Mike Simard

Are there any master cylinders with a smaller bore than stock? Anything from another Porsche?
I've seen references to different MCs in 78-79 but are the bores different?

I ask because a smaller clutch master is the trick to make a sensitive racing type clutch become magically driveable.
By going from a 3/4 to a 5/8 makes a very noticeable difference in controllability. if the linkage is good with little flex or you have a HTOB style, you can afford to trade off some pedal travel.

GregBBRD

Mike:

Quick story.....and an idea.

The factory Cup Cars without ABS had master cylinders that were way too big....and there was absolutely no pedal "feel" at all....it was like pushing on the floorboard.

People started substituting different size master cylinders, immediately. Hell, just "switching" the front and rear master cylinders helped some.....at least one could "feel" the front brakes.

The size of the masters was written on the outside and they were further identified by different color tie wraps.

Of course, the rules required that everything be run exactly as delivered....and the rules people quickly figured out what people were doing....so that gig was over very quickly.....and became one of the "standard" points of inspection.

So.....master cylinders magically started to get "sleeves" installed to allow smaller pistons and cups to be used. Very difficult to detect (without removing the actual master cylinder and taking it apart....which they never did.) Worked quite nicely.

Might this work? Should be simple to get smaller cups from a VW or something....and I'm sure you could make the proper pistons in your sleep.....or machine down the original ones?

Strosek Ultra

Mike, thought this was something you already had figured out. Checked a clutch MS I have in stock for older BMWs which would fit but I am sorry to say same diameter 3/4". What do you think about the Tilton 76-series or Wilwood Compact MS?
http://tiltonracing.com/sites/defaul...0Cylinders.pdf
http://www.wilwood.com/MasterCylinde...ter%20Cylinder
Must be possible to modify any of those to fit.

Ake

Mike Simard

That would be nice, you could use honed tubing of a good material quality.
It would be more effort than I'd be interested in though but if there were a bunch of HTOB cars out there than maybe someday. Thanks for the idea!

Mike Simard

My favorite is the style that has a spherical bearing mount on both ends. That way the piston never sees side loads.
I came close to doing that when I built my old car but felt I needed some semblance to a normal 928.
I did make up pedals and gave the clutch pedal several pivot hole locations but it still would have been better to just have used the pivoting MC in the first place.

jcorenman

Well, we would be in for one for our GT if that helps!

PorKen

Larger slave cylinder?

Restrictor inline? (Slower release.)

Clutch line accumulator?