Spongy pedal, SS teflon lines & MC bore

[Caprimaniac]

I use a adjustable balance bar pedal box. It's adjusted to give maximum pressure to the front brakes or else it will lock at the rear before the front.

The pedal is a little spongy.

OK; let's say all air is out of the brake lines.

I have noe hard lines to the front calipers. SS teflon lines (AN3) directly form the MC to the calipers. Do these lines flex??? Might that cause the bad pedal?

I've also thought about going down one size from 0.725 to 0.7" MC for the front brakes. This will make the adjustability front/ rear better. This may also give me a more positive stop in the brake pedal?

Yes, brakes are quite good (much better than last year), but I'm not 100% certain that everything is OK yet. Out autocrossing yesterday was fun!

RuneS

[strictlypersonl]

Yes, hard lines expand less than stainless steel flex lines. Think of it this way: When a line flexes, it must be "soft" enough to allow shape changes. How much this effects your system, I couldn't tell you.

Going to a smaller front master will probably give you a softer pedal, not a harder one. You'll gain more leverage though, so your required pedal pressure will go down. If you are comfortable with the current pressure, and want a firmer pedal, consider going to a larger rear master cylinder.

[john chesnut]

I run SS flex lines and my pedal is rock hard. I run .75 MC both front and back with great results. The fact that you have to have the balance bar adjusted full front to keep the rears from locking makes me wonder if the pedal is set up correctly. If it's not it could cause the spongy feeling and the lock up. I don't know your set up but if the MC are below the wheel cylinder height you would need residual valves in the lines to keep the fluid from draining out of the lines into the MC. Use a 10# valve for drum brakes and 2# valve for discs. This could also cause a spongy feeling. Good luck

[Caprimaniac]

I agree on that- going to a larger rear MC will make pedal "harder" than changing the front to a smaller. I just had to think it over and yes, that is correct.

As mr. Chestnut says; rock hard pedal with SS flex lines. I have 1,8 m to the right and 1m to the left wheel. And I think this should give no noteicable more flex than a solid line + 20 cm of SS flex line.

No, the MC's are above all the brake pistons. But, there is some strange things happening at the rear where the calipers are somewhat stuck- this is noteicable when reversing the veichle. Brakes makes alot of noice... The rear pads are new and of Mintex 1155 (race...) quality. May need som more brake-in.

Thank you.
RS

[bkozlow]

When you bleed the brakes did you disconnect the bias bar and do front and rear as two separate systems? With Teflon lines your bedal should be rock hard if there is no air in the system.

billk

[Dangerous Doug]

What kind of front caliper are you using? Does it have a singe, large piston or multiple smaller pistons?

I found that switching from a large single piston to the dual pistons of the SSBC front calipers that my pedal went from "spongy" to "perfectly firm".

DD

[Caprimaniac]

I run single piston sliding calipers both front and rear.

Very interesting; my experience is that switching from steel to aluminium calipers makes pedal more spongy. At least some of the Wilwood- types. And SSBC are aluminium aswell, as I recall?

Maybe it's 1 piston/ sliding VS multi piston/ double row calipers?

OK; on the bleeding- I did them both at one time. There's a seperate reservoir for each of the pumps. I could try one more time just to be shure..... (The pumps are not easily accessible, so not a funny job!)

Will post again after bleeding or even changin the rear MC.

Thanks
RS

[Caprimaniac]

Got a tip from my parts supplier.

With 60 mm front and 43 mm rear single piston sliding caliper the correct size for masters should be 0,875 and 0,75".

I got hold of a 0,83" master and tried this with a 0,75" to the rear.

And it works perfectly! Rock hard pedal, unfortunately demanding use of a lot of muscle...... But my leg & foot gets alot of exercise.

RS

[Tommy]

How far does your brake pedal now move before the brakes are fully locked? If there is room for it to travel further, and if your pedal assembly is adjustable, you may be able to get some relief from the heavy pedal force.

Check to see if your brake pedal will allow you to move either the pivot point for the pedal or the connecting point to the piston rods. If you can change the mechanical advantage on the brake pedal so the piston rods move more slowly as you depress the pedal, you can make it easier to press the pedal. But you don't want it adjusted so far that you can't get full brake action before the pedal runs out of travel.

[Caprimaniac]

Hello, Tommy.

Yes, that is a good tip.

Although it is possible to change the pedal ratio, it would involve alot of work. (The pedal box is based on a factory part, and pedals are more or less fixed on an axle rod. The pistons are kind of stuck too, since there's limitid room between the brake box and the dash. Pedals are hanging under the steering coloumn and master cylinders are placed above the coloumn.)

Also when calculating the master cylinder bores, the pedal ratio have been brought into the equation. But; OK- moving the pedal ratio a small ratio would make brake effort better without doing any harm, I'd guess. I also figure there's something to find by changing front/ aft ratio which I will look farther into next spring....

Best regards
RS