Brake fade

[NitroDann]

Took your time there Dann!

How come, now you're a sponsor, your sig doesn't mention your magic tricks? Or do you just rely on certain people dropping your name from time to time?

Which magic tricks though?

[davekmoore]

150rwkw to 244rwkw but better driveability, fuel consumption, reliability, blah, blah .........

Oh, and your driving, not that my eyes were open after the first corner.

[greenMachine]

Dave, it looks to me like there are two possibilities at the root of your problem.

One is brake fade. As Magpie suggested the best way of testing for this is to put some of those heat sensitive strips/paint on your callipers/disks (read the instructions) and then do a track test. They will change colour according to the max temperature reached. If that exceeds the temperature range of your current pads, you now know what temperature range you need in your new pads. (I am assuming you bleed the brakes regularly - like before every event, and perhaps every session - and use high temperature racing fluid.) Pad knock-off shows in a long(er) pedal, as the pads are forced back to the disk from where they have been pushed, but after that movement they should behave as intended - this might require a quick pump of the pedal depending on how far the pads have to move.

The other is lack of brake boost. I don't know what demon tweaks Dann may have on your engine, but I do know of one turbo MX5 racecar that required a vacuum pump for the brake booster - and it transformed the car (as it did mine). I assume (again) that you are datalogging engine parameters, including boost. Have a look at the boost trace, and see how much time it spends in negative territory (ie, vacuum in the inlet manifold rather than boost, which means vacuum in your brake booster) during a track session. You might also want to check that the one-way valve in the vacuum line between the booster and the manifold is working correctly, allowing the manifold to suck air out of the booster but not allowing air to flow back towards the booster. You could also put a pressure sensor on your brake line(s), and datalog that to see what your line pressures are. By looking at line pressures, braking 'g', and boost/vacuum pressure, you should be able to confirm/discount this as a/the cause/contributor to your problem.

Good luck.

[davekmoore]

Datalogging?

[Ned Loh]

Using some heat paint on the discs and temperature strips on the calipers will help you track where the issue is.

do this before buying any new parts.

[Magpie]

Check to see that the one way valve is still on the brake booster line. This prevents the vacuum from being bleed by other sources.

[Steampunk]

What brake fluid are you using?
How often do you flush/replace?

[davekmoore]

What brake fluid are you using?
How often do you flush/replace?

400
6 monthly

[davekmoore]

Dave, it looks to me like there are two possibilities at the root of your problem.

One is brake fade. As Magpie suggested the best way of testing for this is to put some of those heat sensitive strips/paint on your callipers/disks (read the instructions) and then do a track test. They will change colour according to the max temperature reached. If that exceeds the temperature range of your current pads, you now know what temperature range you need in your new pads.

Temp range of current pads seems to be above the range of the strips/paint.

(I am assuming you bleed the brakes regularly - like before every event, and perhaps every session - and use high temperature racing fluid.)

Not presently - so possibly boiling fluid during a long braking event? What fluid do you recommend?

Pad knock-off shows in a long(er) pedal, as the pads are forced back to the disk from where they have been pushed, but after that movement they should behave as intended - this might require a quick pump of the pedal depending on how far the pads have to move.

It's not that.

The other is lack of brake boost. I don't know what demon tweaks Dann may have on your engine, but I do know of one turbo MX5 racecar that required a vacuum pump for the brake booster - and it transformed the car (as it did mine).

Dann might chip in with a comment here?

I assume (again) that you are datalogging engine parameters, including boost. Have a look at the boost trace, and see how much time it spends in negative territory (ie, vacuum in the inlet manifold rather than boost, which means vacuum in your brake booster) during a track session. You might also want to check that the one-way valve in the vacuum line between the booster and the manifold is working correctly, allowing the manifold to suck air out of the booster but not allowing air to flow back towards the booster. You could also put a pressure sensor on your brake line(s), and datalog that to see what your line pressures are. By looking at line pressures, braking 'g', and boost/vacuum pressure, you should be able to confirm/discount this as a/the cause/contributor to your problem.

No datalogging going on here. It all sounds too clever for me.
Will have the one-way valve checked.

Good luck.

[/quote]

[greenMachine]

Temp range of current pads seems to be above the range of the strips/paint.

Are you saying that the temp strips/paint is showing you are within the pads operating range? If that is so, it means that the pads are not fading, and you don't need (more) ducting - but it would be a good idea anyway as insurance.

Not presently - so possibly boiling fluid during a long braking event? What fluid do you recommend?

How old is the fluid - when did you do a full flush last? When did you last do a bleed? Sounds like a full flush would be a good idea, not a lot of effort/money, and it would remove another variable. I would check with the pad supplier for a fluid to suit those pads. On preview, is that 400 degree brake fluid - and your pads are 800 degrees?! I'd be looking for one with a much higher temperature rating, but see what your pad supplier says.

The other is lack of brake boost. I don't know what demon tweaks Dann may have on your engine, but I do know of one turbo MX5 racecar that required a vacuum pump for the brake booster - and it transformed the car (as it did mine).

Dann might chip in with a comment here?

I assume (again) that you are datalogging engine parameters, including boost. Have a look at the boost trace, and see how much time it spends in negative territory (ie, vacuum in the inlet manifold rather than boost, which means vacuum in your brake booster) during a track session. You might also want to check that the one-way valve in the vacuum line between the booster and the manifold is working correctly, allowing the manifold to suck air out of the booster but not allowing air to flow back towards the booster. You could also put a pressure sensor on your brake line(s), and datalog that to see what your line pressures are. By looking at line pressures, braking 'g', and boost/vacuum pressure, you should be able to confirm/discount this as a/the cause/contributor to your problem.

No datalogging going on here. It all sounds too clever for me.
Will have the one-way valve checked.

If the pads are ok, and the fluid flush doesn't help, you will need to look more deeply at the callipers, and the brake line pressures. But do the simple things first, change the brake fluid and see what, if any, difference that makes. With a bit of luck it will fix the problem, but if not you will know what parts of the braking system are not the problem.

[Magpie]

Old discussion, but could be helpful http://ww.w.mx5cartalk.com/forum/viewtopic.php?style=3&p=844355#p844355

[davekmoore]

Sorted by correct pads and no other changes. Same ones as used by Flyin' Miata on their V8s.

[Ned Loh]

You say you can't get the ABS to engage. Is that on these high speed to slow speeds stops only, or you cannot engage ABS on slower corners also?

You may have brake issues aside from just pads.