"Invisible" Hydraulic handbrake

[AlanC]

I've just completed a fantastic tweak to my Williams that I thought a few here might appreciate - so I thought I'd post a few pictures...

As with most hatchbacks with disk rear brakes, the standard Clio handbrake is absolutely useless for flinging the rear end around a tight corner (Obviously accompanied with whelps of delight from the highly impressed lady in the passenger seat: http://topgearlessons.tumblr.com/pos...s-are-a-womans). A yank on the standard limp-wristed willy lever certainly isn't going to impress.
I use my Williams for Targa rallies, for which a well-executed handbrake turn is essential. These are run under MSA rules for road rallies, which states in R18.6.3:
"Brakes are free but must comply with Construction & Use Regulations. A hydraulic handbrake is permitted. This must incorporate the existing manufacturers handbrake lever, mounting position and pivot point"

This rules out the usual handbrake setup used on stage rallies with an extra lever, or extra rear calipers. I also didn't want to switch from dual-circuit to single circuit brakes at the rear, and didn't want to start adding extra master cylinders inside the car (I have seen people adding an extra handbrake master cylinder inside, behind the original lever, but that looks a bit of a mess and gets in the way inside).

My Williams has no exhaust centre silencer (it's straight through from the cat bypass to the backbox), so there's actually quite a bit of space underneath the car above the exhaust - so I thought I'd try making up a dual-circuit hydraulic handbrake setup to fit into that space. I also don't have the standard exhaust heat shields - I replaced the rusty old heat shields with much lighter zircotech matting glued in place with high temp. adhesive a while ago.

The pictures attached should show what I've done - basically it's just taking the standard lever, drilling out the old riveted pivot for the cable and adding an extra clevis from which to attach the hydraulic cylinders (I actually used an old Clio Mk1 gear linkage end from my bucket of scrap Clio bits as the pivot, but a rose joint might have been better). I welded a short piece of metal to the end of the linkage, drilled to fit the rods from the master cylinders.

The cylinders themselves are just 5/8" bore remote-reservoir master cylinders, £20 each on eBay. A smaller bore would have been better, but I couldn't find any smaller available. I made up the bracket to mount these, bolted through the floor above the exhaust.

I left all the original mechanical cables and linkages in place - so it should technically still operate as normal should all the hydraulics simultaneously fail. In practice, the mechanical linkages don't do anything since the hydraulic cylinders lock up before the slack in the cables is taken up.

I also drilled through the original lever so I can put a small pin though to lock the ratchet button down to use it without having to hold the button down during a rally (The pin is easily removed should I actually want to use it to park)

It needs to be plumbed in in the lines to the rear brakes after the bias valve - since I wanted to move the brake bias valve to somewhere easier to get and, and also not being load-compensated (The standard one that's linked to the rear suspension via a spring seems to give an almost completely random amount of brake bias) I replaced the bias valve with one mounted in the engine bay so I didn't have to route the lines to the back of the car, then forwards to the handbrake, then back again to the rear calipers. I also re-routed the brake lines to being above the exhaust to protect them a bit (They got slightly torn on the last rally I did, and the zircotech heat shield seems to keep them cool enough above the exhaust)

On the first attempt I found that the lever just needed too much effort to lock the rear wheels (using both hands to yank on the lever isn't exactly ideal!) - smaller bore master cylinders would have been better, so I moved the position of the pivot on the lever up a bit to gain a bit more leverage (Sorry - this was after I took the photos) - it now locks the rear wheels nicely, even on dry tarmac. It did take a bit of careful adjustment of the nuts on the master cylinder rods to make sure both rear wheels lock up together, but it now seems to be working perfectly, and you wouldn't notice there was anything different to standard once the heat shield is glued back in place. The handbrake even seems to hold solidly overnight without "leaking" pressure in the hydraulics as some systems apparently do.

[turbjj]

Nice Job

[AlanC]

Nice Job

Thanks - it also helped get a class win at the Wethersfield Targa rally on Sunday - easily saved 2 seconds or more on several tight corners (Also added a few seconds where I got it wrong due to over-flambouance, but that's just driver incompetence) - but was defininitely worth the effort.