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  View original topic: Clutch master cylinder sizing
ORANGECRUSHer Fri Mar 14, 2014 9:51 am

For some reason I get confused when I try to think what size M/C I need for particular apps.
For example, right now I'm looking for a M/C to match the slave on my Vanagon transmission (091). I could just ask what is stock, but I want to understand the why. What confuses me is I've heard people mention using a smaller bore for disc brakes which in my mind seems backwards. Bigger pistons require bigger bore/volume of fluid moved. That's how I understand it. I still need to know what was stock for the OEM slave cylinder because I would imagine if I go too big the slave will open to fast and I'll lose any 'feel' in the clutch.

no1clyde Fri Mar 14, 2014 12:06 pm

I think the stock Vanagon MC is 19mm.

Ed

jsturtlebuggy Fri Mar 14, 2014 12:23 pm

5/8in master cylinder is what is commonly used in Neal/CNC setups.
Makes for a easier to push pedal.
Going to a bigger 3/4in will make the pedal harder to push, but it will have more travel. Meaning the slave will travel further.
Another thing is the length of the pedal will make a differences. Short pedal, less leverage. Wil-Wood makes different length pedals.

Hydraulics brakes and clutch are like your floor jack. lifting your buggy is going to be easier to push the handle down then when you lift up your truck.

FYI you can convert your 091 nosecone side shifter to use a Neal/CNC/Speedway Motors pull type slave cylinder. You need the 20mm diameter clutch cross shaft arm, spring, and cup to replace what there now.
these can be found on used 091 front nose cone shift trans and 1973 and later Bug trans. They are also available new from places selling trans parts.
Also you need to drill and tap a hole in the boss on side for the bracket that would normally be for the Bowden tube.
In picture on the side, the chrome bracket lower bolt is the boss you have to drill and tap.

no1clyde Fri Mar 14, 2014 1:58 pm

The Master Cylinder to Slave Cylinder ratio is why a small MC and large SC has a lot of power with less movement than say a MC the same size as the SC has equal power to the input (your foot pres.) and the same amount of movement. Hope that helps.

Ed

no1clyde Fri Mar 14, 2014 2:00 pm

Also the stock slave cylinder on the Vanagon transmission looks to have a fairly large bore so that is why I think they used a 3/4" master cylinder.

Ed

ORANGECRUSHer Mon Mar 17, 2014 10:28 am

Finally getting around to checking on this thread. Thanks for all the suggestions.

The clutch pedal is of particular importance to me because I have a partial foot amputation on the left and have to use the heel of my foot to operate the clutch which can be tricky when your basically sitting on the floor of the buggy. Also interesting when I work the Tig pedal.

My old pedal I had chopped the pedal and made a projecting pad that was adjustable pushing the contact surface towards my foot about 4". I guess it effectively lengthened the lever.

Anyway, I think rather than buying the $110 pedal I'm just going to get a 3/4" master and build a pedal from the ground up to accommodate my problem. It might even pivot sideways. I'll have to think about it.

donbarnes Mon Mar 17, 2014 8:38 pm

http://www.speedwaymotors.com/Wilwood-High-Volume-Aluminum-Master-Cylinder,1379.html

This has run perfect on my rail for over two years so far for the clutch, and much better quality than the Chinese ones you find on a lot of the VW sites that have the screw on lids that the seals rot on in 4 months and they leak everywhere :( . This Wilwood one uses a snap-on lid just like you would find on old school OE domestic master cylinders and doesnt leak or rot.. There's a drop-down bar that shows three different bore sizes available, I think I running the 3/4 (0750) one..Speedway also carries pedal assemblies..



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