Firewall Braking Flex. Something to take seriously.

[zKars]

Icehouse, never had any funny feeling like warpage flutter with the big brake setup. Felt fine. Other than not being particularly good braking power.

Bigger master piston gives more psi? Assuming same leg pressure, if I change to a larger area, lb/in^2 , so term on the bottom, area, gets bigger, but PSI generated gets smaller.... Am I missing something?

[RMS]

How would it be 'lost travel'? If applying 150 pounds of foot pressure to the pedal both times, the only change is the master moved 0.030" ahead and presumably the pedal and your foot. I doubt you could feel 0.030". The master still 'sees' 150 pounds, times what ever the mechanical advantage of the pedal lever gives, and turns it into brake line pressure. So your foot travels an extra spark plug gap more. It does the same work.

definitely did not apply 150lbs maybe 30lbs with my foot....basically what I apply to hold the car at a light.

for example on the dodge m37 we measured 0.060in of deflection @ the master based on length of the arm and mecanical advantage of the distance between the pivot and the rod. that .060in of flex at the master worked out to 1.5inches of travel at the pedal.

so no .030 of pedal movement would be hard to feel but after the math is worked out how much pedal travel is lost due to fire wall flex ?

[cartel]

Im pretty sure ice is incorrect on master size..

Unless my memory is going...

Larger master =.. more fluid flow.=. more brake effort required..less pedal travel.

Smaller is reverse of all.

That TTT kit isnt very impressive for 900 usd.. not even 2 piece rotors

What size masters are u using now?
5/8 clutch
And like 3/4 rear and 11/16 front?
Master sizing is related to piston size. And with rear drums you might need a residual valve or adjust shoes tight.

[datzenmike]

Icehouse, never had any funny feeling like warpage flutter with the big brake setup. Felt fine. Other than not being particularly good braking power.

Bigger master piston gives more psi? Assuming same leg pressure, if I change to a larger area, lb/in^2 , so term on the bottom, area, gets bigger, but PSI generated gets smaller.... Am I missing something?

Effort to get the same line pressure with a larger master goes up or it would defy the "Ya can't get something for nothing" law.

[datzenmike]

How would it be 'lost travel'? If applying 150 pounds of foot pressure to the pedal both times, the only change is the master moved 0.030" ahead and presumably the pedal and your foot. I doubt you could feel 0.030". The master still 'sees' 150 pounds, times what ever the mechanical advantage of the pedal lever gives, and turns it into brake line pressure. So your foot travels an extra spark plug gap more. It does the same work.

definitely did not apply 150lbs maybe 30lbs with my foot....basically what I apply to hold the car at a light.

for example on the dodge m37 we measured 0.060in of deflection @ the master based on length of the arm and mechanical advantage of the distance between the pivot and the rod. that .060in of flex at the master worked out to 1.5inches of travel at the pedal.

so no .030 of pedal movement would be hard to feel but after the math is worked out how much pedal travel is lost due to fire wall flex ?

150 was just a number but you could easily press over 200 in a panic stop. I've lifted my ass off the seat before and almost pulled the steering column out of the floor stopping.

Yes I thought of this only later. The word loss threw me. Increased travel would be better. I'm not sure what the mechanical advantage of the pedal to the push rod is but it isn't 25 to one. 1.5/0.06=25 . It can't be much more than about 4 to one advantage.

[BrandonS]

Would you happen to have a picture of your internal mounting of the Tilton pedals? I have a set on the way as well and am always up for ideas before I start the install.

[bystickel]

The firewall is a spring. The softer the spring, the less Master piston travel there will be for a given leg effort. A tiny amount of travel lost equals a lot of pressure difference in a well set up system.

I believe you!

[BrandonS]

I would imagine firewall flex would be akin to rubber brake hoses vs steel braided.

I got started today with my pedals. I’m just planning on using a thicker steel plate (3mm) at the firewall and then tie them into all the stock points under the dash. I think that should be sufficient.

With them just bolted to the stock firewall only they flex a ton just pushing the throttle.

[datzenmike]

The firewall is a spring. The softer the spring, the less Master piston travel there will be for a given leg effort. A tiny amount of travel lost equals a lot of pressure difference in a well set up system.

I believe you!

Can't agree with this. If you put 50 pounds of pressure on the pedal pad you will have 50 pounds worth at the master weather the fire wall moves away from you an inch or not. The only way the master won't see 50 pounds is if the firewall moves several feet and you run out of foot travel. Imagine the pedal box and the master are welded together and there is no flex involved. Put a coil spring on the pedal and step on it with 50 pounds of pressure. As soon and you step on the coil, say 5 pounds, it will perhaps start to compress the spring but also the pedal pad will experience 5 pounds on it. At some point the coil will be fully compressed, or maybe not, but the 50 pounds will pass right through it to the master. There can't be any loss of pressure of piston travel in a master just because the firewall moves away slightly. If you brace the firewall you will notice that the pedal travels a shorter distance because the flex is gone but 50 pounds is 50 pounds of foot pressure.

[skippyelwell]

@zKars, glad I found this thread, I still have lots of time in my 510 build to add something like this. I did something very similar on my 240z and it made a big difference to the brake feel. The 240 firewall can flex as much as 1/4".

DSCN0945.JPG (230.11 KiB) Viewed 2399 times

[yenpit]

We "brace" all of our 240Z vintage race set up's, cuz YES, there is obvious flex in the firewall under race conditions!