MC stroke length question

[parsonsj]

I just installed my pedals tonight, and got the pedal ratio squared away at 6:1. I'm using dual Wilwood masters (with balance bar), with a stroke length of 1.1". Should I put the pedals high enough off the firewall to allow the whole stroke? Or will the brakes lock before getting the whole stroke in?

Or ... will it damage the master if one "bottoms" it?

thanks!

jp

[parsonsj]

Nobody?

Let me ask my question this way: how much master cylinder pushrod stroke should I plan on before the pedals hit the floor?

jp

[yody]

I have no idea. However I have never had a car where the brake pedal travelled that much. I don't think it matters. Just adjust the height of the brake pedal to where it feels good. When the brakes are bled properly the pedal only travels like 3" max. Now of course I am no expert, but just me 2 cents.

[Matt@RFR]

Jesus Cody, what if the poor guy gets into some serious brake fade? Would it not be good to have full travel available?????????????

John, FULL travel, and put a stop on the pedal just before the piston bottoms.

[yody]

yes good point. Wow I'm really starting a following! another "jesus cody" fan!
BTW the pedal would have to be seriously low to not get the full travel, on all the adjustable brake pedal setups I have always had, the most comfortable brake pedal height has always provided adequate pedal stroke.

[62fairlane]

I don't think you need to worry about using the full travel. if you NEED the full travel you need a bigger master on there...if it is bottoming out BEFORE the car will stop then you have a real problem there. 6:1 seems kinda low effort? I thought most people shot for around 5:1?

[BMullin]

Maybe this can help


You have to keep several things in mind when setting up a new pedal assembly. Make sure that the pedal height is comforatable for possible long use periods (traffic jams) also be sure your radius swing is not going to take your foot to close to the floor board. You should have full travel without the possibility of ever touching the floor. The pushrod stroke depends upon the master cylinder and is directly related to the pedal ratio. If you are using a wilwood high volume aluminum master and the stroke is 1.1" you should plan on your pedal actually being able to move 6.6". When you fill the system and have 0 air in the system your pedal on a slow stop should move between 1-3" on a panic stop you could potentially move the pedal 5". If you feel you need more info please contact me.

[Mean 69]

6:1 is a good ratio for manual brakes, less than this will require using a smaller bore master cylinder such that enough line pressure is generated to squish down the calipers, which is not terrible, except that is comes with the nasty increase in pedal travel (which is in part negated by the decrease in pedal travel from the ratio).

John, I'd agree with Matt in setting things up, allowing full pedal travel. It is not that big of a deal to adjust later if the pedal is too high, for instance, AND YOU HAVE THOROUGHLY CHARACTERIZED YOUR BRAKES! I have been battling with manual brakes for a while now, and now that I have a pretty darned nice pedal feel, my car is experiencing pad knockback in hard turns, which requires pumping the pedal up a couple times to get the pistons back where I need them. The only reason I bring that up, is to emphasize the comments to allow full pedal travel until you are supremely confident you don't need it.

Don't worry too much about damaging an M/C if you push it down too far, if you do this, with brakes installed in the car, and bled, you have far more important things to deal with than fear of hurting the M/C.

On the stroke length deal, 1.1" should be fine if the bore size of the individual cylinders is matched to the calipers. When you start to bleed things out, etc, start with a 50/50% front-rear bias on the balance bar, this is important. If your M/C's are sized correctly, you shouldn't be too far off of this in the end, if you need to push the bias bar too far one way or the other, replace the offending M/C with the correct bore for that end of the car.

One more critical thing, when the pedal is relaxed, make sure it really is. The piston needs to come back fully to its home position in order to "open" the port back to the fluid reservoir. On a custom deal like yours, you'll undoubtedly need to setup a brake actuation switch, so make certain it doesn't restrict the rearward motion/rest position of the pedal. Critical.

The only thing more important on a car than the brakes is, of course, the tires.

Mark

[yody]

oooh, good real tech :)

[parsonsj]

Now that's what I'm talking 'bout. I knew there was some good answers out there.

Thanks, all.

The rod ends arrived today and I did my final mockup of the setup. I get full 1.1" travel of the master with the pedal moving about 6.5"; close enough. My pedal ratio is complicated: I'm using a Wilwood triple master cylinder "frame", modified Tilton rocker arms, Wilwood masters, all of which mount to the firewall with "anti-flex" stiffeners that mount to the cage underdash bar. The fab'ed pedals also mount to my underdash bar. The pedal pushes the rocker via pushrod which pushes the balance bar which pushes the master cylinder push rods. Since the pedal is swinging in an arc directly opposite the arc of the rockers pushing the balance bar, the pedal ratio changes (goes up) as the pedal is depressed. In other words as the pedal and rocker arm move, the pushrod between them becomes more and more angular with respect to both of them.

But the key point is: I have full master cylinder travel, and the pedals are about 6.75" off the firewall. I have lots of adjustment for fine tuning for performance and comfort.

jp

[Mean 69]

Since the pedal is swinging in an arc directly opposite the arc of the rockers pushing the balance bar, the pedal ratio changes (goes up) as the pedal is depressed.

The numerical ratio as seen by the M/C's would go up? Interesting, that sounds kind of cool. Have you calculated the increase in ratio?

One more thing that seems so obvious, but it isn't, with regard to manual brakes. Especially on the street. The pads you choose are really important, a good track pad is not friendly on the street because you need to get a good amount of heat into them before they really start to bite. Hard to accomplish on the street. A good street pad will overheat and go away on the track. I currently have Andy Porterfield's street/auto-x compound on my car, and they work pretty decent. You can definitely feel a difference after a couple stops, in fact, cold, I can't lock up the brakes (it stops pretty well, but no lock), after a few consecutive hits, I can. Carbotech also makes some nice compounds that offer a decent compromise.

M

[chicane67]

Porterfields "R4-S" compound in an excellent pad. Its cold characteristics are unreal, and will take 900*F without a hitch.

The numerical ratio does slightly change because the master I believe John is using is in a fixed position. Tilton has recently come out with a front pivot type that attempts to keep the master in line with the motion of the pedal and rod as it is put into motion. This part is utilized in a new development product that we have in the works and I thought it was worth mentioning, as it addresses the mechanical issue of ratio change.

Coolio pic here (http://www.tiltonracing.com/incs/proimage.php?sid=25&m=b)

[parsonsj]

The Tilton stuff looks very cool. It must require a remote reservoir with the master moving like that ...

Here are some crude drawings of my pedal setup to see how the ratio goes up through the travel.

jp

[chicane67]

Actually, remote or fixed.

The angularity doesnt look too bad in the pedal, but I do understand your concern. Its the little things like that....... that make me over analize little srap all the time.