And defenitly will not lock the wheels at any speed.And very often sticks on. Then you have the handbrake lever in the calliper type which are a pain in the backside, seldom ever work properly. In my experience most handbrakes really are pretty dodgey, older cars with rear drums will lock the wheels at 50kmh, but you can drive off backwards quite easily.you have to pullit out another 2 or 3 notches to make it hold backwards. It is not designed to be an emergency brake.Not since the late 60s. Here in Oz the ADRs state that the handbrake must hold the vehicle on a incline,A Tapley meter, effectivly a steep incline. No wonder OEM's are going to electric parking brakes - just fit a decent motor and low gearing on the rear hub and power it up, until it all falls apart after a few years due to its vibration and dirt ridden location! So the handbake on th back has to be 70% as good as the hydarulic brake using just mechanical linkages and hand effort not power brake assisted foot power! Put another way the UK pass for the hydrauic brkes is 50% but shared between two axles so its 25% per axle ( 0.5g roughly). I got it to pass (JUST) by lots of "tuning" but I had never realiased the kind of forces you need to generate to get 18% effiency. I think the calculations are probably about right because the GM manual apparently species the parking brake should lock after 5 clicks of the ratchet with a 27kg pull force on the handle.īasically the design is very clever but relies on almost no slack to work. The specified free play on th adjustable stop is 0.024" to 0.027" so it shows how critical some clearnces are! Remember the overall leverge rstio is 44:1 so any slack is critical. So, to get the get the 250kg force you need a brake handle pull force of 12kg and ( the hard part) not use up all the system slack before the lever runs out of ratchet notches. The caliper mechanical advantage is 3.5/1 and the handle ratio is 6.3 to give an overall ratio of 22/1. With two wheels you need 250kg total force. Now the clever Girlock design rocks the pad clamping device against an adjustable stop so to get 250kg on the pad you have to push with about125kg on the little thrust pin ( see patent ). on the pads of 0.4 (?) then the clamping force per wheel must be 250kg or so I think i.e 200kg/2/0.4.= 250kg. So if laden weight is 1190kg the braking effort at the tyres mut be around 200kg to pass. The test effiiency of 16 to 18% is actually quite hard to meet as it is the percent of the fully loaded total vehicle weight applied to just one axle. Shades of my favourite brake hate - sliding calipers over 5 years old. UNFORTUNATELY it relies on very close tolerances and clerances to work at all. Basically its a version of the old VW beetle " jamming" car jack approach. The Vette parking brake mechanism on th caliper is so clever it was subject to a patentįor Girlock in Australia who made the calipers. There are good reasons why OEM's are going to electric handbrakes. The high end OEM's use little drum parking brakes inside the disc hubs The cheaper OEM's always said " we kept rear drums so the handbrake would work, instead of fitting rear discs". Very puzzled so I started thinking about mechanical handbrakes and realised they are, in some ways, harder than the main hydraulic brakes to make work reliably. However the car failed its annual inspection last week because the handbrake eficiency was only 14%. The car passed the registration (SVA) test handbrake standard of 18% efficiency so I though no more about such a boring subject as handbrakes. It had adjustable reaction plate for the cable outers for slack setting. I sourced two cables, the lightest handbrake lever asembly I could find, and made a sheet steel box to hold the handle mounts and enclose my home made equaliser bar. When I built my toy car I had to design and fit a handbrake ( parking brake) mechanism to link up to the rear calipers which are 1988 C4 corvette items with the handbrake operating onto the main pads. A bit of a rambling and OT post but anyway.
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