Hi guys I'm contemplating using a motorsport style handbrake in my project Mainly for launches and gymkhana type of use But how ever the I would still like to use the car on the queens highway! I understand that a traditional electro/mechanical hand brake is required to meet MOT requirements I'm guessing my questions are more about how to design/build/plumb a suitable system that will behave in normal use and allow me to misbehave on private land Ordinarily the brakes are paired diagonally, does this need to be changed to front and rear pairings? Could some kind of manual valve selection allow the system to be configured for the two styles of driving? What about front/rear brake balance adjustment? Any advice greatly received I am fully aware I maybe aiming for the impossible, or at least something prohibitively expensive BBB
Hi there, to answer your questions it depends on how serious you are and how much you want (or need) to spend along with your skills. To fit a hydraulic handbrake you will need to split the front and rears into separate lines, get rid of the standard diagonal split. If you are still running the bias valve on the rear sub frame it should be okay but if not then you may have to introduce an adjustable bias valve into the rear line, to stop the rears locking up under heavy braking. Then it is just a case of plumbing the hydraulic cylinder into the rear line. Easy as they say. However you do have to be careful on how you operate the hydraulic cylinder. The most common form of installation is to mount the cylinder behind the handbrake and weld a lug on the handbrake to connect to the pushrod of the cylinder. This does work but I've found from prolonged use this does 'jack up' the self adjuster on the rear callipers and eventually starts to bind up the rear brakes. A quick solution to this is to loosen off the cables at the handbrake end so the cables are slack. The handbrake would still work the hydraulics and if that fails the cable would still operate the rear brakes. This also meets the MOT requirements as there is still a mechanical means operating the rear brakes. Once again I found this not to be 100% satisfactory so in the end I just unclipped the handbrake cables and plate from the bottom of the handbrake and just ran on the hydraulics, of course remembering to clip it again for road use. All parts for this conversion are widely available from many of the rallying outlets. Your next option would be to fit a separate upright handbrake which operates the hydraulics and leave the standard handbrake on its cables. Here is an image of my set up on the Rally Golf If you wish to go the 'whole hog' then a bias pedal box is the ultimate setup, and of course it comes with the additional cost. I would estimate that it would cost about 500 for this setup and that includes braided hoses throughout. Hope this info gives you some food for thought.
Thanks Terry Its easier than I thought then....... I already have a bias pedal box ready to go in......... So the change from diagonal to F/R pairings isnt an issue for road use? To plumb this lot in would be along these lines:- Brake fluid resevoir to both the front + rear pedal MC's and the handbrake MC Front pedal MC to front 2 calipers, tee'd at the MC, with a line to each front caliper Rear pedal MC to rear 2 calipers, single line tee'd at the rear axle Hand brake MC tee'd into the same rear pair brake line The pedal box i have has a bias balance bar arrangement, so no need for a bias valve for the rear end. Would I need to fit a bias valve on the handbrake MC to better control the handbrake action, or leave it at its full force? After all if I'm yanking on the handbrake I probably want the rears to lock up? Have I got that right? Many thanks BBB P.S. I was thinking of a seperate upright hydraulic handbrake, alongside a 'motorsport' shift tower. Similar to what you have pictured.
Hi BBB Yes you are almost there, but I'd change the rear set up. The output from the 'rear' m/c is then fed into the input of the handbrake cylinder and the output taken to the rear callipers. Whether the tee is in the car after the handbrake cylinder or on the rear beam does not matter. Also I'd run separate resevoirs for the front and rear lines (basically one reservoir for the front m/c and one for the rear m/c), as you already have a balance bar pedal box there is no need for a bias valve. You don't necessarily want the rears to 'lock up' too much but this can be controlled, to some extent, by different size m/c on the handbrake.
Cheers Terry...... Forgive my ignorance, but if I 'series' up the rear and handbrake MC's.......... how does it work? I didn't think the MC would pass fluid, or does it use the fluid to push the MC, mimic ing the mechanical input from the lever? Like below......... ignoring the fact Ive pipe the MC's in reverse, normally the inlet it nearer the actuated end.... Many thanks BBB
Yes thats it. just plumb the output from the pedal box rear m/c into the feed for the handbrake m/c (i.e. where you would normally connect the reservoir) and plumb the rear from the normal output on the handbrake m/c. You may find it a bit strange on first use as when you apply foot pressure to the pedal the handbrake goes solid, also if you operate the handbrake and then push and hold the pedal down and release the handbrake the pedal goes down even further. Nothing to worry about though, it's just the way it works. Just for belt and braces you may want to fit a 'saddle' onto the handbrake m/c for extra security, it stops the pushrod exiting the cylinder under very extreme hard use. Its only a small piece of metal which covers the cylinder end and is fastened with the cylinder mounting bolts with a small hole in it so the pushrod can pass through but not the ball end of the rod. Good luck with the installation.
Thanks terry that's been great help Next question, how do I size the MC's? I'm going to be using mk3 golf rear calipers and porsche boxster rear calipers upfront Many thanks BBB
Hi BBB Just had a quick look at my own set up and I have the following; Front m/c 0.625 Rear m/c 0.75 Handbrake m/c 0.625 My front brakes are Wilwood GNIII 6 pot calipers while the rears are standard Golf discs and calipers. Hope that helps.
What size pistons does your Porsche Boxster rear calipers have, when I looked into them they had very small pistons which makes them almost impossible to use with a bias box... Example piston area: Girling 54 caliper: 54mm piston, piston area 4580mm2 Mk1 Golf caliper: 48mm piston, piston area 3620mm2 Wilwood Dynalite: 41mm piston x 4, piston area 5320mm2 Boxster rear caliper: 25mm/27mm pistons x 4, piston area 2128mm2 Boxster S rear caliper: 28mm/30mm pistons x 4, piston area 2644mm2 So if you use a 5/8" master cylinder, which has 198mm2 piston area, the hydraulic ratio is Wilwood 26.8:1 Girling 54 23:1 Mk1 GTI 18:1 Boxster S 13:1 Boxster 10.7:1
Don't know what size they are Forgive my ignorance but what makes it difficult to use small pistons with a pedal box? Do I understand correctly that the hydraulic action is instantly transferred to the 'action' end. The volume being moved would be determined by the size of the MC and it's stroke Or is it the fact it's not servo assisted that causes issues? It's all new to me learning on the job! Are there better calipers to use on a Mk1 chassis car and 280mm discs (I don want to run wheels bigger than 15") Any schooling would be greatly received BBB
Hi BBB, I probably edited my reply while you were writing More info added above. If you apply 65kg (industry standard!) of pressure to your brake pedal, have a 6:1 pedal ratio, a 5/8" master cylinder and Wilwood Dynalites you will generate 10452kg of clamping force. If you swap the Wilwoods for Boxsters you would only generate 4173kg of clamping force.
Those numbers make the porsche brakes look naff Might have to look at other options then Can I assume those calculations are 'unassisted' forces? If there was a vacuum assut servo in the system the forces would be greater, is that right? Other than putting in remote servos a better choice of caliper will dramatically increase braking forces Cheers Mickey
They're not naff.. they're just rears... the fronts have 36mm/40mm pistons and power assistance. Curiously the Boxster fronts have almost exactly the same piston area as the Girling 54 @ 4550mm2
