FasterIsBetter

This is a cross-post of a message I put up in the C5 Z06 section. Hoping someone might have some suggestions:

I just got back from three days of running the '04 Z06 at Watkins Glen. I have upgraded the brakes to Wilwood 6 pot fronts, 4 pot rears, on 13" rotors. I was running Wilwood H pads up front, B pads on the rear. Also, bled the brake system with ATE Super Blue before going up to the Glen, and again during the first day at the track. The car got heavy use, as I drove it hard, and my gf drove it in the novice group.

Anyway, by the afternoon of the third day, the brake pedal started getting very spongy. It was not as firm to begin with as when I had done the upgrade on my '03 Z two years ago.

So, the question is this -- do I need to upgrade the master cylinder? Or should l just go to a higher boiling point fluid like Castrol SRF? Has anyone had this problem, and how did you solve it? I still have a good amount left on the brake pads, and the rotors have held up well. It's the spongy pedal that give me concern. I don't think I boiled the fluid, just a very soft feel in the pedal (initial push on the pedal took it most of the way to the floor, pumped it once and then got fairly firm pedal... does this mean a bad mc?).

And if anyone has upgraded the master, what did you switch to (part numbers would be greatly appreciated). I did a forum search, but didn't find any suggestions for an upgrade to the MC.

Thanks,
Steve

John Shiels

I had one of the first sets of Wilwoods and never had a problem. SRF is the best by far. You may be getting some knockback. How many miles on the calipers? How are the seals on the pistons? You can also add heat shields when the pads wear a bit. They can be Mica, SS, or aluminum which makes them feel better and adds insulation to keep the fluid cooler. You always get sightly more travel from when you install a new set of pads. Are the pads tapered? You do not need a new master. Someone here tried it and the peal was high but very hard so the removed it as I remember. What color are the calipers now black or copper?

magnetic1

Spongy? or lower engagement?

Could just be due to you using up the pads. As the pads wear, it will take more pedal travel for them to engage.

There are other fluid you can also try that is better than ATEblue and not costing as much as SRF.

0Anthony @ LGMotorsports

SRF has been the best fluid, hands down.

Depending on the car and the setup, you may have to bleed the car during the day to keep the pedal solid. While this might not have to be a full flush, just a quick pressure bleed to get fresh fluid at the caliper.

Knock back could be at work as well, but if it is just getting softer throughout the day, I'm going to say a better fluid should be used and you should probably bleed during the day.

Bill Dearborn

Steve,
With the SL6 fronts and 7420 H pads I get consistent pedal (unless I boil the fluid) throughout the life span of the pads which can be as much as 8 or 9 single driver track days. In 3 seasons of useage the one time I got a soft pedal is when I boiled the fluid while trying to stretch useage of the pad without using an insulator spacer. I was using a fresh load of Wilwood's 600+ fluid at the time which is about as good of a fluid as you can buy. 95% of my track time is at the Glen.

It sounds like your Wilwood setup probably uses the thinner 7416 H pads which will not last as long as the 7420s. If your pads got thin on the third day (equivalent to 6 track days with two users) it is possible you just put too much heat into the brake fluid in the calipers.

Bill

FasterIsBetter

John,

The setup is brand new, so hopefully the seals, pistons, etc. are all is new condition. Even after the three days, the calipers are black, only looked lighter because of brake dust.

Bill,

IIRC, I have the 7420 H pads, not 7416, but I'll check that. Interesting point. On my old car, I had the same setup, and I never got a soft pedal. But, of course, it was just me driving the car, and it would have an hour or more between sessions to recover. I may try some SRF to see if that helps down at NJ Motorsport Park in three weeks.

Now, about the heat shields -- where can I find them? Are they specific to the shape of the pads?

Thanks,
Steve

FasterIsBetter

BTW, what exactly is "knock-back" and how do I know if that's what I'm having here?

Thanks again,
Steve

VetteDrmr

The fact that you get a good pedal after a pump aims me towards piston knockback. That could happen due to a slight rotor runout (much more susceptible with your caliper setup), or could be pad taper.

HTH, and have a good one,
Mike

Wicked Weasel

Steve I have your same setup as you (H-pads all around though) and never had a soft pedal with Wilwood 600+ brake fluid.

Is it possible that you killed the fluid?

Bob

MNCrystalRed2011

As the rotors get hot they may expand a slightly different rates, so the high spot will push the caliper pistons back into the caliper a bit, thus causing knockback. If you watch the footwell cams in any road race, you will almost always see the driver tap the brakes before a corner to push the pads back on the rotors.

C6400hp

Castrol SRF and some anti knockback springs from HRP world.
Kill one bird with two stones.

0Todd TCE

I'd look at the following:

Bleeding; preferred use is only manual method. No pumps or pressure bleeders as they can induce an aeration to the fluid. Gravity is your friend, use it. When bleeding be certain the caliper is at or nearly vertical. Bleeding beyond about a 10 degree angle can trap air in the crown of a piston due to the bleed passage position. No so much an issue here but I've seen this a lot on a 350Z.

Check the mount brackets and be certain the hardware is tight. Obvious but not always considered.

When this happens next, jack up the car while hot and see if you have any bearing free play. Excessive bearing play can cause some of this pad knock back.

Even the 16mm pads should not be an issue until you could be down to less than 20% pad material. Piston sizing is the same on both calipers so o-ring pull back is not any different on any of these.

FasterIsBetter

Checked the pads last night and they are 7416 H, not 7420. The pads on the car don't seem to show excessive wear, but I'm going to pull them out before my next event, which is two days at NJ Motorsport Park in late September. I may also pick up some Motul 600 or Castrol SRF fluid and bleed the whole system out again.

I also located some anti-knock back springs on line. Has anyone installed them? If so, how are they installed, and how many are needed per caliper?

thanks,
Steve

0Todd TCE

The springs are installed behind the pistons and require you disassemble the caliper to fit them. And the BSL6r won't have a ton of room in there for these without reducing the total compression of the piston, thus making new pads a tight fit I suspect. You'll need them to fit the 1.625 piston at least. Wilwood has these but I don't believe there are any for the 1.00" part.

If it were me I'd look at this as a last resort only after analyzing the other possibilities first. From one who sells many of that same caliper for other applications I can safely say it's not the caliper that's causing your problem.

gonzalezfj

If you remove the pads, make sure to check them for taper. This typically gives you a long pedal that is firm once the pads make complete contact with the rotor.

Usually boiling the fluid makes the pedal go all the way to the floor and your nuts to your throat.

Frank Gonzalez

FasterIsBetter

Thanks for the info, Todd. You've been very helpful throughout this process of getting the brakes and rotors straightened out. Much appreciated.

I was viewing the springs as a last resort, as you suggest. I wondered if they went between the pads and calipers, or under the pistons themselves, and you answered my question for me. I think I'm going to check the pads for taper, flush the system with some Castrol SRF or Motul 600, and see if that eliminates or reduces the problem.

C6RAPTOR

http://www.stoptech.com/tech_info/wp_knockback.shtml