Need info/advice re torque wrench for motorhome

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3239 posts

Uber Geek

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#3384437 15-Jun-2025 17:08

Breaker bars being incompatible makes no sense mechanically. The pivot points for the modern style is right up towards the socket end and doesn't rely on the outer shaft to flex like they used to many many years ago with analogue gauges and a pin.

Bung

6479 posts

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#3384459 15-Jun-2025 18:16

tweake:

mudguard:

10% of 180 is almost 200NM. Snapping a stud could be a complete PIA.

which is still well under for a high grade 14mm. (the 180nm is really high for the usual grade they use, so its either less than that or they are using high grade).

Apparently the 180nm Ducatos have 16mm bolts with 24mm heads 10.9 grade high tensile.

weasel13

38 posts

Geek

#3384476 15-Jun-2025 19:43

I'm not sure if it'd been covered already. Torque wrenches should not be used for undoing nuts. You will need a normal wrench/spanner/bar for removing them.

Using them for removal can stuff with their calibration (plus the fact that some only operate in 1 direction)

pdh

341 posts

Ultimate Geek

#3384503 15-Jun-2025 20:56

I second an extension pipe working well with a 'click' torque wrench (TW).
No way the TW knows if its Arnie (Schwarzenegger) on the handle - or you on the breaker bar.
As long as you don't get so distant that you can't hear the TW's 'click' ;-)
(Speaking here as a mechanical engineer.)

Nobody has addressed this - but as a 60 Kg person, if you put all your weight on the end of a 1' (300 mm) bar, you'll exert 180 Nm of torque.
If you get a 600 mm long 'breaker bar' (or torque wrench with 'extender' - that bit of pipe), you need to get half your weigh on it (30 kg).
Make it 1200 mm long - and you need only 15 kg of push / pull.
Double the length, halve the weight - that's how torque works.
Just to give you an idea of the force / length required...

I do believe that 3/4" drive is serious overkill for your application.
They often range from 200 to 1000 Nm... way more weight and cost than you would ever want.
Repco sells a 60-340 Nm 1/2" drive TW (RT34220) that's a bit expensive, but is easily strong enough.
As it is rated for doing things up to twice your target torque, this should be fine to undo the lugs.
Don't abuse it by jumping / hammering on it - but it should be fine.

I very much agree with the suggestions for:
(a) trying out lifting the wheel/tyre - they may be really heavy for you, and you may need a helper.
(b) using a top 'guide pin' (as suggested by Tweake) may make all the difference.
(c) a good jack

FIAT's torque figures will be for dry threads.
Any lube opens a large can of worms.

Everything I see online tells me that, in the Ducato world, 14mm wheel bolts take 160 NM, while 16 mm take 180 Nm.
So please double-check any info that's been given to you.

pdh

341 posts

Ultimate Geek

#3384506 15-Jun-2025 21:07

Just following up on 'weasel13's warning about using the TW for undoing fasteners.
He/she's quite right that some will not like it.

The Repco example I gave is inherently bi-directional - you swap the drive end to go the other way.
It also looks to have a nice long 680 mm handle - so you'll get your torque with a 30 kg pull (and no extender pipe required).

Bung

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#3384539 16-Jun-2025 00:10

"Why GRIP Position on Torque Wrenches MATTERS!" https://youtu.be/0f746pF1xc0?si=CC5dRB87SoTMdK5G

Covers the design of the clutch mechanism in typical click type torque wrenches and the maths involved. In short if you choke up on the handle by the time it clicks you will have applied more torque to the bolt and an extension results in less torque.

pdh

341 posts

Ultimate Geek

#3384540 16-Jun-2025 01:52

>In short if you choke up on the handle by the time it clicks you will have applied more torque

With or without an extension, if you _don't_ choke up on the TW - it will give you a good result.
Slip an extender over the 'handle' bit of the tool - and you merely augment the strength of your arm.

Where the 'handle' bit is normally a black plastic/rubber sheath - silently saying 'grab here'.

If you operate near the limit of the force your body can apply - you are likely to go beyond the click and over-torque...
because you're not able to exercise the same level of precise control you might have at, say, 25% of your max.

But hey - we're really just trying to be (a lot) better than some cowboy with a rattle-gun.

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

MartinGZ

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#3384541 16-Jun-2025 02:00

@Bung, that is an excellent video if you like the maths 😁. I used to think hand postion do not matter until I started seeing some of these videos five years or so ago. It does matter where your hands go, and never use an extension bar as it will lead to undertorquing the bolts.

Lubing threads. Never Ever do this unless the instruction manual says to and I have never seen a vehicle manual tell me to lube wheel nut threads. The following video goes through a lot of myths, but a few of the takeaway points I took were: You're Using a Torque Wrench Wrong: MythBusting 10 Do's & Dont's

Anti-sieze DOUBLED the applied torque, not just an extra 10% that has been talked about above. That is putting a lot of stress on the bolt.
Hand postion matters as above.
Always set your torque wrench back to zero.

But if you do for whatever reason lube the threads, then you should reduce the torque used. I used to have a chart showing the k factor for reducing torque values for different lubes, but it has been misplaced, here is a short version from the Engineering Toolbox - Lubricated Bolts and Reduced Torque

Goosey

2829 posts

Uber Geek

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#3384591 16-Jun-2025 07:02

Every reputable tyre shop and mechanic has a torque bar….some really cool electronic ones out there these days.

you would be better off just letting them know the torque when you get your tyres serviced. (Saves them a job of looking it up).

The less reputable, well they would be selling more budget than main brand budget brands which is probably not what you are going to be shopping for…

tweake

2391 posts

Uber Geek

#3384806 16-Jun-2025 17:33

MartinGZ:

@Bung, that is an excellent video if you like the maths 😁. I used to think hand postion do not matter until I started seeing some of these videos five years or so ago. It does matter where your hands go, and never use an extension bar as it will lead to undertorquing the bolts.

Lubing threads. Never Ever do this unless the instruction manual says to and I have never seen a vehicle manual tell me to lube wheel nut threads. The following video goes through a lot of myths, but a few of the takeaway points I took were: You're Using a Torque Wrench Wrong: MythBusting 10 Do's & Dont's

Anti-sieze DOUBLED the applied torque, not just an extra 10% that has been talked about above. That is putting a lot of stress on the bolt.
Hand postion matters as above.
Always set your torque wrench back to zero.
But if you do for whatever reason lube the threads, then you should reduce the torque used. I used to have a chart showing the k factor for reducing torque values for different lubes, but it has been misplaced, here is a short version from the Engineering Toolbox - Lubricated Bolts and Reduced Torque

interesting i will have to follow up on that later on. i'm not sure why i had the 10 % figure.

however in real world application, we have never broken a stud. even when we torqued to spec, which in one case was LESS than doing it up by hand. they are so over engineered, even if its double its not causing a problem.

Mehrts

1063 posts

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#3384822 16-Jun-2025 18:17

Bung:

5 years ago Mehrts posted "A few years ago I bought a Mechpro branded torque wrench from Repco, it's the exact same as that Craftwright unit from Bunnings which was linked a few posts above." @Mehrts are you still happy with the Mechpro?

Repco currently $55, Bunnings $59. The Repco one has a 21mm socket to suit the Ducato bolts.

@Bung Yep, still have it, and yep still works fine, I've had it on the calibration machine at work a couple of times over the years, and it's only been out by a few Nm throughout the range. I keep a record of the expected torque vs the indicated torque to allow an accurate figure to be set.

CycleTourer

21 posts

Geek

#3384847 16-Jun-2025 19:15

pdh:

I second an extension pipe working well with a 'click' torque wrench (TW).
No way the TW knows if its Arnie (Schwarzenegger) on the handle - or you on the breaker bar.
As long as you don't get so distant that you can't hear the TW's 'click' ;-)
(Speaking here as a mechanical engineer.)

Nobody has addressed this - but as a 60 Kg person, if you put all your weight on the end of a 1' (300 mm) bar, you'll exert 180 Nm of torque.
If you get a 600 mm long 'breaker bar' (or torque wrench with 'extender' - that bit of pipe), you need to get half your weigh on it (30 kg).
Make it 1200 mm long - and you need only 15 kg of push / pull.
Double the length, halve the weight - that's how torque works.
Just to give you an idea of the force / length required...

I do believe that 3/4" drive is serious overkill for your application.
They often range from 200 to 1000 Nm... way more weight and cost than you would ever want.
Repco sells a 60-340 Nm 1/2" drive TW (RT34220) that's a bit expensive, but is easily strong enough.
As it is rated for doing things up to twice your target torque, this should be fine to undo the lugs.
Don't abuse it by jumping / hammering on it - but it should be fine.

I very much agree with the suggestions for:
(a) trying out lifting the wheel/tyre - they may be really heavy for you, and you may need a helper.
(b) using a top 'guide pin' (as suggested by Tweake) may make all the difference.
(c) a good jack

FIAT's torque figures will be for dry threads.
Any lube opens a large can of worms.

Everything I see online tells me that, in the Ducato world, 14mm wheel bolts take 160 NM, while 16 mm take 180 Nm.
So please double-check any info that's been given to you.

Huge thanks for this pdh. I now have the spare wheel and I was shown today that the wheels actually have guide bolts that will make getting the spare on much more straightforward (sadly, not the case for the alloy wheels, they have fancy sh*t in front of the holes...sigh...). The tyre shop guy also recommended sitting on the ground and using my feet to lever the wheel into place, thus using my leg muscles instead of my useless upper body. The van will be here for 10 days as of this Thursday night so I'll be able to do a test wheel removal <dread> and see just how bad it is.

I got new tyres on the front and they actually did obey my instructions to hand-tighten. As I understand it from elsewhere online, I need to check the torque after 100km so the clock is now ticking to get my torque wrench!

I might call Fiat NZ and see if I can get the 180Nm figure confirmed. I have that from LoadSafe who install airbags and other fancy suspension (and did so on this van for the previous owner) so I figure they know what's what (also have it from another Ducato owner), but thank you for the prompt to make sure. I do not want to snap a bolt!

I think I'll go conservative and keep the torque wrench just for doing bolts up. And definitely get a half-metre or so extender. Many thanks for the simple explanation of weight and lever action. It all seems very mysterious but it's 100% logical when you put it like that.

Big "plus" of that RT34220 one is it's bi-directional, meaning if my threads do go in different directions it'll handle that. (forgot to ask at the tyre shop today...)

CycleTourer

21 posts

Geek

#3384849 16-Jun-2025 19:18

Mehrts:

Bung:

5 years ago Mehrts posted "A few years ago I bought a Mechpro branded torque wrench from Repco, it's the exact same as that Craftwright unit from Bunnings which was linked a few posts above." @Mehrts are you still happy with the Mechpro?

Repco currently $55, Bunnings $59. The Repco one has a 21mm socket to suit the Ducato bolts.

@Bung Yep, still have it, and yep still works fine, I've had it on the calibration machine at work a couple of times over the years, and it's only been out by a few Nm throughout the range. I keep a record of the expected torque vs the indicated torque to allow an accurate figure to be set.

Goodness, I just looked them up, and they're astonishingly cheap! It's very tempting to get one...but of course one doesn't know what quality degradation they may have had in those 5 years. Frankly not sure which way to go on this one.

I'm intending on getting whatever I buy checked in my annual tyre checks at my tyre shop, so I guess at this price I could always, if necessary, buy one every year!! 😂

CycleTourer

21 posts

Geek

#3386260 23-Jun-2025 09:04

Huge thanks to all who participated in this thread. I bought the Repco RT34220 on the weekend -- price was a little ouchy, but it's a once-er hoepfully. Nice and long, bi-directional, comes in a fairly tough looking plastic case which I can lash into the rear storage in the motorhome. Found a nice 21mm socket to go with it at the same time. Job done 😁

pdh

341 posts

Ultimate Geek

#3386485 23-Jun-2025 22:20

Glad to hear that you've got it all sorted - thanks for coming back and updating us ;-)
Best of luck with the travels - and here's hoping that you never have occasion to take off a wheel !

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