Was having a chat with some friends the other day, we got onto the subject of hydraulic handbrakes. Does anyone know why the motor industry have not pursued this equipment in production models?
Interested to hear your views / opinions.
Leon
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Hydraulic systems are likely to leak pressure very slowly over time if kept under pressure so an hydraulic hand brake (or should we say 'parking brake'?) would not be a good idea. Seals can leak slowly or suddenly 'go' without warning. I wouldn't like to rely on one.
And before someone says it, yes I know cables can break! Pity they're not fitted with grease nipples these days.
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Probably it could be done with something like a hydraulic accumulator depending on gas pressure, and Leon's message implies that it has been done, but not in production vehicles; one would like to know more.
There would seem to be the certainty that it would be complex, costly and of no obvious advantage.
Whatever, leave it in gear, or P!
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Two reasons I think.
As mentioned before, brake systems are not supposed to be continuously pressurised. Seal life would be lower.
The second reason is construction and use. You are required to have a handbrake independent of the main braking system. Therefore to do this legally, you would need two completely separate hydraulic circuits.
Non legal types are often found on rally cars, although there is a way of combining hydraulics with a backup cable, but even then this can be of questionable legality.
Why do they do it? Simple, handbrake turns are easier.
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Grogg, hydraulic handbrakes are widely used in Rallying and other such variants of the sport. Handbrake lever allows the rear brakes to be applied under hydraulic pressure and with greater force to enable handbrake turns to be executed without the incurring the problem of stretching or snapping cables, which given the strain and frequecy of use, a cable operated handbrake would be unlikely to last to the end of a stage never mind an event.
one other minor difference with hydraulic setup is that the button is only used to engage the handbrake for parking, to handbrake turn the car you only need to pull on the lever and let it go again, and it will drop to the floor.
Leon
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the answer to your question then is, they dont fit hydraulic handbrakes because most customers dont carry out handbrake turns frequently enough for snapped cables to be a issue.
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Not quite convinced that is the reason, I was hoping for something by way of a technical explanation why manufacturers didn't consider it feasible.
However, if your reason is based on cable operated systems being "fit for purpose" I am happy to accept it.
Leon
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a technical answer might be whats the point? a cable set up is quite sufficeint to exert the force required to do the job easily so why go to the trouble of compicating things for no good reason, you would require a totally seperate hydraulic circuit , a accumulator, a means of charging it, all the extra plumbing etc etc for no good reason
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Thanks Leon.
I should have guessed.
We had the same principle pre-war, when we had the handbrake with the button used only to latch it on. On Lagondas, for example, around the late twenties / early thirties the hand brake operated completely separate full width shoes within the rear drum, though perhaps just supplementary braking effort was contemplated, rather than hand brake turns on a (at least) 10' 9" wheelbase!
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I thought that "hydraulic handbrake" sounded like a job for Citroen so did a web search but even Cits have never had one except on rally cars as mentioned above. Did find a reference on some message board where someone was asking about it and a reply said "beware because it will never pass the MOT because it specifies that handbrakes must be mechanical" Don't know how true that is but maybe it explains why there aren't any hydraulic handbrakes if so - and I guess it's because of the reasons mentioned in posts above.
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Cost!
--
groups.msn.com/honestjohn - Pictures say a thousand words.....
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Why on earth should we develop a hydraulic handbrake?
Most people use a handbrake when stationary.
Stopped.
Not moving.
Lift a couple of fingers and apply a brake to a metal box, not in motion.
If you like, a la Merc, apply a footbrake to a metal box....
Please explain.
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Have a look here:
www.motuk.co.uk/manual_310.htm
Hydraulic handbrake not allowed since 01/01/1968. Don't know why though.
RichardW
Is it illogical? It must be Citroen....
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I always thought that they weren't allowed as there's supposed to be a mechanical 'emergency' brake - not that many car's have a handbrake that would do anything to stop a them at any sort of speed, especially now they operate on rear-discs...
The only thing that blows this theory is the electronically operated handbrakes that are appearing.
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Well spotted, the MoT doesn't allow them because the construction & use law doesn't. It's supposed to be an 'emergency' brake in case of hydraulic failure and the cost of doing it with a completely separate hydraulic system (pipes, resevoir, master and slave cylinders) would be unfeasible.
Gareth
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