Handbrake damaged by collision?

Barclayloan_query

I was involved in a very minor bump, I was stationary with the handbrake on and a large car has hit my bumper. There's only paintwork damage and it's all being sorted out amicably through the insurers (we're both with the same company).


I noticed that after the accident the handbrake seems higher than normal, would having the handbrake on and being bumped from behind cause the cable to stretch?



I've been reading that driving with the handbrake on won't cause it to stretch so can't see how it would have stretched from a small bump. I don't want to say to the insurance company that it's been damaged in the accident if it's just normal wear and tear and I'm putting 2 and 2 together and making an impossible 5!

Joe_Horner

Handbrake cables "stretching" is a bit of a myth.

A 4mm (fairly typical diameter for handbrake cables) 7x7 stainless steel cable has a minimum breaking load of around 900kg. For stainless steels the yield point (the load above which permanent stretching occurs) is usually taken as the "0.2% proof strength" - the point where 0.2% permanent stretching occurs.

It's generally around 50% of the ultimate tensile strength. So, for our 4mm 7x7 cable, would be about 450kg load. Most handbrake levers have around 4:1 leverage so (ignoring friction) you'd have to apply a 112kg pull on the handbrake to gen anywhere near stretching the cable.

Bear in mind that 112kg is 17 stone 9lb. So you'd need to have enough strength in your arm to lift a 17 stone 9 lb person off the ground at the angle you use your handbrake at.

Even allowing for the fairly wide assumptions made in the above, you won't even come close!

lister

Joe_Horner wrote: »

Handbrake cables "stretching" is a bit of a myth.

A 4mm (fairly typical diameter for handbrake cables) 7x7 stainless steel cable has a minimum breaking load of around 900kg. For stainless steels the yield point (the load above which permanent stretching occurs) is usually taken as the "0.2% proof strength" - the point where 0.2% permanent stretching occurs.

It's generally around 50% of the ultimate tensile strength. So, for our 4mm 7x7 cable, would be about 450kg load. Most handbrake levers have around 4:1 leverage so (ignoring friction) you'd have to apply a 112kg pull on the handbrake to gen anywhere near stretching the cable.

Bear in mind that 112kg is 17 stone 9lb. So you'd need to have enough strength in your arm to lift a 17 stone 9 lb person off the ground at the angle you use your handbrake at.

Even allowing for the fairly wide assumptions made in the above, you won't even come close!

I don't get it. What's all this hard fact on an internet forum? Don't you realise you are supposed to wet your finger, hold it up in the air and then post your best guess (i.e. what you would like to think the truth might be)

To back up your facts with anecdote. I have had some massively built blokes pull the handbrake on in my tuition car to the point I was expecting them to hold up the broken handbrake lever with a slightly gormless look. Strangely, car manufacturers have allowed for ridiculous levels of redundancy...

arcon5

LOL
That's certainly a brilliant read and well backed up. However it does ignore fatigue and how it being used everyday and exposed to different weathers and conditions over years affects it.


From a ford manual

The handbrake cable is normally self-adjusting in use, however adjustment may be required to compensate for cable stretch over a long period, and is also necessary after fitting a new cable.

Joe_Horner

lister wrote: »

I don't get it. What's all this hard fact on an internet forum? Don't you realise you are supposed to wet your finger, hold it up in the air and then post your best guess (i.e. what you would like to think the truth might be)

I have to put up with [STRIKE]old wives tales[/STRIKE] received wisdom about watches and clocks all day every day in work - including the risk of "stretching mainsprings by overwinding" (you can't - even a ladies watch mainspring will hold 50kg or more in tension and your fingers aren't that strong!)

So when I'm on down time my remaining tolerance for myths is somewhere close to zero

arcon5 wrote: »

LOL
That's certainly a brilliant read and well backed up. However it does ignore fatigue and how it being used everyday and exposed to different weathers and conditions over years affects it.


From a ford manual

[cynic mode]Althernatively: "Our brakes / handbrakes are supposed to be self adjusting but it's more common than we're willing to admit for the adjusters to fail and tightening the cable will hide that"[/cynic mode]



Can honestly say that I've never known a car where correctly adjusting the brakes, or sorting out the auto adjusters, doesn't also sort out any excess travel in the handbrake without altering the cable adjuster.

That's on everything from manual adjustment drums, disks with separate drum handbrakes, to disks with the adjusters in the calipers.

Yes, you need to adjust a new cable because the tolerances aren't that close in their manufacture (they don't need to be). But once that's done they tend to stay the same until you've broken so many rusted strands that you should be replacing rather than adjusting.

reeac

If a parked car is bumped by a moving car and moves along a bit the most likely mechanism is by the parking brake shoes slipping on their drum surface. The second but less likely possibility is by the tyres skidding on the tarmac. I can't easily envisage a scenario where the hand brake cable would be stretched by such events or indeed any other part of the parking brake mechanism being distorted or displaced.

Norman_Castle

^^The cables might not stretch but there could be wear such as outers cutting into inners and poorly greased connections that rub that needs to be compensated for.


OP If you think there is a noticeable difference since the accident speak to your insurer. They may advise getting it checked which should be free or cheap and should be included as part of the claim.

iltisman

Perhaps the cable is unchanged and the car is now shorter.

facade

iltisman wrote: »

Perhaps the cable is unchanged and the car is now shorter.

Or the axle/subframe has moved slightly.


Tell the repairer, and get it checked.

Barclayloan_query

Thanks all, it was a really minor bump so can't imagine the axle/subrame moving. The insurers are sending a mobile 'spraying station' to re-spray the bumper on my drive so there won't be any opportunity to get it checked by the insurers mechanic.


By the sounds of reeac's post I'm putting 2 and 2 together to make an impossible 5, glad I asked though.