Lateral-g Forums - Spongy Brakes

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I'm running a 7/8ths manual and have what I would consider a good pedal. I can stab it at 35-40 mph and chirp the fronts......if that means anything.

.........but I also have rear drums. :underchair:

Quote:

Originally Posted by chr2002ca (Post 500921)

Here's a simple question. Anybody here running the 7/8" Wilwood master cylinder with a manual brake setup that doesn't feel a little spongy? I have that same setup and mine is slightly spongy also. I was doing some research on it a few months ago and it seems that it's a fairly common side effect as you reduce the bore size on a master cylinder in a manual setup(regardless of the calipers). As you increase the bore size, you get a harder pedal, but less brake pressure.

I'm sure there are plenty of people out there are running this master cylinder and bore size OR have done so in the past that could chime in. Would love to hear from someone who has this exact setup(Wilwood MC, 7/8", manual brakes, 4 disc) and can say they have a hard pedal.

I have a few thoughts & would add, if you're comparing your manual brakes to power boosted brakes, the feel is going to be very different. Power brakes travel shorter & get really hard. If you want factory production street car braking feel, you may want to utilize a boosted system.

I'll preface what I'm about to say ... as this applies to race cars & hardcore PT cars that do track days. You don't need, nor want, that short travel, hard pedal feel in a hardcore performance or track car braking system. It makes it hard to modulate the brakes & they act more like an "on/off" switch.

For racing, hardcore PT cars & track cars ... you need:
1. To be able to easily modulate the braking pressure with pedal position instead of intense leg pressure.
2. You can't afford for the brakes to be all or nothing ... or anywhere close to it. So you need more pedal travel than a street car to have easily controlled modulation.
3. You want to be able to apply moderate foot pressure (say 100#) & achieve serious braking.
4. You don't want the brakes to "wear you out" on an hour session at the road course, braking 10-12 times a lap.

If all of this above does not apply to your type of driving, you may want to consider a more street style braking system with a power booster. If all of this above does apply to your style of braking ... and you don't have enough braking force ... I would recommend you look into ways to increase your braking force without adding more pedal travel ... which is larger rotor size and/or more aggressive brake pad compounds.

Compounds are a much bigger change than people think. Changing to a brake pad with .05 higher CoF adds a little more braking force than going up 1" in rotor size.

Per usual, excellent point Ron.

We tend to forget that many of the younger generations may have never had any experience with manual brake systems.

My first muscle car ('66 GTO) had manual drums.......Fred Flintstone could stop faster than that car.

Quote:

Originally Posted by Sieg (Post 500946)

:rofl:

Quote:

Originally Posted by Sieg (Post 500934)

I can lock up my brakes also and my car now stops beautifully, so my setup is now working better than ever. I had that same problem described by the original poster with my previous brake system. Had 13" discs with Baer 4-piston calipers up front with 1-piston 13" setup in the back and could never get enough braking power no matter which MC I tried. When I upgraded the fronts to the 14" 6-piston Wilwood setup with BP-10 pads, it was a huge improvement. The BP-10 pads are grippy when they get warmed up, and that's a big contributing factor. My first response was geared towards the actual pedal feeling slightly spongy. I agree with everything Ron wrote, which is why I like the manual setup and the extra control, but I also feel a little 'sponginess' in mine, and I know there's no air in the system and I'm using stainless lines(flex and hard) all around. I read a post somewhere, I think it was a Wilwood rep or someone extremely familiar with Wilwood MC's and manual setups, that stated that you should expect a little more sponginess in a manual setup as you decrease bore size. Part of that 'sponginess' you're perceiving is just extra pedal travel which is expected(and desired by people who want that extra modulation). For me, the feel is not a problem, I was just trying to help the original poster with 'feel' expectations on his setup. (that he could have everything matched up perfectly, high grip pads, no air in the system, and might still have a slight 'spongy' feel). Now, if he needs more actual breaking power beyond just the spongy feel, then Ron's write-up is perfect for resolving that. I'd start with upgrading the pads first. And get some extra rags to wipe the extra brake dust off.

ok,, i have now wound up the rear calipers so my emergency brake now works.. I have re bled the system ,,no air in lines that is visible and my brake pedal bottoms out on carpet still. very little resistence.. I have bench bled the master several times and was confident it was done correctly.. I will try one more time ..I can pump them up a bit but even at that the car will not stop under braking. It has to be in the master ? air or could the piston stroke be dodgy? Wilwood lists 1.10 inches .. so how much is sufficient ?- Note -- this camaro has been converted to RHD in Australia and the pedal box is foreign to the car.

Quote:

Originally Posted by usa-69z (Post 501253)

You have a BAD master cylinder.... swap it out.

Quote:

Originally Posted by GregWeld (Post 501272)

You have a BAD master cylinder.... swap it out.

Agreed - It's sounding like a bad seal on the piston. I believe Wilwood has a rebuild kit available.

Quote:

Originally Posted by usa-69z (Post 501253)

...Note -- this camaro has been converted to RHD in Australia and the pedal box is foreign to the car.

What is your pedal ratio?

Tobin
KORE3

Quote:

Originally Posted by Apogee (Post 501313)

What is your pedal ratio?

Tobin
KORE3

6-1 i believe or there abouts Tobin,, it was a standard ratio pedal and i have moved it up (pivot point) approx 3/4 inch.. The brakes were pretty much the same (bottoming out) before ratio change. When i pump them up i get a drag on rotors at best.. Im thinking now that maybe the master rod has damaged the master cyl seals ? pushed in too far ? or ? I will check the stroke today..