better intial bite?

[foolio2k4]

Ok so i bled my brakes today and I feel that the pedal doesnt feel any different. I saw lots of bubbles coming out but pedals still pretty mushy. I would have thought that it would have firmed up a bit.

What would i have to do to get a better initial bite at non-operating temps.

I know that my brakes get pretty good initial bite when it gets "up to temp" but i would like some better bite at street temps though. Thanks

 

[SoundGuyDave]

Ok so i bled my brakes today and I feel that the pedal doesnt feel any different. I saw lots of bubbles coming out but pedals still pretty mushy. I would have thought that it would have firmed up a bit.

What would i have to do to get a better initial bite at non-operating temps.

I know that my brakes get pretty good initial bite when it gets "up to temp" but i would like some better bite at street temps though. Thanks

A couple of things here..

1) If you have bubbles, then you have air, which is probably what's giving you the spongy pedal feel. Assuming that you've bled the brakes properly (proper sequence, proper technique), and you still have a spongy pedal, then you probably have air in the ABS HCU. Two ways to handle that... The right way is to take it to Ford and have them do a bleed while cycling the HCU. The "other" way is to bleed them as best as you can, then take the car out on a dirt road, and intentionally lock the brakes up (cycle the ABS) repeatedly, until you get a spongy pedal back again, then re-bleed and repeat...

2) Initial bite is ALL about compound selection. What pads are you running now? If you're running track pads (Hawk HT or DTC, Carbotech XP for example), you will simply NOT get aggressive bite out of them without getting heat in them first. It's a function of the physics. Track pads are engineered to operate at, and withstand, temp ranges that would turn street pads into cinders. The downside is that below ~400*F, the initial bite is compromised. If you do a lot of street driving, then you're best served having a set of "track" rotors and pads, and a set of "street" rotors and pads. If your car is more of a track whore (like mine), then just keep the race package on the car, and be CAREFUL on your way to and from the track. Keep solid spacing from the cars in front of you, and don't speed or push the car on the street.

 

[Philostang]

+1 to everything Dave said, but then I have a question.

Are you sure you are looking for better initial "bite" when you complain of a "mushy pedal?" Bite, as I understand it, is a dynamic quality (the "feel" of deceleration), whereas a mushy pedal sounds like it has more to do with the quality of the system itself (air in the line, etc.). They can (and I suspect, often do) have very different causes, so it's important to isolate exactly what ails you.

What sounds odd to me is that you claim the "ailment" goes away at track speeds. That could be, as Dave points out, due to the fact that your compound is up to temp is in its happy zone. But when you say it goes away, is it going away after a few pedal pumps, or do you have an instantly better braking experience? If it's instant, I'd say your pads are just happier. If otherwise, I'd say something is not well with the basic system.

I'd try another bleeding of the system at all four corners, and after you cycle the ABS. I'm not sure that bad fluid in the ABS system would cause the ailment you're experiencing, as that (old) fluid should stay out of the rest of the system until called upon. But hey, might as well try to get it out of there anyway. As you describe a lot of bubbles in the system, that has me concerned. Be sure to follow the right bleeding procedure.

Last thought, I hope some brake guru can chime in on "old calipers" as a possible culprit. I know I was never terribly happy with the firmness of the OEM calipers, and I've heard others say similar things. Dave has roasted (I think) a couple of pairs of them, so maybe he has something to say on what they feel like when they're on their last leg. I know pad taper becomes nasty, but maybe they also start to feel extra "mushy," Dave?

Best,
-j

 

[Philostang]

Oh, and I can't resist...

You're never going to get great breaking using those "bike" brakes! You're driving a car!

 

[SoundGuyDave]

Yes, I've heated a couple pairs of the stock calipers to the point where the bridge softened and started to flex. Symptomatically, though, that will just give you a little bit of a "rubbery" feel at the very end of the brake stroke, and only when REALLY hot...

The air-in-the-HCU thing only comes into play when you trigger ABS. And let's face it, we NEVER do THAT on a race track... What was a perfectly bled hydraulic system suddenly has an air bubble or two, and that's all it takes to get mush for a pedal.

And I agree, using "bike brakes" really won't work well...

 

[foolio2k4]

Im using HPS compound all around. The pedal firms up after a few hard stops from 80-0. Basically when the system gets up to temp. It was the same for my stock pads as well.

So what your saying, soundguydave, air in the HCU isnt likely an issue? I havent done ABS triggering since i got my car haha.


BTW, how low can I let the master cylinder get before refilling, I can see 2 hoses connected to it. fill it when it gets close to the second hose or can i get it pretty much all the way down.

 

[Sleeper_08]

On the track I keep my fluid so that it comes up to the level of the baffle just below the filler cap.

During fluid flush we let it get down to just below the level of the seam in the reservoir.

 

[SoundGuyDave]

When you start pushing the car harder, those HPS pads are going to start crying for mercy... The HPS compound is really a "hot street" compound, and should have decent initial bite at room temp, but they will get a little grippier with some temp.

It sounds to me, from your description, that your brakes are pretty much normal. The "soft" feeling pads are usually pretty gentle on the rotors, which is a good thing for a dual-purpose setup. Race pads, particularly when cold, are like trying to rub two boulders on the rotor to get the car to stop. Put some heat in them though, like at least 400*F (which is about where the HPS starts to fall off the deep end), and it's like the hand of God reached down and stopped your car...

Good "novice" level package would be HT-10 up front, and HP+ in the rear. Once you're able to drive past the limits of those pads, go to DTC-60 front, and HT-10 in the rear. Track-only applications, though!

 

[foolio2k4]

Thanks!

Yeah I plan on sticking through with the HPS, once i get a feel for them and actually know what faded brakes feel like...Ill go with better pads.

In the meantime, I've ordered ford racings brake ducting kit in order to reduce the brake fade that i'll probably encounter. First event for me is at California speedway, interior course in a couple weeks time. CANT WAIT!!!

I went out for a spirited drive today after watching "Love the Beast" and the brakes felt a "little" firmer than what i experienced yesterday.

 

[FR500GT]

Thanks!

In the meantime, I've ordered ford racings brake ducting kit in order to reduce the brake fade that i'll probably encounter. First event for me is at California speedway, interior course in a couple weeks time. CANT WAIT!!!

Who are you going out there with?

 

[foolio2k4]

With Hurst/B&M American Muscle Car Shootout.

 

[Vapour Trails]

On my way home from tracking the car today I noticed my brake pedal was feeling "mushier" than usual. I can't recall triggering the ABS, what might have caused this?

 

[SoundGuyDave]

On my way home from tracking the car today I noticed my brake pedal was feeling "mushier" than usual. I can't recall triggering the ABS, what might have caused this?

Ah, grasshopper!! Methinks you actually used your brakes yesterday! What happened, most likely, is that you got them hot enough to boil the fluid a bit, and as a result, you now have some bubbles in the lines. Simple fix: bleed them down! If you haven't flushed the brakes (complete fluid change, by bleeding through the old fluid) in the last year or two, then that's something that should be on the list, near the top.

Brake fluid is aggressively hygroscopic, meaning that it LOVES to absorb moisture. That moisture, which is in reality water, does two things. First, it allows for some corrosion throughout the braking system if you don't purge it, and second, and most important from our viewpoint, it lowers the boiling point of the brake fluid. Stock fluid has a dry boiling point of around 450*F, but that drops to the high 200* range once the fluid is contaminated with moisture.

When you start USING the brakes, like you do on track, you heat the pads up, which is conducted through the pistons and caliper castings into the fluid. Once you get the fluid hot enough, the water becomes vapor (steam), and you get a "spongy" pedal. Fluid is not compressible, however gas (vapor/steam) is, which is what allows the pedal to move around without a linear increase in braking.

Moral of the story: bleed them out!

 

[Sleeper_08]

Also are you using DOT 4 fluid which has a higher boiling point but should be changed yearly as it is more affected by water absorption.

 

[Philostang]

FWIW, this is part of why I'm not a fan of Wilwood's High Temp fluid (I used it for a couple of years). It has a very respectable "dry" boiling point, but it's "wet" boiling point bottoms out like it dropped off a cliff. It also seems to get wet very quickly, so you need to plan on bleeding it out frequently (before every track session is highly advised).

Really, take a look at both dry and wet boiling points of any fluid you're considering to use if you track your car (then get Motul RBF600...at least you'll be informed as to why you're spending that much).

Best,
-j

 

[Vapour Trails]

Ah, grasshopper!! Methinks you actually used your brakes yesterday! What happened, most likely, is that you got them hot enough to boil the fluid a bit, and as a result, you now have some bubbles in the lines. Simple fix: bleed them down! If you haven't flushed the brakes (complete fluid change, by bleeding through the old fluid) in the last year or two, then that's something that should be on the list, near the top.

Brake fluid is aggressively hygroscopic, meaning that it LOVES to absorb moisture. That moisture, which is in reality water, does two things. First, it allows for some corrosion throughout the braking system if you don't purge it, and second, and most important from our viewpoint, it lowers the boiling point of the brake fluid. Stock fluid has a dry boiling point of around 450*F, but that drops to the high 200* range once the fluid is contaminated with moisture.

When you start USING the brakes, like you do on track, you heat the pads up, which is conducted through the pistons and caliper castings into the fluid. Once you get the fluid hot enough, the water becomes vapor (steam), and you get a "spongy" pedal. Fluid is not compressible, however gas (vapor/steam) is, which is what allows the pedal to move around without a linear increase in braking.

Moral of the story: bleed them out!

I'm aware that fluid likes to absorb moisture, but from where? It's a closed system.

I was using super blue fluid and EBC yellow pads.

 

[Sleeper_08]

Have you had a look at your rear pads since the event?

I ran the EBC Yellowstuff on the rear last year at the start of the season and on a short track with lots of braking they didn't hold up and looked like they melted. For the rest of the season I ran Hawk HP Plus and they held up well but squeal badly on the street.

I'm also running the ATE fluid and for me it works.

 

[SoundGuyDave]

Vapor: Yes, the brakes are a closed system, however the reservoir itself isn't, and the ambient moisture in the air, over time, is sucked into the fluid and does manage to distribute itself throughout the braking system... I use Motul RBF600 fluid, which seems to hold up well to track rigors, but does *require* a full flush about every six months! ATE SuperBlue and SuperGold seem to be about the same, in terms of "aging," but have a slightly lower wet boiling point than the Motul, but otherwise is a good fluid.

Also, while I haven't used any EBC pads, I seem to see a disproportionate number of people that run the yellows having issues with pad over-temp. I would bet that the compound was engineered for 2200-2800lb cars, which is about a half-ton short of what we're throwing around the corners. If you can find a pad equivalency to the Hawk HT-10, that would be a good choice up front, and the HP+ would be the best for the rears, assuming stock rotor size. I made a quick visit to the EBC website, and found this: http://www.ebcbrakes.com/automotive/ebc_disc_pads_for_racing/blue_stuff_latest_tech.shtml

They are recommending the Bluestuff pad for "Longer Race use on Sportscars, GT cars and any street based car over 2200lb"

Their comment on the Yellowstuff compound: "Race and Trackday use on cars up to 2200 lbs"

Based on that, I would suggest moving to the Bluestuff at your next pad change, if you don't want to run Carbotech or Hawk.

That right there would indicate that the Yellowstuff is just too light-duty for our chassis weight. Now, add a blower to the mix...

 

[Vapour Trails]

I bought the yellows as I thought it would be a good street/track compromise, maybe not, but I was likely over-braking too. The pads and fluid are only 2 weeks old.

Anyway, the brakes seemed back to normal today.

 

[SoundGuyDave]

Anyway, the brakes seemed back to normal today.

I would still bleed them out. It'll only cost you MAYBE a quarter-liter of fluid, and I bet that when you do bleed them, the first spurt of fluid coming out of the calipers is closer to black than that beautiful liquid gold color... The steam may have condensed back into liquid form and been absorbed by the fluid, but it's still in there (closed system!) just waiting to flash into steam again. Once you boil them, the fluid is contaminated and needs to be flushed out. Think 4-6 brake pumps per caliper, start right-rear, then left-rear, then right-front, and finish up on left-front. That's working from the furthest to the nearest, and is the "proper" sequence.