800 ft-lbs. Really good steel will bump this up, while special tools like a wobble extension may cut it to half.
Answered by MetalsGeek on December 18, 2020
Failure of the 3/8 extension is very likely a poor tool or maybe a one time defect. I have put 200 ft/lb on Craftsman extensions ( with "cheaters", I carry a 12" cheater in my tool box.). You should have a hardness about HRc 30 /35 ( Rockwell hardness) for a good tool. I have split a Craftsman 3/8 drive socket with an impact wrench- there is a limit to what load you can put on them.
Answered by blacksmith37 on December 18, 2020
Many tools are made to Fed Spec GGG-W-641E which you can still find on the internet as of July 2019. This spec gives test-torque requirements for 1/4, 3/8, 1/2, 3/4 and 1.0 inch drives for ratchets, universals, hinged breaker bars, extensions, etc.
Answered by George on December 18, 2020
if you have high quality tools it is common to get 200-230 lbs on 3/8 breaker bar but you will most likely be using a cheater pipe to add a foot or two of leverage. If you do the same to a ratchet it will probably break at 200 lbs. assuming the tooth count is high(90- 100).Ratchets with lesser tooth counts are stronger and normally come in 1/2 inch drives. see youtube for demonstrations.
Answered by Moriel on December 18, 2020
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