BE3 Hydraulic Clutch Conversion - Wilwood pull type

[SweetBadger 98]

 

 

Hi all, I’ve been having more fun with race clutches, specifically finding a way to get an acceptable pedal feel and travel.

 

I have a single plate AP Racing 7.25 lug clutch with cerametallic clutch plate on the race car, and it has a strong diaphragm spring with a max release bearing throw of 5.5mm.

 

This translates to a very heavy clutch pedal with low travel when using a standard clutch cable and pedal. And even after modifying the cable pull point on the pedal to increase leverage (giving longer pedal travel and an acceptable clutch pedal pressure) there is still far more tension in the clutch cable than it’s been designed for.

 

I have found that the rubber bushes in the cable compress, and the clutch pedal travel is very inconsistent -> as the clutch / engine gets hot the pedal drops slightly and then the cable requires more adjustment to fully disengage the clutch. Basically I’ve never been 100% happy with it, often coming in off a track day or race and struggling to select 1st gear due to it needing adjustment.

 

So I started looking at ways to change to a hydraulic clutch system - as hydraulic clutches with a reservoir automatically adjust to account for wear or any minor change to the clutch setup height as things get hot. You can also change the master cylinder size to alter the overall ratio of pedal movement / effort to release bearing movement.

 

I have figured out a way to use a wilwood pull type slave cylinder directly mounted on the standard clutch arm, and a master cylinder connected to the standard clutch pedal with no major modifications required - in fact you could unbolt the hydraulic setup and change back to a cable setup without changing anything else.

 

It uses one of these slave cylinders:  https://www.rallydesign.co.uk/product_info.php?products_id=4080

 

The slave cylinder mounts as so using standard clutch plastic bushes:

 

 

For some reason Wilwood recommend you mount the slave cylinder so that the body moves and the piston stays still, but it has to be mounted the other way round on the BE box, I can’t see a good reason why this would be a problem though.

 

Clutch arm needs bending up slightly to accommodate the cylinder, and the gearbox housing needs a little material removing to make room for the slave cylinder body (nothing significant, just a tickle with the power file!).

 

The master cylinder is an AP racing CP6465 https://apracing.com/race-car/master-cylinders/pull-type-trunnion-mounted/cp6465 bloody expensive new (£400 ish), but available from the US 2nd hand for £60 posted (loads of ex nascar ones available)

 

Master cylinder is mounted directly below the pedal box on a simple bracket made up from some 25mm box section, combined with a 20mm alloy stand-off (cut at the correct angle for where it meets the bulk head), and a long m8 12.9 cap head to anchor the master cylinder, plus a cheap ebay rubber boot which goes over the master cylinder and creates a decent seal to the pedal box.

 

 

Where it bolts through:

 

 

 

Master cylinder bolted on:

 

 

It connects to the standard pedal clutch cable point via an M8 Clevis fork (readily available on eBay for not much money). Note early non-hook type clutch pedal required.

 

 

A custom Hel Performance hose runs where the standard clutch cable does (£35), and it works a treat:

 

 

 

Video above shows slave cylinder movement with a 21.2mm diameter master cylinder - this would be about right for a standard clutch, but too much travel for the AP racing clutch.

 

I ran it on a track day last week with an 18.8mm master cylinder, and it was really good. Far nicer pedal feel, and most importantly consistent over the whole day.

 

I’m moving to a 17.3mm master cylinder next (another one just arrived from the US!) as clutch pedal travel was still slightly too short for my liking. This should give a 10% lighter pedal with slightly increased travel over the 18.8mm one.

 

The external slave cylinder has the advantage of being easily serviceable if something does go wrong with it, and it can simply be replaced with a clutch cable for a quick fix on the side of a race track should the worse happen!

 

Video at the top of the post (sorry can't move the damn thing) shows it working with the 18.8mm master cylinder (clicking noise is just the rubber boot - sorted with some grease on the piston)

 

 

 

Hope this is of some use - I’d recommend this for anyone considering fitting a clutch with a strong spring which would otherwise put the cable under much more tension.

Edited April 2 by SweetBadger
attempt to move video at top later in post (failed!)