trailing arm torque, torque wrench questions

[ichthos]

Hello,

I am still in the process of refurbishing the rear end of my TR6. In Tinster's article "Trailing Arm Refurbish" he cautions against tightening the six nuts that hold the brake backing plate by hand, which should be tightened to 14 ft/lbs. My questions concern the torque wrench. I have one of the bar torque wrenches that bend a rod that points to the ft/lbs on a scale as you tighten the bolt. I have used this for the past 20 years - is this sufficient for the job at hand, or am I asking for trouble? I don't have the money to by a Snap On torque wrench for $250-300. I am not sure if I can rent any locally or how accurate they are. There are many used torque wrenches on Ebay. How would I know if they are still in calibration? What does it cost to calibrate a torque wrench, and can anyone recommend a company? Any suggestions are greatly apprecited.

Kevin

 

[sail]

I am curious also but don't know. Since we are both up my take would be feel would be better than a bar wrench at that range. The ranges and drive size vary greatly. Anyone have experience with a cheapie like this Harbor Freight?
https://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=807
Or of course TR3driver knows how to calibrate your bar:
https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/524216/torque_wrenchs#Post524216
I should add I bought a nice Snap-on 20-100# off ebay for $100, a couple years old but new. You might prefer an even lower range and use the bar for the big stuff.

 

[Tinster]

Kevin- I used a $90 torque wrench I bought at sears.
I dial in the torque # I need to achieve and the wrench
"clicks" when I have attained it.

In my opinion- the six each, trailing arm studs
and nuts are the single most critical item in a
restoration of the rear suspension. The trailing arm
aluminum is very soft and it is easy to overtighten
the six steel studs and strip their aluminum holding threads.

dale

 

[WedgeWorks]

Here is the myth about torque wrenches:
-Torque wrenches need to be calibrated once a year/anually as a minimum either by a testing & calibration lab or the manufacturer.
-The pointer type wrenches are fine for a bare minimum, but unless it has been WELL taken car of there can be issues; stuck pointer or bent pointer or scale. If you have a wrench that requires a high torque it is not easy to pull the wrench make sure you dont slip and get the exact scale reading you are required as you are pulling on the wrench, no clicky-clicky.
-The digital torque wrenches are good but they use batteries. If the battery dies your hosed or if you drop it you will never know if it is fine to keep using it. Some of the old ones had a light that would light up when you hit the predetermined value and the other click.
-The twist handle dial type are the best of all. They all click, they have both Nms & Ft-lbs, lock ring to keep the values set and are best value for the dollar.
-MOST IMPORTANT never drop a torque wrench, never leave the wrench set on a desired torque setting when stored or not being used for a lenghty period of time if they have dials on the handles and when not in use set the wrench on the lowest setting on the scale never lower than that or higher. The internal springs get messed up.

I have been using torque wrenches for automotive, industrial and construction for over 20 years with values from inch-pounds to 2000 to 2500 ft-lbs. Last thing you need is to under torque a bolt, so it falls off or losens up or over torque a bolt to a failure.

 

[19_again]

Wedgeworks,
I'm not clear on the message, and this is an important one. Is it a myth that they should be calibrated ?
Thanks, Mike

 

[Tinster]

Michael- I agree with everything you stated.
In the pharmceutical world, we have all measuring devices,
gauges, etc, calibrated and stamped on a yearly basis.

I think that is overkill for most of the work we perform
on our old cars. I have used many types of torque wrenches in
my very long career in construction.

For my car, I purchased a Sears quality dial #/clicker unit.

I'll repeat from other mistakes.

<span style="color: #3333FF">DO NOT OVER TORQUE THE 6 TRAILING ARM STUDS !!</span>

14# feels like so tiny an amount, your brain will tell
you to add more just for extra measure. Don't do it.

The DPO of my car stripped the trailing arm aluminum threads
and I lost a rear wheel at 40 mph going around a bend in the road.
Real scary to say the least.

Use the Bentley Blue book for torque values.
Don't guess-timate.

True, I know nothing about auto mechanics but I am familiar
with torque wrenches and that end of the business.

dale

 

[DougF]

I have a Sears torque wrench that our local store would not stand behind when it failed at the handle. This particular store claimed that only the head was guaranteed. I also read an article in a restoration magazine that I subscribe to where a man's newer Craftsmans TW tested to be off by quite a bit. After exchanging, the new one was off by 14 lbs.

Our local store said they could recalibrate TWs for a fee, which at the time was about half the price of a new one.

Sears has sold many TWs over the years. Many of my customers(mechanics) are quite pleased with theirs. Mine failed after very little use and weighs heavily on the reason I no longer buy tools from Sears.

I purchased a new KD at our local Parts-a-Rama that I am quite happy with.

Torque wrenches do wear out, so I'd be very careful when buying one used.

 

[Twosheds]

Wedgeworks,
I'm not clear on the message, and this is an important one. Is it a myth that they should be calibrated ?
Thanks, Mike

I think Wedge meant to write <span style="font-style: italic">truth</span>, not <span style="font-style: italic">myth</span>.

I agree with everything else he wrote.

My Lab Aide at the A&P school kept the torque wrenches in his desk. He would issue them to the students when they needed them.

Woe betide any student who returned the wrench without first setting it on the lowest value!

 

[vagt6]

The "bar" type torque wrenches in which a separate arm points to a dial gauge are just fine for practically all of our amateur jobs.

The more modern "clicker" and digital torque wrenches are great, however, professional auto mechanics did perfectly well without them for decades.

Don't rush out and spend several hundred clams or more on a fancy digital or clicker wrench unless you're thinking about going pro, or maybe if you do a whole lot of mechanical work and need professional-grade tools (or, unless you have money to burn).

The old, dial gauge lever arm torque wrenches are just fine, for all but the most intricate mechanical work, IMHO.

 

[Tinster]

Hey Mark!!

I make no bones that I know almost nothing about automotive
mechanics.

But I DO KNOW what it is like to have a rear wheel come off
at 40 mph speed because some prior idiot over torgued the
trailing arms studs and then tried to fix the mess with all
but worthless helicoils.

I'll repeat- proper torque of the six trailing arm studs
is a critical issue. I am sure a "clicker" could be borrowed
from someone. For me, after the wheel came off? My $90 Sears
wrench was decent insurance.

<span style="color: #993300">The old, dial gauge lever arm torque wrenches
are just fine, for all but the most intricate mechanical work,
IMHO.</span> Mark - you said it yourself. The T/A studs
are intricate and important..

 

[RonMacPherson]

If you are still on the assembly stage, I would like to offer a suggestion. Find stud that are coarse threaded to go into the trailing arms.

Why? The fine threads in the aluminum grind through the threads too quickly. Coarse threads spread the load better.

Ideally coarse on one end and fine on the other(McMaster-Carr, maybe) if not then coarse on each end and change the retaining nuts to coars.

14 ft lbs. almost don't need a torque wrench. As that is less than the pressure for installing spark plugs. If you do want to "torque" them, for that get an inch pound and convert up when torquing. Should be less than 50 at most tool suppliers.

 

[Tinster]

Ok Ron!!

When a wheel falls off at 40 mph you are
REAL CAREFUL when you replace the trailing arm
studs..

d

 

[WedgeWorks]

The point of my reply was to not cut corners and make assumptions with torquing of bolts. Unless your arm has been calibrated to click when it gets to 20 ft-lbs you dont know if you have over torqued or under tourqued a bolt or nut. I had a bad experience in my first days of my MGB with rebuilding an engine with head studs/nuts. I had studs and/or nuts that were stripping threads. It turned out a torque wrench that was to be 70 ft-lbs was actaully 85 ft-lbs. The wrench was a year old and when I got it calibrated that's when the 15lb difference was clear. I have wrenches for my work that every year go out for calibration no matter the application. You would be amazed that how much of a difference between the dial/setting and actual values are when you get the certification and data sheet. I also carried a calibrated wrench for track and autocross days to check and recheck lug nuts. By the way why would the work shop manuals have torque requirements for all the major parts and I do not see a +/- tolerance with the values? There is a reason.....not to cut corners since the manufacture knows best for servicing their products!

 

[Tinster]

Michael!!

I bow to the experts..................... since I know almost
nothing about auto mechanics. I am a simple architect that designs
extreme wind, building envelopes. Of auto mechanics, I know very little.

so..................

Go out a purchase a torque wrench and have it calibrated/certified.
It costs me $600 per pressure gauge/ per year to have my $80/hurricane
testing pressure gauges calibrated and certified with written documentation
and a certification of accuracy sticker on the gauge.

Personally? I would NOT spend $600. to have my torque wrench calibrated
and certified. In five years use, none of my hurricane pressure gauges have
ever been off. That's $3000 per gauge for needness calibration and testing.

To each his own!! Go test yer torque wrench to yer heart's content.
Just don't over-spin the T/A nuts and studs over 14 foot pounds.
dale.

 

[TR3driver]

"Clicker" wrenches are notoriously inaccurate (at least the less expensive ones). They basically compare the torque against the tension of a small coil spring, so anything that changes the spring (like being stored under tension or thermal cycling due to weather) upsets the accuracy of the wrench. That's why they need frequent calibration. The beam and dial type wrenches still use a spring (the beam), but being so much larger it's also less apt to be effected. That said, I love my clicker torque wrenches, especially when working in awkward positions, as I don't have to be able to see the dial/scale to know when I've hit the correct torque.

Another thing to keep in mind is that you should always read the torque while the fastener is still turning (slowly). Torque values are for "dynamic" torque, and static torque can be substantially higher. But this is only an issue for high stress areas, like head studs or bearing caps. No need to worry about it for trailing arm studs.

BTW, my Triumph shop manuals all give tolerances for torque values. My feeling is that, if no tolerance is given, it doesn't matter much and can be taken to be +/- 20% of the given value.

 

[ichthos]

A few more questions. To convert to ft/lbs with an inch/lb torque wrench, wouldn't I just multiply the value on the inch/pound torque wrench by 12, in other words would I just set the wrench to 168 inch/pounds if I wanted a value of 14 ft/lbs? Why wouldn't I just get a foot pound wrench, since that is what I would most likely be using all the time? Michael, who do you send your torque wrench to, and how much does it cost?

Kevin

 

[RonMacPherson]

Reason I recommend the inch pound conversion, is that at lower readings the inch pound is more accurate than most foot pound torque wrenches. Most foot pound torque wrenches are calibrated above 20 ft lbs.....

 

[ichthos]

That makes sense,Ron, but is my conversion method correct? Also, does it make a difference on torque settings if the metal is new or old? In other words, would old studs or bolts tend to fatique more if torqued previously.

Kevin

 

[WedgeWorks]

Ichthos-
I will look into what companies/labs do the smaller wrenches 20 to 120 ft-lbs wrenches. I had mine done 6-months ago by the manufacturer and it was about $45.00 and they gave me the dial vs. actual torque values. I had a value change at 75ft-lbs of +.6 and at 100 it was +1.2 ft-lbs and I have had the wrench since 1992. Anyone have the inch to foot pound conversion? I do in a book either at home or the office. I will take a look when I get a chance if no one can get the conversion.

 

[TR3driver]

Anyone have the inch to foot pound conversion? I do in a book either at home or the office.

You mean 12 inch-pounds per foot-pound?