Does the clutch fake you out?

[Ultramaroon]

Originally Posted by 37

Killer. That's exactly what I'm after.


Looks like the AutoZone part might be the same as the 30620-AA111. The compound angles on the banjo area look the same to me.





edit: If the line doesn't fit with your slave then I don't see why you couldn't just route it like this -3 AN line from Chase Bays:



edit again:

That explains the alignment issue you're seeing. The OEM Forrester part looks like it's in the same casting as the BRZ.

Now I wonder what might be different in the part you bought versus the original part from Subaru. Yours might be lacking a delay valve (if it exists) where the OEM parts have them. Just a thought.

Man, that's great. Thanks for the assist! I may just turn my fitting perpendicular like in your photo and call it a day. There's no delay anything in either slave. just a piston and a couple holes.

[37]

Originally Posted by Ultramaroon

Man, that's great. Thanks for the assist! I may just turn my fitting perpendicular like in your photo and call it a day. There's no delay anything in either slave. just a piston and a couple holes.

Yeah, the way it's set up in that photo will keep it from loosening. "Easy peasy" as the kids say.

If there are no delay valves in either slave then shrinking the line diameter should have the same effect as shrinking the slave size. There might be two ways to skin this cat.

[Ultramaroon]

Originally Posted by 37

Yeah, the way it's set up in that photo will keep it from loosening. "Easy peasy" as the kids say.

If there are no delay valves in either slave then shrinking the line diameter should have the same effect as shrinking the slave size. There might be two ways to skin this cat.

That will have no effect. I came up with an example while discussing this with a friend yesterday.

Think of the master and slave as 2 syringes connected by a tube.

Imagine the syringes are both the same diameter. Push 5 cc liquid from the first into the second. The second one will have travelled the same distance to displace the liquid.

Repeat the same thing with a skinnier tube. Same effect.

Now replace the second syringe with a skinnier one and push that same 5 cc.

...make sense? It worked better yesterday when I was able to wave my hands around.

edit: decreasing the diameter of the tube will only increase the velocity of the fluid in the tube as the same volume is transferred between cylinders.

[37]

Originally Posted by Ultramaroon

That will have no effect.
...
edit: decreasing the diameter of the tube will only increase the velocity of the fluid in the tube as the same volume is transferred between cylinders.

I've built and installed both -4 AN and -3 AN stainless lines on other clutch systems and the difference is two-fold:

-4 line (0.25" ID) moves fluid slower and allows the slave to return quicker. Pedal effort is easier than -3 given no change in master or slave diameters.

-3 line (0.1875" ID) moves fluid quicker but slows the slave return slightly compared to -4. Pedal effort is slightly more difficult than -3.

Originally Posted by Ultramaroon

Imagine the syringes are both the same diameter. Push 5 cc liquid from the first into the second. The second one will have travelled the same distance to displace the liquid.

Repeat the same thing with a skinnier tube. Same effect.

Same end result, yes, but the smaller line will require more effort on both sides of the equation. Fluid from end-to-end will flow easier with less restriction (ie: a larger tube) versus smaller. Saying the effect is the same isn't technically correct unless we're only talking about an action with no account to the time value of said action.

If installing a smaller slave makes pedal effort more difficult then the effect (from a fluid dynamics standpoint) is similar to shrinking the line diameter. The smaller slave cannot accept or return fluid as easily due to it having less volume, thus making pedal effort greater. Mechanical advantage is reduced in both scenarios.

In other words, the pressure plate is now pushing the same volume of fluid using a smaller slave cylinder on the return stroke, therefore the return action is slowed down due to the increased effort required. The same thing would theoretically happen using a smaller feed line.

[Ultramaroon]

Originally Posted by 37

I've built and installed both -4 AN and -3 AN stainless lines on other clutch systems and the difference is two-fold:

-4 line (0.25" ID) moves fluid slower and allows the slave to return quicker. Pedal effort is easier than -3 given no change in master or slave diameters.

-3 line (0.1875" ID) moves fluid quicker but slows the slave return slightly compared to -4. Pedal effort is slightly more difficult than -3.

If installing a smaller slave makes pedal effort more difficult then the effect (from a fluid dynamics standpoint) is similar to shrinking the line diameter. The smaller slave cannot return fluid as quickly due to it moving less volume.

Ok, I see your point but it has no effect on the mechanical advantage. That's the issue I'm targeting here.

Also I'm struggling with comparing the above ID to the hole in the banjo bolt. Isn't that really small?

[Ultramaroon]

LOL - we're just a couple of editing fools.

[Ultramaroon]

Originally Posted by 37

Saying the effect is the same isn't technically correct unless we're only talking about an action with no account to the time value of said action.

Well said. IMO viscous effects are negligible in this case.

[37]

Originally Posted by Ultramaroon

Ok, I see your point but it has no effect on the mechanical advantage. That's the issue I'm targeting here.

It does change mechanical advantage. If you reduced the slave diameter to 10mm rather than 16mm, it would be even more difficult to push and slower to return. Reverse the equation and picture a 10mm master versus a 16mm master. The 16mm master will push fluid through the same size tube more easily.

Originally Posted by Ultramaroon

Also I'm struggling with comparing the above ID to the hole in the banjo bolt. Isn't that really small?

The banjo should have the same flow diameter as the tube feeding it. Typically they have opposing holes in the banjo bolt to accept as much fluid as needed given that particular thread size. I've never found the banjo to be a restriction as long as you're not trying to drive what should be a -3 or -4 banjo using -6 or -8 line. In the case of the slave cylinder it should accept 0.25" without a problem.

Originally Posted by Ultramaroon

Well said. IMO viscous effects are negligible in this case.

Depends on the strength of your left leg. I've installed larger clutch lines in race cars with no other purpose than to reduce fatigue in longer races. Pedal feel isn't as crisp but race clutches aren't as forgiving as street vehicles. The stock clutch system in the BRZ is a wet noodle in comparison.

[Ultramaroon]

You are confusing mechanical advantage with throttling.

[37]

Originally Posted by Ultramaroon

You are confusing mechanical advantage with throttling.

If the stock clutch line was purposefully increased to soften the clutch feel then it would be mathematically difficult to argue against mechanical advantage. If reducing the line returns mechanical advantage to its original design state then that's not the same as throttling.

My guess is the master cylinder was made smaller with a longer throw to make effort easier. Conversely, a larger master with shorter throw should bring back the feeling most long-time manual drivers are used to having. Shrinking the slave should have the same effect as the latter assuming throw on the slave isn't increased too much and results in damage to the fork or pressure plate.

[chaoskaze]

What did I just spot here? I think I found my new found love. Subbed and waiting for DIY write up! Cuz I'm a total noon.

[Ultramaroon]

@Andrew025 and I just drove each other's cars. Sweet ride. Gotta get me some OFT ...and your header is sublime.

But your clutch, something's wrong. feels all mushy. ...oh, wait

[Andrew025]

Originally Posted by Ultramaroon

@Andrew025 and I just drove each other's cars. Sweet ride. Gotta get me some OFT ...and your header is sublime.

But your clutch, something's wrong. feels all mushy. ...oh, wait

It's definitely much better with the new slave.
The pedal feels more "normal" (like every other manual I've driven) and would probably be perfect once the spring is taken out.

As is, it has similar resistance as my pedal that has the spring removed except Ultramaroon's doesn't have the somewhat vague squishy feeling.
I'll be buying one for sure.

[arobb10]

I will definitely be waiting for a write up on this! Before, I had a 2002 Celica and the clutch was heavier and shifting was a lot easier because you could actually feel the catch point. I've had the frs for two months now and I've been frustrated the entire time. Between having the squishy feeling and dbw, I've had trouble shifting consistently without lunging forward or giving too much gas.. I work at an autogroup and we have have a vw dealership and I drove a new 2015 2 door GTI we got in the other day and the clutch felt like a dream. It had resistance and you could feel exactly where it was engaging. Honestly the response in the gas pedal was awesome too.. because of this issue with the frs I've been questioning my decision to get it... I'm hoping to fix this so I can finally be happy driving on a consistent basis!