Thought you might like this.
OK, so I'm just about to button up my new diff'.
To do this as per the factory Toyota manual, I have to torque everything up accurately, as the bearing preloads etc are a function of these tightening torques.
Problem is, I have no idea how accurate my torque wrenches are.
45 minutes of rummaging, hammering and welding I came up with this:
Basically a 1 meter beam (off an old bed frame) running in two bearings (part of my old steering system).
The water-cooler bottle is my adjustable 'force' (water being precisely 1Kg per litre at 4C).
The brake disc is just a counterweight to negate the weight of the beam and empty water bottle.
A 12mm bolt passes through one of the bearings and is welded to the beam.
With no water in the bottle, the beam is perfectly balanced (due to the brake disc) and has very low friction (due to the bearings) and can be rotated via the 12mm bolt with the slightest torque applied by hand.
I know it all looks a bit ghetto, but the important measurements and relationships are quite accurate.
So adding 1 litre of water to the container, you now need to apply 1Kg/m (9.8Nm) of torque through the 12mm bolt, to get the beam to lift - simple beam physics.
Firstly I tried my expensive Norbar wrench.
2Kg of water (19.6Nm):
Clicks at a displayed 19Nm
Lifts at a displayed 20Nm
4Kg of water (39.2Nm):
Clicks at a displayed 39Nm
Lifts at a displayed 40Nm
6Kg of water (58.8Nm):
Clicks at a displayed 59Nm
Lifts at a displayed 60Nm
Not bad huh!
Problem is 60Nm is the max on the Norbar, and I need about twice that on some of the diff' settings.
So onto my bigger 25 year old abused, cheap torque wrench.
6Kg of water (58.8Nm):
Clicks at a displayed 73Nm
Lifts at a displayed 75Nm
I stopped after 1 test as the error was so large.
I've put this down to not storing the wrench properly (with tension on the spring) and over 25 years the spring has shortened.
Stripped down the wrench and fitted the first thick washer I found that fitted.....
...and tried again:
6Kg of water (58.8Nm):
Clicks at a displayed 55Nm
Lifts at a displayed 57Nm
8Kg of water (78.4Nm)
Clicks at a displayed 75Nm
Lifts at a displayed 77Nm
10Kg of water (98Nm)
Clicks at a displayed 95Nm
Lifts at a displayed 97Nm
11Kg of water (107.8Nm) - maximum I need:
Clicks at a displayed 105Nm
Lifts at a displayed 106Nm
Considering the washer was a complete guess, I'm quite happy with that.
Checked it a few times and seems very repeatable.
Not spot on, but as I now know the error, I can just compensate for this when I dial up the required torque.
So here are my 'new' wrenches that I can now use confidently:
OK, so I'm just about to button up my new diff'.
To do this as per the factory Toyota manual, I have to torque everything up accurately, as the bearing preloads etc are a function of these tightening torques.
Problem is, I have no idea how accurate my torque wrenches are.
45 minutes of rummaging, hammering and welding I came up with this:
Basically a 1 meter beam (off an old bed frame) running in two bearings (part of my old steering system).
The water-cooler bottle is my adjustable 'force' (water being precisely 1Kg per litre at 4C).
The brake disc is just a counterweight to negate the weight of the beam and empty water bottle.
A 12mm bolt passes through one of the bearings and is welded to the beam.
With no water in the bottle, the beam is perfectly balanced (due to the brake disc) and has very low friction (due to the bearings) and can be rotated via the 12mm bolt with the slightest torque applied by hand.
I know it all looks a bit ghetto, but the important measurements and relationships are quite accurate.
So adding 1 litre of water to the container, you now need to apply 1Kg/m (9.8Nm) of torque through the 12mm bolt, to get the beam to lift - simple beam physics.
Firstly I tried my expensive Norbar wrench.
2Kg of water (19.6Nm):
Clicks at a displayed 19Nm
Lifts at a displayed 20Nm
4Kg of water (39.2Nm):
Clicks at a displayed 39Nm
Lifts at a displayed 40Nm
6Kg of water (58.8Nm):
Clicks at a displayed 59Nm
Lifts at a displayed 60Nm
Not bad huh!
Problem is 60Nm is the max on the Norbar, and I need about twice that on some of the diff' settings.
So onto my bigger 25 year old abused, cheap torque wrench.
6Kg of water (58.8Nm):
Clicks at a displayed 73Nm
Lifts at a displayed 75Nm
I stopped after 1 test as the error was so large.
I've put this down to not storing the wrench properly (with tension on the spring) and over 25 years the spring has shortened.
Stripped down the wrench and fitted the first thick washer I found that fitted.....
...and tried again:
6Kg of water (58.8Nm):
Clicks at a displayed 55Nm
Lifts at a displayed 57Nm
8Kg of water (78.4Nm)
Clicks at a displayed 75Nm
Lifts at a displayed 77Nm
10Kg of water (98Nm)
Clicks at a displayed 95Nm
Lifts at a displayed 97Nm
11Kg of water (107.8Nm) - maximum I need:
Clicks at a displayed 105Nm
Lifts at a displayed 106Nm
Considering the washer was a complete guess, I'm quite happy with that.
Checked it a few times and seems very repeatable.
Not spot on, but as I now know the error, I can just compensate for this when I dial up the required torque.
So here are my 'new' wrenches that I can now use confidently:
My tools are in total disarray, but somehow I've managed to remember to always unwind my torque wrench after using it. Hopefully it's still accurate... 
