Ed Newman

Ok here is a question...

If I bleed the brakes after each track day and use about 1/4 liter each time, in theory the fluid will be completely cycled (sans clutch line) every 4 track days. If so, do still need to 'change' the fluid completely ever? It seems like a waste.

Geoffrey

Ed,

I saw you at LRP on Saturday, nice car, I was running in black. I originally started bleeding my brakes before every event, but lately, I've done it only here and there. In fact, my club racer friend doesn't bleed his brakes but once per season on his Cup car.

Tom W

I don't see the reason to go through all the effort without gaining the full benefit. If you don't completely replace the fluid, yu still have fluid that has more moisture in it left in you lines. The moisture will equilibrate with the new fluid fairly quickly and negate most of the benefit of the fluid change. In addition, if you only use 1/4 liter out of a 1 liter can, you will have the rest of the fluid sitting in the can gaining moisture before you use it for the next flush.

On this basis, it would seem much, much better to completely purge using the full liter of fresh fluid every 4 events instead of the minor flush after every event.

JC in NY

Ed,
I would think the bleeding cycle you described is overkill. If you use a fluid like Castrol LMA with its low moisture affinity you should not need to bleed that frequently. Unless of course you're boiling the fluid...

Ed Newman

I am running Castrol SRF and had an experience recently with boiling the fluid and do not want to chance it again. The brakes on my car are seriously lacking. It is soooo far from a cup car in terms of braking. Think of it this way... the car weighs more than almost any other Porsche except the turbo series and has Boxster S brakes. The front brakes are the same as the rears on the turbo... go look at a turbo and see how much bigger the fronts are. The rational has been to remove the heat cycled fluid and any air from the caliper. I usually get a few bubbles when I first open the valve. I have added the cooling ducts and have not had any soft pedal (boiling fluid) problems before the brakes start to fade. I can run 10 hard laps at LR or 6 at the Glen before I have to back off a little. Taking it easy on the brakes is work a second or two per lap depending on the track. My understanding from Castrol is the hydoscopy is not the problem, but the breakdown of the fluid and air bubble generation from the heat cycles.

JC in NY

Sorry I meant SRF.

In that case I would think bleeding with the frequency that you do would preclude a full flush.

M758

Ed,
I run a 944 spec car. 131 whp & 2620 lbs with driver. Our class rules require us to run stock brakes (rotor size & caliper). I currenty run Hawk Blue pads. These cars typically don't require much braking since they momentum cars and never go very fast.

I also bleed may brakes before each track day. I run super blue fluid & have 3" cooling ducts. I found that I much prefer my tight pedal pressure that I get from freshly bleed brakes. I have a power bleeder and it takes only a few minutes at the start of each day. I have gone without and don't like it. I don't feel confident in the car. I normally bleed until I no longer see air bubbles from each caliper.

In 3 years of track/race duty I have never "changed" the fluid. I have only bleed the brakes when needed (each track day). Personally I don't see any reason to change they way I maintain my brakes.

mark kibort

Here is a question

why do you need to use the bleeders on either side of a 4 piston caliper. doesnt the fuid have to travel from one side to the other to get out?? I have one nipple that is broken off on one side, and with my kinesis wheels, I can bleed the outside nipple/fitting ,without taking the wheel off.

anyone know the interworkings of the brembo 4 piston calipers?

MK

Ed Newman

I'd probably say that some fluid would stagnate in the caliper if ou only bleed the outside. It would only be partially effective.

Palting

Aren't you supposed to only use "fresh" brake fluid from an unopened can? The assumption being that it would have the least bit moisture vs a conatiner that has been opened then resealed with ambient air now in the container.

Unless there are 1/4 liter containers, wouldn't that pretty much mean you have to use up the 1L container?

Ed Newman

Keep in mind that for a 3 day event, I'm using most of a can and I've been doing 1-3 days per week recently so it does stay for long.

Greg Fishman

Ed,
What brake pads are you using? Maybe try a different compound or find some ceramic/asbestos-type liners for the pads to disipate some heat.

If you are needing to bleed before every run just "tap" the calipers, no reason to flush all the fluid out. The fluid doesn't cycle back to the reservior.
You do need to bleed both sides of the calipers. I start with the outside, go to the inside and do the outside one more time briefly and then double check that the bleeders are closed. If you leave one open you are in big time trouble.

Dave in Chicago

I like the cycle you have, have recently gone to a similar set-up myself. Bleed the calipers a bit after hard track days. Flush the whole thing with clutch about every 4th track day. This frequency never leaves fluid exposed in the system for more than a month or so, pulls any bubbles out of the calipers, firms up the pedal before each event, and provides a semi-regular flush of the clutch (it gets pretty darn hot too, do not underestimate the heat at the clutch).

I'm running the ATE Blue and KFP pads on my winky 944 NA brakes. Like M758 above, it's a momentum car. That said, I do like to try to brake like the big cars whose brake pads are bigger than my whole caliper. It's all relative.

I agree that you may want to experiment with other pads. They do differ a fair amount in the degree with which they transfer heat to the calipers. The dark side is too much heat to the rotors. There may be a more attractive balance of these two factors with a different compound.

JPhillips-998

I have been told on many occasions, by many different people that brake fluid will last about 6 months once opened. No need to open a new can w/each bleed or flush.

Steve Weiner-Rennsport Systems

Hi Ed:

I'll just chime in here and "second" Tom W's suggestion.

If you are experiencing boiled fluid using SRF, you are seriously underbraked-undercooled (or both), for what you are doing and the very least you do is keep fresh fluid in the system.

All of these fluids save for silicone fluids, (which are totally inappropriate for track use) begin immediately to absorb moisture in varying degrees and should be changed if the brake operating termperatures are close to the fluid's dry & wet boiling points. It makes no economic sense to pinch pennies on brake fluid when your car's bodywork and your health is at stake.

I'm sorry to say that I've witnessed this too many times and I do not need or want that kind of business. I take NO satisfaction from repairing someone's damaged car,..............

To know exactly what your brake temperatures are, I'd strongly suggest that you purchase the temp paint kit from Pegasus Racing (or others) and use that to get definitive information about your brakes.

These kits will enable you to see what your caliper & rotor peak temperatures are, and proceed from there to find the best and a final "solution",...