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Handbrake Operation
scootz - 28/7/16 at 06:19 PM

Daft question time... I get how a typical handbrake system pushes the inner pistons out.

But how do the pistons retract once you've let the handbrake off? Is it just a case of the hydraulic system pulling them back?

Reason I'm asking is that I was going to use a pair of handbrake calipers as a handbrake only device to save on buying spot-calibers and new cables, but then it occurred to me, "will I need to retain some brake fluid in the caliper"!?

britishtrident - 28/7/16 at 06:27 PM

Exactly as in hydraulic operation it is all done by the distortion of the inner seal,

scootz - 28/7/16 at 07:54 PM

Thanks for that.

Any recommendations on how to make it 'handbrake only' function?

gremlin1234 - 28/7/16 at 10:48 PM

any, and all run-out of the disk will knock the pads back far enough that they clear the disk. -just don't make it too perfect ;-)

Slimy38 - 29/7/16 at 07:25 AM

If I am understanding this, you want to run the calipers 'dry', or at least not feed them with fluid? If so I'm not sure it will work. At the very least it won't be able to compensate for pad wear. Even just filling them from a short length of terminated brake pipe will not give you the wear characteristics required. Eventually the handbrake will stop working.

Is there no cost effective handbrake only caliper?

Edit: Actually, thinking about it, if you do seal it, as long as the mechanical action can overcome the vacuum, then the vacuum would do the retraction. Maybe have a little bit of brake fluid in there for seal lubrication but keep it mostly air? Would that do what you're after?

[Edited on 29/7/16 by Slimy38]

JAG - 29/7/16 at 07:40 AM

quote:

Eventually the handbrake will stop working


Not true - the handbrake lever will travel further as the pads wear but it won't stop working. Pads won't wear very quickly so long as you only use it for Parking. It may eventually need adjusting but I'm sure you can manage that.

You should also put some brake fluid inside the caliper as the handbrake mechanism and the seal rely upon the brake fluid for lubrication. On road cars with handbrake only calipers we put 10 ml of brake fluid inside.

Cars like this;

Slimy38 - 29/7/16 at 08:00 AM

quote:
Originally posted by JAG

Not true - the handbrake lever will travel further as the pads wear but it won't stop working. Pads won't wear very quickly so long as you only use it for Parking. It may eventually need adjusting but I'm sure you can manage that.



Good point, thinking about it handbrake pads (in theory) shouldn't wear at all if they're just used to hold the vehicle.

(edit: Nice pic by the way! )

[Edited on 29/7/16 by Slimy38]

micksalt - 29/7/16 at 09:03 AM

Is it not an awful lot of extra unsprung weight to use a combination caliper compared to a dedicated spot?

JAG - 29/7/16 at 02:15 PM

Not really - when you do have a handbrake only caliper on a production car it's usually teamed with an opposed piston caliper. The opposed piston caliper is Aluminium and lighter so it offsets the extra handbrake caliper.

On the Jaguar we also have the weight saving of the Carbon-Ceramic disc which is only 5.3 kg compared to an equivalent Iron disc around 12 kg.