Clutch plumbing

[Brian]

O.K., time to finish up some hydraulics. Everything I have read says to use 1/4" hardlines with AN4 fittings for running clutch lines, this is because we are more interested in moving fluid volumes rather than transfering pressure. Why then are all of Tilton's master cylinder outlet ports AN3? If I use reducers down to AN3, won't I loose the volume transfer that I am striving for?

If someone could shed some light on the correct hardware to use, or a perhaps give a short lesson on fluid dynamics, I would appreciate it.

Thanks
Brian

 

[Ian Anderson]

Brian

I asked the same question when planning the Dax build.

Reasoning is that a standard Renault 21 slave cylinder is about an inch an a quarter diameter and in order to get movement of the clutch the slave needs to move about 3/4 inch.

Calculating the volume of fluid that is needed to get the 3/4 inch movement and some said that much fluid would not go through the 3/16 hard lines fast enough and the clutch would not bite immediately.

So I thought a while and said bugger it and ran 3/16

The clutch works fine and I cannot feel a hesitation in the clutch taking up.

But my car is a road car so probably not that important.

But as you say if you have a restrictor somewhere down your plumbing you will always be restricted to that part's flow rate.

If you are still unsure you can also have the slave cylinder sleaved down to about 3/4 inch and use a similarly reduced Master cylinder - same result with a smaller fluid movement. (I believe Frank Catt does this)

And for reference on the Dax I have a 0.75 inch master cylinder


Cheers
Ian

 

[Bob Putnam]

You are transferring both volume and pressure. The problem lies with the pressure drop a long and small line presents when there is a large flow, which is why you should use a 1/4" or larger line.

The total pressure drop through a circuit is the sum of the pressure drops through all the lines and fittings. While having one fitting smaller than the rest of the system adds some extra drop, it alone does not define the whole system.
We use a 3/8" Banjo bolt into the master to a -4 line adapter.

 

[Malcolm]

Brian

Use 1/4 lines as you have read. If you have a reducer at the cylinder end it is a reduction of diameter over a very short distance and the effect of the reduction is minimal. I came across a similar problem. I was able to drill out the diameter in teh reducerss and in the cylinder to make it so that there was no reduction in the line diameter. Just wash the bits properly afterwards.

 

[Brian]

Thanks everyone!!
I can make this work both in my head and with the hardware now.

Brian