Classic cars forum & vehicle restoration.

[Peter_L]

The centre nuts on the front hubs of my truck have a recommended torque of 280 ftlbs.

My wrench stops at 150 and a 50-400 to buy is about $400.

When I changed a hub bearing assembly on a similar truck some years back I rented a wrench but when it "clicked" out at 280 ft lbs I wasn't convinced it was tight enough.

I took the truck to a local mechanic and for $20 he put on his wrench set at 200 and it clicked before turning the nut. He then re-torqued them at 280. His advice was not to waste time and money renting torque wrenches as they are invariably left tensioned and hardly ever tested.

So..... my question. I have a 48" breaker bar. I also have a set ofspring suspension scales. If I run the cable from my bumper winch, over a pulley and pull up on the top of the scale while having the bottom attached to the breaker bar would 280/4 i.e 70 lbs on the scale, be giving me 280 ft lbs at the hub nut.

The theory sounds good but am I missing something ?

Of course I can get them torqued again for $20, but, well sometimes we just like to do things ourselves.

[buzzy bee]

Hi

I am not very good with these things, but does it matter how far you put the hook on the lever, would 48" make it tighter than at 24"?

We have a few big torque wrenches, 3/4" drive I think for the tractors, they are tested every other year and calibrated. If you were closer I would lend you one!

Sometimes torquing up doesn't give the desired results, do you not need to set the preload, or am I barking up the wrong tree?

Cheers

Dave

[RotaryBri]

The answer is in the units, lb.ft, which means that the torque is a multiplication of the force in lbs and the distance that the force is applied in feet.

To get 280 lb.ft you would need a force of 280lb pulling on a lever 1 foot long. If your force was applied at 2ft then the force required would be 140lb and for your 4ft lever the force required is 70lb.
_________________
Keep Torqueing,

RotaryBri

1976 NSU Ro80

[buzzy bee]

Hi

I was half way there! he he

Cheers

Dave

[Peter_L]

Thanks for your replies.

These bearings are actually a bearing assembly. i.e the hub that carrys the wheel, bearings, seals and the speed sensor. A $3 part that can't be replaced, (allegedly).

There is no preload, but the nut should be tightened with the wheel off the ground.

I may get to it this weekend, so will let you know.

The last one I did required the 4ft breaker bar to be put in place with a vertical piece of 6x6 under the end and the truck lowered back down.

Either the nut was going to turn, the bar break or the truck would be suspended in mid-air.

After a couple of seconds suspended, it dropped to the ground and the nut was free.

[Nic Jarman]

Torque wrenches are a dangerous tool in the wrong hands. If the nut/bolt is rusty or a bit out of shape then the tension on the fixing will not be enough. To acheive the correct tension the thread should run freely, be clean and lightly oiled/greased, THEN the torque wrench will give you a correct tension on the thread.
_________________
1936 Morris 8 Series 1
1973 MGB roadster
1977 MG Midget 1500
Dax Rush