commasense

It would be pretty hard to scratch the pistons, I think. See my thread about rebuilding the calipers. After nearly five years and lots of track time, the pistons were like new.

That said, I've ordered the piston tool, too, 'cause it looks like it will be a little easier than my method, and it was a lot cheaper than the big one in post #11.

Kolia

iTrader: (2)

Just remember to open the bleed valves when pushing the pistons back so you don't send wasted fluid in the ABS system.

You want to bleed the brakes anyways.

commasense

Wasted? It's a closed system. What happens if a tiny little bit of fluid that has been in the lines between the ABS and the calipers goes back in to the ABS?

Why? I've owned my car for five years, put 79 track days on it, and have bled the brakes exactly once: when I rebuilt the calipers. I've changed the fluid (or had it changed) regularly, but I don't bleed the brakes when changing pads or before or after track events, and I've had no problems. Why bleed the brakes if there's no evidence of lost fluid or air in the lines?

mhoward1

Changing the fluid is bleeding the brakes. Even the good stuff like Motul degrades after repeated 1200 degree fluxuations.

commasense

I know that, of course, but Kolia and others here and elsewhere seem to think that one should bleed the brakes routinely, the way one might check the torque on your lug nuts. I'm not saying that's wrong, I just want to understand why they think so, since I've never seen any reason to do it.

I suspect it may be one of those "because my father said so" things that was true 20-30 years ago, but isn't really necessary these days. Clearly, it's unlikely to do any harm (unless you do it wrong or leave a valve open), but I don't see much of a positive benefit. In fact, frequently bleeding the brakes could make stripping or damaging the nipple valves more likely, and do more harm than good.

But I'm willing to hear why I may be wrong.

Axelerate

iTrader: (19)

There's some truth to that. With my previous car that I tracked, boiling the brake fluid happened from time to time. I just started bleeding them regularly and havent stopped.

I'm trying to reduce my track weekend spending, so I might try to hold out on the bleeding. Plus I have a seized rear bleeder screw, so this will give me some more time to get that taken care of.

Kolia

iTrader: (2)

Because I find that my pedal gets softer after a day of lapping. The fluid does degrade and when it does, it turns to water and acid. I'm not leaving acid in my brakes.

Nor do I want that stuff in the valves and pumps of the ABS system!

The fluid comes out brownish when I bleed.

It might be overkill. I'm not taking chances on brakes...

commasense

I think you have a problem in your system that you should look into. Or try using a different fluid, or changing it more frequently. My pedal never gets soft, and when I bleed the brakes, the fluid that comes out is the some color as the stuff in the reservoir. I use ATE SuperBlue or TYP200 (the same stuff, but yellow instead of blue).

BTW, I assume you're talking about your old Z, not the STi? And did you have the Brembos or a BBK? It could be that on a tracked car with the stock Nissan brakes, more frequent bleeding would be a good idea. So that may explain our different experiences.

Kolia

iTrader: (2)

Yes, I'm talking of the Z. Haven't track the STi yet.

I use RGS610 brake fluid and had the OEM Brembo's with Cobalt Friction XR2/XR3 pads on Toyo RA1 (255/275).

Caliper temps was a steady 450F while the rotors reached 1,200F.

I doub't my brakes had any problems. The pedal was rock solid most of the time. I just cycled my fluid each time I was swapping pads.

Try and flush the fluid while pushing the pistons in next time. Before I did that, my fluid looked clean too. Like me, you might be surprized at what comes out. The "bad stuff" just stayed behind the pistons...

I might have been harder on my brakes too.

n1cK!

iTrader: (21)

so it looks like it's a tie - on one end of the spectrum, we have a member who doesn't bleed the brakes on every pad change, obviously tracks his car, but has had no problems. on the other hand, we have another member who also tracks the car, reguarly bleeds the brakes/changes fluid on pad changes, but who's pedal feels soft after a day of lapping.

i would tend to agree with commasense to wonder if there was anything wrong with your brake system kolia. you may have been hard on your brakes, since 1200 degrees on a stock rotor is a lot. maybe your fluid degraded faster because your rotors couldn't dissipate the heat fast enough.

n1cK!

iTrader: (21)

in addition, you could also distort the seating surface of the bleeder in relation to the caliper. obviously this is bad since the bleeder won't do it's job and hold in fluid anymore.

Kolia

iTrader: (2)

What would constitute a "problem" regarding the question at hand?

Brake failure during a 120-40mph decelleration into a turn? Are we willing to risk that?

One thing I know. IF your fluid degrades, it will degrade first right behind the piston. Now if you bleed the brakes without pushing the pistons back, the cavity will not be flushed and if there is "bad" fluid in there, it will stay there. That is also where the piston seal is.

I'm also pretty sure you can not have "too fresh fluid". So my bleeding often can't hurt. Just have to be careful when torquing the valve.

I had the Z for 50k miles. Did many 1k's miles on the track(20+ track events?). Went thru 5 or 6 sets of pads in the front and 2 sets of rotors. Actually, I changed the rotors before they we're thinned to the minimum. I don't think 1,200F is that extraordinairy for rotor temp. Did not have wear issues.

Maybe my fluid isn't that good (specs are much higher than ATE thought)? Maybe I'm simply harder on my brakes. Maybe I have a lower tolerance for soft pedal feel. Who knows?

My suggestion is to see for yourself, check your fluid at the caliper once in a while.

Maintenance on a track car is something that needs to be proactive. Avoid having to fix after a problem arrise.

I still believe my brakes were in excellent conditions. I've rebuilt them too.

Marc Mc

I am with Kolia.
I bleed the system everytime I change the pads for my track days.
The bled fluid - while not brown - isn't crystal clear. I want fresh stuff when I am going to be depending on my brakes so much.

Bleeding the brakes after a pad change also makes the pedal feel more solid.

I see the bleed as cheep insurance. Just buy a Motiv speed bleeder. It becomes routine.
Marc

n1cK!

iTrader: (21)

i guess the question is why your brakes always felt so soft. i don't think there is a tolerance for what feels soft and what doesn't. if it's not high, it's not right.

1200deg is actually quite significant, especially on stock stuff. the (relatively) small diameter of the stock rotor just can't dissipate heat as effectively. however, just because you are hitting 1200deg doesn't necessarily mean you will "wear" down the rotor faster. the heat cycling however will change the ductility of the rotor itself, which will affect the wear. that's why we eat through rotors like cookies (i like cookies).

i do a quick bleed after a couple of track events, but not a full fluid change-out (normally only bi-annual). now when you say that the fluid will degrade behind the piston, and you won't be able to see it unless you push back the piston and bleed, how will that fluid get all the way up to the actuator (see post 21 and 23)?

i'm not trying to be an @$$, but i really am curious as to what effect this "wasted" fluid behind the piston will have on the system as a whole? is there actual particulate matter that could cause scarring of the master cylinder?

to be quite honest, after all my track days, my pedal only feels soft because of knockback.

n1cK!

iTrader: (21)

just to make sure, are there a few arguments going on here? whether or not to change your fluid before every track day, or whether or not it is necessary to bleed the brakes after a simple pad change out. i just want to make sure we are all on the same page.

Kolia

iTrader: (2)

Well, I didn't eat my rotors at an alarming rate despite my 1,200F peaks. What temp do your rotors reach? I had 2 pieces rotors by the way. And I don't think the Brembo's are too small for the application.

I'm surprized that you guy's brake can hold on so well.

Fluid will degrade and separate into acid and water. Water in the hottest part of the brake system is a problem. Steam isn't ideal to apply brake pressure!

Water and acid in the maze of the ABS system can't be good either.

I'm still waiting to hear from someone that he did do like I suggest (flushing the fluid out from the caliper vs pushing back in) and found his fluid in perfect condition after a track day.

In any cases, I don't expect a fluid rated at 610F to survive indefinitely to track abuse. I wouldn't leave it in place on faith alone.

As a side note. Pad knock back doesn't affect the feel of the pedal once the initial gap of the pad is removed. Pump the brakes once, and the pedal should be solid. If it's not, your fluid is fading.

n1cK!

iTrader: (21)

i have two piece 355mm aerorotors so my temps are lower. i've got pretty new fluid in there now, but won't see a track day for a couple of months i may have to give your method a try just to see.

pad knock back - you're right, it doesn't ONCE the initial gap of the pad is removed. like you said, you still have to pump the brakes which is what i have to do almost all the time (BBK's just make the effects of knock back even worse).

i'm not saying to leave it in there indefinitely, i'm just asking when is too much, too much? should we take these same principles and apply it to the rest of the car? failed diff fluid can be just as dangerous as failed brake fluid, so on and so forth.

on a side note, my brakes hold up pretty well - hawk dtc-70 front, dtc-60 rear, 355mm aerorotor front, 328mm aerorotor rear.

Kolia

iTrader: (2)

It can't be too much!

Flushing the fluid when changing pads by "venting" the bleed valves:

-makes it easier to push the pistons
-guarantiees fresh fluid
-Prevents reservoir spillage
-Prevents any would be bad fluid to enter the ABS system.

All good stuff!

Kolia

iTrader: (2)

I hope everybody does check their diff and tranny fluid regularly too!

Diesel350

iTrader: (6)

Where are the bleeder valves?