back with master cylinder questions

[fl327]

hey guys, are any of you familiar with the

howe racing and mcleod master clutch cylinders??? they are 7/8 bore and i dont know if they will help my clutch engagement on the z, do any of you v8ers use one or know if it will work right in the z. sorry if im wasting space in this forum, but i dont know if anyone would answer if i posted it in the bottom of my last one.

thankz

Leonard

fairlady

3-2-savage

[pparaska]

Leonard,

 

First off, the way the board works here means that newly updated topics show up at the top of each forum, so if it's responded to, even months later, everyone is aware that it was. Of course, the new post to the thread will be at teh bottom. I always go to the bottom and see what's been added. I think most people do as well. This is a MUCH better way than the way zcar.com works, as you have to go way back to see if a thread was added to. Some threads even a day or too old on zcar.com don't get looked at and the thread dies before it was finished. This is one of the things I hate about zcar.com (aside from the incredibly childish behavior of many of the yoyos that get on there).

 

Anyway, As far as master cylinders (MCs), you need to be aware of the stroke of them as well as the diameter. If it's 7/8" for your datsun slave and GM "M-21"-ish fork, that may or may not be enough, if the stroke is too short.

 

Realize also that the stroke of the cylinder doesn't have to be much beyond 1" (if any) in the Z, because the pedal ratio:

(length of pedal to pivot)

-------------------------------

(length of MC clevis to pivot)

Is 6.2:1 versus the normal 4:1 for many American cars. If you have 6 inches of pedal throw (I think this is close to what you have in a Z, with the pedal stop and rubber remaining), then you need less than 1 inch of stroke capability in the MC. Most MC's have at least this much throw (including the short ones from AP Racing).

 

The upshot is that if 3/4" diameter is almost enough to disengage the clutch enough (sounds like it is) than 7/8" ought to be enough (1.36 as much fluid being moved by a 7/8" diameter versus a 3/4" diameter MC). Just make sure the 7/8" has enough stroke. My guess is it will. Try to measure how much the clevis moves when the clutch is fully depressed to determine the stroke needed (add a bit more for safety).

 

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Pete Paraska - 73 540Z - Marathon Z Project - pparaska@home.com">pparaska@home.com -

[blueovalz]

Pete has a good reply here. I would like to add that with the extra fluid transport of the larger 7/8" master cylinder, you also will have a decreased mechanical advantage. The ratio in bores is related to the mechanical advantage of the system. Increase the MC bore, or decrease the SC bore and you decrease the mechanical advantage (higher pedal pressure). I use a high pressure pressure plate on my T-5 equiped Z, and found that I had to use a 3/4" inch bore. Anything bigger started bending rods and flexing the firewall. The biggest limitation of the smaller bore is that the stroke must be long enough. Pete was correct in that a 1" stroke (in general) must be used. This is where swapping parts is tricky. The ratios of MC to SC are important for correct "feel" and operation.

 

Terry

[pparaska]

Good call on the mechanical advantage and the firewall flexing, etc. The decrease in the mechanical advantage (and therefore the increase in the pedal force needed to depress the clutch) is exactly the inverse of the increase in fluid volume moved in the equation I gave above.

 

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Pete Paraska - 73 540Z - Marathon Z Project - pparaska@home.com">pparaska@home.com -